Am. J. Respir. Crit. Care Med., Vol 153, No. 4, Apr 1996, 1248-1252.
Do tidal expiratory flow patterns reflect lung mechanics in infants?
PC Seddon, GM Davis and AL Coates
Division of Respiratory Medicine, McGill University-Montreal Children's Hospital, Quebec, Canada.
It has been suggested that during tidal breathing, the time to maximal
expiratory flow, as a proportion of total expiratory time (Tme/TE), can be
used as an index of airways obstruction. However, the relationship of
Tme/TE to lung mechanics in infants is unclear. We examined this
relationship in 42 premature infants (21 intubated and 21 not intubated) by
comparing direct measures of pulmonary mechanics (lung resistance, dynamic
lung compliance, and lung impedance) with Tme/TE measured over the same
sample of tidal breathing. Tme/TE was positively correlated with lung
compliance, expressed as a percent of the predicted value, in both
intubated (r = 0.69, p < 0.005) and nonintubated (r = 0.64, p < 0.02)
infants. There was no significant association between Tme/TE and lung
resistance, expressed as a percent of the predicted value, in intubated (r
= 0.32) and nonintubated (r = 0.23) infants. Tme/TE also showed, in
nonintubated infants, a positive association with lung impedance, expressed
as a percent of the predicted value, on the basis of the predictive values
for compliance and resistance at the infant's unique respiratory rate, but
this was significant only because of the influence of compliance on Tme/TE.
These findings suggest that, in infants, the relationship between pulmonary
mechanics and Tme/TE is complex, with Tme/TE being influenced by the
elastic rather than the flow-resistive properties of the lungs.
