Reduced Middle Cerebral Artery Blood Velocity Response during Low-Volume High-Intensity Interval Exercise in Chronic Stroke

Abstract

Background: High-intensity interval exercise (HIIT) is currently being implemented in stroke rehabilitation to improve walking function. HIIT alternates between high-intensity and recovery bouts, which causes rapid increases and decreases in blood pressure, which may impact cerebrovascular function in people post-stroke. To date, there is no information on the acute cerebrovascular response in people post-stroke. To address this gap in knowledge, we tested whether the cerebrovascular response was reduced when compared to sedentary age- and sex-matched adults (CON) at the following timepoints: 1) baseline (BL), 2) during a single 10-minute bout of low-volume HIIT, 3) immediately following HIIT, and 4) 30 minutes after HIIT. Methods: Middle cerebral artery blood velocity (MCAv), mean arterial pressure (MAP), heart rate (HR), and end tidal carbon dioxide (PETCO2) were recorded at all timepoints. A submaximal exercise test was used to determine the estimated maximal workload. The low-volume HIIT bout was performed on a recumbent stepper and consisted of 1-minute high-intensity bouts (70% estimated maximal watts) separated by 1-minute active recovery (10% estimated maximal watts). Statistical analysis used linear mixed models and ANCOVA. Results: Individuals post-stroke demonstrated a reduced MCAv response during HIIT compared to CON (p = 0.03) and MCAv remained lower immediately following HIIT and 30-minutes after HIIT. MCAv decreased below BL immediately following HIIT in both groups (p ≤ 0.04) and returned to BL at 30-minutes after HIIT. No between differences were found for MAP, HR, and PETCO2. Conclusions: The key finding from this study suggests a reduced MCAv response during low-volume HIIT in individuals post-stroke compared to age and sex-matched sedentary adults and these differences remained up to 30 minutes following HIIT. Future work is needed to better understand the reduced MCAv response during HIIT despite increased metabolic demand. Clinicaltrials.gov #NCT04673994.

Sex-Specific Cardiovascular Adaptations to Simulated Microgravity in Sprague-Dawley Rats

“…Sex differences were reported in the adaptations of the cardiovascular system to spaceflight, however only a few studies investigated the effects of microgravity on arterial stiffness by including subjects of both sexes, and even fewer have made explicit side-by-side comparisons between male and female subjects (1,8,10,(18)(19)(20)(21)(22)(23). Although published reports also suggest that arterial stiffening is reversible in astronauts upon returning to Earth (24), the long-term consequences of the exposure to arterial stiffening are unknown but may influence future abnormal hemodynamic responses to stressors and the risk of developing cardiovascular disease (25)(26)(27)(28)(29) particularly in older females (30). A greater aortic PWV in the female SD rats compared to males after HLU suggests sex differences in the development of central arterial stiffening following the exposure to simulated microgravity in this model.…”

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

“…12 While no studies have examined dCA after an acute bout of HIIT in individuals poststroke, 9 prior work in healthy adults reported dCA was less effective during repeated squatstands following HIIT. 18 During exercise recovery following HIIT, MAP decreases 16,19 which could challenge the dCA response, as dCA seems less effective at buffering decreases compared to increases in MAP at rest. 20 During recovery following moderate to vigorous intensity continuous exercise in healthy adults, dCA at rest has been shown to be effected immediately following exercise and recover by 30 min.…”

“…21,22 However, the dCA response may take longer than 30 min to recover in individuals post-stroke potentially due to post-exercise hypotension and prolonged recovery of MAP. 12 Recovery of end tidal carbon dioxide (P ET CO 2 ) may also influence cerebral blood velocity following HIIT 23 in individuals post-stroke compared to healthy adults 19 and could also play a role in the dCA response during recovery. 16,24,25 To address these critical gaps in knowledge, we characterized the dCA response using spontaneous fluctuations in MAP and middle cerebral artery blood velocity (MCAv) as well as during a single sit-to-stand following an acute bout of low-volume HIIT in individuals with chronic stroke compared to age-and sex-matched adult controls (CON).…”

“…Our methods have been described previously. 16,19 Individuals with stroke were included within this study if they were: 1) between 40-85 years old, 2) treated for stroke 6 months to 5 years ago, 3) classified as inactive by performing <150 min of moderate intensity exercise per week, and 4) able to answer consenting questions and follow a 2-step command. Individuals within the CON group were matched to the sex and age ± 5 years of an individual post-stroke and also classified as inactive.…”

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

“…6 In this issue, Whitaker and colleagues report on the cerebrovascular response during a single bout of HIIE in individuals with chronic stroke (n ¼ 25) compared to age-matched controls (n ¼ 25). 7 This represents an important step in furthering our understanding of the role of HIIE in stroke rehabilitation, but also an appropriate point of reflection as to how we move forward.…”