Figure 4.

Cerebrovascular reactivity at three months post-injury. CO₂ evoked responses of the cerebrovasculature of C57BL/6 mice are diminished at three months post-injury. Representative traces of CBF flux, as measured by laser speckle contrast imaging, show a reduced mean response in CBF at ROIs both proximal (a) and distal (b) to the site of injury, in the brains of both r-mTBI mice, versus r-sham controls, following 60 s of 5% CO₂ hypercapnic challenge. The area under the curve (c, AUC) and peak response of each individual mouse, normalized to the animal’s peak change in ETCO₂ (d, CVR ratio), were both analyzed using a non-parametric, unpaired Wilcoxon Mann–Whitney U test. The AUC of both the proximal and distal ROI CBF of r-mTBI mice was significantly less than that of r-sham controls (c, P < 0.05, Mann–Whitney). There was a statistically significant difference in CVR ratio between groups at both the proximal and distal ROIs at three months post-injury (d, P < 0.05, Mann–Whitney), with a significantly lower value in proximal CVR ratio of r-mTBI mice of 0.97 ± 0.14, compared to a value of 1.27 ± 0.16 for r-sham controls (d, Mann–Whitney; r-sham vs. r-mTBI, P < 0.05), and a significantly lower value of distal CVR ratio of r-mTBI mice of 0.95 ± 0.30, compared to a value of 1.41 ± 0.31 (d, Mann–Whitney, P < 0.05). R-sham and r-mTBI mice; n = 5 per group. CVR ratio; % Peak Response in CBF/Change in ETCO₂ (mmHg).