Inspiratory muscle training improves inspiratory muscle strength and functional exercise capacity in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension: a pilot randomised controlled study

Background: Exercise intolerance is present even in the early stages of pulmonary arterial hypertension (PAH) and is associated with poorer prognosis. Respiratory muscle dysfunction is common and may contribute to exercise limitation. We sought to investigate the effects of inspiratory muscle training (IMT) to improve exercise capacity in PAH. Methods: Adults with PAH were prospectively recruited and randomly assigned to either IMT or a control group. At baseline and after 8 weeks, assessment of respiratory muscle function, pulmonary function, neurohormonal activation, 6-minute walk distance and cardiopulmonary exercise testing variables were conducted. Inspiratory muscle strength was assessed by maximal static inspiratory pressure (PImax). The IMT group performed two cycles of 30 breaths at 30–40% of their PImax 5 days a week for 8 weeks. Results: Twelve (12) PAH patients (60±14 years, 10 females) were recruited and randomised (six in the IMT group and six in the control group). After 8 weeks, the IMT group improved PImax by 31 cmH₂O compared with 10 cmH₂O in controls, p=0.02. Following IMT, 6-minute walk distance improved by 24.5 m in the IMT group and declined by 12 m in the controls (mean difference 36.5 m, 95% CI 3.5–69.5, p=0.03). There was no difference in peak oxygen uptake between-groups (mean difference 0.4 mL/kg/min, 95% CI −2.6 to 3.4, p=0.77). There was no difference in the mean change between-groups in neurohormonal activation or pulmonary function. Conclusion: In this pilot randomised controlled study, IMT improved PImax and 6-minute walk distance in PAH patients.