INFLUENCE OF ARTERIAL OXYGEN TENSION ON APNEIC THRESHOLD FOR CARBON DIOXIDE IN NORMOTHERMIC AND HYPOTHERMIC DOGS

摘要

Anesthetized dogs were hyperventilated with various C02-free gas mixtures containing 6-100% O2 at a rate of 16 l/min. for 4 minutes at normal and reduced body temperatures (28°). Arterial blood samples were withdrawn at the start of the first breath following the apnea period and analyzed for PCO2, PO2, and phi The PaC02 was used as an index of the respiratory threshold for PC02 and designated as PTC02. At both normal and reduced body temperatures the PTCO2 decreased when the PaO2 was lowered as a result of hyperventilation with a low oxygen gas mixture. The PTCO2 was highest when the Pa02 was highest following hyperventilation with 100% 02 . The relationship between Pa02 and PTC02 was linear at both temperatures, During normothermic the slope of a plot of the mean values of the PTC02-Pa02 relationship was steepest below a Pa02 of 35 mm Hg and in hypothermia the relationship was steepest below approximately 20 mm Hg Pa02 „ The results indicated no real apnea threshold for PaC02 during normothermic or hypothermia but rather one which directly is related to the Pa02.