The long-term effect of four hours of hyperventilation on neurocognitive performance and lesion size after controlled cortical impact in rats.

BACKGROUND

We investigated the effects of 4 h of posttraumatic hyperventilation on neurocognitive performance, motor function, and coordination as well as lesion volume in rats subjected to focal traumatic brain injury.

METHODS

After a 14-day training period with various neurocognitive tests including hole-board, beam walk, and beam balance, 21 male Sprague-Dawley rats (369 +/- 15 g) were anesthetized with halothane, tracheally intubated, their lungs mechanically ventilated, and subjected to controlled cortical impact (1.75 mm depth, diameter 5 mm, 4 m/s). They were then randomized to either normoventilation (n = 10; PaCO(2) = 38-42 mm Hg) or hyperventilation (n = 11; PaCO(2) = 28-32 mm Hg) and ventilated for 4 h, respectively. Posttraumatic performance in the behavioral and motor tests was evaluated for 20 days. Rats were then decapitated under deep anesthesia, and their brains frozen and sliced to evaluate lesion volume.

RESULTS

Hyperventilated animals performed significantly worse in explicit memory tests compared with normoventilated rats over time. Both groups showed deficits in advanced motor function and coordination (evaluated by beam walk and beam balance) initially, with a significantly worse performance of hyperventilated compared with normoventilated animals. However, there was no difference between groups by the end of the study. On Day 20 after injury, lesion volume was significantly larger with hyperventilated (69.7 +/- 13.0 mm(3)) compared with normoventilated animals (48.3 +/- 15.6 mm(3)).

CONCLUSIONS

Although hyperventilation enhanced histologic damage, there was no long-term adverse neurocognitive effect from 4 h of posttraumatic hyperventilation (PaCO(2) = 28-32 mm Hg) in rats.