Effect of metabolic rate on ventilatory rolloff during hypoxia

1994.-This study was done to determine 1) whether goats dem-onstrate the roll-off phenomenon, i.e., a secondary decrease in minute ventilation (VE), after an initial hyperventilation dur-ing various levels of hypoxia and, if so, 2) whether roll-off could be due to changes in metabolic rate. We hypothesized that roll-off occurs in the goat during hypoxia but is not due to hypome-tabolism. To answer question 1, eight unanesthetized adult goats were exposed to 15-20 min of hypoxia at 0.15, 0.12, and 0.09 inspired 0, fraction (FI~J, resulting in 60,40, and 30 Torr arterial PO,, respectively. Goats were fitted with a face mask connected to a spirometer to measure VE, and arterial blood gas samples were obtained via carotid arterial catheters. Roll-off was seen with 0.15 and 0.12 FIEF, whereas VE steadily in-creased with 0.09 FIEF. During hypoxia, arterial PCO, fell 2, 3, and 7 Torr at 0.15, 0.12, and 0.09 FIEF, respectively. In the sec