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Pediatr Pulmonol. 2018 Jul;53(7):907-916. doi: 10.1002/ppul.24063. Epub 2018 May 23.

Reference equations for the interpretation of forced expiratory and plethysmographic measurements in infants.

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Division of Respiratory Medicine, Department of Pediatrics, and Program in Translational Medicine, SickKids Research Institute, The Hospital for Sick Children, University of Toronto, Toronto, Canada.
Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
Curtin University of Technology, Perth, Western Australia.
Department of Medicine, McMaster University, Hamilton, Canada.
Division of Pediatric Pulmonology, Allergy and Sleep Medicine; Department of Pediatrics; Riley Hospital for Children, Indiana University School of Medicine, Indianapolis, Indiana.
Department of Pediatrics and Child Health, University of Manitoba, Children's Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada.
Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada.
Department of Pediatrics, Child & Family Research Institute, BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada.



Pulmonary function testing is commonly performed for diagnosis and clinical management of respiratory diseases. It is important to use appropriate reference equations from healthy subjects for interpretation of data from infants with lung disease. This study aimed to determine if published reference equations were similar to forced flow measures and plethysmographic infant pulmonary function testing data collected in the Canadian Healthy Infant Longitudinal Development (CHILD) Study.


Reference equations for five pulmonary function variables (FEV0.5 , FVC, FEF25-75 , FEV0.5 /FVC ratio and plethysmography (FRCpleth )) were developed using data from the nSpire system. New reference equations developed using healthy data from the CHILD Study were compared to previously published reference equations for forced flow and plethysmographic measures.


The current analysis included 131 infants (on 181 test occasions) with forced flow measures and 161 infants (on 246 test occasions) with plethysmography measures, aged 3-24 months. Age and length were major determinants of both forced flow and plethysmography measures. In addition, ethnicity (Caucasian vs non-Caucasian) was significantly associated with FEV0.5 /FVC and FEF25-75 measures. We found that the published reference equations based on custom-built equipment or commercially available systems provided poor fit to our current pulmonary function testing data, resulting in placing a large proportion of our healthy population outside the normal ranges.


Our current data support the need for population and device specific reference data for infant pulmonary function studies. By deriving new equipment-specific reference equations for our healthy population, we provide normative data to other centers utilizing this equipment.


CHILD Study; forced flow measures; infant pulmonary function testing; plethysmography; reference equations


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