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

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.