How Intravenous Infusions Modify the Water Contents of Tissues.

To find what factors influence the exchanges of fluid between blood and tissues, muscles and arterial blood were sampled at frequent intervals before, during, and after various acute procedures upon anesthetized cats and dogs. The percentage water contents of the muscles, and occasionally of other tissues, were determined, and blood concentration was measured in parallel by several methods.

When 50 cc. of Locke solution per kilo were infused, the muscle water content remained constant for a few minutes, then suddenly increased by 1 to 8% and promptly returned almost to normal. The dilution of the blood was maintained for a much longer period of time. The only factor measured which varied in parallel with muscle hydration was the mean arterial blood pressure. That blood pressure was more important than blood dilution in regulating the water content of tissues was shown by infusions of gelatin-Locke and of acacia-Locke solutions. In these experiments the blood dilution persisted for at least 3 hours, while the muscle water content returned to normal within one hour.

A remarkable lag occurred in the onset of tissue hydration in all infusion experiments. The water content of muscle began to increase only at 8 to 20 minutes after the blood dilution and the rise of blood pressure had been produced. The hydration reached a sharp peak and fell with a lag of about 10 minutes after the fall of blood pressure.

After hemorrhage the muscle became dehydrated, following the blood pressure with the usual lag. The blood, both as a whole and with respect to plasma proteins, became diluted without any lag. In hemorrhage the composition of the blood was being varied only through exchanges with the tissues, and pressure changes evidently initiated these.