RESPIRATORY MUSCLE FUNCTION AND EXERCISE CAPACITY IN MULTIPLE-SCLEROSIS

Patients with multiple sclerosis (MS) show a poor exercise tolerance. A reduction in respiratory muscle strength has also been reported. The purpose of this study was to evaluate whether reduction in exercise tolerance was related to respiratory muscle dysfunction. Twenty four multiple sclerosis patients (mean+/-SD age: 48+-/9 yrs, duration of illness 12.2+/-6 yrs, severity of illness as assessed by Expanded Disability Scale Score (EDSS) 5.3+/-2), underwent detailed evaluation of lung function tests, arterial blood gas analysis, respiratory muscle strength and endurance, and exercise test on an arm ergometer. Sixteen of the 24 patients were able to perform the exercise test (Group I), whilst the other eight were not (group II). Arterial blood gases and lung function tests were normal for both groups. Respiratory muscle strength as assessed both by maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) was significantly reduced (MIP 18-76 cmH(2)O; MEP 16-82 cmH(2)O) compared to predicted values. Inspiratory muscle endurance time was significantly reduced in Group II in comparison to Group I (247+/-148 vs 397+/-154 s, respectively). Both MIP and MEP were significantly related to inspiratory muscle endurance time. Endurance time, MIP and MEP were inversely significantly related to duration of illness, whilst only endurance time was significantly related to Expanded Disability Scale Score. Exercise test on arm ergometer as assessed by maximal oxygen consumption (Vo(2)max) (11+/-2 ml.kg(-1) 42% pred), maximal workload (Wmax) (22.6+/-6.8W) and maximal heart rate (HRmax) (73+/-11 51% pred) was reduced. Vo,max and HRmax were slightly, but significantly, related to endurance time. Wmax was significantly related to MIP. We conclude that, in patients with multiple sclerosis, reduction in exercise tolerance may be related, at least partially, to respiratory muscle dysfunction.