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

Godinas L, Sattler C, Lau EM, Jaïs X, Taniguchi Y, Jevnikar M,
Weatherald J, Sitbon O, Savale L, Montani D, Simonneau G, Humbert
M, Laveneziana P, Garcia G.

J Heart Lung Transplant. 2017 Nov;36(11):1234-1242. doi:
10.1016/j.healun.2017.05.024. Epub 2017 May 22.

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.