Controlled Cardiac Output Studies in Dogs (Part II)

Abstract

Refinements in the technique of performing the "control caval return preparation" were outlined, such as those which enable one to control the caval return in the closed-chest intact dog for an arbitrary period of time, at the end of which atrial cannulation and re-establishment of caval flow were accomplished without re-entry into the chest cavity. These latter two maneuvers were accomplished by using a self-constricting rubber band to seal off the atrium and eyed stainless steel wires to release the sutures about the cavae. Coronary flow was estimated by the previously described regression equation and the value added to the known value for '' caval return'' to give a value which was called the "estimated cardiac output." The experiment was conducted sterilely, in order to study survival. It would appear that dogs in this experiment could withstand a reduction in the "caval return" to as low a value of "estimated cardiac output" as 25 ml./Kg./min. The total peripheral vascular resistance was easily calculated, owing to the fact that a close '' estimate of the cardiac output" was obtainable throughout the period of reduced "caval return." The response in "the total peripheral vascular resistance" (TPVE) was most marked during the two-hour period of reduced "caval return," in the range of estimated cardiac output 20 to 40 ml./Kg./min., when there occurred a progressive increase in the TPVR. Above this range, the TPVR remained relatively unchanged throughout the period of control. Below this range the TPVR rose slight^, then began to fall before the end of the controlled period.Refinements in the technique of performing the "control caval return preparation" were outlined, such as those which enable one to control the caval return in the closed-chest intact dog for an arbitrary period of time, at the end of which atrial cannulation and re-establishment of caval flow were accomplished without re-entry into the chest cavity. These latter two maneuvers were accomplished by using a self-constricting rubber band to seal off the atrium and eyed stainless steel wires to release the sutures about the cavae. Coronary flow was estimated by the previously described regression equation and the value added to the known value for '' caval return'' to give a value which was called the "estimated cardiac output." The experiment was conducted sterilely, in order to study survival. It would appear that dogs in this experiment could withstand a reduction in the "caval return" to as low a value of "estimated cardiac output" as 25 ml./Kg./min. The total peripheral vascular resistance was easily calculated, owing to the fact that a close '' estimate of the cardiac output" was obtainable throughout the period of reduced "caval return." The response in "the total peripheral vascular resistance" (TPVE) was most marked during the two-hour period of reduced "caval return," in the range of estimated cardiac output 20 to 40 ml./Kg./min., when there occurred a progressive increase in the TPVR. Above this range, the TPVR remained relatively unchanged throughout the period of control. Below this range the TPVR rose slight^, then began to fall before the end of the controlled period.