Changes in respiratory control induced by amino acid infusions

We compared the metabolic and respiratory responses to a 4-h infusion of an amino acid solution consisting primarily of branched-chain amino acids (BCAA) to those after a standard amino acid solution in healthy subjects. Both the BCAA solution and the standard amino acid solution increased minute ventilation (mean increase 22%, p < .001, and 18%, p < .01, respectively), mean inspiratory flow (19%, p < .01 and 19%, p < .05) and oxygen consumption (9%, p < .02, and 5%, NS). PaCO₂ decreased (mean decrease 6%, p < .01); there was a major increase in the ventilatory response to CO₂ inhalation during administration of the BCAA solution but not the standard amino acid solution. Increased plasma norepinephrine concentration (mean increase 75%, p < .001) during the infusion of the standard amino acid solution but not the BCAA solution suggested the increased sympathetic activity. The results demonstrate augmented respiratory effects of amino acid infusions by BCAA enrichment, and a dissociation between the respiratory stimulation, metabolic rate, and sympathetic activity.