Effects of Acute Exercise Intensity on Cerebral Blood Flow and Cognitive Function in Older Adults

Study Overview
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Brief Summary
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This study will analyze the influence of acute bout exercise intensities (continuous moderate and HIIT) on middle cerebral artery velocity (MCAv) to identify which intensity elicits the greatest increase in CBF in older adults (65+ yrs). Additionally, this study will help verify positive correlations between MCAv and cognitive function. These findings are important in determining the optimal exercise prescription for increased resilience against the age-related cognitive degradation.

Detailed Description
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With an increasingly aging population, it is paramount that we further understand the changes that occur during aging, especially those which contribute to cognitive decline. Evidence shows that cognitive function is closely linked to brain blood flow. When comparing cerebral blood flow (CBF) between old and young individuals, older adults appear to have lower baseline levels of CBF. One of the principle determinants of CBF is CO2. Since exercise results in rises in CO2 production, changes in CBF can be monitored. Older adults appear to have diminished changes in CBF compared to younger individuals during moderate intensity exercise. This then leads to the idea that older adults may need a greater exercise stimulus (i.e. HIIT) to see these changes in CBF. However, the effects of HIIT on CBF in older adults is largely unstudied. Purpose: To analyze the acute influence of HIIT on middle cerebral artery velocity (MCAv) in older adults, and to verify the positive association between MCAv and cognitive function. Experimental Design: Recruiting 16 healthy adults age 65 and older. The study will require each participant to report to 4 visits: a screening visit, a control, a moderate intensity exercise bout, and a high intensity exercise bout. The order of the experimental visits will be randomized to each subject, and exercise bouts will be work-matched. During the experimental visits, MCAv, end-tidal CO2, MAP, and HR will be measured continuously. Vascular measures such as pulse wave analysis and pulse wave velocity will be taken pre- and post-exercise. Additionally, blood flow through the internal carotid artery and cognitive measures (n-back test) will be measured and administered pre-exercise, and at 15 mins, 30 mins, and 45 mins post-exercise. A two-way repeated measures ANOVA will be used to determine significant differences for time (pre vs. post measures) x condition (control/moderate/HIIT). Results: In the process of collecting data. Implications: If the study is successful in its findings, this could change how exercise is prescribed to older adults. It could also lead to the question regarding if a greater exercise stimulus (i.e. SIT) may be even more beneficial for these individuals.

Official Title
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Effects of Acute Exercise Intensity on Cerebral Blood Flow and Cognitive Function in Older Adults

Conditions
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Aging Well

Intervention / Treatment
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* Other: Acute bout of Continuous Moderate Intensity Exercise
* Other: Acute bout of High Intensity Interval Training
* Other: Control


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 65+ years of age Comfortable with experiencing exercise-induced fatigue Willingness and ability to comply with scheduled visits and study procedures Able to provide consent on their own behalf Type 2 Diabetics accepted Exclusion Criteria: Competitive athlete (Recreationally active is okay but no more than 3 days/week of structured exercise) VO2max below 18 ml/kg/min in men, 15ml/kg/min in women (minimum thresholds for independent living seniors) Inability of study staff to acquire signal from the MCA using TCD Diagnosis of mild cognitive impairment, Parkinson's Disease, Alzheimer's Disease, multiple sclerosis, or psychiatric illness (unless mild depression or anxiety) History of brain damage/stroke/concussions Cardiovascular Disease, Pulmonary Disease, or dependence of supplemental O2 Type 2 Diabetics who aren't cleared by the study physician during the first screening visit (HbA1C > 8.5%) Neuromuscular or musculoskeletal dysfunctions impairing one from cycling Changes in vasoactive medication dose or quantity, recently prior to or during the study time course, or inability to maintain regular timed ingestion of vasoactive medication Currently involved in Estrogen or Testosterone Replacement Therapy Unable to abstain from food consumption (3hrs), caffeine/alcohol consumption (12hrs), and vigorous exercise (24hrs) prior to experimental procedures

Ages Eligible for Study
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Minimum Age: 65 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: This is a repeated measures cross-over design, in which all subjects will complete all acute exercise intensity conditions: HIIT, continuous moderate intensity at lactate threshold (LT), and rest (control). The order of the acute treatment bouts will be randomized for each subject over three experimental visits (not counting the screening visit).
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Acute bout of Continuous Moderate Intensity Exercise<br> | Other: Acute bout of Continuous Moderate Intensity Exercise<br>* In this experimental intervention subjects will cycle continuously at moderate intensity (VO2 corresponding to lactate threshold) until a 200 kcal equivalent energy expenditure is reached.<br>|
| Experimental: Acute bout of High Intensity Interval Training (HIIT)<br> | Other: Acute bout of High Intensity Interval Training<br>* In this experimental invention subjects will alternate between 1 minute of high intensity cycling (watts corresponding to 85% VO2peak) and 1 minute of low intensity cycling (watts corresponding to 35-40% VO2peak) until a 200 kcal equivalent energy expenditure is reached.<br>* Other names: HIIT;|
| Experimental: Control<br> | Other: Control<br>* In this intervention placebo, subjects will lay down on a flat, soft surface for 30 minutes in a dimly light room. They will not be allowed to use any electronic devices or read during this time to avoid potentially influencing continuous data recording.<br>* Other names: Rest;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Middle Cerebral Artery Velocity (MCAv) | Blood flow velocity measured in the Middle Cerebral Artery via Transcranial Doppler probe secured to the right temporal window. | Measured continuously over the course of each experimental session (i.e. 2-3 hours) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Working Memory | Measured via n-back test (2-back); Subject's will be presented a sequence of letters (25 of them from a base set of 15 letters) one-by-one and will have 3 seconds to indicate whether the letter they see currently matches the letter from 2 frames ago. If there is no match, then they do not need to respond.They will complete three rounds each with a different sequence. Accuracy score (%) = correct inputs/# of stimuli, averaged across 3 blocks. | 4 individual measurements taken during each experimental session with each session lasting up to about 3 hours. 1 pre-intervention measurement and 3 post-intervention measurements spaced at least 15min apart | 
| Internal Carotid Artery (ICA) Diameter | Measured via Ultrasound; diameter will be measured as the peak of the pulse wave | 4 individual measurements taken during each experimental session with each session lasting up to about 3 hours. 1 pre-intervention measurement and 3 post-intervention measurements spaced at least 15min apart | 
| Internal Carotid Artery (ICA) Pulse Velocity | Measured via Ultrasound; velocity will be assessed at the peak of each pulse wave | 4 individual measurements taken during each experimental session with each session lasting up to about 3 hours. 1 pre-intervention measurement and 3 post-intervention measurements spaced at least 15min apart | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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MCAv, Working Memory, Cognition, Exercise Intensity, Cerebral Blood Flow, HIIT