GUILLEMINAULT ET AL RECENTLY REPORTED IN SLEEP A SERIES OF SEVEN NON OBESE YOUNG WOMEN AFFECTED WITH SLEEP-RELATED RESPIRATORY noises that they diagnosed as cases of catathrenia (sleep-related groaning).¹ In their patients sleep-related respiratory noises occurred mainly during light NREM sleep and diminished during REM sleep. Respiratory noise in these patients was expiratory. In view of the presence of a significant, mainly inspiratory flow limitation, with anatomic evidence of a small upper airway and small jaws, the authors put their patients on nasal CPAP treatment, plus successive surgical intervention or oral device appliance in four of them, that abolished/reduced sleep-related hypopnoeas and inspiratory flow limitation with resolution of the respiratory noise.

They argued therefore that catathrenia may have different subtypes related to sleep stage specificity or to the presence of sleep disordered breathing. Together with a recent report of continuous airway pressure benefit in a case of nocturnal groaning associated with mild obstructive sleep apnoea, oxygen desaturation and irregular abdominal wall movements,² Guilleminault et al. raise the question regarding the definition, the heterogeneity and the pathophysiology of catathrenia.¹

Catathrenia was first reported as sleep-related expiratory groaning during REM sleep in abstract form.³ Pevernagie et al. described apparently the same phenomenon as “vocalization during prolonged expiration during REM sleep”,⁴ and, in our description of nocturnal groaning, we proposed the term of catathrenia (meaning “groaning”) in 4 cases in which the groaning sounds, though sometimes present also during NREM, were prevalent during REM sleep.⁵ The same prevalence, or even the recurrence solely during REM sleep, was emphasized by Oldani et al. in their report of 21 patients, 16 examined by polysomnography (PSG).⁶ In all of the PSG performed in catathrenia, the features were quite similar and stereotyped: a deep inspiration without sound production was followed by a prolonged expiration with groaning, usually lasting from at least 2 s to 20 seconds; there was bradypnea during catathrenia, no evidence of respiratory muscular effort and no oxygen desaturation.⁵,⁶

Thus, the hallmark of catathrenia is that inspiration is followed by protracted expiration during which a prolonged or fragmented sound is produced, and this recurs especially during REM sleep. Vetrugno et al. recently reported ten patients with catathrenia and without any evidence of other facial, airway or lung disease in whom intrathoracic pressure recordings was performed.⁷ During the expiratory groaning sounds, neither the diaphragm nor the intercostalis EMG were active and endoesophageal pressure, monitored in all patients, showed a slight initial positive rise subsequently returning to values around 0 cm H2O. Strikingly, during the groaning, the respiratory pattern was distinctly abnormal, with a substantial slowing of the respiratory rate (breathing rate was actually decreased by 2/3) and a disproportionate increase in the length of expiration. Remarkably again, nocturnal groaning alternated with normal breathing in the same night, sometimes in the same sleep state.⁷

This respiratory pattern, that we consider as typical for catathrenia, is clearly different from what reported by Guilleminault et al.¹ In their seven patients, the produced sound was expiratory but short lasting (about 1 s in their figure 1, and again 1–1.5 s in figure 2, compared to 2–20 s in our patients) and occurred at the peak of expiration; in particular, expiration was not prolonged, and there was no bradypnea during the “groaning” (see Figures 1 and 2 in Guilleminault et al.);¹ sometimes, a noise could be detected also at the peak of inspiration (see Figure 1 in Guilleminault et al);¹ finally, the sounds were not produced during REM sleep.¹ All of these differences are substantial, and indicate that the case of Guilleminault et al¹ are not catathrenia, but rather instances of expiratory snoring.

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Figure 1

Catathrenia (A) compared to expiratory snoring in a snorer patient (B). The recordings are shown at the same time scale. Please note: 1) the different duration of the groaning sounds (microph.), 2) the prolonged expiration (oral, thoracic and abdominal respirograms), and 3) the bradypnoic pattern in catathrenia.

EOG: electro-oculogram; Mylohyoid.: mylohyoideus; microph.: microphone; Interc.: intercostalis; Oral Resp.: oral respirogram; Thor. Resp.: thoracic respirogram; Abd Resp.: abdominal respirogram; Intraoesoph. Press.: intraoesophageal pressure; SaO2: oxygen saturation; R.: right; L.: left.

In order to show that these two phenomena are quite distinct, we provide a picture comparing the polysomnographic features of a catathrenic patient of ours versus expiratory snoring, both displayed at the same time scale. The differences are readily evident (Figure 1).

Narrowing of the upper airway and flow limitation is not solely an inspiratory phenomenon but may also occur with expiration in healthy subjects, in snorers, in patients with upper airway resistance syndrome (UARS) and in patients with obstructive sleep apnoea syndrome (OSAS) (Stanescu et al, 1993).⁸

Observations of expiratory obstruction during sleep are not new. Weitzman et al. first postulated expiratory obstruction⁹ and Lugaresi et al. provided an illustration of expiratory flow limitation in a snorer.¹⁰ Gravity (mainly during the supine body position) together with relaxation of pharingeal dilator muscles, such as the tensor palatini and genioglossus, have been considered to promote local upper airway narrowing during expiration more frequently at the supraglottic/retroglossal level. Isolated expiratory flow limitation has been reported to recur in breaths and to be coupled with inspiratory flow limitation in sleep.⁸

Whether catathrenia is an abnormal, possibly vestigial, central respiratory pattern during sleep, due to abnormality in brainstem respiratory centers, as we proposed,⁷ and whether narrowing of the airways occurs during catathrenia, must be left to further studies. We also consider that whether catathrenia is a parasomnia rather than a sleep-related breathing disorder is just a matter of definition. In the previous ICSD-1 classification indeed, at the time of most reports of catathrenia, snoring too, itself a respiratory phenomenon, was classified as a parasomnia. What we are really concerned about and wish to emphasize with this letter is that catathrenia presents with a distinctive pattern on the PSG, and should be clearly differentiated from other respiratory disturbances during sleep. This has clear and important consequences on prognosis and treatment.