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Changes in respiratory rate affect tidal expiratory flow indices in infants with airway obstruction
Author(s) -
Rusconi Franca,
Gagliardi Luigi,
Aston Hazel,
Silverman Michael
Publication year - 1996
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/(sici)1099-0496(199604)21:4<236::aid-ppul6>3.0.co;2-m
Subject(s) - medicine , wheeze , airway obstruction , anesthesia , methacholine , respiratory system , tidal volume , airway , respiratory rate , ventilation (architecture) , asthma , cardiology , respiratory disease , lung , heart rate , blood pressure , mechanical engineering , engineering
Among the tidal expiratory flow measurements that have been suggested as surrogate tests for airway obstruction, a short time to reach peak tidal expiratory flow (t pef ) is the most widely used. Time to peak expiratory flow is most often expressed as the ratio between t pef and total expiratory time (t e ). As t e strictly depends inversely on respiratory rate (RR), we studied the hypothesis that an increase in RR (and a fall in t e ) with the development of airway obstruction during methacholine or histamine challenge in infants could mask a decrease of t pef when expressed as t pef /t e . Thirty‐three infants (ages 6.5–23 months) with recurrent wheeze were studied during sedated sleep. Runs of tidal breathing and maximal expiratory flow at FRC (˙V maxFRC ) measured by the squeeze technique were obtained before and after the challenge. All infants responded to the challenge: the median fall in P cO 2 was 25%, and it was 43% in ˙V maxFRC . RR increased from a median value of 31.1 to a median of 35.1 breaths/min. Both t pef and t e were significantly shorter after the challenge ( P < 0.001 and 0.004, respectively); however, the decrease in t pef /t e was not significant ( P = 0.081). The change in t pef /t e was positively correlated with the change in RR (r = 0.51, P = 0.003). To analyze better the effect of changes in RR on various indices, we divided the patients into two groups: in 17 subjects with a small increase in RR (<10%), t e did not change significantly, while t pef and t pef /t e did; in 16 subjects with a more marked increase in RR (≥10%), the shortening of t e masked the simultaneous shortening of t pef so that t pef /t e did not change. These data demonstrate that t pef /t e cannot be reliably used to evaluate changes in airway obstruction when concomitant changes in RR occur. Pediatr Pulmonol. 1996; 21:236–240. © 1996 Wiley‐Liss, Inc.