Validation of lower body negative pressure as an experimental model of hemorrhage (859.5)

Lower body negative pressure (LBNP), a model of hemorrhage (Hem), shifts blood volume to the legs and elicits central hypovolemia. This study compared the effects of LBNP to actual Hem. Baboons (n=14) were instrumented to measure pulse pressure (PP), central venous pressure (CVP), and stroke volume (SV). Blood was removed in four steps: 6.25%,12.5%, 18.75%, and 25% of total blood volume. Four weeks after Hem, the same animals were subjected to four levels of LBNP which changed PP and CVP as seen during Hem. Blood sampled at baseline and maximum Hem or LBNP measured blood gases, hematocrit, hemoglobin, plasma renin activity (PRA), vasopressin (AVP), epinephrine (EPI) and norepinephrine (NE). Hemodynamic responses to Hem and LBNP were identical. Hem decreased hematocrit, hemoglobin, and central venous oxygen saturation (ScvO 2 ). In contrast, LBNP increased hematocrit, and hemoglobin, while ScvO 2 remained unchanged. Hem caused greater (p蠄0.01) elevations in AVP and NE than LBNP, while PRA and EPI did not differ between studies. Thus, stepwise Hem elicited hemodynamic changes which could be mimicked with distinct levels of LBNP, but loss of red blood cells during Hem may result in greater neurohumoral activation. We conclude that while LBNP does not elicit the same effect on blood cell loss as Hem, LBNP mimics the integrative cardiovascular response to Hem, and validates the use of LBNP as an experimental model of Hem.