INSPIRATORY MUSCLE STRENGTH AND BODY-COMPOSITION IN PATIENTS RECEIVING TOTAL PARENTERAL-NUTRITION THERAPY

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Abstract
The relationship between inspiratory muscle strength and body composition was examined in 59 patients receiving total parenteral nutrition (TPN). Inspiratory muscle strength was assessed by measuring maximal inspiratory pressure (Pm) after a tidal expiration with the patient supine and the nose occluded. Body composition was determined by multiple isotope dilution. Body cell mass (BCM) and extracellular mass were estimated by measuring total exchangeable K(Ke) and total exchangeable Na(Nae), respectively; Nae/Ke, an index of the nutritional state, was calculated from these values. The effect of changes in muscle mass was evaluated in 29 of the patients by simultaneous determination of Pm and body composition, prior to and at 2 wk intervals during TPN therapy. The Pm was lower (mean .+-. 1 SE:33.5 .+-. 2.8 cm H2O) in malnourished patients than in those who were in the normal Nae/Ke range (45.3 .+-. 4.8 cm H2O, P < 0.05). Loss of strength was related to reduction in muscle mass because BCM was also reduced in malnourished patients (15.6 .+-. 0.8 kg) when compared to those with normal Nae/Ke (19.3 .+-. 0.9 kg), (P < 0.05), and Pm was positively correlated with BCM ( r = 0.27, P < 0.01). Changes in BCM were accompanied by appropriate changes in Pm during the study period (r = 0.44, P < 0.01); the majority (21 patients) showed improvement in both BCM and Pm. The hypothesis that loss of body cell mass affects inspiratory muscle strength and may contribute to ventilatory failure was supported. Nutritional support can, in some cases, improve both the nutritional status and inspiratory muscle strength.