Therefore, one may look on the hemodynamic changes in essential hypertension as a continuum of greater degrees of peripheral vasoconstriction. In labile hypertension, the mild arteriolar constriction only slightly increases vascular resistance (the "inappropriately" normal level), and the mild venoconstriction serves to redistribute blood to the heart and lungs, thereby augmenting or increasing cardiac output to its increased level. Thus, in this schema it is possible to find mildly hypertensive patients, or even some subjects with labile hypertension, with a normal cardiac output, especially if their circulating volume is already reduced. With advancing disease, arteriolar constriction increases, providing further increases in total peripheral resistance and stress upon the heart, and the coincident venular constriction reduces circulating plasma volume, venous return, and cardiac output.