Does undernutrition contribute to diaphragm weakness in patients with severe COPD?

Background and aims: The assumption that undernourishment contributes to diaphragm weakness in chronic obstructive pulmonary disease (COPD) remains unproven. Methods: We, therefore, studied diaphragm strength, measured as transdiaphragmatic pressure during a maximal voluntary sniff (Sn Pdi) and cervical magnetic stimulation (Tw Pdi), in two groups of 10 patients with severe COPD. The groups had equally severe COPD as judged by FEV1 and thoracic gas volume (Vtg). The malnourished group had a mean body mass index (BMI) of 17.3 kg/m2 compared with 27 kg/m2 for the normally nourished group (mean difference −9.7 kg/m2; 95% confidence intervals −6.8 to −12.6 kg/m2,P<0.0001). Results: There was no significant difference between Tw Pdi (mean difference 2.1 cm H2O; 95% CI−3 to + 7.4 cm H2O, P=0.39) or Sn Pdi (mean difference −2.4 cm H2O; 95% CI−21 cm H2O to +16 cm H2O,P =0.8). Conclusion: We conclude that undernourishment of the severity studied does not contribute to diaphragm weakness in severe COPD.