Background: the repeated act of heading has been implicated in the link between football participation and risk of neurodegenerative disease, and acutely alters cerebrovascular outcomes in men. This study assessed whether exposure to a realistic number of headers acutely influences indices of cerebral blood flow regulation in female footballers. Methods: Nineteen female players completed a heading trial and seated control trial on two separate days. The heading trial involved six headers in one hour (one every 10 minutes), with the ball travelling at 40 ± 5 km/h. Cerebrovascular reactivity to hypercapnia and hypocapnia was determined using serial breath holding and hyperventilation attempts. Dynamic cerebral autoregulation (dCA) was assessed by scrutinizing the relationship between cerebral blood flow and mean arterial blood pressure during 5 minutes of squat stand maneuvers at 0.05 Hz. Neurovascular coupling (NVC) was quantified as the posterior cerebral artery blood velocity response to a visual search task. These outcomes were assessed before and one hour after the heading or control trial. Results: No significant time by trial interaction was present for the hypercapnic (P=0.48, ηp2=0.05) and hypocapnic (P=0.47, ηp2=0.06) challenge. Similarly, no significant interaction effect was present for any metric of dCA (P>0.12, ηp20.14, ηp2

Cerebrovascular reactivity of the middle cerebral artery velocity (CVR MCAv) to carbon dioxide (CO2) is a common method to assess cerebrovascular function. Yet, the approaches used to calculate CVR outcomes vary. The aim of this study was to explore the within and between-day reliability of traditional CVR outcomes. The second aim was to explore the reliability of novel kinetic-based analyses. Healthy adults (n=10, 22.3±3.4 years) completed assessments of CVR over four minutes using a fixed fraction of inspired CO2 (6%). This was repeated across four separate visits (between-day), and on one visit measures were repeated 2.5 hours later (within-day). No mean biases were present between assessments for traditional CVR metrics, expressed as absolute (cm/s/mmHg) or relative (%/mmHg) outcomes (minute-3, minute-4, peak 1 second, peak 30 second) (between-day: P>0.14, ηp20.22, d>0.27). Absolute, rather than relative CVR, yielded the most reproducible parameters (coefficient of variation: 8.1-13.2% versus 14-83% respectively). There were significant differences between CVR outcomes (P0.89) dependent on the time point used to determine CVR, as a steady state MCAv response was rarely observed. Furthermore, the MCAv response was not reproducible within an individual (kappa=0.15, P=0.09). No mean differences were present for novel kinetic outcomes (amplitude, time-delay, time constant) (between-day: P>0.05, d0.38, d

Longitudinal, cross-sectional, and acute experimental research demonstrate that a short sleep duration is associated with an increased risk of both cardiovascular and cerebrovascular disease. Chronic habitual short sleep duration is associated with an increased dementia risk, however a quarter of the population fail to meet sleep duration guidelines. It is thought that alterations in cerebrovascular function precede symptoms of cognitive decline and dementia. Currently, no evidence exists on measures of cerebrovascular function, such as neurovascular coupling (NVC), and habitual sleep across the lifespan. The association of chronic poor sleep and dementia is likely due to the repeated exposure to a poor night’s sleep. Therefore, there is value in performing controlled, interventional work to understand the acute responses to a single night of sleep restriction. Furthermore, following a night of poor sleep, individuals commonly consume caffeine to increase alertness, but caffeine is known to simultaneously reduce brain blood flow. It is unknown how caffeine affects cerebrovascular function in a sleep restricted state. The purpose of this thesis was therefore to explore 1) the impact of one night of partial sleep restriction on NVC and, 2) whether caffeine ingestion affects NVC after partial sleep restriction in young healthy adults. NVC was determined using transcranial Doppler ultrasound (TCD) to measure blood velocity through the posterior cerebral artery (PCAv) during a visual search task. TCD was also used to measure blood velocity through the middle cerebral artery (MCAv) during cognitive function tests, both of which were assessed before and after normal sleep and partial sleep restriction, and following caffeine ingestion. This study found that NVC was unaltered following partial sleep restriction, and that the magnitude of the NVC response was unchanged after caffeine ingestion in both the rested and sleep restricted state. However, both absolute PCAv and MCAv were lower after caffeine, though this response did not differ between normal and restricted sleep. This study was the first to examine the effects of partial sleep restriction and subsequent caffeine ingestion on a measure of cerebrovascular function. However, sleep restriction was only studied in the form of a 50% sleep restriction, with sleep taking place in the second half of the night. Future research should explore whether the relationship between sleep and NVC is dependent on how sleep is accrued throughout the night, for example fragmented/broken sleep.

The acute effect of exercise intensity on cerebrovascular reactivity, and whether this mirrors changes in peripheral vascular function, has not been investigated. The aim of this study was to explore the acute effect of exercise intensity on cerebrovascular reactivity (CVR) and peripheral vascular function in healthy young adults (n=10, 6 females, 22.7 ± 3.5 years). Participants completed four experimental conditions on separate days: high intensity interval exercise (HIIE) with intervals performed at 75% maximal oxygen uptake (V̇O2max; HIIE1), HIIE with intervals performed at 90% V̇O2max (HIIE2), continuous moderate intensity exercise (MIE) at 60% V̇O2max and a sedentary control condition (CON). All exercise conditions were completed on a cycle ergometer and matched for time (30 min) and average intensity (60% V̇O2max). Brachial artery flow-mediated dilation (FMD) and CVR of the middle cerebral artery were measured before exercise, and one- and three hours post-exercise. CVR was assessed using transcranial Doppler ultrasonography to both hypercapnia (6% carbon dioxide breathing) and hypocapnia (hyperventilation). FMD was significantly elevated above baseline one and three hours following both HIIE conditions (P0.33). CVR to both hypercapnia and hypocapnia, and when expressed across the end-tidal CO2 range, was unchanged in all conditions, at all time points (all P>0.14). In conclusion, these novel findings show that the acute increases in peripheral vascular function following HIIE, compared to MIE, were not mirrored by changes in cerebrovascular reactivity, which was unaltered following all exercise conditions in healthy young adults.