Cardiac Function and Mean Circulatory Pressure in Acute Impediment to Venous Return : Symposium on Dynamics of Cardia

In order to evaluate the response of the circulatory system that occurs when the venous return to the right heart is acutely impeded by a balloon in the right atrium, measurements were made of the mean circulatory pressure (MCP), cardiac out-put and other circulatory parameters in open-chest dogs before and during acute artificial "venous congestion" produced by the right atrial balloon. The results were as follows: (1) When the venous return was acutely impeded, there occurred a marked increase in the MCP, while blood volume decreased slightly or remained unchanged. This means that the capacity of the circulatory system has decreased. (2) This response was abolished markedly, but not completely, when the animals were pretreated with a ganglion-blocking agent, pentolinium tartrate (Ansolysen), although the "venous congestion" after ganglionic blockade was comparable with that obtained before ganglionic blockade with respect to cardiac output and central and peripheral venous pressures. (3) This study showed that there are at least two mechanisms by which the venous pressure is elevated in acute impediment to the venous return, (a) impaired "cardiac function" and (b) increased vasomotor tone. (4) When the venous return was impeded, the peripheral venous pressure rose nearly in parallelism with the MCP, but the venous pressure tended to approach the numerical value of MCP when the impediment to venous return was severe. Possible mechanisms responsible for this tendency were discussed.