Heart rate and hemodynamics

Evidence is presented to show that cardiac output is little affected by changes in heart rate but the heart volumes, systolic and diastolic, are inversely related. Heart rate is controlled by changes in efferent nerves, sympathetic and vagal, which are in turn controlled from central and reflex sources. An argument is presented showing that reflexes from receptors in the atria control heart volumes by affecting, in the short term heart rate, and in the long term water intake (thirst) and urine flow, and therefore blood volume. Explanations of the mechanisms involved are presented.