Regional differences in the vascular response to CO2 among cerebral, ocular, and mesenteric vessels

Abstract Background It is well-known that cerebral and ocular vessels are highly sensitive to changes in the partial pressure of CO 2 (P ET CO 2 ). However, it is unclear whether there are regional differences in the magnitude of the vascular response to CO 2 (CO 2 reactivity) in various vessels of a single individual, and whether there is a relationship in the CO 2 reactivity of specific vessels between different individuals. Methods We compared the CO 2 reactivity of the superior mesenteric artery (SMA), middle cerebral artery (MCA), retinal artery (RA), and retinal and choroidal vessels (RCV) during a 3-min inhalation of CO 2 -rich air (5%) in 70 subjects. Results The blood flow velocities in the MCA, RA, and RCV significantly increased by 21 ± 2% (mean ± SE), 9 ± 1%, and 7 ± 2%, respectively ( P 2 reactivity–the relative change in blood flow to a given change in P ET CO 2 –was significantly greater in the MCA (2.2 ± 0.2%/mmHg) than in the RA and RCV (0.9 ± 0.1%/mmHg and 0.8 ± 0.2%/mmHg, respectively). There was a weak correlation in the CO 2 reactivity only between RA and RCV ( r  = 0.43, P Conclusion These findings indicate that the CO 2 reactivity can vary even in cerebral and ocular vessels, although the correlation is weak.