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 infa
nts and those with prior physician diagnosed, associated, lower respir
atory 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 m
ales), 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 L
RI (n = 79; mean age, 50.0 weeks) compared to a similarly aged group o
f healthy infants (n = 68; mean age, 48.5 weeks), the mean difference
[95% confidence intervals (CI)] being -0.039 (-0.013, -0.064) and -0.4
8 s(-1) kPa(-1) (-0.24, -0.72), respectively. A significant but weak a
ssociation 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. Fur
ther work is needed to elucidate the factors influencing tidal expirat
ory flow patterns in infancy. (C) 1994 Wiley-Liss, Inc.