Novel Application of a Force Sensor during Sit-to-Stands to Measure Dynamic Cerebral Autoregulation Onset

Purpose: Current sit-to-stand methods measuring dynamic cerebral autoregulation (dCA) do not capture the precise onset of the time delay (TD) response. Reduced sit-to-stand reactions in older adults and individuals post-stroke could inadvertently introduce variability, error, and imprecise timing. We applied a force sensor during a sit-to-stand task to more accurately determine how TD before dCA onset may be altered. Methods: Middle cerebral artery blood velocity (MCAv) and mean arterial pressure (MAP) were measured during two sit-to-stands separated by 15 minutes. Recordings started with participants sitting on a force-sensitive resistor for 60 seconds, then asked to stand for two minutes. Upon standing, the force sensor voltage immediately dropped and marked the exact moment of arise-and-off (AO). Time from AO until an increase in cerebrovascular conductance (CVC = MCAv/MAP) was calculated as TD. Results: We tested the sensor in 4 healthy young adults, 2 older adults, and 2 individuals post-stroke. Healthy young adults stood quickly and the force sensor detected a small change in TD compared to classically estimated AO, from verbal command to stand. When compared to the estimated AO, older adults had a delayed measured AO and TD decreased up to ~50% while individuals post-stroke had an early AO and TD increased up to ~14%. Conclusion: The transition reaction speed during the sit to stand has the potential to influence dCA metrics. As observed in the older adults and participants with stroke, this response may drastically vary and influence TD.

The Interaction of Dynamic Cerebral Autoregulation and Neurovascular Coupling in Cognitive Impairment

Background: Dynamic cerebral autoregulation (dCA) remains intact in both ageing and dementia, but studies of neurovascular coupling (NVC) have produced mixed findings. Objective: We investigated the effects of task-activation on dCA in healthy older adults (HOA), and patients with mild cognitive impairment (MCI) and Alzheimer’s Disease (AD). Methods: Resting and task-activated data from thirty HOA, twenty-two MCI, and thirty-four AD were extracted from a database. The autoregulation index (ARI) was determined at rest and during five cognitive tasks from transfer function analysis. NVC responses were present where group-specific thresholds of cross-correlation peak function and variance ratio were exceeded. Cumulative response rate (CRR) was the total number of positive responses across five tasks and two hemispheres. Results: ARI differed between groups in dominant (p=0.012) and non-dominant (p=0.042) hemispheres at rest but not during task-activation (p=0.33). ARI decreased during language and memory tasks in HOA (p=0.002) but not in MCI or AD (p=0.40). There was a significant positive correlation between baseline ARI and CRR in all groups (r=0.26, p=0.018), but not within sub-groups. Conclusion: dCA efficiency was reduced in task-activation in healthy but not cognitively impaired participants. These results indicate differences in neurovascular processing in healthy older adults relative to cognitively impaired individuals.

Prenatal exercise and cardiovascular health (PEACH) study: impact of acute and chronic exercise on cerebrovascular hemodynamics and dynamic cerebral autoregulation

We performed a randomised controlled trial measuring dynamic cerebral autoregulation (dCA) using a sit-to-stand maneuver before (SS1) and following (SS2) an acute exercise test at 16-20 weeks gestation (trimester 2; TM2) and then again at 34-37 weeks gestation (third trimester; TM3). Following the first assessment, women were randomised into exercise training or control (standard care) groups; women in the exercise training group were prescribed moderate intensity aerobic exercise for 25-40 minutes on 3-4 days per week for 14±1weeks. Resting seated mean blood velocity in the middle cerebral artery (MCAvmean) was lower in TM3 compared to TM2 but not impacted by exercise training intervention. dCA was not impacted by gestational age, or exercise training during SS1. During SS2, dCA was altered such that there were greater absolute and relative decreases in mean arterial blood pressure (MAP) and MCAvmean, but this was not impacted by the intervention. There was also no difference in the relationship between the decrease in MCAvmean compared to the decrease in MAP (%/%), or the onset of the regulatory response with respect to acute exercise, gestational age, or intervention; however, rate of regulation was faster in women in the exercise group following acute exercise (interaction effect, p=0.048). These data highlight the resilience of the cerebral circulation in that dCA was well maintained or improved in healthy pregnant women between TM2 and TM3. However, future work addressing the impact of acute and chronic exercise on dCA in women who are at risk for cardiovascular complications during pregnancy is needed.

Midlife Aerobic Exercise and Dynamic Cerebral Autoregulation: Associations with Baroreflex Sensitivity and Central Arterial Stiffness

Midlife aerobic exercise may significantly impact age-related changes in the cerebro- and cardiovascular regulations. This study investigated the associations of midlife aerobic exercise with dynamic cerebral autoregulation (dCA), cardiovagal baroreflex sensitivity (BRS), and central arterial stiffness. Twenty middle-aged athletes (MA) who had aerobic training for >10 years were compared with 20 young (YS) and 20 middle-aged sedentary (MS) adults. Beat-to-beat cerebral blood flow velocity, blood pressure (BP), and heart rate were measured at rest and during forced BP oscillations induced by repeated sit-stand maneuvers at 0.05 Hz. Transfer function analysis was used to calculate dCA and BRS parameters. Carotid distensibility was measured by ultrasonography. MA had the highest peak oxygen uptake (VO2peak) among all groups. During forced BP oscillations, MS showed lower BRS gain than YS, but this age-related reduction was absent in MA. Conversely, dCA was similar among all groups. At rest, BRS and dCA gains at low frequency (~0.1 Hz) were higher in the MA compared with MS and YS groups. Carotid distensibility was similar between MA and YS groups, but it was lower in the MS. Across all subjects, VO2peak was positively associated with BRS gains at rest and during forced BP oscillations (r=0.257~0.382, p=0.003~0.050) and carotid distensibility (r=0.428~0.490, p=0.001). Furthermore, dCA gain at rest and carotid distensibility were positively correlated with BRS gain at rest in YS and MA groups (all p<0.05). These findings suggest that midlife aerobic exercise improves central arterial elasticity and BRS which may contribute to CBF regulation through dCA.

Review of studies on dynamic cerebral autoregulation in the acute phase of stroke and the relationship with clinical outcome

Acute stroke is associated with high morbidity and mortality. In the last decades, new therapies have been investigated with the aim of improving clinical outcomes in the acute phase post stroke onset. However, despite such advances, a large number of patients do not demonstrate improvement, furthermore, some unfortunately deteriorate. Thus, there is a need for additional treatments targeted to the individual patient. A potential therapeutic target is interventions to optimize cerebral perfusion guided by cerebral hemodynamic parameters such as dynamic cerebral autoregulation (dCA). This narrative led to the development of the INFOMATAS (Identifying New targets FOr Management And Therapy in Acute Stroke) project, designed to foster interventions directed towards understanding and improving hemodynamic aspects of the cerebral circulation in acute cerebrovascular disease states. This comprehensive review aims to summarize relevant studies on assessing dCA in patients suffering acute ischemic stroke, intracerebral haemorrhage, and subarachnoid haemorrhage. The review will provide to the reader the most consistent findings, the inconsistent findings which still need to be explored further and discuss the main limitations of these studies. This will allow for the creation of a research agenda for the use of bedside dCA information for prognostication and targeted perfusion interventions.