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

Abstract

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.