Response to low cardiac output: developmental differences in metabolism during oxygen deficit and recovery in lambs

When cardiac output is critically lowered, whole body O2 consumption decreases and an O2 deficit accumulates. With restoration of cardiac output, an excess O2 consumption is expected in order to "repay" some or all of the O2 deficit. We tested the hypothesis that young lambs, with higher resting O2 consumption, cardiac output and growth rates than older lambs, would repay less of their O2 deficit because they have a higher proportion of nonessential metabolism. We reduced cardiac output acutely by inflating a Foley catheter in the right atrium of spontaneously breathing, sedated lambs at ages 2 (n = 5) and 8 (n = 5) wk. Each lamb was studied with low cardiac output periods of 30 and 60 min on different days. Aortic and pulmonary artery blood pressures, gases, and O2 saturations, venous Hb, and arterial lactate concentrations were measured every 10 min during baseline, low output, and 60 min of recovery. Oxygen consumption was monitored continuously. Oxygen deficit and excess O2 of recovery were calculated from the time integral of the difference between O2 consumption at baseline and during the respective study period. The average percent decreases in cardiac output (66.4 and 64.6%) and O2 consumption (38.1 and 35.1%) were similar in the 2- and 8-wk groups, respectively. There was no consistent relation between O2 deficit and O2 repayment in either age group. However, on average the 2-wk group repaid a significantly lower percentage (3 +/- 16%, mean +/- SEM) than 8-wk-olds (76 +/- 29%).(ABSTRACT TRUNCATED AT 250 WORDS)