Dead-space ventilation is linked to exercise capacity and survival in distal chronic thromboembolic pulmonary hypertension

Background: Cardiopulmonary exercise testing (CPET) is frequently used for the evaluation of patients with pulmonary hypertension (PH). Non-operable distal chronic thromboembolic pulmonary hypertension (CTEPH) represents a unique subgroup of PH where microvascular disease resembling pulmonary arterial hypertension (PAH) may predominate and efficacious medical therapy is now available. However, little is known regarding the detailed CPET profile of patients with distal CTEPH, and whether ventilation and gas exchange responses are different from PAH.

Methods: Forty-nine consecutive patients with non-operable distal CTEPH according to multidisciplinary team assessment and 45 PAH patients underwent CPET and right heart catheterization. Patients were followed up for a median of 3.2 years (interquartile range: 1.8 to 4.4).

Results: Pulmonary hemodynamics were similar in distal CTEPH and PAH groups, but patients with distal CTEPH achieved a lower percent predicted peak oxygen consumption (59 ± 13% vs 66 ± 14%, p < 0.05). At peak exercise, higher physiologic dead-space fraction (VD/VT) (0.45 ± 0.07 vs 0.35 ± 0.07, p < 0.0001) and higher arterial-to-end-tidal carbon dioxide gradient (9 ± 3 vs 5 ± 3 mm Hg, p < 0.0001) were observed in distal CTEPH compared with PAH. Ventilatory efficiency, expressed as VE/VCO₂ slope, was also more impaired in distal CTEPH (52.2 ± 10.1 vs 43.8 ± 8.4 liters/min, p < 0.0001). In the distal CTEPH group only, higher VD/VT was associated with lower peak oxygen consumption (r = -0.46, p = 0.003) and worse survival.

Conclusions: Compared with PAH, a distinct pattern of response to exercise was observed in distal CTEPH, characterized by increased dead-space ventilation that resulted in worse ventilatory efficiency and greater impairment of exercise capacity. In distal CTEPH, dead-space ventilation correlated with exercise capacity and was associated with survival.