Heterogeneous regional vascular responses to simulated transient hypovolemia in man.

OBJECTIVE

To describe the evolution of systemic and regional blood flows during and after hypovolemia in humans.

DESIGN

Simulation of hypovolemia by a prolonged application of lower body negative pressure (LBNP).

SETTING

Laboratory of Clinical Research, Surgical Intensive Care Unit of an University Hospital.

PARTICIPANTS

8 healthy male volunteers.

INTERVENTIONS: 3 successive and increasing 15 min-levels of LBNP were followed by a progressive return (10 min) to atmospheric pressure, then a 60 min-recovery period.

MEASUREMENTS AND MAIN

RESULTS

Simulated hypovolemia induced a parallel one-third decrease in cardiac output (bioimpedance), musculocutaneous (venous plethysmography) and splanchnic (ICG clearance) blood flows. Adrenergic-mediated peripheral vasoconstriction 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 increased. All the cardiovascular and biological variables returned to pre-LBNP values during the recovery period except for splanchnic blood flow which remained below control values 60 min after the return to atmospheric pressure.

CONCLUSIONS

Since a sustained splanchnic vasoconstriction follows a transient normotensive hypovolemia in healthy men despite 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.