Differences in Ventilatory Inefficiency Between Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension

BackgroundMeasures of ventilatory efficiency during cardiopulmonary exercise testing (CPX) are increasingly being used as prognostic markers in heart failure and pulmonary hypertension (PH). Little is known about whether these measures can be applied to all forms of PH, in particular chronic thromboembolic pulmonary hypertension (CTEPH), wherein thrombotic vascular occlusion has an impact on gas exchange.MethodsOne hundred twenty-seven patients, 50 with CTEPH and 77 with pulmonary arterial hypertension (PAH), underwent incremental CPX.ResultsPhysiologic ventilatory dead space fraction (Vd/Vtphys) measured at peak exercise with arterial blood gas analysis was higher in CTEPH than PAH (52.9% vs 41.8%, P < .001). The eco2 slope was higher in patients with CTEPH than in patients with PAH (50.7 L/min/L/min vs 44.4 L/min/L/min, P = .024) and was mirrored by similar changes in the ventilatory equivalent for CO2 at anaerobic threshold (Eqco2_AT) (47.7 L/min/L/min vs 42.0 L/min/L/min, P = .008). In a multivariate linear regression analysis, disease subtype was found to be an independent predictor of Vd/Vtphys (P < .001), eco2 slope (P = .003), and Eqco2_AT (P < .001). These three measures could distinguish between World Health Organization functional classes I/II and III/IV in PAH but not CTEPH.ConclusionSignificant differences in gas exchange exist between CTEPH and PAH, due to differences in Vd/Vtphys likely as a result of vascular occlusion due to thromboembolic disease. This dissociates measures of ventilatory efficiency from disease severity and also contributes to our understanding of the differences in exercise limitation and breathlessness in PAH and CTEPH. Common prognostic end points from CPX cannot be applied to all forms of PH.