Emily Witte1, Yumei Liu1, Jaimie L. Ward1, Katie S. Kempf1, Alicen Whitaker1, Eric D. Vidoni2,Jesse C. Craig3, David C. Poole3, Sandra A. Billinger1 *

1University of Kansas Medical Center, Kansas City, KS; 2University of Kansas, Alzheimer’s Disease Center, Fairway, KS; 3Kansas State University, Manhattan, KS

Understanding the middle cerebral artery dynamic response during different exercise intensities is vital for understanding brain health and designing and evaluating exercise strategies for maximizing therapeutic potential. However, whether there is an interaction between exercise intensity and cerebrovascular kinetics is unknown. PURPOSE: To characterize mean middle cerebral artery blood flow velocity (MCAv) kinetics associated with two exercise work rates: low and moderate. We tested the hypotheses that increasing work rate would increase the MCAv amplitude and that age and estimated maximal oxygen uptake (O2max) would be related to the MCAv amplitude. METHODS: Baseline values were collected for 90-seconds followed by a 6-minute exercise bout on a recumbent stepper. Heart rate, end tidal CO2 (PETCO2), beat-to-beat blood pressure, and MCAV were recorded at rest and during exercise. The MCAv kinetics response for participants from baseline (BL) was described by the response amplitude (Amp), time delay (TD), and time constant (τ). RESULTS: Sixty-four adults completed the low and moderate intensity exercise transitions. MCAv Amp increased from rest as a function of work rate, low and moderate intensity, respectively, (11.8 and 14.7 cm/s; p<0.001) while no difference between work rates were observed in either TD (43.5 and 45.8 s; p=0.65) or τ (35.2 and 31.4 s; p=0.47). Age showed a moderate, negative association with MCAv Amp (r=-0.40 and r=-0.42; p<0.01). Higher estimated O2 max demonstrated a moderate, positive correlation with MCAv Amp (r=0.41 and r=0.50; p<0.01). CONCLUSION: Moderate intensity exercise induced a greater MCAv response amplitude compared to low intensity exercise. The amplitude of the initial MCAv response for both exercise intensities increased systematically with work rate whereas the TD and τ kinetics parameters were invariant. Therefore, the possibility exists that the cerebrovascular system may have protective mechanisms in place to avoid the more rapid responses as seen in skeletal muscle, however more work is needed to address this hypothesis. Finally, although the MCAv Amp declines with age, maintaining higher cardiorespiratory fitness may benefit the cerebrovascular response to exercise.

ACKNOWEDGEMENTS: S. A. Billinger was supported in part by K01HD067318 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and from the Wohlgemuth Faculty Scholar Award. A. Whitaker and K. Kempf were supported in part by T32HD057850 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development. E. D. Vidoni received partial support from the University of Kansas Alzheimer's Disease Center (P30AG035982). REDCap at University of Kansas Medical Center is supported by CTSA Award # ULTR000001 from NCRR and NCATS awarded to the University of Kansas Medical Center for Frontiers: The Heartland Institute for Clinical and Translational Research. The Georgia Holland Research in Exercise and Cardiovascular Health (REACH) laboratory space was supported by the Georgia Holland Endowment Fund.

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