Cardiopulmonary response to exercise in patients with neuromuscular disease

BACKGROUND Standard of care for patients with neuromuscular disease (NMD) includes exercise testing and exercise therapy. The focus of exercise in this group is to respond to muscular skeletal pathologies related to NMD, improve general health and fitness and health related quality of life. Cardiopulmonary exercise testing CPX is the gold standard for assessing cardiorespiratory fitness, but the use of CPX has been limited in NMD, especially for those patients with low mobility. We present our data on peak CPX and submaximal A6MCT exercise testing in patients with NMD and limited mobility. METHODS We prospectively recruited and consented consecutive patients who were performing outpatient physical therapy at the Neuromuscular Clinic at Stanford University Hospital. Patients performed CPX to volitional exhaustion on a total body trainer and/ or A6MCT at highest pace possible for six minutes on an ergometer. Respiratory gas data were collected on a breath-by-breath basis and analyzed after applying a rolling 30 second average filter. Collected data were compared and contrasted between CPX and A6MCT and compared to normative data and controls. RESULTS There were no complications or adverse events during the study, and data quality was adequate for CPX and A6MCT and comparable to controls. Average respiratory exchange ratio (RER) for patients with NMD was 1.08±0.16 and average rating of perceived exertion (RPE) was 18.4±2.1 compared to 1.16±0.12 and 18.1±2.0 for controls. NMD patients on average showed markedly reduced percent predicted VO2 max (55.6±24.9 percent predicted) and impaired ventilatory efficiency. CONCLUSIONS Quality exercise testing is possible and worthwhile in patients with NMD and low mobility. Especially CPX may offer strong and standard assessment of CRF which may provide valuable clinical data both specific to NMD and nonspecific to improve outcomes. Although a commonly performed procedure, A6MCT would need more study to illustrate its utility for patients with NMD.