Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA176

Poster Communications

The influence of matched increases in cerebral artery shear stress induced via hypercapnia and exercise on neurovascular coupling

H. G. Caldwell1, K. J. Smith2, R. L. Hoiland1, P. Ainslie1, D. Green2

1. Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia - Okanagan, Kelowna, British Columbia, Canada. 2. Cardiovascular Research Group, School of Human Sciences (Exercise and Sport Science), University of Western Australia, Perth, Western Australia, Australia.


Increases in arterial carbon dioxide tension (i.e., hypercapnia) and exercise both lead to increases in cerebral perfusion, and consequently, increase shear rate on the wall of cerebral arteries (Smith et al. 2017). The nature of how these blood flow patterns may influence the matching of cerebral blood flow to cerebral metabolism (termed neurovascular coupling, NVC) has not been explored. Exercise leads to improved vascular health, likely due to these shear stress responses [reviewed in: (Green & Smith 2017)]; therefore, we hypothesized that matched increases in cerebral artery shear stress induced via hypercapnia and exercise would both improve NVC. Ten healthy male individuals (25±6 yrs) participated in three 30-min experimental interventions, each separated by >48 hrs: 1) hypercapnia (CO2; 4.5% CO2, 21% O2, and balanced N2); 2) submaximal cycling (EX; 60% of heart-rate reserve); and 3) resting (CTR; time-matched control). Transcranial Doppler ultrasound was used to assess mean posterior cerebral artery blood velocity (PCAv). Overall, the NVC response appeared to favour improved NVC following CO2 but not EX or CTR (relative peak response of PCAv pre- vs. post-; CO2: 20.2±6.5% vs. 22.6±9.3%; EX: 21.6±10.4% vs. 18.7±12.6%; CTR: 19.1±9.4% vs. 17.6±7.8%; P=0.52); however, there were no significant differences between these NVC responses irrespective of matched increases in extracranial blood flow, vasodilation, and shear rate following CO2 and EX conditions. The influence of exercise and hypercapnia-mediated changes in NVC will be explored in a larger sample size to further elucidate this relationship.

Where applicable, experiments conform with Society ethical requirements