Serum amino acids in relation to nutritional status, lung function and energy intake in patients with advanced pulmonary disease.

Malnutrition, hypoxia and energy deficit may affect protein metabolism. We wanted to evaluate the cross-sectional association between serum amino acids and fat-free mass in a group of hypoxic patients. We also wanted to explore, in the same group of patients, whether the blood amino-acid pattern could possibly be influenced by differences in lung function and energy intake. Serum amino acids were measured in 71 hypoxic underweight and normal-weight patients with advanced pulmonary disease and related to the fat-free-mass index, arterial oxygen (PaO2) and carbon dioxide tension (PaCO2), forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV1) and energy intake. Only one amino acid (aspartic acid) remained significantly correlated to the fat-free-mass index after adjustments for age and sex (beta = -0.30, P=0.011). None of the amino acids were significantly correlated to PaO2 but alanine was significantly negatively correlated to PaCO2 (beta = -0.46, P<0.001), phenylalanine to FVC1 (beta = 0.52, P=0.001) and tyrosine to FVC (beta = 0.36, P=0.008). Citrulline and tryptophan were significantly correlated to energy intake (beta = 0.32, P=0.008; beta=0.37, P=0.009 respectively). In conclusion, there was no convincing association between fat free mass and serum amino acids. The negative effect of hypercapnia and reduced lung function on some serum amino acids was suggested and some amino acids were sensitive to reduced energy intake.