HETEROGENEOUS REGIONAL VASCULAR-RESPONSES TO SIMULATED TRANSIENT HYPOVOLEMIA IN MAN

Objective: To describe the evolution of systemic and regional blood fl ows during and after hypovolemia in humans. Design: Simulation of hypo volemia by a prolonged application of lower body negative pressure (LB NP). Setting: Laboratory of Clinical Research, Surgical Intensive Care Unit of an University Hospital. Participants: 8 healthy male voluntee rs. Interventions. 3 successive and increasing 15min-levels of LBNP we re followed by a progressive return (10 min) to atmospheric pressure, then a 60min-recovery period. Measurements and main results: Simulated hypovolemia induced a parallel one-third decrease in cardiac output ( bioimpedance), musculocutaneous (venous plethysmography) and splanchni c (ICG clearance) blood flows. Adrenergic-mediated peripheral vasocons triction prevented any change in mean arterial pressure. The decrease in renal blood flow (PAH clearance) was limited, glomerular filtration rate (inulin clearance) unchanged and thus filtration fraction increa sed. All the cardiovascular and biological variables returned to pre-L BNP values during the recovery period except for splanchnic blood flow which remained below control values 60 min after the return to atmosp heric pressure. Conclusions: Since a sustained splanchnic vasoconstric tion follows a transient normotensive hypovolemia in healthy men despi te adequate treatment considering arterial pressure and cardiac output , the therapeutic goals of fluid resuscitation after hypovolemic shock might be revisited and a supranormal value of cardiac output proposed .