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Topic

Cerebral Endothelial Function and Pulsatile Metaboreflex Hemodynamics in Adults

School of Exercise Science, Physical and Health Education

Date & location

• Friday, July 26, 2024

• 11:00 A.M.

• McKinnon Building

• Room 155

Reviewers

Supervisory Committee

• Dr. Kurt Smith, Department of Exercise Science, Physical & Health Education, ·¬ÇÑÉçÇø (Supervisor)

• Dr. Kirstin Lane, Department of Exercise Science, Physical & Health Education, UVic (Member) 

External Examiner

• Dr. Mike Tymko, Department of Human Health & Nutritional Sciences, University of Guelph 

Chair of Oral Examination

• Dr. Paul Schure, Department of Economics, ·¬ÇÑÉçÇø

   

Abstract

Existing measures of cerebral blood flow (CBF) during metabolic afferent stimulation disregard the mechanistic implications of endothelial function and compliance of vessels supplying the brain; whether pulsatile cerebral hemodynamic damping (DFi) plays a role in understanding how the afferent muscle metaboreflex impacts brain hemodynamics during exercise was central to this thesis study. Using ultrasound imaging techniques on 28 subjects (11 biological females, 17 biological males; 23.6±4.2 years of age; BMI of 24.0±3.2 kg/m2), measures of DFi from the extracranial internal carotid artery (ICA) to the intracranial middle cerebral artery (MCA) did not change during a paced-breathing metaboreflex stimulation (7.5 breaths per min. [bpm]; p = 0.89); stimulation of the blood pressure-dependent metaboreflex with a 30% maximal voluntary contraction (MVC) dynamic handgrip protocol that preceded post-exercise muscle ischemia (PEMI) was effective (p = 0.005). Endothelial function indexed by the %Δ in ICA vessel diameter (ICAd) during a transient 30-second hypercapnic breathing test (7.5 bpm) showed significant shear-mediated vasodilation to the transient 9% CO2 Douglas bag breathing, which included two deep breaths preceding the 30-second stimulus-response (p = 0.021). This method may provide an easy and reproducible stimulus to increase PaCO2 transiently without hypocapnic vasoconstriction post-Douglas bag removal. A weak positive correlation between %ΔICAd to the absolute and %Δ in DFi during PEMI (r = 0.35; r = 0.35), but not handgrip (r = 0.041; r = 0.026) suggests that we were underpowered for this relationship; endothelial function may positively relate to metabolic afferent stimulation in healthy adults. Future research should increase the sampling power for this correlation and control for differences in sex hormone levels and/or investigate chronic disease-state populations, to better understand how the EPR may have a role in healthy CBF regulation.