Chapter  1:  Systematic Review of the Literature Regarding the Diagnosis of Sleep Apnea: Evidence Report/Technology Assessment Number 1

Preface

The Agency for Health Care Policy and Research (AHCPR), through its Evidence-based Practice Centers (EPCs), sponsors the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. The reports and assessments provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies. The EPCs systematically review the relevant scientific literature on topics assigned to them by AHCPR and conduct additional analyses when appropriate prior to developing their reports and assessments.

To bring the broadest range of experts into the development of evidence reports and health technology assessments, AHCPR encourages the EPCs to form partnerships and enter into collaborations with other medical and research organizations. The EPCs work with these partner organizations to ensure that the evidence reports and technology assessments they produce will become building blocks for health care quality improvement projects throughout the Nation. The reports undergo peer review prior to their release.

AHCPR expects that the EPC evidence reports and technology assessments will inform individual health plans, providers, and purchasers as well as the health care system as a whole by providing important information to help improve health care quality.

We welcome written comments on this evidence report. They may be sent to: Director, Center for Practice and Technology Assessment, Agency for Health Care Policy and Research, 6010 Executive Boulevard, Suite 300, Rockville, MD 20852.

Structured Abstract

Objective. The objective was to establish the evidence base for diagnosing sleep apnea (SA) in adult patients using systematic review methods. Tests covered were sleep monitoring devices, radiologic imaging, laboratory assays, and clinical signs and symptoms posited for use in screening or diagnosing SA. The standard sleep lab polysomnogram (PSG) was the gold standard.

Search strategy. Literature published from 1980 through November 1, 1997 (cutoff) was searched using Medline and Current Contents, supplemented by a manual review of the bibliographies of all accepted papers.

Selection criteria. Studies of at least 10 adult patients suspected of or diagnosed with SA had to report the results of any test to establish or support a diagnosis of SA, relative to a standard PSG-derived apnea index (AI, the number of apneic episodes/Hour sleep); apnea-hypopnea index (AHI, the total apneas plus hypopneas during total time asleep, divided by the number of hours asleep); or respiratory distress index (RDI). Eligible languages were English, German, French, Spanish, or Italian. Diagnostic papers reporting prevalence or clinical comorbidities of SA were also accepted.

Data collection and analysis. Based on scores for study characteristics (e.g., random order test, blinding of test readers, and use of PSG comparison), 147 studies met or exceeded the minimum evidence score. From these, data on study, patient, and test characteristics and on results were collected. Nondiagnostic studies reporting prevalence or clinical comorbidities were separately extracted.

Study and patient-level covariates were summarized and the results were analyzed using fixed effects models. Results were evaluated using summary receiver operating characteristic (ROC) curves where data were available.

Main results. In 71 analyzable diagnostic or screening studies (7,572 patients), the sensitivity and specificity of partial channel and partial time PSGs appeared most promising as possible prescreening tests or replacements for full PSG. Prediction models achieved good sensitivity and specificity. Studies of portable devices were variable due to study and device heterogeneity. Radiologic studies and several miscellaneous studies of questionnaires, anthropomorphic signs, and ears/nose/throat (ENT) exams could not be analyzed due to insufficient data. Global clinical impressions and oximetry provided moderate sensitivity and specificity. Least accurate were flow volume loops. The review and analysis were limited by variability in PSG definitions of apnea and hypopnea, and thresholds for SA diagnosis. For sensitivity and specificity determinations, the lowest AI/AHI threshold for SA diagnosis was used. Necessary components of "standard" PSG were not consistent.

SA prevalence studies in different patient populations were reviewed. Few such studies utilized gold standard PSG to diagnose SA; so the diagnosis was based on unvalidated tests. Such prevalence estimates are suspect.

Conclusions. The best available evidence from literature sources suggests the diagnosis of SA is still best accomplished with full PSG. Progress has been made in establishing reasonable sensitivity and specificity of tests other than full PSG, and future researchers should focus on building this evidence base. Standardization of terms and diagnostic criteria is an absolute requirement to expedite development and enhance the utility of this literature in the future.

Suggested citation:
Ross, SD, Allen IE, Harrison KJ, et al. Systematic Review of the Literature Regarding the Diagnosis of Sleep Apnea. Evidence Report/Technology Assessment No. 1. (Prepared by MetaWorks Inc. under Contract No. 290-97-0016.) AHCPR Publication No. 99-E002. Rockville, MD: Agency for Health Care Policy and Research. February 1999.

Summary

Introduction

Sleep apnea in adult patients is a recently recognized disorder of sleep characterized by recurrent apneic and hypopneic episodes. Apnea was typically defined as complete cessation of airflow, but in some studies, a >80 percent reduction in airflow was used. For defining hypopnea, most papers suggested a 50 percent or greater reduction in airflow was used, with or without a coincident O₂ desaturation of anywhere from 2 percent to 4 percent from some average SaO₂ over a preceding interval of time. Most cases are characterized by recurrent airway obstruction (obstructive SA), and a minority of cases are central (i.e., neurologic) in origin. In view of its purportedly high prevalence and serious associated morbidity, SA has recently been described as a major public health concern (Phillipson, 1993). The National Commission on Sleep Disorders Research (1993) estimated that SA may be responsible for 38,000 cardiovascular deaths per year and costs of $42 million annually for related hospitalizations. The cumulative 8-year mortality of untreated SA has been estimated as high as 37 percent for patients with an apnea index >20, where AI is defined as the number of apneic episodes/hour sleep compared to 4 percent for patients with lower AIs (He, Kryger, Zorick, et al., 1988). Patients with obstructive SA need not go untreated, however, since there is a well accepted first line therapy - continuous positive airway pressure (CPAP). A major problem in the field in 1998, however, is diagnosis: whom to test; how to test; and what are the implications of test results regarding the risk of serious clinical sequelae?

SA is a condition where the gold standard diagnostic method, overnight full polysomnography in a sleep laboratory, is intrusive and costly, and the interpretation can be difficult. A standard PSG typically consists of electroencephalogram, submental (± tibialis) electromyogram, electrooculogram, respiratory airflow (usually by oronasal flow monitors), respiratory effort (usually by plethysmography), and oxygen saturation (oximetry). Electrocardiography and body position are also frequently monitored in formal sleep studies and stated to be standard requirements of PSG by some groups. The contribution of each of these components to the PSG diagnosis of SA has not been well substantiated (Pack, 1993).

If the estimated prevalence of SA at 2 percent to 4 percent of middle-aged adults (Young, Palta, Dempsey, et al., 1993) is correct, the costs of full PSGs for all suspected cases would be prohibitive. The development of simpler and less costly alternatives for diagnosis or pre-PSG screening and/or testing would be highly desirable. Diagnostic approaches that might be viewed either as alternatives to PSGs or as screening tests to better select patients for PSG include partial channel PSGs; partial night or daytime PSGs; portable sleep monitoring devices for use at home; radiologic imaging of the head and neck for anatomic abnormalities predictive of SA, including cephalometry; MRI and CT scans; anthropomorphic measurements such as neck circumference; nasopharyngeal and laryngeal endoscopic measurements of upper airway structure and function; and focused questionnaires.

Accepted guidelines for testing are now very different between Europe and the U.S. (Schafer, Ewig, Haspr, et al., 1997), with Europeans promulgating simpler step-wise approaches to reduce testing costs by home-based studies with screening devices. Others have suggested "split-night" studies (Iber, O'Brien, Schulter, et al., 1991), or home studies with new automated CPAP devices (Burk, Lucas, Axe, et al., 1992). The type of sleep evaluation study preferred (and reimbursed) varies widely among physicians, sleep centers, and managed care organizations (Lindblom, 1997).

This lack of consensus may have been facilitated by the fact that SA can be viewed as an orphan condition, shared by many healthcare specialties, yet owned by none. Neurology, psychiatry, dentistry, otolaryngology, pulmonology, and internal medicine all share diagnosis and management of SA, and as a result, the evidence base is uneven and dispersed, and clinical management perspectives are sometimes in conflict. When evidence is scattered, and possibly conflicting, a rigorous and comprehensive assessment of all of the best available evidence is critically important, and in the case of SA, long overdue.

In this study, MetaWorks investigators have developed an evidence base via a systematic review of the literature published in the five major Western European languages pertinent to diagnostic testing and screening in SA. The development of practice guidelines or test recommendations was beyond the scope of this project. This evidence base should, however, be useful to health care providers in the development of evidence-based strategies and algorithms to guide the diagnostic work-up of patients suspected of SA. Furthermore, this evidence base can be efficiently updated as the literature evolves. This work should provide guidance for future researchers to generate new data to fill the information gaps discovered during the review.

Methodology

Flow Diagram 1: MetaWorks Process Diagram

   Flow Diagram 1: MetaWorks Process Diagram

Flow Diagram 1

Specific objectives were to establish the evidence base relevant to answering the following key questions in the diagnosis of SA: 1) what diagnostic and screening tests are presently available? 2) what is the strength of the evidence in support of each? 3) what is the predictive value of these tests in different populations? (which requires estimating the prevalence of SA in different populations) 4) what are the implications of certain PSG results in terms of serious clinical events occurring as comorbidities in association with a diagnosis of SA?

Flow Diagram 2: Causal Pathways for Sleep Apnea Diagnosis (more...)

   Flow Diagram 2: Causal Pathways for Sleep Apnea Diagnosis

Flow Diagram 2

MetaWorks investigators did not intend to review technical considerations of various tests and devices, which are beyond the scope of this project. Readers are referred to the American Sleep Disorders Association (ASDA) 1994 statement on portable devices for discussion of technical issues related to data acquisition, storage, retrieval, and analysis.

The review followed a prospective protocol that was developed a priori and shared with the nominating partners on the project (BC/BS of Massachusetts and the Sleep Disorders Centre of Metropolitan Toronto); a technical experts panel (TEP) (with representation from consumer groups and professional specialties: neurology, pulmonology, dentistry, otolaryngology, epidemiology, and nursing); and the Task Order Officers at the AHCPR. The protocol outlined the methods to be used for the literature search, study eligibility criteria, data elements for extraction, and methodological strategies to minimize bias and maximize precision during the process of data collection, extraction, and synthesis.

Results

Search Results

Evidence Table 1: Reject reasons

Evidence Table 1: Reject reasons

Number of studies	Reject reason
56	< 10 patients
20	Other (language, publication date <1980, incorrect citation, pediatric study, confounding disease, duplicate population, statistical paper)
31	Pathophysiology papers
76	Not sleep apnea
69	Letters/editorials/commentaries/abstracts
147	Reviews and meta-analyses
46	Treatment studies
51	Not diagnostic
111	Outcomes not extractable
50	No correlations to gold standard PSG
65	Evidence score less than 16

Flow Diagram 3: Study Screening

   Flow Diagram 3: Study Screening

The initial search through MEDLARS and Current Contents® yielded 3,730 citations. An additional 202 citations were identified from a manual search of reference lists. After screening these citations, 937 studies were potentially eligible. Most citations were rejected at Level I screening due to reasons of ineligible patient populations, treatment studies, or not relating to SA syndrome. Screening may be duplicated at Level II when the abstract is unclear as to its primary focus and it is then necessary to review the full publication before excluding it. During the second level of screening, some papers initially believed to be eligible were determined to be treatment papers and therefore were rendered ineligible. Seven hundred twenty-two studies were excluded after Level II screening for the following reasons: <10 patients=56; other (language, publication date <1980, incorrect citation, pediatric studies, confounding disease, duplicate population, statistical paper)=20; pathophysiology=31; not SA=76; letters, editorials, commentaries, abstracts=69; reviews and meta-analyses=147; treatment studies=46; not diagnostic studies=51; outcomes not extractable=111; no correlation to gold standard PSG=50; evidence scores <16=65. Refer to Evidence Table 1 for a display of the rejection reasons. All accepted studies are listed in the bibliography displayed in Appendix E. The screening process is charted in Flow Diagram 3. All studies rejected at Level II screening are listed in the bibliography as the study reject log (Appendix F). The eligibility of 135 studies still remains pending (Appendix G). These studies had not yet arrived via interlibrary loan at the time of locking of the database.

From the 937 potentially eligible studies, 495 initially appeared to fit all inclusion criteria of the protocol (k=249 diagnostic test studies, k=246 prevalence/comorbidity studies). Of these 249 diagnostic studies, 65 were low scorers on the rating instrument and did not proceed to data extraction (listed in Appendix F). Of the 184 that did proceed to data extraction, 147 were eventually accepted for the data matrix, the remainder rejected by the extractors as being unextractable or otherwise ineligible. Of the 147 diagnostic studies fully extracted and displayed in the data matrix,⁽¹⁾ 71 reported outcomes with sensitivity, specificity, and/or correlations, and relative to a standard PSG. These studies were chosen for further statistical analysis (see "Characteristics of Diagnostic Studies").

Characteristics of Diagnostic Studies

Of the 147 diagnostic studies accepted for data extraction, 129 were in English, and 18 were in other languages (12 German, 3 French, and 3 Spanish). Forty-nine studies were performed in the United States, 63 in Europe, and 35 elsewhere, including Australia, Israel, and Japan. The years of publication spanned 1981 through 1997, with 106 studies published since 1991. The average score on the diagnostic evidence rating instrument was 20.0 ± 3.9 (range 16 to 34). The total number of patients enrolled in these studies was 17,679 (range 10 to 1,409), and the average enrolled per study was 120.3 ± 184.6. Industry sponsorship was noted in only 5 studies. Study designs were almost entirely cross-sectional diagnostic assessments at one point in time, and only 7 used a randomized study design.

Evidence Table 2: Overall study level covariates

Evidence Table 2: Overall study level covariates

Covariate	Extracted studies (k=147)	Data set for analysis (k=71)
Location
Europe	63 (43%)	33 (47%)
United States	49 (33%)	21 (30%)
Other	35 (24%)	17 (23%)
Language
English	129 (88%)	63 (89%)
German	12 (8%)	5 (7%)
Spanish	3 (2%)	3 (4%)
French	3 (2%)	0 (0%)
Sponsor
Industry	5 (96%)	3 (4%)
Not industry	142 (4%)	68 (96%)
Year published
>1990	106 (72%)	52 (73%)
1981-1990	41 (28%)	19 (27%)

Of the 71 diagnostic studies reporting outcome formats required for inclusion in the analyzable dataset (sensitivity and specificity, or correlation coefficients), 63 were in English, 5 in German, and 3 in Spanish. Locations of study were Europe in 33, the United States in 21, and elsewhere in 17. These studies were published from 1981 to 1997, and 52 of them were published after 1990. The average diagnostic evidence score was 20.6 (range 16 to 34). Study level covariates for the extracted studies are summarized in Evidence Table 2. In total, there were 7,572 patients enrolled, and the average number of patients per study was 106.6 (± 115.0). Only 3 studies stated industry sponsorship. There were 25 studies with results of portable monitoring devices, 3 of partial channel PSGs, 12 oximetry alone studies, 7 partial time PSGs, 5 reporting radiologic test results (1 MRI, 3 cephalometry, and 1 reporting CT and cephalometry), 17 studies with clinical measures (including flow volume loops and global impressions), only 1 study with chemical assay, and 3 studies with focused questionnaires. Also, 8 studies reported results of multivariate models as predictors of PSG results.

Patient Characteristics

Of the 147 accepted diagnostic studies, gender was reported in 130, of which the majority of patients were male (79 percent). Of 136 studies that reported age, the average age was 48.8 ±8.0 years (range, 20 to 95). Most patients were referred to a sleep laboratory or were already sleep clinic patients at the time of the study. In the dataset of 71 studies considered for analysis, of the 4,400 patients who entered with a suspected sleep disorder, a PSG diagnosis of SA was made in 2,037 (49 percent), using the lowest AI or AHI diagnostic thresholds reported. Note the PSG definitions of apnea and hypopnea varied somewhat from study to study, and the AI or AHI thresholds for diagnosis varied more widely from study to study, from 5/hour up to 40/hour. The severity of SA and thresholds for same were too infrequently reported to analyze further. Similarly, historical information on patients was not usually reported; so no analyses could be made of the relationships of patients' medical histories to test results.

In the majority of studies, the presence of relevant symptoms at study entry was not consistently reported. The presence of daytime sleepiness, involuntary falling asleep, nocturnal snoring, gasping or choking, and observed apneas were most frequently mentioned as reasons for suspecting SA. The relationship of symptoms to diagnostic test results could not be measured for each test, due to insufficient reporting.

Evidence Table 3: Summary of patient level covariates (more...)

Evidence Table 3: Summary of patient level covariates

Study sets	K	Mean quality score (range)	Number of patients	Percentage males (k)	Mean age (k)	Mean BMI (k)	Sensitivity percentage	Specificity percentage
Analyzable	71	20.6 (16-34)	7,572	81 (61)	49.0 ± 5.1 (65)	30.9 ± 3 (44)	ND	ND
Oximetry	12	20 (16-32)	1,784	83 (10)	50.6 ± 4.7 (11)	31.7 ± 1.1 (12)	87.4 ± 3.8	64.9 ± 6.7
Partial channel PSG	3	17.7 (17-19)	213	81 (3)	51.7 ± 1.2 (3)	32.0 ± 1.0 (3)	ND	ND
Partial day/night PSG	7	18.6 (17-20)	505	86 (6)	51.4 ± 3.5 (7)	33.9 ± 5.5 (5)	69.7 ± 5.3	87.4 ± 5.4
Portable devices	25	22.1 (16-34)	1,631	84 (21)	48.5 ± 5.5 (24)	30.0 ± 1.6 (15)	ND	ND
Flow volume loop	4	18.3 (17-20)	594	79 (4)	50.0 ± 1.6 (4)	29.0 (1)	39.1 ± 25.3	60.5 ± 23.7
Global impression	4	23.3 (19-28)	1,139	67 (4)	47.7 ± 2.1 (3)	29.4 ± 0.7 (3)	58.9 ± 4.2	65.6 ± 4.8
Chemical	1	18	88	49	58	28	ND	ND
Other clinical	9	19.8 (18-22)	815	91 (8)	47.4 ± 6.9 (8)	30.3 ± 1.5 (6)	ND	ND
Radiologic	5	18.5 (17-20)	296	73 (3)	43.0 ± 4.7 (4)	30.5 ± 4.4 (4)	ND	ND
Questionnaire	3	19.0 (17-21)	576	58 (2)	45.3 ± 4.7 (2)	28.0 (1)	ND	ND
Prediction equations	8	21.5 (17-30)	1,908	77 (8)	49.4 ± 4.0 (8)	31.4 ± 3.4 (8)	66.5 ± 14.0	88.7 ± 4.9

Eight studies (#9098- Garcia-Diaz, et al., 1997, #9218- Gugger, 1997, #9255- Gyulay, et al., 1993, #9372- Hoffstein and Szalai, 1993, #11888- Pracharktam, et al., 1996, #10565- Schafer, et al., 1997, #10849- Svanborg, et al., 1990, #10986- Viner, et al., 1991) report results for more than 1 test; consequently the sum of all the categories is greater than 71.

ND = Not done.

Of the 71 considered for analysis, there were 7,572 patients: mean age was 49.0 ± 5.1 years (range, 36 to 60). Of the 61 studies in this set which reported gender, 81 percent of patients were male. BMI was reported in 44 of these studies, and averaged 30.9 kg/m² (range, 26.2 to 40.0). Patient level covariates are summarized in Evidence Table 3.

Diagnostic Test Characteristics

All included diagnostic studies were required to report results of a standard PSG. However, criteria that constitute a standard PSG varied among the studies. Most studies monitored respiratory activity (chest and abdominal movements and airflow) and oxygen saturation (oximetry). All included measures of sleep (EEG, EOG, or submental EMG), and some included measures of cardiac activity (ECG). Tibial EMG, snoring, and body position were less frequently monitored. Most noted that the traditional scoring system for sleep stages of Rechstahffen and Kales was used, and PSG data were assessed manually in nearly all cases. Nearly all studies based the AI (or AHI) upon the time asleep, as opposed to the time spent in bed, in contrast with the portable devices intended for home use, which are described further below. All standard PSGs were performed in the sleep laboratory, which was either a free-standing unit or a hospital setting with trained attendants present. Different thresholds for AI or AHI (or RDI) were used in different settings to make a diagnosis of SA, ranging from 5 to 15 for AI and 5 to 40 for AHI. Some studies required the presence of signs or symptoms of sleep disturbance in concert with an elevated AI (or AHI) for SA diagnosis, and some did not. Most did not report distinctions between obstructive SA, central SA, or mixed SA.

Findings of Diagnostic Test Studies

Oximetry

Evidence Table 4: Oximetry studies

Evidence Table 4: Oximetry studies

Study ID	# Enrolled	Group at entry	Comparison	Comparison measures	PSG # patients with SA	PSG mean (per hour) AI(*=AHI)	Test mean AI (*=AHI)	PSG threshold	Oximetry threshold	Sensitivity %	Specificity %	Correlation coefficient
8910- Douglas, et al., 1992	200	2	Oximetry	Measured as 4% desaturation frequency	91			AI> 15	> 5 desat/h	67	92
					91			AI> 15	> 10 desat/h	53	97
					91			AI> 15	> 15 desat/h	41	97
					91			AI> 15	> 20 desat/h	36	99
8920- Duchna, et al., 1995	207	2	Oximetry	Positive if min. O2 saturation <90% and/or > 5 desat > 4% /h	138			AHI> 5		97.1	23.2	0.85
8983- Farney, et al., 1986	54	2	Oximetry	Apnea if at least one transient desaturation >4% per 3 min interval		24.4				80	71
11665- Levy, et al., 1996	301	2	Oximetry	Measured by variation index (variation between successive O2 sat.; apnea induces a high variability)	30			RDI>15		90	75
10453- Rodriguez Gonzalez-Moro, et al., 1996	96	2	Hospital room Oximetry	Desat. >4% maintained	67	46.78*		AHI>10		91	69
10636- Series, et al., 1993	240	2	Home Oximetry	Positive in the presence of repetitive episodes (mean >10/night) of transient desaturations				AHI>10		98.2	47.7
12346- Yamashiro and Kryger, 1995	300	2	Oximetry	Frequency of desat >3% /hour (desat. index)	137			AI>5		94.2	73.5
9218- Gugger, 1997	67	2	Oximetry	Positive if > 20 4% O2 dips/hour				AHI>20		66	94
9255- Gyulay, et al., 1993	98	2	Home Oximetry	# desat/hour	43			AHI>15	>2%	65	74
									>3%	51	90
									>4%	40	58
				Positive if > 1% of time spent under 90% sat.						93	51
10849- Svanborg, et al., 1990	94		Oximetry	Oxygen desaturation index (ODI) > 2				AI>5		100	48	ODI to AI 0.41
	77	2		ODI= number of > 4% desat./hour	55
	17	3
9098- Garcia Diaz, et al., 1997	101	2	Oximetry	ODI >10	60			AHI>10		96.6	82.9	ODI to AHI 0.78
	26
10229- Pepin, et al., 1991	15	1	Oximetry	Oxygen saturation oscillations	15			RDI >5	Oscill of sat O2 > 1.5	75	86
	8	4							> 0.8	95	64
	3	4

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea Index= # of apneic episodes/hour sleep

Desat= Desaturations

Min= Minimum

ODI= Oxygen desaturation index

RDI= Respiratory distress index= AHI

Sat= Saturations

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Sensitivity, specificity, and/or correlation of oximetry results to standard PSG results were reported in 12 studies. In 3 of these studies (#10453- Rodriguez Gonzalez-Moro, de Lucas Ramos, Sanchez Juanes, et al., 1996, #10636- Series, Marc, Cormier, et al., 1993, and #9255- Gyulay, Olson, Hensley, et al., 1993), oximetry was measured separately (in time and different setting) in place from the PSG, including overnight at home in 2 studies (#10636- Series, Marc, Cormier, et al., 1993 and #9255- Gyulay, Olson, Hensley, et al., 1993) and on 2 different nights in 1 study (#9255- Gyulay, Olson, Hensley, et al., 1993). In the other 9 studies oximetry was measured during the nocturnal PSG. MetaWorks investigators did not include in this analyzable set any studies where results from the oximetry channel on a multi-channel portable device were compared with PSG results. All analyzable oximetry studies are listed in Evidence Table 4. The publication dates spanned 1986 to 1997. There were 1,784 patients in total, 1,756 of whom were suspected of having SA. The number of diagnosed SA patients was not reported in all studies. Their average age was 50.6 (k=11 studies reporting) and the percentage of patients who were male was 83 percent (k=10 studies reporting). The average BMI was 31.7 kg/m².

Figure 1: Oximetry tests: Summary ROC curve and 95% (more...)

   Figure 1: Oximetry tests: Summary ROC curve and 95% confidence interval

These oximetry studies used various formats for presentation of results: hourly frequency of desaturations of 3 percent or 4 percent, frequency of desaturations less than 90 percent, O₂ variability, or patients exceeding a certain number of desaturations per hour or per night. The type of probe was not consistently reported. Overall sensitivity of oximetry ranged from 36 percent to 100 percent, and specificity ranged from 23 percent to 99 percent, providing moderate sensitivity and specificity, with varying AI/AHI thresholds. The overall meta-analytic estimates (with Standard Error) of sensitivity and specificity are 87.4 percent (± 3.8) and 64.9 percent (± 6.7), and the summary ROC curve was generated (Figure 1). This curve shows that the studies all fell close to the estimated curve indicating little heterogeneity. The evidence score ranged from 16 to 32, and the mean score was 20.

Partial Time Polysomnogram

There were 7 studies reporting results with sensitivity, specificity, and/or correlations of partial night or day PSGs relative to full night, standard PSGs. All PSGs were performed in sleep laboratories with the standard array of physiologic monitors. Four studies compared partial night to full night PSGs, and the other 3 studies compared daytime PSGs to full night PSGs. These studies included 505 patients in total, most of whom were suspected of SA. The number of patients with a diagnosis of SA was not completely reported. Their average age was 51.4 (k=7 studies reporting) and the percentage of patients who were male was 86 percent (k=6 studies reporting). The average BMI was 33.9 kg/m².

Of the 4 studies (# 8685- Carmona Bernal, Capote Gil, Sanchez Armengol, et al., 1994, #12211- Fanfulla, Patruno, Bruschi, et al., 1997, #10533- Sanders, Black, Costantino, et al., 1991, #10572- Scarf, Garshick, Brown, et al., 1990) with comparisons of partial night to full night PSGs, all used AHI as the PSG metric for diagnosis of SA. One also provided results using AI. One of these studies reported only correlations, not sensitivity or specificity. Of the remaining 3 studies, the sensitivity of the partial night PSG ranged from 42 percent to 93 percent, and the specificity ranged from 70 percent to 100 percent. However, these ranges reflect varying AHI thresholds for diagnosis of SA.

Of the 3 studies (#11854- Persson and Svanborg, et al., 1996, #10631- Series, Cormier, and La Forge, 1991, #12559- Van Keimpema, Rutgers, and Strijers, 1993) of daytime PSG compared to full night PSG, 2 used AHI and 1 used AI as the PSG metric for diagnosis of SA. The sensitivity of the daytime PSG for results of full night PSG ranged from 66 percent to 100 percent, and the specificity ranged from 50 percent to 100 percent, again depending upon the AHI or AI thresholds used for diagnosis.

Evidence Table 5: Partial time polysomnogram studies (more...)

Evidence Table 5: Partial time polysomnogram studies

Study ID	# Enrolled	Group at entry	Comparison	Test results mean AI (*=AHI)	Patients with SA	PSG mean AI (per hour) (*=AHI)	PSG threshold	Sensitivity % to full PSG	Specificity % to full PSG	Correlation coefficient to full PSG	Site
8685- Carmona Bernal, et al., 1994	25	2	Partial night PSG	*35	16		AHI > 10	84	100	r = 0.97	Lab
			Full night PSG		19	*36					Lab
12211- Fanfulla, et al., 1997	29	2	1st Half night PSG	*33.4			AHI > 10			r = 0.89	Lab
			2nd Half night PSG	*44.9						r = 0.92	Lab
			Full night PSG			*39.8					Lab
11854- Persson and Svanborg, 1996	20	2	Day PSG	*37 median			AHI > 5	81	50		Lab
			Full night PSG			*13.5 median	AHI > 10	85	57		Lab
							AHI > 15	90	70		Lab
							AHI > 20	100	75		Lab
10533- Sanders, et al., 1991	50	2	Partial night PSG	27.9			AI > 5	87.9	86.7	r = 0.94	Lab
			Full night PSG	28.9			AI > 10	85.7	95		Lab
			Partial night PSG	*44.7			AHI > 5	93	100	r = 0.97	Lab
			Full night PSG	*44.2			AHI > 10	89.5	70		Lab
10631- Series, et al., 1991	35	2	Day PSG		22		AI > 5 or AHI > 10	88	100		Lab
			Full night PSG		25						Lab
12559- Van Keimpema, et al., 1993	306	2	Day PSG (1 hr)		84		> 3 apnea in 1 hr				Lab
			Full night PSG		89		AI > 5	66	88		Lab
							AI > 10	81	87		Lab
							AI > 15	81	85		Lab
							AI > 20	89	83		Lab
10572- Scarf, et al., 1990	40	4 HBP Males	Partial night PSG (90 min)		15		AHI > 5	63	86	r = 0.51	Lab
			Day PSG		7						Lab
			Full night PSG		22						Lab
			Partial night PSG		8		AHI > 10	42	100		Lab
			Day PSG		6						Lab
			Full night PSG		19						Lab
			Partial night PSG		5		AHI > 20				Lab
			Day PSG		5						Lab
			Full night PSG		12						Lab
			Partial night PSG		4		AHI > 30				Lab
			Day PSG		4						Lab
			Full night PSG		5						Lab

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

HBP= High blood pressure

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Figure 2: Partial PSG tests: Summary ROC curve and (more...)

   Figure 2: Partial PSG tests: Summary ROC curve and 95% confidence interval

Results for all 7 studies are displayed in Evidence Table 5, and the summary ROC curve derived from these studies is presented in Figure 2. Most studies were quite homogeneous with one exception which had low sensitivity and extremely high specificity. Sensitivity at AI/AHI threshold of 5 was 69.7 percent (± 5.3) and improved at a threshold of 10 to 79.5 percent (± 5.2). Specificity at AI/AHI threshold of 5 was 87.4 percent (± 5.4) and at the higher threshold of 10, changed little, at 86.7 percent (± 4.6). At still higher AI/AHI thresholds, there were too few studies with analyzable results. The average evidence score of all 7 studies was 18.6, with a narrow range, from 17 to 20.

Partial Channel Polysomnogram

Evidence Table 6: Partial channel polysomnogram studies (more...)

Evidence Table 6: Partial channel polysomnogram studies

Study ID	# Enrolled	Group at entry	Comparison	Test results mean AI (*=AHI)	Patients with SA	PSG mean AI (per hour) (*=AHI)	PSG threshold	Sensitivity % to full PSG	Specificity % to full PSG	Correlation coefficient to full PSG	Site
8687- Carrasco, et al., 1996	36	2	Partial channel				AHI > 20				Lab
			oximetry, chest movements, airflow
9098- Garcia Diaz, et al., 1997	101	2	Partial channel	26	60	27	AHI > 10	93	100	r= .99	Lab
			chest movements, airflow
9778- Lloberes, et al., 1996	76	2	Partial channel	22.7	50	32.2	AHI > 10	82	90		Respiratory
			oximetry, chest movements, airflow								ward

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

In 3 studies (#9778- Lloberes, Montserrat, Ascaso, et al., 1996, #8687- Carrasco, Montserrate, Lloberes, et al., 1996, #9098- Garcia Diaz, Capote Gil, Cano Gomez, et al., 1997) results of a partial set of PSG channels monitored for a full night were related to the full channel, full night PSG results. In all 3 studies, oximetry, airflow, and thoracoabdominal movement were recorded. In 2 studies, patients were monitored on 2 different nights, and in the third study, same night results were compared using respiratory channels versus full PSG. These studies totaled 213 patients with suspected or confirmed SA. Their average age was 51.7 (k=3 studies reporting) and the percentage of patients who were male was 81 percent (k=3 studies reporting). The average BMI was 32.0 kg/m². Sensitivity ranged from 82 percent to 94 percent and specificity from 82 percent to 100 percent. The sensitivity and specificity of partial channel and partial time PSGs appeared most promising as possible prescreening tests or replacements for full PSG. There were too few studies to meta-analyze. The average evidence score was 17.7 (17, 17, and 19). The results are displayed in Evidence Table 6.

Portable Devices

In total there were 25 portable device studies with sensitivity, specificity, and/or correlations to standard PSG. In terms of sensitivity and specificity, these studies were variable due to study and device heterogeneity. These studies enrolled 1,631 patients, and 1,368 were suspected SA patients at entry. Their average age was 48.5 (k=24 studies reporting) and the percentage of patients who were male was 84 percent (k=21 studies reporting). The average BMI was 30.0 kg/m².

Evidence Table 7: Portable device studies

Evidence Table 7: Portable device studies

Study ID	# Enrolled	Group at entry	Comparison measures	PSG # patients with SA	PSG mean (per hour)	Test mean	PSG threshold	Sensitivity %	Specificity %	Correlation coefficient	Site
8380- Acebo, et al., 1991	14	2	3, body movements		AI = 13	AI= 11.6				0.99	Lab
8605- Bradley, et al., 1995	31	2	3		AHI = 25		AHI> 15	100	92	0.85 (AI time in bed vs. AHI PSG time in bed)	Lab
8953- Emsellem, et al., 1990	63	2	1, 2 , 3 , 8			PRI	AHI>5	95	96		Lab
8967- Esnaola, et al., 1996	150	2	1, 8, snoring, body position	90			AHI > 5	97	18
							AHI> 10	98	78	0.73 (MESAM IV vs. AHI)
							AHI > 15	96	76
							AHI > 20	97	70
9019- Finke, et al., 1993	28	2	3		AI=40.7	AI=44.9				0.564 (AI vs. AI)	Lab
9063- Fleury, et al., 1996	44 (6 excluded)	2	3		AI=16.7	AI=19.3	AI>5	100	76	0.98 (AI vs. AI)	Lab
							AI>10	100	87
							AI>15	100	88
							AI>20	100	100
9218- Gugger, 1997	67	2	3		AHI=26.2	AHI=30.4	AHI>20	97	77	0.95 (AHI vs. AHI)	Lab
										0.95 (AI vs. AI)
9254- Gylulay, et al., 1987	14	1	1, 2, 8, body movements		RDI = 43.8	RDI= 40.3		78		0.70 (PSG vs. portable)	Lab
9267- Hamm, et al., 1990	11	1+3	1, 3, 8	6				97.3 (# apneas)	99.5 (# apneas)		Lab
9330- Hida, et al., 1993	170	4	3, 8, snoring				AI>5	93.8	79.3		Lab
				6			AI>10	92.5	87.5
							AI>15	93.6	68.3
							AI>20	90.7	68.4
11548- Issa, et al., 1993	129	2	1, snoring	70			RDI>7	89	95		Lab
				58			RDI>10	84	97
				47			RDI>15	87	96
				40			RDI>20	90	98
9575- Kiely, et al, 1996	36	2	3(+ 1 but not used for results)				AHI>10	85	87	0.92 (AHI vs. AHI)	Lab
							AHI>15	100	92	0.85 (AI vs. AI)
							AHI>20	88	93
11620- Koziej, et al., 1994	56	2	1, 8, snoring, body position	37			AHI>10	100	63	0.95(HSI vs. AHI)	Lab
9836- Man and Kang, 1995	104	2	1, 2, 3, 8, body position	23			AI>5	82.6	91.4	AI vs. AI 0.94	Lab
				28			AHI>15	85.7	94.7	AHI vs. AHI 0.97
12225- Parra, et al., 1997	89	2	1, 2, 3, 8, body position	75			AHI>10	73 (if test AHI threshold >18)	80 (if test AHI threshold >18)		Lab
							AHI>10	95 (if test AHI threshold >8)	33 (if test AHI threshold >8)
10380- Rauscher, et al., 1991	53	2	8, snoring			RDIS				0.33 (AHI vs. RDIS)	Lab
						RDIH				0.32 (AHI vs. RDIS)	Lab
10390- Redline, et al., 1991	51 (20 analyzed)	(mixed population)	1, 2, 3, 8, body movements		RDI	RDI	RDI>10	95	100	0.96	Lab
10464- Roos, et al., 1993	68	2	1, 8, snoring, body position		AI	AI (manual)	AI>10	92	88	0.82 (AI vs. AI)	Lab
					RDI	RDI (manual)	RDI>20	98	73	0.94 (RDI vs. RDI)
					RDI	RDI based on HR		53	80	0.61 (RDI vs. RDI)
					RDI	RDI based on snoring		87	33	0.51 (RDI vs. RDI)
10786- Stoohs and Guilleminault, 1992	56	2	1, body position, snoring, HR	26	RDI	HVI	RDI>10	32	58	0.67	Lab
					RDI	ISI	RDI>10	27	96	0.54
10785- Stoohs and Guilleminault, 1990	50	2	8, snoring	25	RDI	RDI based on HR	RDI>10	92	12		Lab
					RDI	RDI based on snoring	RDI>10	96	8
					RDI	RDI scored manually	RDI>10	92	72
10937- Tvinnereim, et al., 1995	10	2	3		AI	AI		85	96		Lab
12154- White, et al., 1995	30	2	1, 2, 3, 8, body movements, body position		AHI	AHI	>10	100	63.6	0.94	Lab
	70				AHI	AHI	>10	90.7	70.4	0.92	Home
11170- Zucconi, et al., 1996	29	2	1, 2, 3, 8, body position, snoring	19	AHI	AHI manually	>10	100	100		Lab
				16			>20	94	100
				11			>40	55	95
						AHI manually+ computer	>10	100	100
							>20	94	92
							>40	91	94
10565- Schafer, et al., 1997	114	2	1, 8, snoring, body position	80	RDI	ODI (based on O2 sat+HR)	RDI>10	95	41		ME- SAM- IV- Home
								note the ODI threshold used is 10/h	note the ODI threshold used is 10/h
10849- Svanborg, et al., 1990	94	2+3	1, 3, body movements		AI	combination of periodic respiration, movement, and desaturations	AI>5	100	67		Lab
	77	2		55		periodic respiration and movement alone	AI>5	100	62
	17	3

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

HR = Heart rate

HSI= Hand score index

HVI= Heart rate variation index

ISI= Intermittent snoring index

MESAM IV= Madaus electronics sleep apnea monitor

ODI= Oxygen desaturation index

PRI= Portable respiratory index

RDI= Respiratory distress index= AHI

RDIH= Respiratory distress index based on heart rate

RDIS= Respiratory distress index based on snoring

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Comparison measures (PSG channels): 1= O₂ ; 2= plethysmography; 3= airflow; 4= EMG submental; 5= EMG tibial; 6= EEG; 7= EOG; 8= ECG.

Of the 854 suspected SA patients whose subsequent diagnosis was reported, 500 (58.5 percent) were diagnosed with SA, using an AI/AHI threshold of > 5/hr. In all except 2 studies (#12154- White, Gibb, Wall, et al., 1995 and #10565- Schafer, Ewig, Hasper, et al., 1997), the portable device results were only available as measured in the setting of a sleep laboratory, and not at home, where they are generally intended for use. Devices were issued from different manufacturers, thresholds used for diagnosis of SA varied from 5 to 40 (AI or AHI) per hour, and results were reported in different formats. The average evidence score was 22.1 (range, 16 to 34). Details of these studies are listed in Evidence Table 7.

Evidence Table 8: Portable device measurement parameters (more...)

Evidence Table 8: Portable device measurement parameters

Study ID	Airflow	Respiration	Oximetry	Heart rate	Body position	Body movement	Snoring
8967- Esnaola, et al., 1996			X	X	X		X
11620- Koziej, et al., 1994			X	X	X		X
10464- Roos, et al., 1993			X	X	X		X
10786- Stoohs, et al., 1992			X	X	X		X
10565- Schafer et al., 1997			X	X	X		X
10785- Stoohs, et al., 1990				X			X
10380- Rauscher, et al., 1991				X			X
8605- Bradley, et al., 1995	X		X
9063- Fleury, et al., 1996	X		X
9218- Gugger, 1997	X		X
9575- Kiely, et al., 1996	X		X
11170- Zucconi, et al., 1996	X	X	X	X	X		X
12225- Parra et al., 1997	X	X	X	X	X		X
10390- Redline, et al., 1991	X	X	X	X		X
9836- Man et al., 1995	X	X	X	X	X
12154- White, et al., 1995	X	X	X	X	X	X
8953- Emsellem, et al., 1990	X	X	X	X
9019- Finke, et al., 1993	X
10937- Tvinnereim, et al., 1995	X
11548- Issa, et al. 1993			X				X
8380- Acebo, et al., 1991		X				X
10849- Svanborg, et al., 1990		X				X
9254- Gylulay, et al., 1987		X	X	X		X
9267- Hamm, et al., 1990	X		X	X
9330- Hida, et al., 1993	X			X			X

Studies listed in Evidence Table 8 were categorized according to the channels monitored by portable devices.

Figure 3: Portable device with oximetry, heart rate, (more...)

   Figure 3: Portable device with oximetry, heart rate, snoring, and body position: Summary ROC curve and 95% confidence interval

The first 5 studies measured oximetry, snoring sounds, heart rate, and body position (#8967- Esnaola, Duran, Infante-Rivard, et al., 1996, #11620- Koziej, Cieslicki, Gorzelak, et al., 1994, #10464- Roos, Althaus, Rhiel, et al., 1993, #10786- Stoohs and Guilleminault, 1992, and #10565- Schafer, Ewig, Hasper, et al., 1997). These studies included 444 patients total. Figure 3 gives the summary ROC curve for these studies.

In 2 studies (#10785- Stoohs and Guilleminault, 1990 and #10380- Rauscher, Popp, and Zwick, 1991) totaling 103 patients, only 2 channels were monitored: snoring sounds and heart rate.

Figure 4: Portable device with airflow and oximetry: (more...)

   Figure 4: Portable device with airflow and oximetry: Summary ROC curve and 95% confidence interval

Four studies (#8605- Bradley, Mortimore, and Douglas, 1995, #9063-Fleury, Rakotonahary, Hausser-Hauw, et al., 1996, #9218- Gugger, 1997, #9575- Kiely, Delahunty, Matthews, et al., 1996) recording airflow and oximetry enrolled a total of 178 patients. Figure 4 gives the summary ROC curve for these studies.

Figure 5: Portable device with airflow, respiration, (more...)

   Figure 5: Portable device with airflow, respiration, oximetry, heart rate, body position, and snoring: Summary ROC curve and 95% confidence interval

The next 6 studies tested portable devices monitoring oximetry, airflow, respiration, and heart rate (#11170- Zucconi, Ferini-Strambi, Castronovo, et al., 1996, #12225- Parra, Garcia-Esclasans, Montserrat, et al., 1997, #10390- Redline, Tosteson, Boucher, et al., 1991, #9836- Man and Kang, 1995, #12154- White, Gibb, Wall, et al., 1995, and #8953- Emsellem, Corson, Rappaport, et al., 1990). Some of them also included measurements of body position, body movement, and snoring sounds. There were 436 patients enrolled in these studies. The summary ROC curve for the 4 studies which included airflow, respiration, oximetry, heart rate, and body position are shown in Figure 5.

The remaining 8 studies could not be grouped by channels.

Non-sleep Tests

There were 17 studies that provided sensitivity, specificity, and/or correlations of results of some clinical measure in relation to standard PSG results. Pulmonary function tests and spirometry were included in this set of studies.

Evidence Table 9: Flow volume loop studies

Evidence Table 9: Flow volume loop studies

Study ID	# Enrolled	Group at entry	Comparison	Comparison measures	Test results	PSG # patients with SA	PSG mean (per hour) AI (*=AHI)	PSG threshold	Sensitivity %	Specificity %	Correlation coefficient
9373- Hoffstein, et al., 1989	405	2	MVCFR	Extrathoracic airway stenosis Same as FEF50/FIF50
	207	1			0.68	207	41*	AHI > 10	12	86
	198	4			0.69	0	4*	AHI > 10
9646-Krieger, et al., 1985	57	2
	30	1	FEF50/FIF50 mean	Mid exp. flow ratios >1 = extrathoracic airway stenosis	1.27	30	37.2	AI > 5	67	29
	27	4	FEF50/FIF50 mean		1.39		1
		1	Sawtooth sign	% of pts with pharyngeal fluttering during breathing	61%				61	54
		4	Sawtooth sign	% of pts with pharyngeal fluttering during breathing	46%
		1	FEF50/FIF50 mean plus sawtooth sign	Both tests abnormal					86	13
		4	FEF50/FIF50 mean plus sawtooth sign
11908- Rauscher, et al., 1990	102	1+4+3
	32	1	FEF50/FIF50 >1	As above	19%	29		AI > 10	17	83
	40	4			8%	1
	30	3			7%	2
		1	Sawtooth sign	As above	69%				72	61
		4			35%
		3			33%
		1	Both FEF50/FIF50 >1 plus sawtooth sign	As above	9%				7	89
		4			5%
		3			3%
12381- Shore and Millman, 1984	31**	2	FEF50/FIF50 >1	As above
	17	1			1.09	17	45		41	69
	13	4			1	0
		1	Sawtooth sign						29	85
		4
		1	FEF50/FIF50 >1 plus sawtooth sign						59	54
		4

** 1 patient with pure central apnea was excluded.

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

FEF₅₀/FIF₅₀= ratio of forced expiratory flow at 50% of vital capacity

MVCFR= ratio of the maximal experatory flow at 50% of the vital capacity to maximal inspiration flow at 50% of vital capacity

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Figure 6: Flow volume FEF₅₀/FIF₅₀: Summary ROC curve (more...)

   Figure 6: Flow volume FEF₅₀/FIF₅₀: Summary ROC curve and 95% confidence interval

FEF₅₀/FIF₅₀ =ratio of forced expiratory flow at 50% of vital capacity

Flow volume loops. Four studies reported results of flow volume loops (#9373- Hoffstein, Wright, and Zamel, 1989, #9646- Krieger, Weitzenblum, Vandevenne, et al., 1985, #11908- Rauscher, Popp, and Zwick, 1990, and #12381- Shore and Millman, 1984) and are listed in Evidence Table 9. These studies included 595 patients total, of which 286 were diagnosed with SA. One patient with pure central apnea enrolled on study #12381- Shore and Millman, 1984, was excluded from all analyses. Their average age was 50.0 (k=4 studies reporting) and the percentage of patients who were male was 79 percent (k=4 studies reporting). The average BMI was 29.0 kg/m². PSG results were expressed as AI in 2 studies (diagnostic cutoffs, 5 and 10) and AHI in 1 study (diagnostic cutoff 10). One study did not state the PSG metric used for SA diagnosis. Sensitivity of FEF₅₀/FIF₅₀, a measure of extrathoracic airway obstruction, ranged from 12 percent to 67 percent, and the specificity ranged from 29 percent to 86 percent. In 2 studies FEF₅₀/FIF₅₀ was reported as a mean, and in 2 studies the percentage of patients with results exceeding 1.0 was reported. The presence of the sawtooth sign, indicative of pharyngeal fluttering during respirations, had a sensitivity ranging from 29 percent to 61 percent and a specificity ranging from 54 percent to 85 percent. Using both measures combined, the sensitivity ranged from 7 percent to 86 percent, and specificity from 13 percent to 89 percent. The average AI of the SA patients and of the non-SA patients was comparable, despite differing diagnostic cutoffs for SA. The meta-analysis of sensitivity and specificity yielded pooled estimates and ROC curve, as shown in Figure 6. The sensitivity of FEF₅₀/FIF₅₀ was 19.6 percent (± 9.6) and the specificity was 79.2 percent (± 9.7). Thus, flow volume loops provided the least accurate sensitivity and specificity.

For the sawtooth sign, the sensitivity was 61.9 percent (± 10.7) and the specificity 62.7 percent (± 7.2). When both measures were analyzed together, the sensitivity was 39.1 percent (± 25.3) and specificity 60.5 percent (± 23.7). The evidence scores of these studies ranged from 17 to 20 (average = 18.3).

Evidence Table 10: Global impression studies

Evidence Table 10: Global impression studies

Study ID	# Enrolled	Group at entry	Comparison	Comparison measures	Test results	PSG # patients with SA	PSG mean (per hour) AI (*=AHI)	PSG threshold	Sensitivity %	Specificity %	Correlation coefficient	Site
10986- Viner, et al., 1991	410	2	Global impression	After clinical assessment		190		AHI > 10	52	70		Clinical setting
	190	1
	220	4
9276- Haponik, et al., 1984	37	2	Global impression	Observation during sleep	20/37	31		AI > 5	64.5	100		Lab
	31	1					57.6
	6	4					55.1
9372- Hoffstein and Szalai, 1993	594	2	Global impression	After clinical assessment		275		AHI > 10	60	63		Clinical setting
	275	1			140/275		36
	319	4			225/319		4
9255- Gyulay, et al., 1993	98	2	Global impression	After clinical assessment		43		AHI > 15	79	50		Clinical setting
	43	1
	55	4

Blank cells represent data not reported.

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Figure 7: Global impression: Summary ROC curve and (more...)

   Figure 7: Global impression: Summary ROC curve and 95% confidence interval

Global impressions. There were 4 studies reporting the global impression of clinicians: 3 studies in clinic settings (#10986- Viner, Szalai, and Hoffstein, 1991, #9372- Hoffstein and Szalai, 1993, and #9255- Gyulay, Olson, Hensley, et al., 1993), and 1 study of sleeping patients in a sleep laboratory (#9276- Haponik, Smith, Meyers, et al., 1984). These studies are listed in Evidence Table 10. Together these studies included 1,139 patients total, 539 of whom were diagnosed with SA. AHI was the PSG metric used in 3 studies, with diagnostic cutoffs of 10 and 15. In the study of sleeping patients, the PSG metric was AI, and the cutoff for SA diagnosis was 5. Their average age was 47.7 (k=3 studies reporting), and the percentage of patients who were male was 67 percent (k=4 studies reporting). The average BMI was 29.4 kg/m². Sensitivity of global impressions of SA relative to PSG diagnosis of SA ranged from 52 percent to 79 percent, with a pooled estimate of 58.9 percent (±4.2); specificity ranged from 50 percent to 100 percent, the latter result from the observation of sleeping patients. The pooled estimate of specificity was 65.6 percent (±4.8), thus providing moderate sensitivity and specificity. The evidence scores of these studies ranged from 19 to 28 and averaged 23.3. The summary ROC curve for these 4 studies is in Figure 7. These show that while sensitivity was relatively constant across studies, specificity varied a great deal. For individual study results see Evidence Table 10.

Other clinical. Nine studies reporting sensitivity and specificity were identified for several clinical measures, but there were too few in each category to permit meta-analysis: neck circumference, airway dimensions via acoustic reflection (#11585-Katz, Stradling, Slutsky et al., 1990), nasopharyngeal airway resistance (#12075- Suratt, McTier, and Wilhoit, 1985), pulmonary function tests without flow volume curves (#11812- Onal, Leech, and Lopata, 1985), laryngoscopy (#12212- Geibel, Schonhofer, Rolzhauser, et al., 1997), snoring sound analysis (#11404- Fiz, Abad, Jane, et al., 1996), pupillary light reflex (#11892- Pressman and Fry, 1989), heart rate variability by ECG monitoring (#9567- Keyl, Lemberger, Pfeifer, et al., 1997), and body mass index alone (#11689- Lowe, Fleetham, Adachci, et al., 1995 and #10951- Vaidya, Petruzzelli, Walker, et al., 1996). No conclusions regarding the usefulness of any of these clinical measures as aids in the screening or diagnosis of SA can be made on the basis of so few studies.

Chemical. Similarly, there was only 1 study of a chemical test (urinary uric acid and creatinine) as a screen for SA: (#8610- Braghiroli, Sacco, Erbetta, et al., 1993). There were 88 patients enrolled, 49 with SA. Patients who desaturated at night differed from those who did not, but no correlation can be made on the basis of a single study.

Prediction Equations

Evidence Table 11: Prediction equation studies

Evidence Table 11: Prediction equation studies

Study ID	# Enrolled	Group at entry	Comparison	Comparison measures	Test results	PSG # patients with SA	PSG mean AI (per hour) (*=AHI)	PSG threshold	Sensitivity %	Specificity %	Correlation coefficient	Site
9255- Gyulay, et al., 1993	98	2	Model	Age, obesity, HBP, apnea spells					68	55
	43	1				43		AHI > 15
	55	4						AHI > 15
	98	2	Model + home oxygen					AHI > 15	72	88
12219- Kushida, et al., 1997	254	1	Model (mean results)	BMI, neck circumference, and overjet	95.3		40.7	AHI > 5	97.6	100
		1	Model (cut off results)	(#pts >70)	248				60.6	93.4
	46	4	Model (mean results)		61.6		0.8
		4	Model (cut off results)		0
11897- Quera-Salva, et al., 1988	25	2	Model	Age, BMI, cephalometry, % stage/sleep, ABG, PFTs			68	RDI > 10			r=0.70
10951- Vaidya, et al., 1996	309	2	Model	Fell asleep driving, snoring, apnea spells, BMI		225		RDI > 10	96.7	21.4
	225	1
	84	4
10986- Viner, et al., 1991	410	2	Model	Gender, age, BMI, snoring		190		AHI > 10	28	95
	190	1
	220	4
9372- Hoffstein and Szalai, 1993	594	2	Model	BMI, age, apnea spells, gender, pharyngeal exam		275		AHI > 10			r=0.06
	275	1					36
	319	4					4
11888- Pracharktam, et al., 1996 **	58	2	craniofacial index score (MODELS)	Model 1=13 cephalometric & 4 anthropometric measurements		28		RDI>20	82.1	86.7		Lab (but not all pts had full PSG)
	28	1					RDI=52.9
	30	4					RDI=5.1
	58	2		Model 2=3 variable stepwise model				RDI>20	67.9	83.3		Lab
10565- Schafer, et al., 1997	114	2		Model 1=BMI, observed apneas, falling asleep (involuntary), oxygen desat index >10/hr(MESAM)		80	RDI=29.2	RDI>10	41	91		Lab
	80	1					RDI=38.9
	34	4					RDI=6.9
		2		Model 2=BMI, observed apneas, falling asleep (involuntary), oxygen desat index >20/hr(MESAM)				RDI>10	34	94		Lab

** This study appears in both the radiologic and prediction equation tables. However, for summary purposes this study is only included with the prediction equation results on Table 3.

Blank cells represent data not reported.

ABG= Arterial blood gas.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

BMI= Body mass index

HBP= High blood pressure

MESAM IV= Madalus electronics sleep apnea monitor

PFTs= Pulmonary function tests

RDI= Respiratory distress index= AHI

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Figure 8: Prediction equations: Summary ROC curve and (more...)

   Figure 8: Prediction equations: Summary ROC curve and 95% confidence interval

Eight studies (#9255- Gyulay, Olson, Hensley, et al., 1993, #12219- Kushida, Efron, and Guilleminault, 1997, #11897-Quera-Salva, Guilleminault, Partinen, et al., 1988, #10951- Vaidya, Petruzzelli, Walker, et al., 1996, #10986- Viner, Szalai, and Hoffstein, 1991, #9372- Hoffstein and Szalai, 1993, #11888- Pracharktam, Nelson, Hans, et al., 1996, #10565- Schafer, Ewig, Hasper, et al., 1997) reported the sensitivity, specificity, or correlations of multivariate models relative to PSG results. MetaWorks investigators did not capture the predictive accuracy of each separate component of each model, although it was reported in some studies. Only the predictive features of the model as a composite result were captured. These studies included 1,908 patients, 254 of whom were known at entry to have SA; an additional 841 were diagnosed during the study. Their average age was 49.4 (k=8 studies reporting) and the percentage of patients who were male was 77 percent (k=8 studies reporting). The average BMI was 31.4 kg/m². Each model included at least 3 of the following variables: gender, age, obesity, hypertension, neck circumference, overjet, BMI, cephalometry measurements, arterial blood gases, home oximetry, pulmonary function tests, apnea spells, snoring, falling asleep while driving, percentage of time spent in Stage 1 sleep. Sensitivity of the models for the PSG result ranged from 28 percent to 97.6 percent, and specificities ranged from 21.4 percent to 100 percent. The pooled estimate for sensitivity was 66.5 percent (±14.0) and specificity was 88.7 percent (±4.9), achieving high sensitivity and specificity. The evidence scores of these studies ranged from 17 to 30, and averaged 21.5. All results are displayed in Evidence Table 11, and the summary ROC curve is shown in Figure 8. In this figure, both sensitivity and specificity were high for most studies.

Radiologic

Evidence Table 12: Radiologic studies

Evidence Table 12: Radiologic studies

Study ID	# Enrolled	Group at entry	Comparison	Test results	Patients with SA	PSG mean AI (per hour) *=AHI	PSG threshold	Sensitivity % to full PSG	Specificity % to full PSG	Correlation coefficient to full PSG	Site
11936- Rodenstein, et al., 1990	40	2	MRI	AHI	10	56.3 SA	AI > 15			r= .55	Lab
						6.7 snorers				AP/T & AHI
12021- Shinohara, et al., 1997	37	2	Cephalometry	AHI	21		AI > 5			r= .63
										AT area & AI
11888- Pracharktam, et al., 1996 **	58	2	Cephalometry	RDI	28	52.9 SA	AI > 20				Lab
						5.1 snorers
8832- Davies, et al., 1990	66	2	Cephalometry and neck circumference							r= .63 Neck circum & SA	Lab
11689- Lowe, et al., 1995	80	1	Cephalometry	AHI	80	30.2 SA	AI > 5				Lab
	25	4
11081- Will, et al., 1995	48	1	Cephalometry	RDI	48		AI > 20			r= .306 MPH & RDI

** This study appears in both the radiologic and prediction equation tables. However, for summary purposes this study is only included with the prediction equation results on Table 3.

Blank cells represent data not reported.

AP/T= diameter ratio in each section of the pharyngeal anteroposterior and transverse diameter

AT= Adipose tissue

AHI= Apnea-hypopnea Index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

Circum= circumference

HBP= High blood pressure

MPH= Perpendicular distance from gonion gnathion to hyoid body

MRI= Magnetic resonance imaging

RDI= Respiratory distress index= AHI

SA= Sleep apnea patients

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

One study correlated MRI results with PSG. This study included 40 patients whose results (#11936- Rodenstein, Dooms, Thomas, et al., 1990). One study correlated CT scans with PSG and included 37 patients (#12021- Shinohara, Kihara, Yamashita, et al., 1997). The latter also reported cephalometry, in relation to PSG results. There were additional cephalometry studies, which reported a multitude of different measurements of patients in different positions. Most of these studies did not, however, report correlations to PSG results, and none reported sensitivity or specificity in relation to PSG results. Of the 5 radiologic studies which did report correlations to PSG results, 1 study (#11888- Pracharktam, Nelson, Hans, et al., 1996) combined cephalometric results with morphometric results in a statistical model, which is discussed in the Prediction Equations section above. Among the remaining 4 studies (#8832- Davies and Stradling, 1990, #11689- Lowe, Fleetham, Adachi et al., 1995, #11081- Will, Ester, Rameriz, et al., 1995, #12021- Shinohara, Kihara, Yamashita, et al., 1997) with 256 patients in total, there is too little overlap of measurements to pool data, or even to synthesize data in a strictly qualitative way. The average evidence score of these studies was 18.5 (range, 17 to 20). These studies are displayed in Evidence Table 12.

Questionnaires

Evidence Table 13: Questionnaire studies

Evidence Table 13: Questionnaire studies

Study ID	# Enrolled	Group at entry	Comparison	PSG threshold	Sensitivity % to full PSG	Specificity % to full PSG	Correlation coefficient to full PSG
9479- Johns, 1991	55	1	Questionnaire				ESS vs. RDI
	30	3	ESS Score				r= .55
9279- Haraldsson, et al., 1992	42	2	Questionnaire	AHI > 5	80
			snoring, breathing cess	AHI >10	91
			daytime sleepiness
10334- Pouliot, et al., 1997	354	2	Questionnaire	AHI >20	42	68
			ESS score

Blank cells represent data not reported.

AHI= Apnea-hypopnea index= # of apneic episodes/hour sleep

AI= Apnea index= # of apneic episodes/hour sleep

Cess= cessation

ESS score= Epworth Sleepiness Scale

RDI= Respiratory distress index= AHI

Group at entry: 1 = SA; 2 = suspected sleep disorder; 3 = normal; 4 = other.

Three studies reported sensitivity, specificity, or correlations of focused questionnaires to PSG results. Only 1 study (#10334- Pouliot, Peters, Neufeld, et al., 1997) out of 2 studies which used the Epworth Sleepiness Scale (ESS), reported sensitivity (42 percent) and specificity (68 percent) in 354 suspected SA patients, using a PSG AI threshold of 20. The other ESS paper (#9479- Johns, 1991) reported a correlation (r=0.55) to PSG RDI. The third paper (#9279- Haraldsson, Carenfelt, Knutsson, et al., 1992) did not use standard questionnaires, but selected questions about observed apneas, falling asleep or daytime sleepiness, and snoring. One additional paper (#8557- Bliwise, Nekich, and Dement, 1991) should be noted in this category (but is not included in Evidence Table 13), since it studied the sensitivity and specificity of several questions in a large number of patients (n=1,409). However, it only reported these outcomes by patient subgroups stratified by gender; as such it was not considered analyzable with the other studies in this set. These 3 studies are presented in Evidence Table 13.

Prevalence and Comorbidity Studies

Prevalence and comorbidities of SA and based on AI or AHI were captured from 65 studies (11,921 subjects) which spanned the years 1981 to 1997, 36 published after 1990. Thirty-two of these 65 studies were performed in the United States, 21 in Europe, and 12 elsewhere. Average study size was 183 patients (range, 10 to 1,620). Data listings for these studies are provided separately.⁽²⁾ All averages which follow are weighted for sample size. Variability in the reported prevalence of SA, or in the prevalence of associated conditions in SA patients, is likely due to different distributions of age and gender among the populations sampled, and more so due to different criteria for a diagnosis of SA. As with the diagnostic test studies, there appeared to be no consensus in the literature regarding a consistent definition of SA, or common criteria for making the diagnosis. These limitations in the literature should be considered when interpreting the results which follow.

Evidence Table 14: Prevalence of sleep apnea

Evidence Table 14: Prevalence of sleep apnea

Population	Number of studies	Number of patients	Mean % of patients with sleep apnea
General population	11	2,410	9.2
Elderly	7	469	34.6
Coronary artery disease	8	461	54.9
Hypertension	4	166	26.9
Impotence/erectile dysfunction	3	1,138	42.2

Evidence Table 15: Summary of studies with comorbid (more...)

Evidence Table 15: Summary of studies with comorbid conditions

Comorbidity	Number of studies	Number of sleep apnea patients	Mean % of sleep apnea patients with condition
Death	5	2,281	7.0
Hypertension	24	3,497	42.0
Coronary artery disease/myocardial infarction	9	1,086	20.3
Ventricular arrhythmias	5	205	13.1

Limitations and Strengths of the Evidence Base

There are many limitations to this evidence base. In general the diversity of designs and study objectives was high and the methodological rigor of the diagnostic studies included was so low that, contrary to our usual practice of using evidence scores only in sensitivity analyses, MetaWorks investigators decided to use the diagnostic evidence rating instrument as a filter for selecting consistent studies for data extraction. MetaWorks investigators thereby rejected studies scoring in the bottom 20 percent of the distribution of scores. Even so, the studies that remained constitute Level III to IV (Cook, Guyatt, Laupacis, et al., 1992) evidence, that is, primarily derived from case series and observational studies. There were very few diagnostic studies that employed randomized assignment of tests, and very few studies performed blinded assessments of test results, both key features of rigorous diagnostic studies.

Other limitations that apply to the whole dataset are numerous. With regard to the gold standard PSG, there was considerable variability in how PSGs were administered, i.e., which measures were considered essential components of standard PSGs. As a consequence several questions are raised: Is the "standard" PSG really a gold standard for the diagnosis of SA? Does the ability to measure sleep stage improve diagnostic accuracy? Is an entire night necessary? Proof is lacking, and the reasonably high sensitivity and specificity of partial channel PSGs and partial time PSGs only serve to reinforce this uncertainty. There was considerable inconsistency in how apnea and hypopnea were defined, let alone what metric (AI or AHI) and what threshold (>5, 10, 15, 20, 30 per hour) was used to diagnose SA. There was inconsistency in the incorporation of clinical signs and symptoms with PSG results in diagnosing SA. Distinctions between types of SA were usually not made. Night to night reproducibility of the gold standard is still not well documented, and may also be different using different diagnostic thresholds. Few studies included normals, to achieve a broad spectrum of test subjects. In fact, there is still debate over what may be the frequency distribution of apnea during sleep in the general population. Is any amount of apnea ever normal? Lastly, authors appear to often be conflicted about the best screening approach: some seek tests to rule in the diagnosis, and others to rule it out. It was often unclear whether the intended use of the test was in high-risk populations, or low-risk general populations.

For the portable device studies, many of the issues noted above regarding PSG also apply. In addition, device features such as equipment failure rates, night to night reproducibility, price, compliance, and safety are rarely reported. Differences in method of analysis of data recordings were often not tested or appreciated (visual vs. automated). Most importantly, few portable devices intended for unattended use at home have been validated under those conditions of use. Portable studies are also typically not based upon sleep time, as are the standard PSGs to which they are compared. Therefore, the question remains as to the necessity of basing AI or AHI upon sleep time, and whether commonly used surrogates of sleep in these studies, such as body movement, are valid.

In the studies which report high frequencies of comorbidities, a causal association has not been shown. Much has been presumed on the basis of the physiologic observations of repeated hypoxemia contributing to systemic and pulmonary hypertension, and coronary and cerebrovascular insufficiency. However, studies reporting actual clinical consequences of certain AIs, with or without treatment, are not well represented in this literature base. Perhaps a review of treatment studies would yield more useful information in this regard. Also, the ongoing Sleep Heart Study (A. Pack, personal communication) may eventually clarify whether SA is an independent risk factor for cardiovascular events.

Estimates of prevalence of SA in general populations are weak due to the fact that these estimates are typically based upon unvalidated tests, not the gold standard PSG. The one stand-out in this set of studies is that of the ongoing Wisconsin Sleep Study Cohort (Young, Palta, Dempsey, et al., 1993).

With regard to strengths of the evidence base, there are several. This evidence base represents the best available evidence derived from relevant diagnostic literature in 5 languages. It is more comprehensive than previous reviews, and it is unlikely that any important diagnostic studies were missed. Restricting data extraction and data analysis to those studies with features most likely to yield useful diagnostic test information, specifically to those studies reporting sensitivity and specificity of diagnostic maneuvers, is consistent with study selection approaches previously employed by the ASDA Standards of Practice Committee in its 1994 statements (Ferber, Millman, Coppola, et al., 1994), in its 1997 statements (Chesson, Ferber, Fry, et al., 1997 and Polysomnography Task Force, 1997), and the Blue Cross/Blue Shield Technology Evaluation Committee 1996 assessment of portable sleep studies. Furthermore, this established database is now updatable. It serves as a valuable resource to practitioners and researchers, provided it is maintained current.

Another strength is the statistical approach. This is the first time summary ROC curves have been constructed for studies with sufficient data in SA. These curves indicate the degree of heterogeneity between the study sets, as well as the relationship between sensitivity and specificity within each study set.

Another strength lies in the fact that the review has been performed by investigators independent of the field of SA and hence is free of conflicts of interest. On the other hand, multiple stakeholders have had a voice in the project from its inception: consumers, government, insurers, sleep laboratory personnel, and clinicians have all had opportunity to contribute ideas and perspectives.

Conclusions

This systematic review of the best available evidence suggests the answers to the questions posed at the start of the project are as follows:

• What diagnostic and screening tests are presently available? And what is the strength of the evidence in support of each? Numerous diagnostic strategies have been reported, but the published evidence for most is still insufficient. There is some evidence in a relatively small number of patients, which should be expanded with more studies, which suggests that a full PSG may not be necessary to diagnose SA. Rather that sleep laboratory measured oximetry, thoracoabdominal respiratory movements, and airflow alone (partial channel PSG), in the context of clinical suspicions of SA, may have sufficient sensitivity and specificity. There is still insufficient evidence that any multi-channel portable device can be used reliably in the home setting. With regard to all the other types of assessments which were hoped to be somehow predictive of SA, including anthropomorphic signs, ENT and dental assessments, and radiologic measures, the etiologic relevance of most is at best controversial. While statistically significant associations have been noted in some studies, causal associations have not been proven. Flow volume loops do not appear to be useful diagnostic tests in SA. Lastly, sensitivity and specificity were good for clinical prediction rules in general, but additional studies would be required to build the evidence base to justify widespread adoption of any single model.

• What is the predictive ability of these tests in different populations? This cannot be answered, given the fact that nearly all "tests of tests" were performed in patients suspected of having SA on the basis of clinical signs and symptoms. There are very few studies of different tests in different populations that are validated against a PSG diagnosis of SA.

• What are the implications of certain PSG results in terms of serious clinical events occurring as comorbidities or as sequelae in association with a diagnosis of SA? This question cannot be definitively answered. While there are very few follow-up studies available, the few included here suggested that the prevalence of coronary artery disease and hypertension are both quite high. It is not clear, however, whether SA is an independent risk factor for these conditions.

Future Research

Future studies of diagnostic strategies should address the many limitations of the literature noted above. The field could benefit from adoption of a common terminology for fundamental concepts such as apnea and hypopnea, and the relation between AI and AHI should be established in order to allow conversions and comparisons across studies. Researchers should seek to clarify the prevalence of apnea and hypopnea in general populations by gender and age. More naturalistic sleep studies (in the home) are still of interest, as it is possible that much of the uncertainty about the nature of SA and its pathophysiology, risk factors, and clinical consequences derives from the fact that the phenomenon called SA may be altered by the very fact of observing it via standard PSG. All sleep monitoring systems that are proposed as prequalifiers or replacements for PSG must be validated in the setting in which they are intended to be used.

Appendix A Evidence Scoring Form

Appendix B Data Extraction Form for Diagnostic Studies

Appendix C Data Extraction Form for Prevalence and Outcome Studies

Appendix D Peer Reviewer Questionnaire

Appendix H AHCPR Data Matrix

append-h.pdf (1926322 bytes)

Appendix I AHCPR Data Matrix of Prevalence or Outcomes of Sleep Apnea Studies

append-i.pdf (18474 bytes)

Appendix J Legend for Data Matrices

Abn=abnormal

abn sleep movt=abnormal sleep movement

AI=apnea index

AHI=apnea-hypopnea index

ap=apnea

AP/T=anterior posterio/transverse

BP=blood pressure

Br=breathing

CAD=coronary artery disease

Categorization of papers:

• 1=Testing tests

• 2=Signs and symptoms for sleep apnea

• 3=Outcomes of sleep apnea

Cephalometric measurements :

• MP-H=distance from mandibular plane to hyoid bone (in mm)

• PAL=length of soft palate measured on cephalometric x-ray - distance from posterior nasal spine to top of soft palate

Cephalometric measurements :

• PAS=posterior airway space (in mm) defined as the space behind the base of the tongue space (in mm)

• PNS-P=distance from posterior nasal spine to the tip of the soft palate (in mm)

• SNA=angle measurement from sella, nasion, subspinale (point A)

• SNB=angle measurement from sella(s), nasion(N), supramentele (point B) Cranial base: VI SN=length of anterior cranial base V2 BaN=overall length of cranial base V3 BaSN=angulation of cranial base Face: V7 SNA=angle of maxillary prognathism V8 SNB=angle of mandibular prognathism V9 ANB=difference in prognathism V10 PnsA=maxillary length V11 BaA=sagittal dimension of median upper face from Ba to A

Cephalometric measurements :

• Face:

• V12 DcA=sagittal dimension of median upper face from Dc to A

• V13 DcGn=overall length of mandible

• Face Height:

• V14=upper face height

• V15=lower face height

• Upper Pharynx:

• V4 BaPns=dimension of bony pharynx

• V5 BaH=depth of soft tissue in front of basion

• V6 HPns=airway opening on BaPns line

• [RS]=retroglossal space

• [MRH]=mandibular plane to hyoid (mm)

• [HP-CS]=head flexion, hard palate to spine

CHD=coronary heart disease

Circum=circumference

Cm=centimeters

Comp=computer scoring

COPD=chronic obstructive pulmonary disease

Corr=correlation

CPAP=continuous positive airway pressure

CT=computed tomography

CT₉₀ =% of time spent at SaO₂ below 90%

CVA=cardiovascular accident

D=diastolic (blood pressure, mmHG)

DBR=disordered breathing rate

Desat=desaturation

DI=desaturation index

HRA=difference of heart rate during apnea in non-REM sleep (min^-1 )

HRB=difference of heart rate during breatholding (min^-1 )

HRM=diffrence of heart rate during Mueller maneuver

HRV=difference of heart rate during Valsalva maneuver

Diff=difference

Disrupt=disruptively

DSat=desaturation

Dur=duration

DX=diagnosis

ED=Erectile dysfunction

ERV=expiratory reserve volume

ESRD=end stage renal disease

Ev=event

Expir=expiratory

FeF₅₀ /FIF₅₀ =ratio of forced expiratory flow at 50% of vital capacity

FEV₁ =maximum forced expiratory volume in 1 second

FN=false negative

FP=false positive

FR=flow rates

FRC=functional residual capacity

FVC=forced vital capacity

Fx=failure

Gnrl=general population

H=hour

HBP=high blood pressure

HR=heart rate (beats/minute)

HMS=home monitoring system

HTN=hypertension

Hx=history

Hypophar=hypopharynx

Imprd=impairment

In=inches

Intell deterior=intellectual deterioration

LPR=laboratory portable recording

M=meters

Ma/H=movement arousals/Hour

Manu=manufacturer's criteria

Med=median

MESAM=Madaus Electronics Sleep Apnea Monitor

MI=myocardial infarction

MM=milimeters

Mod=moderate

MRI=magnetic resonance imaging

MSLT=multiple sleep latency test

MWT=maintenance of wakefulness test

MVCFR= ratio of the maximal expiratory flow at 50% of vital capacity to maximal inspiration flow at 50% of vital capacity

Nasophar=nasopharynx

NM=nocturnal myoclonus

NMS=neuromuscular disorder

NPV=negative predictive value

NTRR=night time respiratory recording

Orophar=oropharynx

Oscill=oscillations

PA=pharyngeal area

PFT=pulmonary function test

phar=pharyngeal

PHR=portable home recording

PPV=positive predictive value

Pros=prospective study

PSG=polysomnogram

RDI=respiratory disturbance index

Reflect=reflection

Reg=regular

Rel=related

Resist=resistance

Resp=respiratory

Retro=retrospective study

RV=residual volume

RVH=right ventricular hypertrophy

S=systolic (blood pressure, mm HG)

S=second

SA=sleep apnea

SaO₂ =saturation of O₂

SCSB=static charge sensitive bed

SIDAS=recording instrument for diagnosing sleep-related breathing disorders

SIT=Saturation impairment index

Sl=sleep

Snore=snoring

Spcl=special population

Tc=treated for hypertentsion, but remained high

T_c PO₂ =transcutaneous arterial oxygen tension

T_c PCO₂ =transcutaneous carbon dioxide tension

Th=treated for hypertension and under control

TN=true negative

TP=true positive

TST=total sleep time

VC=vital capacity

VPB=ventricular premature beats

VIS=visual scoring

W/=with

*comparison with PSG AHI>10; **comparison with PSG AHI>20