Browsing by Author "Phillips, Aaron Alexander"

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    Effect of age, sex and aerobic exercise on cerebrovascular regulation in older adults: Results from the Brain in Motion Study
    (2019-09-17) Wyer, Leanna; Poulin, Marc J.; Phillips, Aaron Alexander; McDonough, Meghan H.; Longman, Richard Stewart
    Background: By 2024, 20% of Canada’s population will be 65 and older. Aging is associated with progressive declines in cerebrovascular and cognitive function and an increased prevalence of age-related diseases such as Alzheimer’s Disease (AD). Physical activity has been associated with improvements in cerebrovascular function and cognitive performance, and may help to prevent and/or delay AD. However, the underlying time-course by which enhanced physical activity may be protective for brain health and differences between men and women is poorly understood. Objective: To determine the influence of age and sex on the cerebrovascular responses to submaximal exercise and euoxic hypercapnia in older adults. Furthermore, this study assessed the effects of a 6-month aerobic exercise intervention on cerebrovascular measures and evaluated outcomes after three and six months of exercise. Design: 202 participants aged 66.5 ± 6.5 years (mean ± SD, 101 females) completed the aerobic exercise intervention. Measurements took place pre-, mid- and post-intervention including demographic information, maximal aerobic capacity (VO2max) and cerebrovascular function. Linear mixed models adjusted for covariates were used to measure the physiological responses to submaximal exercise and euoxic hypercapnia pre-intervention and the changes in middle cerebral artery peak blood flow velocity (VP), mean arterial pressure (MAP) and cerebrovascular resistance (CVRi) and conductance (CVCi) indices after three and six months of aerobic exercise. Results: Pre-intervention, both age and sex were significant predictors of VP (p=0.002; p<0.010), CVRi (p<0.001; p=0.029), and CVCi (p<0.001; p=0.004) during exercise. Compared to rest, acute exercise led to increases in VP, CVRi and MAP and decreases in CVCi (p<0.001). Three months of aerobic exercise led to increases in VP (p=0.005) and CVCi (p=0.021) and decreases in CVRi (p=0.002) in women only, with no further changes observed after an additional three months of exercise. Conclusion: Male sex and increasing age were associated with lower VP, CVCi and higher CVRi. Three months of aerobic exercise led to improvements in cerebrovascular measures in women that were maintained in the latter three months of the intervention in healthy, older adults. Such results have important implications for the role of physical activity in improving health outcomes and the differences observed with aging and sex.
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    Pendulum Study: Active Visual Tracking Elicits Non-Selective Elevations in Cerebral Blood Flow
    (2019-04) Hodge, Sarah V. L.; Spence, Emma E. M.; Suraj, Rejitha; McGirr, Alexander; Phillips, Aaron Alexander
    Neurovascular coupling (NVC) describes the effective matching of cerebral blood flow (CBF) to regions of neuro-metabolic demand. There is increasing interest to assess human NVC for both basic research and its potential role in vascular-cognitive impairment. The clinical utility of NVC relies on a standardized protocol for which the driving metabolic demands are highly-selective. Various research groups deploy divergent strategies to elicit visual NVC responses, including inactive processes (visual grating), passive visual tracking (target with predictable motion) and active visual tracking (target with unpredictable motion). These strategies differ in degree of cognitive and metabolic demand and may elicit different NVC responses, thus precluding study comparison. The present NVC assessment evaluated temporal and regional responsiveness of blood flow (transcranial Doppler) to the visual cortex [via the posterior cerebral artery (PCA)] and blood pressure (Finapres NOVA) during visual stimulation in 19 healthy subjects while also measuring middle cerebral artery (MCA) blood flow. Visual stimulation included 10 cycles of 30 seconds with eyes closed, followed by 30 seconds with eyes open tracking a moving computerized target. Each subject completed three trials of passive tracking and three trials of active tracking (114 NVC protocols, 1140 individual hyperemias). A custom eye-scanning apparatus followed eye motion to quantify visual target-tracking vigilance. Additional custom software was used to quantify NVC. The data demonstrated that active tracking elicited greater NVC responses compared to passive tracking. Specifically, there was 26% greater change in the mean elevation of PCA blood velocity (p=<0.000) and 13% greater peak NVC response (p<0.01). The MCA response was also greater during active tracking (mean response 111% greater, peak response 41% greater; both p<0.001). Visual target-tracking vigilance was linearly correlated to the degree of hyperemia in the MCA and PCA, as well blood pressure during NVC. It was observed that active and passive visual tracking elicit different NVC responses and cannot be reliably compared. That PCA and MCA responses were greater with active tracking suggests an elevated global CBF (i.e. not selective to regions perfused by the PCA) that may result from recruitment of brain centres responsible for sustained attention and executive function. In other words, active tracking leads to non-selective elevations in global CBF and greater target-tracking vigilance impacts the NVC response. These findings are a critical step to better understand and standardize the evaluation of NVC in humans and for potential clinical deployment of NVC assessments.