Jonathan D Smirl1, Alexander D Wright2,3,4,5, Philip N Ainslie6, Yu-Chieh Tzeng7, Paul van Donkelaar2. 1. Sports Concussion Research Lab, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada. jonathan.smirl@ubc.ca. 2. Sports Concussion Research Lab, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada. 3. MD/PhD Program, University of British Columbia, Vancouver, BC, Canada. 4. Southern Medical Program, University of British Columbia, Kelowna, BC, Canada. 5. Experimental Medicine Program, University of British Columbia, Vancouver, BC, Canada. 6. Centre for Heart, Lung and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, BC, Canada. 7. Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, Wellington, New Zealand.
Abstract
OBJECTIVE: Cerebral pressure-flow dynamics are typically reported between mean arterial pressure and mean cerebral blood velocity. However, by reporting only mean responses, potential differential regulatory properties associated with systole and diastole may have been overlooked. MATERIALS AND METHODS: Twenty young adults (16 male, age: 26.7 ± 6.6 years, BMI: 24.9 ± 3.0 kg/m2) were recruited for this study. Middle cerebral artery velocity was indexed via transcranial Doppler. Cerebral pressure-flow dynamics were assessed using transfer function analysis at both 0.05 and 0.10 Hz using squat-stand manoeuvres. This method provides robust and reliable measures for coherence (correlation index), phase (timing buffer) and gain (amplitude buffer) metrics. RESULTS: There were main effects for both cardiac cycle and frequency for phase and gain metrics (p < 0.001). The systolic phase (mean ± SD) was elevated at 0.05 (1.07 ± 0.51 radians) and 0.10 Hz (0.70 ± 0.46 radians) compared to the diastolic phase (0.05 Hz: 0.59 ± 0.14 radians; 0.10 Hz: 0.33 ± 0.11 radians). Conversely, the systolic normalized gain was reduced (0.05 Hz: 0.49 ± 0.12%/%; 0.10 Hz: 0.66 ± 0.20%/%) compared to the diastolic normalized gain (0.05 Hz: 1.46 ± 0.43%/%; 0.10 Hz: 1.97 ± 0.48%/%). CONCLUSIONS: These findings indicate there are differential systolic and diastolic aspects of the cerebral pressure-flow relationship. The oscillations associated with systole are extensively buffered within the cerebrovasculature, whereas diastolic oscillations are relatively unaltered. This indicates that the brain is adapted to protect itself against large increases in systolic blood pressure, likely as a mechanism to prevent cerebral haemorrhages.
OBJECTIVE: Cerebral pressure-flow dynamics are typically reported between mean arterial pressure and mean cerebral blood velocity. However, by reporting only mean responses, potential differential regulatory properties associated with systole and diastole may have been overlooked. MATERIALS AND METHODS: Twenty young adults (16 male, age: 26.7 ± 6.6 years, BMI: 24.9 ± 3.0 kg/m2) were recruited for this study. Middle cerebral artery velocity was indexed via transcranial Doppler. Cerebral pressure-flow dynamics were assessed using transfer function analysis at both 0.05 and 0.10 Hz using squat-stand manoeuvres. This method provides robust and reliable measures for coherence (correlation index), phase (timing buffer) and gain (amplitude buffer) metrics. RESULTS: There were main effects for both cardiac cycle and frequency for phase and gain metrics (p < 0.001). The systolic phase (mean ± SD) was elevated at 0.05 (1.07 ± 0.51 radians) and 0.10 Hz (0.70 ± 0.46 radians) compared to the diastolic phase (0.05 Hz: 0.59 ± 0.14 radians; 0.10 Hz: 0.33 ± 0.11 radians). Conversely, the systolic normalized gain was reduced (0.05 Hz: 0.49 ± 0.12%/%; 0.10 Hz: 0.66 ± 0.20%/%) compared to the diastolic normalized gain (0.05 Hz: 1.46 ± 0.43%/%; 0.10 Hz: 1.97 ± 0.48%/%). CONCLUSIONS: These findings indicate there are differential systolic and diastolic aspects of the cerebral pressure-flow relationship. The oscillations associated with systole are extensively buffered within the cerebrovasculature, whereas diastolic oscillations are relatively unaltered. This indicates that the brain is adapted to protect itself against large increases in systolic blood pressure, likely as a mechanism to prevent cerebral haemorrhages.
Entities:
Keywords:
Blood pressure; Cardiac cycle; Cerebral autoregulation; Cerebral blood flow; Middle cerebral artery; Transfer function analysis
Authors: Jonathan D Smirl; Dakota Peacock; Joel S Burma; Alexander D Wright; Kevin J Bouliane; Jill Dierijck; Michael Kennefick; Colin Wallace; Paul van Donkelaar Journal: Eur J Appl Physiol Date: 2022-02-16 Impact factor: 3.078
Authors: Patrice Brassard; Lawrence Labrecque; Jonathan D Smirl; Michael M Tymko; Hannah G Caldwell; Ryan L Hoiland; Samuel J E Lucas; André Y Denault; Etienne J Couture; Philip N Ainslie Journal: Physiol Rep Date: 2021-08