Organ blood flow protection in hypertension and congestive heart failure.

The nutrients to the different organs of the body are provided through the blood supply to these organs. Since the nutrient requirements change considerably and abruptly according to the demands set by, for example, physical activity, organ blood flow has to be adjusted accordingly. This is achieved by a complex interplay between neural (parasympathetic and sympathetic nerves), humoral (vasopressin, angiotensin, etc.), and local (ions, pH, adenosine, etc.) factors. It is also well recognized that diseases, such as hypertension and heart failure, as well as the drugs to treat them, can substantially affect organ blood flow. Using tracer microspheres, several studies in animals have shown that, during the established phase of hypertension, there is some decrease in cardiac output, which is then redistributed, with the brain, small intestines, and heart receiving a higher proportion. Blood flow to and vascular conductance in the other organs, particularly the kidneys, is decreased. Similar findings have also been observed in human hypertension. During congestive heart failure, most organs show a decrease in blood flow and there is a conspicuous increase in the sympathetic nerve activity. The drug responses may differ in the disease state and, from a clinical viewpoint, changes in some circulatory beds (e.g., cerebral, cardiac, renal, skeletal muscles) as well as the partition of blood flow into nutrient (tissue) and non-nutrient (arteriovenous anastomoses or shunts) parts can be of great importance. For example, overzealous antihypertensive therapy or the use of cerebral vasodilators may adversely affect cerebral circulation in certain situations and increased arterial blood flow may only be in the arteriovenous anastomotic part of the circulation.