Validity of Cardiopulmonary Exercise Testing for Assessing Aerobic Capacity in Neuromuscular Diseases

Objectives: To determine the content validity of cardiopulmonary exercise testing (CPET) for assessing peak oxygen uptake (VO_2peak) in neuromuscular diseases (NMD). Design: Baseline assessment of a randomized controlled trial. Setting: Academic hospital. Participants: Eighty-six adults (age: 58.0±13.9 y) with Charcot-Marie-Tooth disease (n=35), postpolio syndrome (n=26), or other NMD (n=25). Intervention: Not applicable. Main Outcome Measures: Workload, gas exchange variables, heart rate, and ratings of perceived exertion were measured during CPET on a cycle ergometer, supervised by an experienced trained assessor. Muscle strength of the knee extensors was assessed isometrically with a fixed dynamometer. Criteria for confirming maximal cardiorespiratory effort during CPET were established during 3 consensus meetings of an expert group. The percentage of participants meeting these criteria was assessed to quantify content validity. Results: The following criteria were established for maximal cardiorespiratory effort: a plateau in oxygen uptake (VO_2plateau) as the primary criterion, or 2 of 3 secondary criteria: (1) peak respiratory exchange ratio (RER_peak) ≥1.10 (2), peak heart rate ≥85% of predicted maximal heart rate; and (3) peak rating of perceived exertion (RPE_peak) ≥17 on the 6-20 Borg scale. These criteria were attained by 71 participants (83%). VO_2plateau, RER_peak ≥1.10, peak heart rate ≥85%, and RPE_peak ≥17 were attained by 31%, 73%, 69%, and 72% of the participants, respectively. Peak workload, VO_2peak, and knee extension muscle strength were significantly higher, and body mass index was lower (all P<.05), in participants with maximal cardiorespiratory effort than other participants. Conclusions: Most people with NMD achieved maximal cardiorespiratory effort during CPET. This study provides high quality evidence of sufficient content validity of VO_2peak as a maximal aerobic capacity measure. Content validity may be lower in more severely affected people with lower physical fitness.