The Effect of Urea on the Human Respiratory Exchange and Alveolar Carbon Dioxide

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Abstract
The respiratory exchange of a human subject was determined for 3 or 3½ hours after ingestion of 400 and 500 cc. of water or 30 or 40 gm. of urea in 400 and 500 cc. of water, respectively. Two methods were used for the determination of the respiratory exchange, 1) an open circuit apparatus with mouthpiece, and 2) an open circuit apparatus with helmet. When the apparatus with the mouthpiece was used, simultaneous determinations of the alveolar carbon dioxide were made every 7 to 8 minutes. There was no effect upon the total metabolism as a result of the ingestion of 30 or 40 gm. of urea when compared with the measurements for the same periods of time in no-dose experiments and those with water. In the experiments with water there was a slight drop in the alveolar carbon dioxide for most of the 3½ hours after the ingestion. With 30 and 40 gm. of urea there was a marked rise in the alveolar carbon dioxide for 2 to 2½ hours. The respiratory quotient was not changed significantly in either the no-dose experiments or the experiments with 400 and 500 cc. of water. With 30 and 40 gm. of urea there was a significant rise in the respiratory quotient beginning at the fourth or sixth quarter-hour after ingestion and lasting until the end of the third hour after ingestion. The study shows that along with an alteration in the alveolar carbon dioxide there is an alteration in the respiratory quotient as the result of the alkalosis following the ingestion of urea. As the alveolar carbon dioxide also rises due to the gastric secretion after the ingestion of protein, it is pointed out that there may be two causes for alterations in the respiratory quotient from the true respiratory quotient after the ingestion of protein, one the gastric secretion containing hydrochloric acid and the other the urea that ultimately results as a metabolic product of the transformations of protein in the body.