| Abstract: | Six groups of six conditioned dogs each were instrumented with an electromagnetic flow-meter transducer around the pulmonary artery, and indwelling silastic cannulae in the pulmonary artery, the left ventricle, the ascending aorta, and the right atrium. After allowing a minimum of 5 d for recovery, the dogs were studied under normobaric conditions, breathing air, at 2.8 atmospheres absolute (ATA), breathing 100% oxygen (PO2 2128 mm Hg) and at 6 ATA breathing air (PO2 960 mm Hg). Baseline recordings were made at 1 ATA and repeated after arrival at depth. The dogs were hemorrhaged until the mean aortic pressure fell to 40 mm Hg. Mean aortic pressure was maintained between 40-50 mm Hg for 30 min. This required a rather constant 40 +/- 4.5 ml X kg-1 body weight of total blood removed. Three groups, one at each depth perturbation, were then given Dextran 70, the other three groups 10% dextrose. Fluids were administered at a constant rate until the mean aortic pressure rose to within 90% of its original 1 ATA baseline value. At this point, the infusion was stopped and the total amount of fluid administered was recorded. Hemodynamic parameters were measured or calculated for eight different time periods during each experiment. The amount of Dextran 70 required did not change with hyperbaric exposure but only half as much 10% dextrose was required at depth. Dextran 70 held the cardiovascular parameters constant for 30 min following administration but after 10% dextrose, cardiac output tended to decrease at 15 and 30 min posttreatment. There were no significant differences in the cardiovascular effects of hemorrhage between or among the dogs exposed to the three different environmental conditions. |
