Journal of Applied Physiology, Vol 70, Issue 2 889-894, Copyright © 1991 by American Physiological Society
Assessment of airway resistance in preterm infants during incremental inspiratory flow-resistive loading
S. Duara, T. Gerhardt and E. Bancalari
Department of Pediatrics, University of Miami School of Medicine, Florida 33101.
Extrathoracic airway (ETA) stability was tested by inspiratory
flow-resistive loading in 10 preterm infants to determine whether ETA
collapsibility was directly related to the size of the added load. A fall
in intraluminal pressure was produced by applying two inspiratory
flow-resistive loads of lower (L1) and higher (L2) magnitudes. An increase
in intrinsic resistance was used as an index of upper airway
collapsibility. Total pulmonary resistance did not change from baseline
with L1 (73 +/- 26 to 71 +/- 25 cmH2O.l-1.s) but increased significantly
with L2 (72 +/- 21 to 99 +/- 34 cmH2O.l-1.s, P less than 0.02) secondary to
a rise in inspiratory resistance (55 +/- 21 to 109 +/- 55 cmH2O.l-1.s, P
less than 0.05). Expiratory resistance did not change significantly with
either load. Proximal airway pressure was more negative with L2 than with
L1 in every infant (mean -4.5 +/- 0.6 vs. -3.6 +/- 0.9 cmH2O, P less than
0.05). This study shows that the ETA of preterm infants is pressure passive
at high but not at low collapsing pressures, and possible explanations
include limited "active" compensation by upper airway dilator muscles and
an overwhelming of the "passive" defense offered by the intrinsic rigidity
of the ETA to large changes in transmural pressure.
