Clinical utility of ventilatory and gas exchange evaluation during low‐intensity exercise for risk stratification and prognostication in pulmonary arterial hypertension

Background and objective Peak oxygen consumption (pVO 2 ), determined from CPET, provides a valuable indication of PAH severity and patient prognosis. However, CPET is often contraindicated in severe PAH and frequently terminated prior to achievement of a sufficient exercise effort. We sought to determine whether in PAH low‐intensity [i.e. freewheeling exercise (FW)] exercise reveals abnormal V E /VCO 2 and P ET CO 2 responses that are associated with pVO 2 and serve as indices of PAH risk stratification and mortality. Methods Retrospective analysis of CPET from 97 PAH patients and 20 age‐matched controls was undertaken. FW V E /VCO 2 and P ET CO 2 were correlated with pVO 2 % age‐predicted. Prognostication analysis was conducted using pVO 2 > 65% age‐predicted, as known to represent a low mortality risk. Primary outcome was mortality from any cause. Results FW P ET CO 2 was correlated with pVO 2 ( P < 0.0001; r = 0.52), while FW V E /VCO 2 was not ( P = 0.13; r = −0.16). ROC curve analyses showed that FW P ET CO 2 (AUC = 0.659), but not FW V E /VCO 2 (AUC = 0.587), provided predictive information identifying pVO 2 > 65% age‐predicted (best cut‐off value of 28 mm Hg). By Cox analysis, FW P ET CO 2 < 28 mm Hg remained a predictor of mortality after adjusting for age and PAH aetiology (HR: 2.360, 95% CI: 1.144–4.866, P = 0.020). Conclusion Low P ET CO 2 during FW is associated with reduced pVO 2 in PAH and provides predictive information for PAH risk stratification and prognostication.