Effect of blood viscosity on pulmonary vascular resistance

Abstract

In the treatment of congenital cyanotic heart disease, the effectiveness of palliative shunts between the systemic arterial or systemic venous circulation and the pulmonary arterial circulation is dependent in no small part upon resistance to pulmonary blood flow. Factors that increase pulmonary vascular resistance tend to decrease the volume flow to the lungs by way of these shunts, and hence, to decrease their effectiveness. It has long been known that increased blood viscosity increases systemic vascular resistance and, secondarily, decreases total cardiac output in the intact circulation. 1 Similar changes of increased pulmonary vascular resistance have been seen when blood viscosity is increased; but since increased pulmonary vascular resistance occurs in the face of diminished cardiac output for whatever cause, it is not known whether increased blood viscosity is a primary factor in increasing resistance in the pulmonary circulation or if the increased pulmonary vascular resistance observed is a consequence only of diminished cardiac output. Since the functional effectiveness of systemic arterial or venous-pulmonary artery shunts is dependent primarily upon pulmonary vascular resistance, it seems important to determine what effect changes in blood viscosity have on pulmonary vascular resistance independent of changes in cardiac output.