Journal of Applied Physiology, Vol 70, Issue 2 895-899, Copyright © 1991 by American Physiological Society
Metabolic and respiratory effects of flow-resistive loading in preterm infants
S. Duara, G. Silva Neto, T. Gerhardt, C. Suguihara and E. Bancalari
Department of Pediatrics, University of Miami School of Medicine, Florida 33101.
Oxygen consumption (VO2) was measured during hypoventilation induced by
moderate-sized flow-resistive loading in 12 preterm infants, and the
results were compared with those obtained under basal conditions
immediately before and after the loaded run, each of which lasted for 7-10
min. Loading was performed with a continuous flow-resistive load
(inspiratory and expiratory), which was approximately threefold greater in
magnitude than the intrinsic resistance of preterm infants. VO2, minute
ventilation (VE), transcutaneous oxygen tension (PtCO2), and transcutaneous
carbon dioxide tension (PtcCO2) were continuously monitored. Results
revealed that VE decreased significantly with loading, from 336 +/- 103 to
231 +/- 58 (SD) ml.min-1.kg-1 (P less than 0.001), while returning to basal
levels of 342 +/- 59 ml.min-1.kg-1 after discontinuation of the load. VO2
decreased from 7.2 +/- 1.2 to 5.9 +/- 0.9 ml.min-1.kg-1 with loading (P
less than 0.001) and returned to 7.2 +/- 1.2 ml.min-1.kg-1 at the second
basal measurement. PtcCO2 remained unchanged with loading, and PtcCO2 only
increased from 39 +/- 8 to 41 +/- 9 Torr (P less than 0.05) with loading,
while returning to 40 +/- 9 Torr at the second basal measurement. Results
indicate a decrease in the metabolic rate and ventilation with loading,
with relatively little increase in PtcCO2. These data can explain prior
observations that minimal disturbances in oxygen and carbon dioxide
tensions occur with hypoventilation during flow-resistive loading in
neonates, although the precise mechanism for this reduction remains to be
determined.
