The relationship between t PTEF :t E and specific airway conductance in infancy

This study examines the association between the time taken to achieve peak tidal expiratory flow as a proportion of total expiratory time t PTEF :t E and specific airways conductance (SG aw ) in healthy infants and those with prior physician diagnosed, associated, lower respiratory illness with wheezing (prior LRI) during the first year of life. We compared t PTEF :t E and (SG AW ) the latter estimated during both initial inspiration (II) and end‐expiration (EE), in 168 infants (94 males), measured on 220 occasions. Mean (range) t PTEF :t E was 0.321 (0.150–0.522) in 73 healthy infants aged less than 3 months (mean, 7.8 weeks), in whom mean (range) EE(SG aw ), and plethysmographic thoracic gas volume at functional residual capacity (FRC pleth ) were 2.47 s −1 kPa −1 (0.6–5.8) and 141 mL (87–204), respectively. Both t PTEF :t E and EE(SG aw ), were significantly lower in older infants with prior LRI ( n = 79; mean age, 50.0 weeks) compared to a similarly aged group of healthy infants ( n = 68; mean age, 48.5 weeks), the mean difference [95% confidence intervals (Cl)] being −0.039 (−0.013, −0.064) and −0.48 s −1 kPa −1 (−0.24, −0.72), respectively. A significant but weak association between t PTEF :t E , and EE(SG aw ),was found among infants above 3 months of age, irrespective of prior wheezing status. However, this relationship was not significant in healthy younger infants, in whom a significant but weak association with FRC pleth was found. Further work is needed to elucidate the factors influencing tidal expiratory flow patterns in infancy. Pediatr Pulmonol. 1994;18:299–307 © Wiley‐Liss, Inc.