Cardiopulmonary exercise performance and factors associated with aerobic capacity in neuromuscular diseases

Aerobic deconditioning, due to lower levels of physical activity, could impact independence for people with neuromuscular conditions. We report the maximal cardiopulmonary response in a cohort of people with Charcot Marie Tooth disease type 1A (CMT 1A) and inclusion body myositis (IBM). We also explored potential predictors of aerobic capacity with measures of physical impairment and functional performance.

Participants underwent maximal cardiopulmonary exercise testing (CPET) using a semi-recumbent cycle ergometer. Data were analyzed to determine the peak O₂ consumption (VO₂ peak), anaerobic threshold (AT), maximum heart rate (MHR), ventilatory equivalent for CO₂ slope (V_E /VCO₂ ), and respiratory exchange ratio (RER). Impairment, functional and patient reported measures were also recorded. Predicted CPET variables were calculated based on published normative data for age, gender, and weight.

Twenty-two people with CMT and 17 people with IBM were recruited. Both groups showed significantly lower VO₂ peak, MHR, AT, and V_E /VCO₂ . The CMT group overall performed better than the IBM group, with significantly higher VO₂ peak, MHR, and AT, but lower V_E /VCO_2. Linear regression analysis demonstrated that VO₂ peak was related to body fat percentage and 6-min walk distance for both groups, and steps per day for the IBM group.

Lower than predicted CPET variables were observed that were not explained by cardiopulmonary limitations or reduced effort, implicating peripheral factors in limiting the cycling task. Regression analysis implied prediction of VO2 peak by body fat percentage and 6-min walk distance. Six-minute walk distance could be a potential proxy measure of cardiopulmonary fitness.