Temperature of mixed venous blood during exercise.

The temperature of mixed venous blood (PA-temp) was measured in the pulmonary artery of healthy male volunteers at rest and during bicycle exercise in the supine position. Oxygen uptake, arteriovenous oxygen difference, and heart rate were determined simultaneously. The subjects were studied both in their basal normokinetic circulatory state and in a hypokinetic circulatory state induced by beta-receptor blockade with propranolol. The PA-temp increased linearly with rising oxygen uptake. During beta-receptor blockade the exercise-induced rise in PA-temp was considerably steeper in relation to work load and to oxygen uptake. Thus when the ordinary ability to increase cardiac output was suppressed by propranolol, an identical dynamic exercise induced a significantly higher PA-temp. A significant correlation (r = 0.92) was found between the rise in PA-temp during exercise and the increase in the arteriovenous oxygen difference. This correlation, which has not been described previously, was not altered by beta-receptor blockade. It is concluded that the close correlation between blood temperature and arteriovenous oxygen difference has a clinical potential for hemodynamic measurements. A simple method for the indirect estimation of arteriovenous oxygen difference by means of blood thermometry would be a considerable laboratory advantage.