Simplified protocols and indices of aerobic capacity among patients suffering from multiple sclerosis with mild neurological disability

Background: Peak oxygen uptake (VO2peak) is the gold standard to assess aerobic capacity. However, due to other impairments, a maximal cardiorespiratory effort is not always achievable by patients with MS. Moreover, gas exchange analyzers are roughly available in daily clinical practice. Objective: To examine the validity of aerobic capacity indices that do not necessitate maximal exercise effort and/or gas exchange analysis among patients with MS with mild neurological disability (EDSS≤4). Methods: 25 patients with MS with mild neurological disability (EDSS≤4) performed a maximal exercise testing on a cycle ergometer, including gas exchange measures. Criteria of maximal exercise effort were verified. Relevant indices of aerobic capacity were calculated: Peak Work Rate (PWR), Oxygen Uptake Efficiency Slope (OUES) derived from different durations (total, first 4 and 6 minutes, until RER=1), normalized Physical Working Capacity at 75% of predicted maximal heart rate (PWC75%/kg), normalized Working Capacity Index at 65% of heart rate reserve (WCI65%/kg) and normalized Peak Work Rate to Heart Rate increasing ratio (PWR/ΔHR.kg). These indices were compared to normative values. Each index was confronted to VO2peak by the means of Pearson correlation coefficient. OUES derived from different times were compared using ICC(1) and Bland-Altman plots. Results: Twenty patients (80%) complied with the maximal exercise criteria. Indices of aerobic capacity were lower than healthy references. All OUES were highly correlated to VO2peak (All r>0.80,p<0.001). All OUES derived from submaximal efforts appeared to have a high predictive validity for OUES derived from the total exercise duration (from ICC(1)=0.85 to ICC(1)=0.92). PWR and PWR/ΔHR.kg correlated moderately with VO2peak (respectively, r=0.56 and r=0.67, p