Oxygen consumption and conservation during apnea in the anesthetized dog

Apnea was initiated by clamping off the tracheal tube in 6 anesthetized dogs. Bradycardia, reduction in cardiac output and peripheral vasoconstriction developed gradually throughout the entire apneic period. O2 consumption during apnea was measured by monitoring the rate of O2 removal from the lung (VLO2), from the arterial blood (Va02), and from the venous blood (VV02). Total 02 consumption (VT02) was calculated by summing (VL02--Va02), VaQ2 and VV02-VL02, estimated by the product of arteriovenous O2 content difference and cardiac output, decreased continuously during apnea. At the end of 80 sec the rate of O2 removal from the lung was one-fourth of the pre-apneic rate, 5.29 +/- 0.51 ml-min-1kg-1. Oxygen disappearance form the blood was estimated by measuring arterial and venous O2 content at 20-sec intervals and by assuming a constant blood volume throughout the apneic period of 86 ml/kg, 25% of which is in the arterial tree and 75% of which is in the venous compartment. During the last 20 sec of an 80-sec apnea, VV02 represented 69% of VT02. The result indicated that VT02 during apnea was not significantly different from that of pre-apneic values. It is concluded from the present study that an oxygen conservation mechanism if existent, was not operative during an 80-sec apnea in the anesthetized dog.