Reductions in Central Venous Pressure by Lower Body Negative Pressure or Blood Loss Elicit Similar Hemodynamic Responses
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
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Reductions in central venous pressure by lower body negative pressure or blood loss elicit similar hemodynamic responses. The purpose of this study was to compare hemodynamic and blood analyte responses to reduced central venous pressure CVP and pulse pressure PP elicited during graded lower body negative pressure LBNP to those observed during graded blood loss BL in conscious humans. We hypothesized that the stimulus-response relationships of CVP and PP to hemodynamic responses during LBNP would mimic those observed during BL. We assessed CVP, PP, heart rate, mean arterial pressure MAP, and other hemodynamic markers in 12 men during LBNP and BL. Blood samples were obtained for analysis of catecholamines, hematocrit, hemoglobin, arginine vasopressin, and blood gases. LBNP consisted of 5-min stages at 0, 15, 30, and 45 mmHg of suction. BL consisted of 5 min at baseline and following three stages of 333 ml of hemorrhage 1,000 ml total. Individual r2 values and linear regression slopes were calculated to determine whether the stimulus CVP and PP-hemodynamic response trajectories were similar between protocols. The CVP-MAP trajectory was the only CVP-response slope that was statistically different during LBNP compared with BL 0.93 - 0.27 vs. 0.13 - 0.26 P 0.037. The PP-heart rate trajectory was the only PP-response slope that was statistically different during LBNP compared with BL -1.85 - 0.45 vs. -0.46 - 0.27 P 0.024. Norepinephrine, hematocrit, and hemoglobin were all lower at termination in the BL protocol compared with LBNP P 0.05. Consistent with our hypothesis, LBNP mimics the hemodynamic stimulus-response trajectories observed during BL across a significant range of CVP in humans.
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