Exercise testing is a noninvasive tool to evaluate the cardiovascular system's response to exercise under carefully controlled conditions. Exercise is the body's most common physiologic stress, and it places major demands on the cardiopulmonary system. Thus, exercise can be considered the most practical test of cardiac perfusion and function. The exercise test, alone and in combination with other noninvasive modalities, remains an important testing method because of its high yield of diagnostic, prognostic, and functional information.
The adaptations that occur during an exercise test allow the body to increase its metabolic rate to greater than 20 times that of rest, during which time cardiac output can increase as much as six-fold. The magnitude of these adjustments is dependent on age, gender, body size, type of exercise, fitness, and the presence or absence of heart disease. The major central and peripheral adaptations that occur from rest to maximal exercise are illustrated in Fig. 16–1. The interpretation of the exercise test requires understanding exercise physiology and pathophysiology as well as expertise in electrocardiography. Certification is extremely important because this technology has spread beyond the subspecialty of cardiology. Training and experience are required as they are for other diagnostic procedures. For these reasons, the American College of Physicians (ACP) and American College of Cardiology (ACC), and the American Heart Association (AHA) have published guidelines on clinical competence for physicians performing exercise testing (www.acc.org/qualityandscience/clinical/statements.htm, www.cardiology.org).1,2
A. Graphs of the hemodynamic responses to dynamic exercise. B. Sequence of physiological responses to dynamic exercise. Cardiovascular Physiology at a Glance, with permission of Blackwell Publishers, 2004.
Two basic principles of exercise physiology are important to understand in regard to exercise testing. The first is a physiologic principle: total body oxygen uptake and myocardial oxygen uptake are distinct in their determinants and in the way they are measured or estimated (Table 16–1).
TABLE 16–1. Two Basic Principles of Exercise Physiology |Favorite Table|Download (.pdf)
TABLE 16–1. Two Basic Principles of Exercise Physiology
|Myocardial oxygen consumption||= Heart rate × systolic blood pressure (determinants include wall tension = left ventricular pressure × volume; contractility; and heart rate)|
|Ventilatory oxygen consumption (VO2)||= External work performed, or cardiac outputa × A-VO2 difference|
Total body or ventilatory oxygen uptake (volume oxygen consumption [VO2]) is the amount of oxygen that is extracted from inspired air as the body performs work. The determinants of VO2 are ...