Q&A Report: Peripheral and Cerebral Vascular Responses Following High-Intensity Interval Exercise

Bert Bond, PhD and Max Weston, PhD Candidate answer top questions from a recent webinar, “Peripheral and Cerebral Vascular Responses Following High-Intensity Interval Exercise”.

The answers to these questions have been provided by:

Bert Bond, PhD
Senior Lecturer
Sport and Health Sciences
University of Exeter

Max Weston, PhD Candidate
Associate Lecturer
Sport and Health Sciences
University of Exeter

Do you think that this acute improvement in peripheral vascular function post-HIT (high-intensity training) would be present the day after? Do we have data for chronic effects of HIT?

There is some evidence that flow-mediated dilation (FMD) remains elevated the morning after high intensity interval exercise (but, also evidence to the contrary). A time course study would be excellent, but challenging.

In your study, you measured cerebrovascular reactivity (CVR) and FMD following different intensity exercise training. Did you measure carotid hemodynamics (ie., pulsatility index)? And would differences in intensity influence the diameter of the middle cerebral artery (MCA)?

No, we didn’t measure this (although we wanted to). An ICA scan would also help us understand volumetric flow. We don’t expect MCA diameter to change when at rest post exercise – and we kept an eye on the PETCO2.

Were all these studies you discussed conducted in men and women?

Yes – and not many have considered a sex effect yes (studies are typically underpowered to do so).

What role do you think sympathetic nervous system (SNS) versus CO2 levels play in the cerebral blood flow (CBF) responses? Generally during moderate exercise, CO2 levels only moderately increases, but what about during HIIT training?

Understanding SNS and CBF during exercise is certainly a challenge. Jodie Koep has some data on this during handgrip exercise, which she will be looking to publish later this year hopefully. Getting such data during exercise is challenging.

Is the beneficial effect of HIIE on FMD a matter of High Intensity or Interval Exercise? And how about arterial pressure comparison after exercise between MIE, HIIE 1, and HIIE 2?

We know that the recovery interval is important from a cell signaling perspective. From a vascular point of view, this allows heart rate (HR) and blood pressure (BP) to drop, only for them to pick up again – so that might alter the shear stimulus of the exercise. In reality, the recovery interval just allows for more work at a higher intensity to be performed. The hypotensive effect of exercise may well be intensity dependent – this is something we are looking at.

How was the VO2-based exercise intensity confirmed during exercise?

We just measured the VO2 during the exercise bout and reported it. It closely aligned with our predictions based off the prior ramp incremental exercise. It’s fine to prescribe HIIE in this manner – but HR is more common because it is easier/more convenient. However, it also has issues with accuracy due to cardiovascular drift, and the error in the classic predictive HRmax equations (especially when considering exercise modality).

Do you think that this acute improvement in both peripheral/cerebral vascular function could positively enhance brain health (neuroplasticity, etc.)?

We wanted to collect BDNF and VEGF, but ran out of funding. It seems plausible that this stimulus might promote cerebrovascular health, and there’s some evidence indicating this could be the case for neuroplasticity – but that’s an area for the future I think. I know that some rodent studies have considered this.

Can you please provide more detailed information on which statistical approach you used to scale FMD allometrically?

We followed the direction of Greg Atkinson’s papers. So, using the common/group exponent from the log linear regression.

A lot of focus has been given to the detriment of increased sedentary time on cardiovascular health, regardless of a bout of exercise during the day. Can you speak to how this might apply to the peripheral and cerebral vasculature?

We know that uninterrupted sitting time can impair peripheral vascular function (although, this can be quickly protected against with movement). I don’t believe it is this profound in the cerebrovasculature, but this hasn’t been explored as well.

Did you see brachial artery diameter changes post exercise compared to baseline?

Often we do, yes. However baseline diameter didn’t change within any of these conditions over the course of the day. I imagine it would have done if we had measured sooner post exercise. Our FMD was allometrically scaled to account for this anyway.

could you provide some opinion (pros and cons) of using MRI techniques to evaluate chronic effects of exercise on cerebral vascularization?

Using an MRI would provide greater certainty about structural changes, vessel diameter, and regional flow. The temporal resolution with transcranial doppler (TCD) ultrasound is great though, and allows for other reactivity tests/challenges which are challenging in the MR scanner. Plus, TCD is more feasible and cheap for a research study.

Do you have any limitations with signal quality while exercising? At times, the wave forms can lose signal due to skull thickness or other anatomical differences even at rest.

Our headsets are really good – we can really lock the probe in place and rarely lose signal. This is true even when working with children during exercise. We use the DiaMon headsets, which I would recommend.

Do you know if the cerebral vessels undergo vasodilation or vasoconstriction under exercise conditions? Suppose if someone gets injured while exercising (consider boxing) and they experience blood loss, how would the cerebral response change then?

This is an interesting question – and we have just submitted a cerebral autoregulation post-boxing study. I’ve now idea how you’d get that data during boxing but you could consider the rodent literature which looks at brain injury perhaps? For during cycling exercise – you can expect some dilation/constriction based upon PETCO2 values and also SNS – but that’s difficult to do with MRI to know for sure.

Have addressed any supramaximal exercise protocols?

We are currently looking at some sprint interval exercise. Hopefully that study will be completed by October.

How is the intraobserver and interobserver variability in image acquisition and analysis ensured? Were there two trained sonographers who independently scan the same series of subjects at different times?

From memory, it was the same sonographer for FMD throughout this study. Our lab provide robust training and reliability assessments prior to starting any project, and we typically avoid using more than one sonographer on a study. We always check for differences at baseline too (there weren’t any). Lastly, we keep the person who does the analysis the same, and in a blinded manner.

Were there differences of rpm between the four conditions?

No – rpm was kept constant, between 70-90 rpm in line with the individual participant’s preference.

How can dynamic realtime vascular dilation responses be measured?

For full body exercise (outside of an MRI), you can use ultrasound to consider diameter if you can get a decent signal. Securing ICA scans might also give you confidence in brain blood flow – rather than MCAv.

Would you expect associations between cognitive abilities (eg., stroop test scores) and CBF during exercise? Could this be an interesting axis of research in human performance (eg., sports, military)?

Certainly – and I think the Brain Training work by Marcora is of interest here. However, I have not yet seen CBF to be the limiting factor to cognitive function during exercise in healthy young adults. I think there’s some work in hypoxia on this though.

Would you speculate on the usage of your research (or just the usage of transcranial doppler measurements) on the rehabilitation of cerebral ischemia?

This is very much what I want to do next. Prof Sandra Billinger and others have done some work in this field, and I think this is a very exciting avenue for future research.

Would it better to do the FMD test on the leg instead of the arm since they are cycling?

Not so much “better”, but it would be interesting certainly. We know that the vascular benefits of exercise extend beyond the active limb, and brachial FMD is associated with coronary artery function – so we use brachial FMD to consider cardiac health here too.

What clinical or physiological benefit we can infer from your research in longer term?

This is difficult to say, as it was one exercise bout in young healthy adults. However, the improvements in FMD are there, and it would indicate that regular high intensity interval exercise will be cardioprotective eventually. However, we really need to consider other populations/ages, and understand what the chronic training effect will be (on cerebrovascular, as well as peripheral vascular function).

When you are looking at changes in cerebrovascular responses in your soccer players/head injury cohort, is peripheral vascular response also affected after injury? Is the relationship seen in this direction after injury?

Yes – some impairment in different metrics of cerebrovascular function (reactivity/autoregulation/neurovascular coupling) are apparent after head impacts and concussion. Check out some of Jon Smirl’s work.

Did you consider fitness or physical activity levels in your cohorts? I imagine that sedentary individuals may have an increased response to a novel and more intense training stimulus.

This is something we’re interested in. Tom Bailey has some data showing that fitness predicts the acute FMD response to exercise. Our sample was only small, without much of a spread in fitness, so we were unable to explore this.