Nutritional depletion and its relationship to respiratory impairment in patients with chronic respiratory failure due to COPD or restrictive thoracic diseases

OBJECTIVE: While malnutrition, especially fat-free mass index (FFMI), is a predictor for mortality in chronic obstructive pulmonary disease (COPD), less information on prevalence and mechanisms is available in patients with chronic respiratory failure (CRF) due to restrictive thoracic diseases (RTD). DESIGN AND SETTING: Cross-sectional study of patients consecutively admitted to an in-patient primary pulmonary centre. SUBJECTS: One hundred and thirty-two patients (30% RTD; 70% COPD) with CRF and intermittent non-invasive positive pressure ventilation. INTERVENTIONS: Malnutrition was quantified by bioelectrical impedance analysis or body mass index (BMI), and its relationship to laboratory, lung function, inspiratory muscle and blood gas parameters and 6-min walking distance (6-MWD) was assessed. RESULTS: Malnutrition in terms of BMI<20 kg/m(2) occurred in 16.1% of patients with COPD but none of those with RTD. FFMI<17.4 (<15.0 in female patients) kg/m(2) was found in 35.4 and 30.7%, respectively. FFMI was correlated with airway obstruction (sR(aw), r = -0.50; FEV(1)/VC, r = -0.28; P< or = 0.01 each) and lung hyperinflation (intrathoracic gas volume, r = -0.41; total lung capacity (TLC), r = -0.50; P< or = 0.001 each) in COPD, and with lung restriction in RTD (TLC, r=0.40; P=0.011). Furthermore, malnourished patients showed a higher inspiratory load (P (0.1)) and reduced 6-MWD in both groups. In COPD, only hyperinflation and P (0.1) were independently related to FFMI. CONCLUSIONS: Malnutrition as indicated by low FFMI was similarly prevalent in patients with CRF and COPD or RTD, but inadequately represented by BMI. The correlations between lung function impairments specific for the disease and FFMI emphasized the link between malnutrition and respiratory mechanical load irrespective of its aetiology.