The Effect of Stroke on Middle Cerebral Artery Blood Flow Velocity Dynamics During Exercise

Feasibility of a Recumbent Stepper for Short-Interval, Low-Volume High-Intensity Interval Exercise in Stroke

BACKGROUND AND PURPOSE

Studies investigating high-intensity interval exercise (HIIE) in stroke typically emphasize treadmill training. However, a literature review suggested that seated devices such as a recumbent stepper or cycle offer a promising alternative for HIIE since exercise can be prescribed using peak power output (PPO). Therefore, this would give health care professionals the ability to monitor and adapt power output for the target heart rate range. The purpose of this secondary analysis was to examine the feasibility of prescribing short-interval, low-volume HIIE using PPO in chronic stroke.

METHODS

We used several methods to test feasibility: (1)Acceptability: Measured by the percentage of participants who completed the entire HIIE protocol; (2) Implementation was assessed by the number of reported cardiac or serious adverse events during submaximal exercise testing and HIIE and the average percentage of participants reaching vigorous intensity, defined by the American College of Sports Medicine as at least 77% of age-predicted maximal heart rate (HR max ).

RESULTS

Data were available for 28 participants who were 32.2 (17.2) months post-stroke and 61.4 (11.9) years of age. Twenty-eight participants completed HIIE per protocol. No cardiac or serious adverse events occurred during the submaximal exercise test or during HIIE. The rapid switching between HIIE and recovery showed no evidence of blood pressure reaching unsafe thresholds. Average intensity during HIIE reached 76.8% HR max , which is slightly below the target of 77.0%.

DISCUSSION AND CONCLUSIONS

A single bout of short-interval, low-volume HIIE, prescribed using PPO, was feasible in chronic stroke.

Video Abstract : Available for more insights from the authors (Supplemental Digital Content, Video, available at: http://links.lww.com/JNPT/A474 ).

Lower middle cerebral artery blood velocity during low-volume high-intensity interval exercise in chronic stroke

High-intensity interval training (HIIE) may present unique challenges to the cerebrovascular system in individuals post-stroke. We hypothesized lower middle cerebral artery blood velocity (MCAv) in individuals post-stroke: 1) during 10 minutes of HIIE, 2) immediately following HIIE, and 3) 30 minutes after HIIE, compared to age- and sex-matched controls (CON). We used a recumbent stepper submaximal exercise test to determine workloads for high-intensity and active recovery. Our low volume HIIE protocol consisted of 1-minute intervals for 10 minutes. During HIIE, we measured MCAv, mean arterial pressure (MAP), heart rate (HR), and end tidal carbon dioxide (PETCO2). We assessed carotid-femoral pulse wave velocity as a measure of arterial stiffness. Fifty participants completed the study (25 post-stroke, 76% ischemic, 32% moderate disability). Individuals post-stroke had lower MCAv during HIIE compared to CON (p = 0.03), which remained 30 minutes after HIIE. Individuals post-stroke had greater arterial stiffness (p = 0.01) which was moderately associated with a smaller MCAv responsiveness during HIIE (r = -0.44). No differences were found for MAP, HR, and PETCO2. This study suggests individuals post-stroke had a lower MCAv during HIIE compared to their peers, which remained during recovery up to 30 minutes. Arterial stiffness may contribute to the lower cerebrovascular responsiveness post-stroke.

Lower dynamic cerebral autoregulation following acute bout of low-volume high-intensity interval exercise in chronic stroke compared to healthy adults

Fluctuating arterial blood pressure during high-intensity interval exercise (HIIE) may challenge dynamic cerebral autoregulation (dCA), specifically after stroke after an injury to the cerebrovasculature. We hypothesized that dCA would be attenuated at rest and during a sit-to-stand transition immediately after and 30 min after HIIE in individuals poststroke compared with age- and sex-matched control subjects (CON). HIIE switched every minute between 70% and 10% estimated maximal watts for 10 min. Mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) were recorded. dCA was quantified during spontaneous fluctuations in MAP and MCAv via transfer function analysis. For sit-to-stand, time delay before an increase in cerebrovascular conductance index (CVCi = MCAv/MAP), rate of regulation, and % change in MCAv and MAP were measured. Twenty-two individuals poststroke (age 60 ± 12 yr, 31 ± 16 mo) and twenty-four CON (age 60 ± 13 yr) completed the study. Very low frequency (VLF) gain (P = 0.02, η2 = 0.18) and normalized gain (P = 0.01, η2 = 0.43) had a group × time interaction, with CON improving after HIIE whereas individuals poststroke did not. Individuals poststroke had lower VLF phase (P = 0.03, η2 = 0.22) after HIIE compared with CON. We found no differences in the sit-to-stand measurement of dCA. Our study showed lower dCA during spontaneous fluctuations in MCAv and MAP following HIIE in individuals poststroke compared with CON, whereas the sit-to-stand response was maintained.NEW & NOTEWORTHY This study provides novel insights into poststroke dynamic cerebral autoregulation (dCA) following an acute bout of high-intensity interval exercise (HIIE). In people after stroke, dCA appears attenuated during spontaneous fluctuations in mean arterial pressure (MAP) and middle cerebral artery blood velocity (MCAv) following HIIE. However, the dCA response during a single sit-to-stand transition after HIIE showed no significant difference from controls. These findings suggest that HIIE may temporarily challenge dCA after exercise in individuals with stroke.

Transcranial Doppler ultrasonography can predict inpatient rehabilitation functional outcome in patients with stroke

BACKGROUND

Despite advances in imaging techniques and treatment modalities, tools to predict recovery after stroke remain limited. The objective of the study was to determine if transcranial Doppler (TCD) mean flow velocities were predictive of functional recovery following ischemic stroke.

METHODS

Data were collected from patients with stroke admitted to an academic tertiary care facility in the southeastern region of the United States between 2012 and 2019 who had a middle cerebral artery distribution ischemic stroke, TCD, and were discharged to our inpatient rehabilitation facility. Mean flow velocities were categorized as low (<40 cm/s), normal (40-80 cm/s), or high (>80 cm/s). Functional Independence Measure (FIM) scores were collected on admission to and discharge from IPR. Multiple linear regression models were used to assess the differences in mean FIM score changes by categories of mean flow velocities.

RESULTS

We enrolled 57 patients, mean age 60 years, 73.7% male. Compared to the normal velocity group, those with abnormally low velocities had a significantly smaller change in their FIM score (adjusted β = -8.42; p = .01). Compared to the normal velocity group, those with abnormally high velocities experienced a greater change in FIM score, but this association was not statistically significant (beta = 1.12; p = .77).

CONCLUSIONS

In this limited population, we found that low mean flow velocity as measured by TCD ultrasonography after a middle cerebral artery stroke is associated with poorer functional recovery following inpatient rehabilitation. Our results suggest that the value of TCD ultrasonography as a tool to predict motor recovery after stroke warrants further investigation.

Exercise breaks prevent attenuation in cerebrovascular function following an acute bout of uninterrupted sitting in healthy children

The purpose of this study was to examine the effect of an acute bout of prolonged sitting with and without exercise breaks on cerebrovascular function in 7- to 13-year-old children. Forty-two children and adolescents were recruited to a crossover trial, with 15 girls (mean age 10.1 ± 2.5 years) and 16 boys (mean age 10.5 ± 1.3 years) completing the two trial conditions: SIT, uninterrupted sitting for 3 h and CYCLE, 3 h of sitting interrupted hourly with a 10-min moderate intensity exercise break. Cerebrovascular function was measured Pre and Post SIT and CYCLE from blood flow (Q ̇ ${\dot{Q}}$ ), diameter, and shear rate of the internal carotid artery (ICA) at rest and in response to CO2 . Blood velocity in the middle (MCA) and posterior (PCA) cerebral arteries was assessed at rest, during a neurovascular coupling task (NVC) and in response to CO2 . We demonstrate that SIT but not CYCLE reduced ICA cerebrovascular reactivity to CO2 (%Δ ICAQ ̇ ${\dot{Q}}$ /Δ end-tidal CO2 : SIT: Pre 5.0 ± 2.4%/mmHg to Post 3.3 ± 2.8%/mmHg vs. CYCLE: Pre 4.4 ± 2.3%/mmHg to Post 5.3 ± 3.4%/mmHg, P = 0.05) and slowed the MCA blood velocity onset response time to hypercapnia (SIT: Pre 57.2 ± 32.6 s to Post 76.6 ± 55.2 s, vs. CYCLE: Pre 64.1 ± 40.4 s to Post 52.3 ± 28.8 s, P = 0.05). There were no changes in NVC. Importantly, breaking up prolonged sitting with hourly exercise breaks prevented the reductions in cerebrovascular reactivity to CO2 and the slowed intracranial blood velocity onset response time to hypercapnia apparent with uninterrupted sitting in children. NEW FINDINGS: What is the central question of this study? What are the effects of interrupting prolonged sitting on cerebrovascular function in children? What is the main finding and its importance? Prolonged sitting results in declines in cerebrovascular reactivity, a valuable index of cerebrovascular health. Breaking up prolonged sitting with hourly 10 min exercise breaks prevented these changes. These initial findings suggest excessive sedentary behaviour does impact cerebrovascular function in childhood, but taking exercise breaks prevents declines.

Dynamic onset response of the internal carotid artery to hypercapnia is blunted in children compared with adults

Intracranial blood velocity reactivity to a steady‐state hypercapnic stimulus has been shown to be similar in children and adults, but the onset response to hypercapnia is slower in the child. Given the vasodilatory effect of hypercapnia on the cerebrovasculature, assessment of vessel diameter, and blood flow are vital to fully elucidate whether the temporal hypercapnic response differs in children versus adults. Assessment of internal carotid artery (ICA) vessel diameter (ICAd), blood velocity (ICAv), volumetric blood flow (Q_ICA), and shear rate (ICA_SR) in response to a 4 min hypercapnic challenge was completed in children (n = 14, 8 girls; 9.8 ± 0.7 years) and adults (n = 17, 7 females; 24.7 ± 1.8 years). The dynamic onset responses of partial pressure of end‐tidal CO₂ (P_ETCO₂), Q_ICA, ICAv, and ICA_SR to hypercapnia were modeled, and mean response time (MRT) was computed. Following 4 min of hypercapnia, ICA reactivity and ICAd were comparable between the groups. Despite a similar MRT in P_ETCO₂ in children and adults, children had slower Q_ICA (children 108 ± 60 s vs. adults 66 ± 37 s; p = 0.023), ICAv (children 120 ± 52 s vs. adults 52 ± 31 s; p = 0.001), and ICA_SR (children 90 ± 27 s vs. adults 47 ± 36 s; p = 0.001) MRTs compared with adults. This is the first study to show slower hypercapnic hyperemic kinetic responses of the ICA in children. The mechanisms determining these differences and the need to consider the duration of hypercapnic exposure when assessing CVR in children should be considered in future studies.

The effect of exercise intensity and cardiorespiratory fitness on the kinetic response of middle cerebral artery blood velocity during exercise in adults

The aim of this study was to compare the kinetic response of middle cerebral artery blood velocity (MCAv) to moderate and heavy-intensity cycling in adults, and explore the relationship between maximal oxygen uptake (V̇O_2max) and MCAv kinetics. Seventeen healthy adults (23.8±2.4 years, 9 females) completed a ramp incremental test to exhaustion on a cycle ergometer to determine V̇O_2max and the gas exchange threshold (GET). Across six separate visits, participants completed three 6-minute transitions at a moderate-intensity (90% GET) and three at a heavy-intensity (40% of the difference between GET and V̇O_2max). Bilateral MCAv was measured using transcranial Doppler ultrasonography and analysed using a mono-exponential model with a time delay. The time constant (τ) of the MCAv response was not different between moderate- and heavy-intensity cycling (25±10 vs. 26±8 s, P=0.82), as was the time delay (29±11 vs. 29±10 s, P=0.95). The amplitude of the exponential increase in MCAv from baseline was greater during heavy (23.9±10.0 cm^.s^-1, 34.1±14.4%) compared to moderate (12.7±4.4 cm^.s^-1, 18.7±7.5%) intensity cycling (P<0.01). Following the exponential increase, a greater fall in MCAv was observed during heavy compared to moderate-intensity exercise (9.5±6.9 vs 2.8±3.8 cm^.s^-1, P<0.01). MCAv after 6 minutes of exercise remained elevated during heavy compared to moderate-intensity exercise (85.2±9.6 vs. 79.3±7.7cm^.s^-1, P≤0.01). V̇O_2max was not correlated with MCAv τ or amplitude (r=0.11-0.26, P>0.05). These data suggest that the intensity of constant-work rate exercise influences the amplitude, but not time-based, response parameters of MCAv in healthy adults, and found no relationship between cardiorespiratory fitness and MCAv kinetics.

What are the effects of acute exercise and exercise training on cerebrovascular hemodynamics following stroke? A systematic review and meta-analysis

INTRODUCTION

Limited data exist regarding the effects of acute exercise and exercise training on cerebrovascular hemodynamic variables post-stroke.

PURPOSE

This systematic review and meta-analysis 1) examined the effects of acute exercise and exercise training on cerebrovascular hemodynamic variables reported in the stroke exercise literature; and 2) synthesized the peak middle cerebral artery blood velocity (MCAv) achieved during an acute bout of moderate-intensity exercise in individuals post-stroke.

METHODS

Six databases (MEDLINE, EMBASE, Web of Science, CINAHL, PsycINFO, AMED) were searched from inception to December 1^st 2021, for studies that examined the effect of acute exercise or exercise training on cerebrovascular hemodynamics in adults post-stroke. Two reviewers conducted title and abstract screening, full-text evaluation, data extraction, and quality appraisal. Random effects models were used in meta-analysis.

RESULTS

Nine studies, including 4 acute exercise (n=61) and 5 exercise training studies (n=193), were included. Meta-analyses were not statistically feasible for several cerebrovascular hemodynamic variables. Descriptive analysis reveals that exercise training may increase cerebral blood flow and cerebrovascular reactivity to carbon dioxide among individuals post-stroke. Meta-analysis of three acute exercise studies revealed no significant changes in MCAv during acute moderate intensity exercise (n=48 participants, mean difference = 5.2 cm/s, 95% CI [-0.6, 11.0], P=0.08) compared to resting MCAv values.

CONCLUSION

This review suggests that individuals post-stroke may have attenuated cerebrovascular hemodynamics as measured by the MCAv during acute moderate-intensity exercise. Higher quality research utilizing agreed upon hemodynamic variables are needed to synthesize the effects of exercise training on cerebrovascular hemodynamics post-stroke.

Apolipoprotein E4 Moderates the Association Between Vascular Risk Factors and Brain Pathology

BACKGROUND

The strongest genetic risk factor for late-onset Alzheimer disease (AD), Apolipoprotein E4 (APOE4), increases cardiovascular disease risk and may also act synergistically with vascular risk factors to contribute to AD pathogenesis. Here, we assess the interaction between APOE4 and vascular risk on cerebrovascular dysfunction and brain pathology.

METHODS

This is an observational study of cognitively normal older adults, which included positron emission tomography imaging and vascular risk factors. We measured beat-to-beat blood pressure and middle cerebral artery velocity at rest and during moderate-intensity exercise. Cerebrovascular measures included cerebrovascular conductance index and the cerebrovascular response to exercise.

RESULTS

There was a significant interaction between resting cerebrovascular conductance index and APOE4 carrier status on β-amyloid deposition (P=0.026), with poor conductance in the cerebrovasculature associated with elevated β-amyloid for the APOE4 carriers only. There was a significant interaction between non-high-density lipoprotein cholesterol and APOE4 carrier status (P=0.014), with elevated non-high-density lipoprotein cholesterol predicting a blunted cerebrovascular response to exercise in APOE4 carriers and the opposite relationship in noncarriers.

CONCLUSIONS

Both cerebral and peripheral vascular risk factors are preferentially associated with brain pathology in APOE4 carriers. These findings provide insight into pathogenic vascular risk mechanisms and target strategies to potentially delay AD onset.

Pilot Study to Characterize Middle Cerebral Artery Dynamic Response to an Acute Bout of Moderate Intensity Exercise at 3- and 6-Months Poststroke

Background The primary aim of this study was to characterize the middle cerebral artery blood velocity (MCAv) dynamic response to an acute bout of exercise in humans at 3- and 6-months poststroke. As a secondary objective, we grouped individuals according to the MCAv dynamic response to the exercise bout as responder or nonresponder. We tested whether physical activity, aerobic fitness, and exercise mean arterial blood pressure differed between groups. Methods and Results Transcranial Doppler ultrasound measured MCAv during a 90-second baseline followed by a 6-minute moderate intensity exercise bout. Heart rate, mean arterial blood pressure, and end-tidal CO2 were additional variables of interest. The MCAv dynamic response variables included the following: baseline, time delay, amplitude, and time constant. Linear mixed model revealed no significant differences in our selected outcomes between 3- and 6-months poststroke. Individuals characterized as responders demonstrated a faster time delay, higher amplitude, and reported higher levels of physical activity and aerobic fitness when compared with the nonresponders. No between-group differences were identified for baseline, time constant, or exercise mean arterial blood pressure. In the nonresponders, we observed an immediate rise in MCAv following exercise onset followed by an immediate decline to near baseline values, while the responders showed an exponential rise until steady state was reached. Conclusions The MCAv dynamic response profile has the potential to provide valuable information during an acute exercise bout following stroke. Individuals with a greater MCAv response to the exercise stimulus reported statin use and regular participation in exercise.

Chronic hyperglycemia before acute ischemic stroke impairs the bilateral cerebrovascular response to exercise during the subacute recovery period

BACKGROUND AND PURPOSE

Chronic hyperglycemia contributes to cerebrovascular dysfunction by damaging blood vessels. Poor glucose control has been tied to impairments in cerebral blood flow, which may be particularly detrimental for people recovering from major cerebrovascular events such as acute ischemic stroke. In this secondary analysis, we explore for the first time the connection between chronic hyperglycemia before acute stroke and the cerebrovascular response (CVR) to exercise 3 and 6 month into the subacute recovery period.

METHODS

We recorded middle cerebral artery velocity (MCAv) using transcranial Doppler ultrasound bilaterally at rest and during moderate-intensity exercise in stroke patients at 3 (n = 19) and 6 (n = 12) months post-stroke. We calculated CVR as the difference between MCAv during steady-state exercise and resting MCAv. We obtained hemoglobin A1c levels (HbA1c; a measure of blood glucose over the prior 3 months) from the electronic medical record (EMR) and divided participants by HbA1c greater or less than 7%.

RESULTS

Participants with high HbA1c (>7%) at the time of acute stroke had significantly lower CVR to exercise for both the stroke-affected (p = .009) and non-affected (p = .007) hemispheres at 3 months post-stroke. These differences remained significant at 6 months post-stroke (stroke-affected, p = .008; non-affected, p = .016).

CONCLUSIONS

Patients with chronic hyperglycemia before acute ischemic stroke demonstrated impaired cerebrovascular function during exercise months into the subacute recovery period. These findings highlight the importance of maintaining tight glucose control to reduce morbidity and improve recovery post-stroke and could have implications for understanding cerebrovascular pathophysiology.

Cerebrovascular assessments to help understand brain-related changes associated with aerobic exercise after stroke

Evidence suggests exercise is "good medicine" after stroke, yet consensus is lacking on the time to initiate, type, exertion level, and duration per session. It remains a challenge to identify outcome measures for stroke-exercise trials that are sufficiently sensitive to intervention parameters. Cerebrovascular assessments, namely cerebral blood flow and intracranial pulsatility, are herein discussed as examples of quantitative brain-specific measures that may be useful to monitor exercise-related brain changes and help to guide stroke rehabilitation interventions. Novelty: Cerebral blood flow and arterial stiffness are potential vascular targets for stroke exercise trials.

Optimizing Recruitment Strategies and Physician Engagement for Stroke Recovery Research

BACKGROUND AND PURPOSE

A major challenge for stroke rehabilitation and recovery research is the recruitment and retention of participants. Our prior challenges and successes have influenced our team to rethink our approach and the potential for large-scale stroke recruitment.

SUMMARY OF KEY POINTS

In this special interest article, we highlight how the adoption and implementation of recruitment strategies such as physician engagement and a streamlined "customer service" approach helped us improve our enrollment and maximize efficiency. Another positive outcome of enrollment was increased representation of those who identify as underrepresented minority or live in rural areas.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Rethinking our recruitment processes and infrastructure allowed for greater interprofessional interactions, minimal burden for our stroke physician team members, and maximized enrollment into our stroke studies.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A324).

Effects of high intensity interval exercise on cerebrovascular function: A systematic review

High intensity interval exercise (HIIE) improves aerobic fitness with decreased exercise time compared to moderate continuous exercise. A gap in knowledge exists regarding the effects of HIIE on cerebrovascular function such as cerebral blood velocity and autoregulation. The objective of this systematic review was to ascertain the effect of HIIE on cerebrovascular function in healthy individuals. We searched PubMed and the Cumulative Index to Nursing and Allied Health Literature databases with apriori key words. We followed the Preferred Reporting Items for Systematic Reviews. Twenty articles were screened and thirteen articles were excluded due to not meeting the apriori inclusion criteria. Seven articles were reviewed via the modified Sackett’s quality evaluation. Outcomes included middle cerebral artery blood velocity (MCAv) (n = 4), dynamic cerebral autoregulation (dCA) (n = 2), cerebral de/oxygenated hemoglobin (n = 2), cerebrovascular reactivity to carbon dioxide (CO₂) (n = 2) and cerebrovascular conductance/resistance index (n = 1). Quality review was moderate with 3/7 to 5/7 quality criteria met. HIIE acutely lowered exercise MCAv compared to moderate intensity. HIIE decreased dCA phase following acute and chronic exercise compared to rest. HIIE acutely increased de/oxygenated hemoglobin compared to rest. HIIE acutely decreased cerebrovascular reactivity to higher CO₂ compared to rest and moderate intensity. The acute and chronic effects of HIIE on cerebrovascular function vary depending on the outcomes measured. Therefore, future research is needed to confirm the effects of HIIE on cerebrovascular function in healthy individuals and better understand the effects in individuals with chronic conditions. In order to conduct rigorous systematic reviews in the future, we recommend assessing MCAv, dCA and CO₂ reactivity during and post HIIE.

Self-Reported Omega-3 Supplement Use Moderates the Association between Age and Exercising Cerebral Blood Flow Velocity in Older Adults

Cerebral blood flow (CBF) decreases across the lifespan, and chronic conditions such as dementia and stroke accelerate this decline. Impaired CBF results in reduced delivery of oxygen and nutrients, which can damage the brain over time. Thus, there is a need to identify lifestyle interventions, including diet and exercise, to maintain CBF with aging and in the presence of chronic disease. In the present study, we used transcranial Doppler ultrasound to record middle cerebral artery velocity (MCAv), a surrogate measure of CBF, during moderate-intensity exercise in sedentary, cognitively normal older adults (n = 90). A multiple linear regression model (F(4, 85) = 3.21, p = 0.02) showed that self-reported omega-3 supplement use significantly moderated the association between age and mean exercising MCAv in these individuals (p = 0.01). Older age was associated with lower exercising MCAv in the group not taking omega-3 supplements, while exercising MCAv showed no decline with increasing age in the group who reported omega-3 supplement use. These findings suggest omega-3 supplementation may have an important role in the preservation of CBF with aging.

Middle cerebral artery velocity dynamic response profile during exercise is attenuated following multiple ischemic strokes: a case report

Blood flow regulation is impaired in people with stroke. However, the time course of change in middle cerebral artery velocity (MCAv) following repeated stroke at rest and during exercise remains unknown. In this case study, we provide novel characterization of the dynamic kinetic MCAv response profile to moderate-intensity exercise before and after repeated ischemic MCA stroke. The initial stroke occurred in the left MCA. At 3 months poststroke, left MCAv amplitude (Amp) was ~50% lower than the right. At the 6-month follow-up visit, MCAv Amp declined in both MCA with the left MCAv Amp ~50% lower than the right MCAv Amp. Following a second right MCA stroke, we report further decline in Amp for the left MCA. At the 3- and 6-month visit following the second stroke, the left MCAv Amp declined further (~10%). The right MCAv Amp dramatically decreased by 81.3% when compared to the initial study visit. The MCAv kinetic analysis revealed a marked impairment in the cerebrovascular response to exercise following stroke. We discuss potential pathophysiological mechanisms contributing to poststroke cerebrovascular dysfunction and the need to test therapeutic interventions (such as exercise) that might attenuate cerebrovascular decline in people following stroke.