The Effects on the Cardiovascular System of Fluids Administered Intravenously in Man. Ii. the Dynamics of the Circulation.

Earlier studies from this laboratory (1, 2, 3) have shown that the intravenous administration of 500 to 1500 cc. of fluids, at rates ranging from 9 to 125 cc. per minute, results in appreciable increases in plasma and blood volumes. Significant changes in cardiovascular dynamics did not occur at rates of injection under 20 cc. per minute; administration of fluids intravenously at faster rates resulted in rises in venous pressure and cardiac output, slight increases in pulse rate and pulse pressure, and, in some experiments, acceleration of the velocity of blood flow. Acceleration of blood flow usually occurred (2) when 500 to 600 cc. of fluid were given intravenously, at rates of 20 to 30 cc. per minute; infusions given in larger volume or at more rapid rates caused unexpectedly small increases, or even transitory decreases, in the velocity of blood flow. It was therefore believed that transitory increase in the amount of blood in the lungs may have occurred under these circumstances. Studies of respiratory dynamics were made (2) in several patients who received 400 to 1000 cc. of fluid intravenously, at rates of between 11 and 36 cc. per minute; no changes were found in respiratory rate or minute volume, tidal air, or vital capacity. However, it was apparent that additional studies of respiratory dynamics should be made after larger infusions, given more rapidly; accordingly, measurements of respiratory dynamics and of the various subdivisions of the lung volume have been made in subjects receiving 1800 cc. of fluid intravenously, at rates of between 39 and 185 cc. per minute.