Regional and sex differences in cerebral vasomotor reactivity to carbon dioxide

Abstract

Studies on cerebral vasomotor reactivity (CVMR) to carbon dioxide (CO2) are often limited to middle cerebral artery (MCA), and rarely include anterior cerebral artery (ACA) and/or vertebral artery (VA); In addition, comparison of reactivity across vessels in the same individuals is rarely performed; Moreover, sex difference in CVMR has also not been carefully investigated. Therefore, it remains unknown whether there are differences in CVMR across arterial territories and/or between females and males. Twenty‐five young healthy subjects (15 females; age: 19–37 yrs, 27±5 yrs) were enrolled. The cerebral blood flow velocities (CBFVs) at the MCA, ACA and VA were simultaneously and continuously recorded with transcranial Doppler during 3‐min resting ventilation, 2‐min inspiration of 8% CO2, 21% O2, balance nitrogen, and 2‐min mild hyperventilation, in the sitting position. The CVMR of each artery is expressed as the percent change in its CBFV per mmHg change in end‐tidal CO2, as quantified by the slope of this relationship. The results are presented as Mean±SD. The experimental protocol resulted in a variation of end‐tidal CO2 from 31.8±4.7 to 46.6±5.5 (baseline, 40.4±3.5) mmHg, with a slight variation of mean blood pressure from 92±13 to 99±13 (baseline, 94±12) mmHg. The repeated‐measures ANOVA for multiple comparisons with Bonferroni correction indicated that the CVMR slope was significantly lower in the VA (1.85±0.61 %/mmHg) than in the MCA (2.30±1.04, P = 0.023) or ACA (2.33±0.92, P = 0.004). Females generally showed steeper CVMR slope than males (2.43±0.91 vs. 1.77±0.31, P = 0.019, for the 3‐artery averaged value), with no interaction found between sex and arterial territory factors. Based on these results, the CVMR appears lower in the posterior (vertebrobasilar) circulation than in the anterior circulation. Consistent with previous data we also found females had higher CVMR values in all arteries than males. The observed regional and sex CVMR differences should play an important role when assessing the cerebral blood flow response to other physiological situations (e.g. dynamic exercise; orthostatic, hypoxia, heat or cold stress), and might explain some neurological symptoms relevant to the posterior circulation ischemia and/or sex differences, which merits further investigation. Future studies are planned to examine the pressure‐ and/or flow‐induced concurrent diameter changes of the insonated artery, when using CBFV rather than volumetric cerebral blood flow to assess the CVMR.Support or Funding InformationSupported by the War Related Illness & Injury Study Center, Veterans Administration and NIH grant R21DC009900.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.