The assessment of aerobic capacity in pulmonary arterial hypertension (PAH) can be done by the six-minute walk test (6MWT) or using an incremental effort test in a cycle ergometer (CPET). Furthermore, there are predictive models of peak oxygen consumption (VO2peak) based on 6MWT. This study aims to compare the VO2peak calculated through the reference equations versus that obtained through a PEIC in patients with PAH, as well as to evaluate the ability to stratify according to the risk scale. 

A retrospective study in patients with PAH candidates for a pulmonary rehabilitation program. Patients underwent 6MWT and CPET <48 hours apart. Both tests followed the recommendations of the ERS/ATS guidelines. The VO2peak obtained from the PEIC was compared with the VO2peak estimated by the Zapico and Appenzeller equations. In addition, based on the value obtained, the subjects were categorized according to the ERS/ESC prognostic scale risk classification.

Data from 39 patients were analyzed. The characteristics of the population are detailed in Table 1. They all performed a 6MWT in which they walked an average of 534m (IQR 434-581m). According to the real data from the CPET, 31 patients (79%) are at intermediate-high risk of mortality in the first year, while according to the Zapico equation, only 17 (43%) are considered to belong to this category. According to the Appenzeller equation, it is considered that only 16 patients (41%) would have an intermediate-high risk, which represents a high percentage of underestimation. 

Using reference equations overestimates the true value of VO2peak and is not helpful in risk categorization in half of the patients with PAH.