Effects of experimental fluid-percussion injury of the brain on cerebrovascular reactivity of hypoxia and to hypercapnia.

To test the hypothesis that concussive brain injury interferes with the normal vasodilator response of the cerebral circulation to hypoxemia, 30 cats were subjected to mild (PaO2 50 mm Hg) and severe (PaO2 30 mm Hg) hypoxemia while measurements were made of arterial and intracranial pressure, regional cerebral blood flow (CBF), and arterial blood gases. Ten cats served as controls, 10 were subjected to mild fluid-percussion injury of the brain (0.8 to 1.7 atmospheres (atm)), and 10 to severe injury (2.4 to 4.1 atm). The CBF response to hypercapnia (PaCO2 50 mm Hg) was also tested in most animals, and the response of CBF autoregulation to hemorrhagic hypotension was tested in four animals of each group. Trauma was found to severely attenuate the capacity of CBF to increase during hypoxemia. Responsiveness to hypoxemia appeared to be better preserved in traumatized animals than was autoregulation, but was less robust than the response to hypercapnia.