Metabolic and respiratory effects of flow-resistive loading in preterm infants.

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.