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 (CI)] 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. (C) 1994 Wiley-Liss, Inc.