Circulatory regulation at rest and exercise and the functional assessment of patients with congestive heart failure.

Congestive heart failure occurs when myocardial dysfunction is advanced. Although clinical manifestations and diminished functional capacity can be traced back to the poor cardiac contractile state, there are major modifying influences from a complex series of compensatory responses. These particularly involve the heart, vessels, kidneys, sympathetic nervous system, the renin-angiotensin system, and other hormone systems. Functional capacity is, therefore, determined by the sum of the effects of the original cardiac insult and the effects, beneficial and adverse, of the secondary events. Functional capacity relates closely to prognosis only in the most severely disabled patients. The latter is mainly related to the extent of ventricular dysfunction, and there can be independent contributions from arrhythmias and sympathetic activity. Measures of resting parameters of cardiac contractility, hemodynamics, or neurohumoral responses are, therefore, of no value in predicting functional capacity but can be useful in examining outlook or examining mechanisms of disease and therapy. Exercise measurements are necessary because adequate resting performance can disguise major limitations in cardiac reserve. Measurement of functional capacity can be used to quantify the effects of therapy on daily living and to give an indication of the overall response of the body to major cardiac inadequacy. Limitation of exercise capacity, the earliest symptom of heart failure, can be quantified during a graded exercise test. Measurements of cardiac output and hemodynamic variables during exercise quantify the extent to which the cardiovascular system can increase performance to meet the demands of exercise. Work capacity and maximum oxygen capacity indicate the limits of physical performance, whereas determination of the anaerobic threshold indicates the highest level of exercise at which cardiorespiratory mechanisms are able to provide adequate oxygen supply to maintain aerobic metabolism in working skeletal muscle.