WEIGHT-LOSS IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Weight loss occurs in about a third or more disabled patients with chr onic obstructive pulmonary disease (COPD), and appears to be a poor pr ognostic factor. As such, it correlates only weakly with FEV1, transfe r factor and other measures of respiratory physiology and is probably, to a certain extent, independent of them. Recent studies of basal met abolic rate (BMR) in COPD using steady-state, non-invasive calorimetry , have shown it to be elevated by 10-20% in up to 40% of such patients . It is likely that this represents true hypermetabolism per kilogram of fat free mass. An elevated BMR cannot be predicted from combination s of detailed lung function tests or arterial gases, as patients with similar physiology have differing BMRs. Thus, although an increased wo rk of breathing is the probable explanation for some of the increase, other factors such as cytokines or possibly drug therapy almost certai nly contribute. Muscle loss in weight-losing COPD appears to involve b oth type I and type II fibres, because of a combination of reduced cal orie intake and disuse atrophy. Respiratory muscles share this fibre l oss. Review of the controlled studies on nutritional supplementation i n COPD suggests that an energy increase of about 30% is needed to achi eve substantial weight gain and improve exercise tolerance. Fat-rich s upplements have some theoretical advantages. Further work is needed pa rticularly with regard to the determinants of the increased BMR in COP D, and the effect of longer term nutritional supplements on prognosis.