Respiratory muscle dysfunction in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a pulmonary vasculopathy of unknown aetiology. Dyspnoea, peripheral airway obstruction and inefficient ventilation are common in IPAH. Data on respiratory muscle function are lacking. This prospective single-centre study included 26 female and 11 male patients with IPAH in World Health Organization functional classes II-IV. Mean +/- SD pulmonary artery pressure was 48.6 +/- 16.9 in females and 53.1 +/- 22.9 mmHg in males; cardiac output was 3.7 +/- 1.3 and 4.2 +/- 1.7 L (.) min(-1). Maximal inspiratory pressure (PI,max) was lower in the female patients than in 20 controls (5.3 +/- 2.0 versus 8.2 +/- 2.0 kPa). In the male patients, PI,max was lower than in 25 controls (6.8 +/- 2.2 versus 10.5 +/- 3.7 kPa). Maximal expiratory pressure (PE,max) was lower in the female patients than in controls (6.2 +/- 2.6 versus 9.5 +/- 2.1 kPa), and in male patients as compared to controls (7.1 +/- 1.6 versus 10.3 +/- 3.9 kPa). There was no correlation between PI,max or PE,max and parameters of pulmonary haemodynamics or exercise testing. The ratio of mouth occlusion pressure within the first 0.1 s of inspiration and PI,max was higher in IPAH than in controls (females 0.067 +/- 0.066 versus 0.021 +/- 0.008; males 0.047 +/- 0.061 versus 0.023 +/- 0.016). In conclusion, this study provides the first evidence of inspiratory and expiratory muscle weakness in idiopathic pulmonary arterial hypertension. The pathomechanisms and the prognostic significance should be further investigated.