Cardiopulmonary Exercise Test Protocol

Exercise capacity was evaluated via a symptom-limited CPET consisting of a treadmill, a gas analyzer, a flow module, and an electrocardiography monitor (Metamax 3B; Cortex Biophysik Co., Leipzig, Germany). Informed verbal consent and written consent were obtained from the subjects and their families, respectively. All subjects and their families received detailed explanations before the exercise test and fully understood the protocol and purpose of this test. We measured oxygen consumption at peak exercise (peak VO₂) and anaerobic threshold (AT VO₂) per the Bruce ramp protocol, as suggested by the American College of Sports Medicine. The peak VO₂ and carbon dioxide production were measured via the breath-by-breath method. The metabolic equivalent (MET), which is equal to 3.5 milliliters of oxygen per kilogram of body mass per minute, was calculated after measuring VO₂. The peak MET and AT MET were obtained as the maximal value throughout the whole exercise test and the value at the anaerobic threshold, respectively. The percentage of the peak VO₂ to the predicted value (peak VO₂%) was the percentage compared with normal standards of cardiopulmonary responses to exercise in Taiwan [21 (link)]. The heart rate (HR), blood pressure (BP), and minute ventilation (VE) were also recorded. The carbon dioxide production divided by oxygen consumption was calculated as the respiratory gas exchange ratio (RER). The anaerobic threshold was decided by the ventilatory efficiency (i.e., the VE/VCO₂ slope) and ventilatory equivalents for the oxygen ratio (i.e., the VE/VO₂ slope) production methods. The oxygen pulse was defined as the ratio of oxygen consumption to heart rate (i.e., VO₂/HR), namely the volume of oxygen ejected from the ventricles with each cardiac contraction. The oxygen uptake efficiency slope (OUES) was calculated as the slope of the curve representing the logarithmic relationship between ventilation and oxygen consumption [22 (link)]. During the test, the rate pressure product, the product of the HR and the systolic arterial pressure, were calculated, and the maximum value was acquired as the peak rate pressure product (PRPP) [23 (link)].
The test was terminated when the maximum effort was obtained or the subjects could no longer continue due to physical symptoms. The maximum effort was achieved when RER > 1.1, the peak HR > 200 beats per minute, or the HR was >85% of the age-predicted maximum. All tests were performed smoothly under the supervision of well-trained physiatrists.