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A novel physiological investigation of the functional residual capacity by the bias flow nitrogen washout technique in infants
Author(s) -
Morris Mohy G.
Publication year - 2009
Publication title -
pediatric pulmonology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.866
H-Index - 106
eISSN - 1099-0496
pISSN - 8755-6863
DOI - 10.1002/ppul.21040
Subject(s) - nitrogen washout , functional residual capacity , medicine , expiration , washout , lung volumes , anesthesia , cardiology , limits of agreement , residual volume , respiratory system , nuclear medicine , lung
The dynamic functional residual capacity (FRC dyn ), the lung volume most routinely measured in infants, is an unreliable volume landmark. In addition to the FRC dyn , we measured the (passive) static FRC (FRC st ) by inducing a brief post‐hyperventilation apnea (PHA) in 33 healthy infants aged 7.4–127.2 weeks. A commercial system for nitrogen (N 2 ) washout to measure FRC, and a custom made system to monitor and record flow and airway opening pressure signals in real‐time were used in unison. Infants were manually hyperventilated to induce a PHA. After the last passive expiration, FRC st was estimated by measuring the volume of N 2 expired after end‐passive expiratory switching of the inspired gas from room air to 100% oxygen during the post‐expiratory apneic pause. Repeatable intrasubject FRC st and FRC dyn measurements overlapped in most infants including the younger ones ( P = 0.2839). Mean (95% confidence interval [CI]) FRC st was 21.1 (20.0–22.3), and error‐corrected FRC dyn was 21.4 (20.4–22.4) ml/kg. Mean (washout time [ t ]) t FRC st was longer than t FRC dyn 60 sec (95% CI 55–65) versus 47 sec (95% CI 43–51) ( P < 0.0001). The FRC and washout time were dependent on body length, weight and age. We conclude that the FRC st is not different from the FRC dyn in infants. The FRC st is a reliable volume landmark because the PHA stabilizes the end‐expiratory level by potentially abolishing the sedated infant's breathing strategies. The FRC st lacks potential sources of errors and disadvantages associated with measuring the FRC dyn . The findings cast significant doubt on the traditional physiology of air trapping in healthy infants' lungs. Pediatr Pulmonol. 2009; 44:683–692. © 2009 Wiley‐Liss, Inc.