The Systemic Vascular Resistance Response: a Cardiovascular Response Modulating Blood Viscosity with Implications for Primary Hypertension and Certain Anemias

Without an active regulatory feedback loop, increased blood viscosity could lead to a vicious cycle of ischemia, increased erythropoiesis, further increases of blood viscosity, decreased tissue perfusion with worsened ischemia, further increases in red cell mass, etc. We suggest that an increase in blood viscosity is detected by mechanoreceptors in the left ventricle which upregulate expression of cardiac natriuretic peptides and soluble erythropoietin receptor. This response normalizes systemic vascular resistance and blood viscosity at the cost of producing 'anemia of chronic disease or inflammation' or 'hemolytic anemia' both of which are better described as states of compensated hyperviscosity. Besides its role in disease, this response is also active in the physiologic adaptation to chronic exercise. Malfunction of this response may cause primary hypertension.