Traumatic brain injury creates biphasic systemic hemodynamic and organ blood flow responses in rats

Traumatic brain injury affects systemic circulation as well as directly damages the brain. The present study examined the effects of fluid percussion brain injury on systemic hemodynamics and organ arterial blood flow in rats. Rats were prepared for fluid percussion injury under anesthesia. Twenty-four hours later, rats were anesthetized (1.0% halothane in N2O:O2) and prepared for radioactive microsphere measurement of cardiac output and organ blood flow. After baseline blood flow and physiological measurements were established, the rats were injured (2.47 +/- 0.02 atm, n = 17) or not injured (n = 20). Additional blood flow determinations were made at two of the following four time (T) points: 5, 15, 30, and 60 min after the injury or sham injury. Fluid percussion brain injury produced an immediate systemic hypertension followed by a hypotension and low cardiac output. Organ blood flows remained constant or increased for 30 min and then declined. Decreased blood flow was most pronounced in the kidneys and the spleen and was less severe in the liver. The reduced cardiac output was redistributed to favor blood flow through the heart and pancreas. These data suggest that traumatic brain injury creates a hyperdynamic period followed by a hypodynamic state with a heterogeneous hypoperfusion among organs.