In contrast to the typical image of heart patients running on treadmills and being hooked up to diagnostic machines while a doctor monitors their heart rate and oxygen consumption, a group of idiopathic pulmonary arterial heart (IPAH) patients cycled in a research study while being evaluated for blood pressure, oxygen consumption, and electrocardiogram (ECG) measurements in order to determine a new means to detect abnormalities in IPAH patients.
As reported in PLoS One, Xingguo Sun and colleagues, of Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing, found that individuals with IPAH have significantly lower oxygen efficiency during exercise than healthy controls. Oxygen uptake efficiency plateau (OUEP) of IPAH patients was 23.4 mL/L, while OUEP of healthy controls was 37.8 mL/L.
To make this finding, the researchers enlisted 32 IPAH patients and 16 healthy controls. The individuals cycled steadily for three minutes, at which point resistance was increased and subjects cycled to the limit of their functional capacity. During this time, pulmonary function tests–such as forced vital capacity, forced expiratory volume in one second, and total lung capacity–and cardiopulmonary exercise tests–such as carbon dioxide output and minute oxygen uptake–were administered to patients.
After calculating parameters related to cardiac and lung function, the researchers noted differences in OUE between IPAH patients and healthy controls during all stages of the tests: rest, warm up, anaerobic threshold, and peak. The team explained the difference between patients and controls may result from the inability of IPAH patients to match oxygen flow with blood flow in order to distribute blood to their working muscles.
Additionally, OUEP correlated well with other established measures of IPAH severity, while another measured parameter–OUE slope (OUES)–did not. OUEP was easier to calculate and less variable than OUES, while also being a better-suited parameter to use for patient assessment because it did not require patients to cycle to maximal exertion. Ideally, tests for disease severity are as comfortable as possible for patients and provide low risks when administered.
Returning to the idea of lung/heart mismatch in patients, it was also found that IPAH patients needed to compensate for limited heart function. Their carbon dioxide content at the end of an inhale did not increase during exercise, although it did for healthy controls, and their ventilator efficiency of carbon dioxide elimination was greater than healthy controls. Therefore, the IPAH patients’ lungs were compensating for limited hear function, giving way to hyperventilation.
Adding OUEP to the toolbox of identifying disease states in IPAH patients was a valuable outcome of the study. Cardiopulmonary exercise tests are increasingly recognized as potent diagnostics for IPAH patients, indicating a greater need for parameters that can be calculated and compared among patients.