Inspiratory muscle weakness contributes to exertional dyspnea in chronic thromboembolic pulmonary hypertension

Abstract

Determination of potentially-reversible factors contributing to exertional dyspnea remains an unmet clinical need in chronic thromboembolic pulmonary hypertension (CTEPH). Therefore, we aimed to evaluate the influence of inspiratory muscle weakness (IMW) on exercise capacity and dyspnea during effort in patients with CTEPH. We performed a prospective cross-sectional study that included thirty-nine consecutive patients with CTEPH (48 ± 15 yrs, 61% female) confirmed by right heart catheterization that underwent an incremental cardiopulmonary exercise test, 6-minute walk test and maximum inspiratory pressure (MIP) measurement. MIP < 70%pred was found in 46% of patients. On a multiple linear regression analysis, MIP was independently associated with 6MWD and [Formula: see text]. Patients with MIP < 70% presented greater [Formula: see text] than those with MIP ≥ 70%. Additionally, they also presented stronger sensations of dyspnea throughout exercise, even when adjusted for ventilation. At rest and at different levels of exercise, mean inspiratory flow (VT/TI) was significantly higher in patients with MIP < 70%. In conclusion, IMW is associated with a rapid increase of dyspnea, higher inspiratory load and poor exercise capacity in patients with CTEPH.

Fig 1

A) Six-minute walking distance (6MWD) and B) oxygen consumption at the peak of cardiopulmonary exercise test ($\dot{V}{\mathrm{O}}_{2\mathrm{PEAK}}$) as a function of maximum inspiratory pressure (MIP). Horizontal gray lines represent median of variables.

Fig 2

Borg dyspnea ratings as a function of work rate (WR) (panel A) and minute ventilation ($\dot{\mathbf{V}}\mathbf{E}$) (panel B) in CTEPH patients showing maximal inspiratory pressure (MIP) < or ≥ 70% predicted according to Neder et al.’s reference equations (closed and open symbols, respectively). Panel C and D shows tidal volume (V_T) /inspiratory time (T_I) ratio–a crude index of neural drive–and respiratory frequency (f) as a function of $\dot{V}\mathrm{E}$ (*p < 0.05).