Interpreting the CPET

Following completion of the test, the test findings need to be systematically examined and a final report conducted that will be meaningful for the health care provider requesting the test. The maximal oxygen uptake is the measurement receiving the most attention, and the identification of both subjective assessment of patient effort and the identification of a ventilatory threshold are the most helpful assurances that the exercise effort was a true cardiovascular maximal effort. While maximal oxygen uptake is traditionally normalized by body weight in kilograms, it is also important to assess maximal oxygen uptake adjusted as a percent of predicted normal value based on the subject's age, height, and sex. That latter perspective on the maximal oxygen uptake is especially important for evaluation of overweight or obese subjects in the setting in which the maximal oxygen uptake is needed as a surrogate measurement of maximal cardiac output. Because of the very substantial variability in maximal exercise heart rate among normal subjects, maximal heart rate should not be used as an index of exercise effort. The maximal O₂ pulse (maximal O₂ uptake/heart rate) provides an estimate of the size of the stroke volume. The exercise ventilatory equivalents for O₂ or CO₂ (VE/VO₂ or VE/VCO₂) in normal subjects provide a measurement of exercise ventilatory sensitivity and efficiency. If exercise blood gases have been obtained, calculations can be made of exercise changes in the A-aO₂ difference and the physiologic dead space. The exercise report should discuss the findings of the measurements relative to normal predicted values and describe whether or not findings are consistent with a cardiovascular, respiratory, or pulmonary-vascular pattern of limitation. If testing an aerobic athlete, one must consider those results in the context of the subject's previous and current capacity. The final impression should relate those findings to the symptoms or prior measurements obtained on the patient, described in a manner comprehensible to both patient and health care provider.