Cardiovascular adjustments to carbon monoxide exposure during rest and exercise in dogs

Cardiovascular, respiratory, and metabolic measurements were made on dogs at rest and during 30 minutes of exercise at either 6.4 km/hour, 10% grade, or 8.0 km/hour, 16% grade, following the bolus administration of CO for 1 or 2 minutes, or room-air breathing mixtures. During rest and exercise elevated mean blood HbCO levels (6 to 21%) reduced the arterial and mixed venous oxygen contents and saturations, and mixed venous P_O2 levels. Arterial-mixed venous oxygen differences were reduced during exercise as a result of CO administration. Elevated blood HbCO levels had a minimal or no effect on other cardiovascular, respiratory, and metabolic parameters. During work the reductions in a-v?_O2 differences were not offset by appropriate increases in cardiac outputs.