Blood viscosity factors in evaluation of submaximal work output and cardiac activity in men.

Sixty-two male subjects, including patients with postmyocardial infarction, angina, other disorders, and normals, were studied by exercise testing on the bicycle ergometer, including exercise ECG, and by in vitro determination of blood viscosity, plasma viscosity, aggregation of red cells, and other factors. Significant correlations were found between the blood viscosity factors on the one hand, and different terms describing physical fitness and cardiac functions on the other. In all correlations an elevation of blood viscosity factors led to lower fitness or lower cardiac efficiency; and a decrease of blood viscosity (or plasma viscosity, or compound viscosity product) was associated with better fitness and higher cardiac efficiency. Similarly, ECG ST-segment depression was proportional to increase of blood viscosity factors. All these highly significant correlations were found within a very narrow range of hematocrits, while the hematocrit value itself was not significant in this study.