Assessing exercise limitation using cardiopulmonary exercise testing

Abstract

The cardiopulmonary exercise test (CPET) is an important physiological investigation that can aid clinicians in their evaluation of exercise intolerance and dyspnea. Maximal oxygen consumption ([Formula: see text]) is the gold-standard measure of aerobic fitness and is determined by the variables that define oxygen delivery in the Fick equation ([Formula: see text] = cardiac output × arterial-venous O(2) content difference). In healthy subjects, of the variables involved in oxygen delivery, it is the limitations of the cardiovascular system that are most responsible for limiting exercise, as ventilation and gas exchange are sufficient to maintain arterial O(2) content up to peak exercise. Patients with lung disease can develop a pulmonary limitation to exercise which can contribute to exercise intolerance and dyspnea. In these patients, ventilation may be insufficient for metabolic demand, as demonstrated by an inadequate breathing reserve, expiratory flow limitation, dynamic hyperinflation, and/or retention of arterial CO(2). Lung disease patients can also develop gas exchange impairments with exercise as demonstrated by an increased alveolar-to-arterial O(2) pressure difference. CPET testing data, when combined with other clinical/investigation studies, can provide the clinician with an objective method to evaluate cardiopulmonary physiology and determination of exercise intolerance.

Figure 1

Interpretation algorithm for cardiopulmonary exercise testing. This figure provides an outline of a CPET interpretation strategy and suggested classification of ventilatory limitation based on previous work [1, 48, 53, 57, 58, 60, 70, 74]. Importantly, the data obtained from a CPET test should not be interpreted in isolation, but rather results should be integrated with other clinical findings/investigations. RER: respiratory exchange ratio, ${\dot{V}}_{{\text{O}}_{\mathrm{2}}}\text{:}$ oxygen consumption, HR: heart rate, SpO₂: arterial saturation, BR: breathing reserve, CV: cardiovascular, EFL: expiratory flow limitation, V _T: tidal volume, EELV: end-expiratory lung volume, PaCO₂: arterial PCO₂.