Cerebrovascular reactivity to CO2 and hypotension after mild cortical impact injury.

Cerebrovascular reactivity to CO2 or hypotension was studied in vivo and in vitro [pressurized arteries (∼82 μm) and arterioles (∼30 μm)] at 1 h after mild controlled cortical impact (CCI) injury in rats. The cortical perfusion response [assessed using laser-Doppler flowmetry (LDF)] to altered CO2 was diminished (up to 81%) after mild CCI injury. The responses to CO2 alterations in arteries and arterioles isolated from the injured cortex were similar to responses in vessels isolated from sham-injured animals. After mild CCI injury, the autoregulatory response to hypotension (measured using LDF) was maintained or even enhanced, depending on the method used to measure the response. Vessels isolated from the injury site showed a response to changes in pressure similar to that in vessels isolated from sham-injured rats. We conclude that mild CCI injury produces complicated alterations in cerebrovascular control. Whereas the autoregulatory response to hypotension was maintained or even enhanced, the in vivo vascular response to CO2 was severely compromised. The altered response to CO2 was not caused by an intrinsic vascular perturbation but rather an altered milieu after mild CCI injury.