The dynamic response to a stimulus such as exercise can reveal valuable insights into systems control in health and disease that are not evident from the steady-state perturbation. However, the dynamic response profile and kinetics of cerebrovascular function have not been determined to date. We tested the hypotheses that bilateral middle cerebral artery blood flow mean velocity (MCA) increases exponentially following the onset of moderate-intensity exercise in 10 healthy young subjects. The MCA response profiles were well fit to a delay (TD) + exponential (time constant, τ) model with substantial agreement for baseline [left (L): 69, right (R): 64 cm/s, coefficient of variation (CV) 11%], response amplitude (L: 16, R: 13 cm/s, CV 23%), TD (L: 54, R: 52 s, CV 9%), τ (L: 30, R: 30 s, CV 22%), and mean response time (MRT) (L: 83, R: 82 s, CV 8%) between left and right MCA as supported by the high correlations (e.g., MRT = 0.82, < 0.05) and low CVs. Test-retest reliability was high with CVs for the baseline, amplitude, and MRT of 3, 14, and 12%, respectively. These responses contrasted markedly with those of three healthy older subjects in whom the MCA baseline and exercise response amplitude were far lower and the kinetics slowed. A single older stroke patient showed baseline ipsilateral MCA that was lower still and devoid of any exercise response whatsoever. We conclude that kinetics analysis of MCA during exercise has significant potential to unveil novel aspects of cerebrovascular function in health and disease. Resolution of the dynamic stimulus-response profile provides a greater understanding of the underlying the physiological control processes than steady-state measurements alone. We report a novel method of measuring cerebrovascular blood velocity (MCAv) kinetics under ecologically valid conditions from rest to moderate-intensity exercise. This technique reveals that brain blood flow increases exponentially following the onset of exercise with ) a strong bilateral coherence in young healthy individuals, and) a potential for unique age- and disease-specific profiles.

The goal of this study was to explore the association of beta-amyloid accumulation and cerebrovascular response (CVR) in cognitively normal older adults. Beta-amyloid accumulation was characterized with [18F] Florbetapir positron emission tomography scans. CVR was calculated as middle cerebral artery blood flow velocity change from rest to moderate intensity exercise. We found that individuals with elevated beta-amyloid aggregation had a blunted CVR ( n = 25, age 70.1 ± 4.8; 3.3 ± 3.7 cm/s) compared to non-elevated individuals ( n = 45, age 72.0 ± 4.9; 7.2 ± 5.0 cm/s, p < 0.001). Further, greater beta-amyloid burden was linearly associated with less CVR across all participants (b = -11.7, p < 0.001). Greater CVR and less beta-amyloid burden were associated with processing speed ( p < 0.05). This study is the first to show that CVR from rest to exercise is blunted across increased global beta-amyloid burden.

PurposeThe purpose of the present study was to determine the reliability of the exercise response (predicted peak VO2) using the total body recumbent stepper (TBRS) submaximal exercise test in: 1) healthy adults 20–70 years of age and 2) adults participating in inpatient stroke rehabilitation. We hypothesized that the predicted peak VO2 (Visit 1) would have an excellent relationship (r > 0.80) to predicted peak VO2 (Visit 2). We also wanted to test whether the exercise response at Visit 1 and Visit 2 would be significantly different.MethodsHealthy adults were recruited from the Kansas City metro area. Stroke participants were recruited during their inpatient rehabilitation stay. Eligible participants completed 2 TBRS submaximal exercise tests between 24 hours and 5 days at similar times of day.ResultsA total of 70 participants completed the study. Healthy adults (n = 50) were 36 M, 38.1 ± 10.1 years and stroke participants (n = 20) were 15 M, 62.5 ± 11.8 years of age. The exercise response was reliable for healthy adults (r = 0.980, p<0.01) and stroke participants (r = 0.987, p<0.01) between Visit 1 and Visit 2. Repeated Measures ANOVA showed a significant difference in predicted values between the two visits for healthy adults (47.2 ± 8.4 vs 47.7 ± 8.5 mL∙kg-1∙min-1; p = 0.04) but not for stroke participants (25.0 ± 9.9 vs 25.3 ± 11.4 mL∙kg-1∙min-1; p = 0.65).ConclusionThese results suggest that the exercise response is reliable using the TBRS submaximal exercise test in this cohort of healthy adults and stroke participants.

Purpose: A motor-assisted elliptical, ICARE, is used to address walking and fitness goals; yet, only limited data guide understanding of the impact of ICARE training parameters (e.g., speed and motor assistance) on cardiovascular response. A repeated-measures design investigated the influence of 5 predetermined ICARE speeds (25, 35, 45, 55, and 65 revolutions per minute) and 2 motor-assistance levels (with and without assistance) on heart rate (HR), Borg ratings of perceived exertion (RPE), and blood pressure (BP). Methods: Ten healthy participants' HR, RPE, and BP were recorded during steady state Active Assist (ICARE's motor assisting leg movement) and Active Assist Plus exercise (without motor's assistance) at 5 speeds. Results: Significant main effects on HR were documented for ICARE speed (F[4,36] = 77.313, P < .001) and motor assistance (F[1,36] = 224.813, P < .001), and an interaction (F[4,36] = 4.410, P = .005). Significant main effects on RPE were documented for speed (F[4,36] = 47.106, P < .001) and motor assistance (F[1,36] = 24.929, P < .001). Significant main effects on systolic BP were documented for speed (F[4,36] = 78.849, P < .001) and motor assistance (F[1,36] = 6.911, P = .027), and an interaction (F[4,36] = 5.695, P = .001). Only the main effect of motor assistance on diastolic BP was significant (F[1,36] = 7.917, P = .020). Conclusions: Increases in ICARE speed and decreases in motor assistance contributed to clinically relevant increases in HR, RPE, and systolic BP in a cohort of young, nondisabled adults.