To evaluate the contribution of body composition measurements to clinical assessment in patients on home nasal positive-pressure ventilation for chronic hypercapnic respiratory failure (CHRF), and their relationship to respiratory impairment.

Patients with CHRF (restrictive lung disease (RLD),  ; chronic obstructive pulmonary disease (COPD),  ), during elective yearly evaluations underwent pulmonary function testing (forced expiratory volumes, arterial blood gases, maximal inspiratory and expiratory pressure (PI_max or PE_max)), and bioelectrical impedance analysis to determine fat-free mass (FFM) index (kg/m²) and body fat mass index.

When compared with age- and sex-matched healthy controls, RLD patients (OR 5.5, CI 1.9–15.6,  ) and COPD (OR 5.2, CI 1.1–24.9,  ) were significantly more likely to have a low FFM index. Roughly one-half of patients with RLD and one-third with COPD had abnormally low FFM index. Estimation of nutritional status by body mass index (BMI) alone clearly underestimated the prevalence of FFM index depletion. Muscle mass assessed by FFM index explained 26% of variance of PI_max ( ) and 27% of that of PE_max ( ).

BMI alone clearly underestimated FFM depletion, and presence of a very high body fat mass index. Indeed, normal or high BMI can be associated with FFM depletion. Because of its relationship to respiratory muscle strength, an assessment of FFM appears to be valuable in CHRF.