Assessment of Functional Capacity in Clinical and Research Settings

Abstract

The assessment of functional capacity reflects the ability to perform activities of daily living that require sustained aerobic metabolism. The integrated efforts and health of the pulmonary, cardiovascular, and skeletal muscle systems dictate an individual’s functional capacity. Numerous investigations have demonstrated that the assessment of functional capacity provides important diagnostic and prognostic information in a wide variety of clinical and research settings. This scientific statement, an update of the previously published American Heart Association (AHA) document,1 highlights the major clinical and research applications of functional capacity assessment. For a comprehensive review of exercise testing, the reader is referred to the American College of Cardiology (ACC)/AHA Guidelines for Exercise Testing.2,3 Functional capacity is the ability of an individual to perform aerobic work as defined by the maximal oxygen uptake (Vo2max), that is, the product of cardiac output and arteriovenous oxygen (a−Vo2) difference at physical exhaustion, as shown in the following equation: ![Formula][1] Where HR indicates heart rate and SV indicates stroke volume. Because Vo2max typically is achieved by exercise that involves only about half of the total body musculature, it is generally believed that Vo2max is limited by maximal cardiac output rather than peripheral factors.4 Although Vo2max is measured in liters of oxygen per minute, it usually is expressed in milliliters of oxygen per kilogram of body weight per minute to facilitate intersubject comparisons. In addition, functional capacity, particularly when estimated from the work rate achieved rather than directly measured Vo, is frequently expressed in metabolic equivalents (METs), with 1 MET representing the resting energy expenditure (≈3.5 mL O2 · kg−1 · min−1). In this instance, functional capacity is commonly expressed clinically as a multiple of the resting metabolic rate. Vo2max … [1]: /embed/graphic-1.gif