FIGURE 4.

This image displays the cross sectional area (CSA) of the left and right middle cerebral artery (MCA) during normocapnia and hypercapnia (6% CO₂ inhalation) in (A) young and (B) older adults. The group average response is shown in black. Gray lines demonstrate individual responses. On average, the left MCA CSA significantly increased from normocapnia to 6% CO₂ in young adults (p = 0.004) but the change in CSA was not significant in older adults (p = 0.08). The right MCA CSA significantly increased from normocapnia to 6% CO₂ in young adults (p = 0.002) but the change in CSA was not significant in older adults (p = 0.19). There were no differences in the response to hypercapnia between the right MCA CSA compared with the left MCA CSA in young (p = 0.28) and older (p = 0.72) adults.