12.03.2 Compensatory Changes in Heart Failure

There are some compensatory changes associated with heart failure that are aimed at increasing cardiac output, but lead to the symptoms of heart failure. When cardiac output is reduced, there is activation of the sympathetic nervous system to increase heart force and of the renin-angiotensin-aldosterone system. Both of these systems have a role in increasing blood pressure, which will initially help oxygen delivery and removal of waste from tissues. However, with increased blood pressure, there is increased loss of fluid from blood vessels, and the fluid has to go somewhere, so there is increased fluid accumulation in legs, which is known as peripheral oedema. Peripheral oedema leads to the swelling of the legs, which is a common symptom of heart failure.

The increased peripheral arteriolar resistance (blood pressure) also leads to decreased renal blood flow, and a decreased glomerular filtration. With a decreased glomerular filtration, the kidney cannot function properly, and there is an increased retention of water and electrolytes. Again this fluid has to go somewhere and it often goes to the lungs to cause pulmonary oedema, which underlies the difficulty in breathing, which is a common symptom of heart failure. Poor kidney function will also contribute to peripheral oedema.