Peripheral muscles weakened in PAH patients

By Eleanor McDermid, Senior medwireNews Reporter

Patients with pulmonary arterial hypertension (PAH) have peripheral muscle weakness that is independent of impairments in their respiratory muscles, research shows.

The findings highlight “the importance of considering rehabilitation in the treatment strategy for PAH”, say Rogerio Souza (Heart Institute University of São Paulo Medical School, Brazil) and study co-authors.

The team found that the patients’ quadriceps were significantly weaker than those of unaffected controls for peak torque (108.9 vs 147.0 N/m) and for total work (659.6 vs 932.7 J). Muscle area was slightly reduced, although not significantly so.

Overall, the patients had a significantly higher fat mass than controls, at 28.6% versus 24.6%, and a lower lean fat mass, at 71.4% versus 76.2%. And they had reduced lung function, with significantly lower maximal inspiratory pressure, at –61.9 versus –92.0 cmH₂O, and expiratory pressure, at 89.0 versus 116.0 cmH₂O.

Patients also had a reduced exercise capacity, being able to walk only an average of 490 metres in the 6-minute walk test. The team says that although this indicates a good prognosis for the PAH patients, it was still significantly less than the control group, which walked an average of 632 metres. In line with this, the patients had a significantly reduced maximal oxygen consumption, at 14.7 versus 22.9 mL/kg per minute. Their partial pressure of CO₂ at end expiration fell with increasing effort, rather than rising as in the controls, and they failed to reach a maximal heart rate.

Maximal oxygen consumption rose as measures of respiratory and peripheral muscle function increased, and it also correlated positively with cardiac output. In bivariate analyses, poorer peripheral muscle function, assessed as total work, was significantly associated with lower maximal oxygen consumption after accounting for the cardiac index, showing that peripheral muscle function influenced exercise capacity independently of respiratory muscle function.

Muscle morphology also played a part; the area of type I fibres was reduced in PAH patients relative to that expected for their age, and lower type I fibre area was significantly associated with lower maximal oxygen consumption independently of the cardiac index.

“Future studies should evaluate whether this finding remains after specific muscular training and should also demonstrate the safety and efficacy of such training programs”, conclude the researchers in PLoS ONE.

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