Exercise-onset heart rate increase is slowed in multiple sclerosis patients: does a disturbed cardiac autonomic control affect exercise tolerance?

Abstract

OBJECTIVE:To explore the etiology of exercise intolerance in patients with MS, it is analyzed whether a disturbed cardiac autonomic control could be observed during exercise testing in patients with MS, and is related to exercise tolerance. PATIENTS AND METHOD:From 26 MS patients and 15 healthy subjects, exercise-onset (first 20 and 60 seconds) and –offset (1-minute recovery) HR change was determined during a 6-minute constant-load exercise bout on bike. Blood lactate, HR, oxygen uptake, expiratory volume and perceived exertion were assessed during exercise, and compared between groups. In 15 MS patients, a 6-min walking test was executed. RESULT:Twenty-second exercise-onset HR increase was significantly smaller in MS patients (14±7 bts/min) vs. healthy subjects (20±8 bts/min,p< 0.05), and independently related to MS and age in total group (p< 0.05). Sixty-second exercise-onset and –offset HR changes were not different between groups, nor independently related to MS presence (p> 0.05). A significant correlation was found between 20-second exercise-onset HR increase and walking capacity in MS patients (r= 0.64,p< 0.01). CONCLUSION:In MS patients, the early increase in heart rate during endurance exercise is significantly slowed, indicating a disturbed cardiac autonomic control, and is related to exercise tolerance.