Viscosity of blood in myocardial infarction.

VISCOSITY is one of the fundamental physical properties of blood that has direct influence on its rate of flow. The viscosity varies mainly with the cell-plasma ratio and the plasma protein content and composition. Viscosity of whole blood is dependent on the number of erythrocytes and increases with the hematocrit but at a faster rate. At the same hematocrit, the viscosity is said to be proportional to the viscosity of the plasma. The viscosity of plasma is largely influenced by its protein content, but the qualitative distribution of protein is also important. Variations in fibrinogen have relatively greater effects than albumin or globulin inasmuch as the fibrinogen molecule is long and slender. Moreover, the complex interrelationships between proteins have an influence. Thus, fibrinogen in saline affects viscosity more than in plasma. True in vivo viscosity is very difficult to measure; consequently, the in vitro methods that are nearly always used must be considered as only approximate reflections of the true in vivo state. In rigid tubes, flow is inversely related to viscosity. In vivo, blood passes through the living capillary with less apparent viscosity than in a glass capillary. Myocardial infarction is followed by increases in fibrinogen in the blood, which are roughly correlated with the severity. Using eleetrophoretic methods, changes in globulin have also been reported. Serum mucoproteins also show increases following myocardial infarction. Presumably, an increase in plasma viscosity will occur following myocardial infarction, which might cause a corresponding increase in blood viscosity and further compromise the impaired circulation. This study was undertaken to ascertain the