Claire V Burley1,2, Rebekah A I Lucas1, Anna C Whittaker1, Karen Mullinger2,3,4, Samuel J E Lucas1,2,5. 1. School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK. 2. Centre for Human Brain Health, University of Birmingham, Birmingham, UK. 3. School of Psychology, University of Birmingham, Birmingham, UK. 4. School of Physics and Astronomy, University of Nottingham, Nottingham, UK. 5. Department of Physiology, University of Otago, New Zealand.
Abstract
NEW FINDINGS: What is the central question of this study? Cerebrovascular reactivity (CVR) is a common functional test to assess brain health, and impaired CVR has been associated with all-cause cardiovascular mortality: does the duration of the CO2 stimulus and the time point used for data extraction alter the CVR outcome measure? What is the main finding and its importance? This study demonstrated CVR measures calculated from 1 and 2 min CO2 stimulus durations were significantly higher than CVR calculated from a 4 min CO2 stimulus. CVRs calculated from the first 2 min of the CO2 stimulus were significantly higher than CVR values calculated from the final minute if the duration was ≥4 min. This study highlights the need for consistent methodological approaches. ABSTRACT: Cerebrovascular reactivity to carbon dioxide (CVR) is a common functional test to assess brain vascular health, though conflicting age and fitness effects have been reported. Studies have used different CO2 stimulus durations to induce CVR and extracted data from different time points for analysis. Therefore, this study examined whether these differences alter CVR and explain conflicting findings. Eighteen healthy volunteers (24 ± 5 years) inhaled CO2 for four stimulus durations (1, 2, 4 and 5 min) of 5% CO2 (in air) via the open-circuit Douglas bag method, in a randomized order. CVR data were derived from transcranial Doppler (TCD) measures of middle cerebral artery blood velocity (MCAv), with concurrent ventilatory sensitivity to the CO2 stimulus ( V ̇ E , C O 2 ). Repeated measures ANOVAs compared CVR and V ̇ E , C O 2 measures between stimulus durations and steady-state time points. An effect of stimulus duration was observed (P = 0.002, η² = 0.140), with 1 min (P = 0.010) and 2 min (P < 0.001) differing from 4 min, and 2 min differing from 5 min (P = 0.019) durations. V ̇ E , C O 2 sensitivity increased ∼3-fold from 1 min to 4 and 5 min durations (P < 0.001, η² = 0.485). CVRs calculated from different steady-state time points within each stimulus duration were different (P < 0.001, η² = 0.454), specifically for 4 min (P = 0.001) and 5 min (P < 0.001), but not 2 min stimulus durations (P = 0.273). These findings demonstrate that methodological differences alter the CVR measure.
NEW FINDINGS: What is the central question of this study? Cerebrovascular reactivity (CVR) is a common functional test to assess brain health, and impaired CVR has been associated with all-cause cardiovascular mortality: does the duration of the CO2 stimulus and the time point used for data extraction alter the CVR outcome measure? What is the main finding and its importance? This study demonstrated CVR measures calculated from 1 and 2 min CO2 stimulus durations were significantly higher than CVR calculated from a 4 min CO2 stimulus. CVRs calculated from the first 2 min of the CO2 stimulus were significantly higher than CVR values calculated from the final minute if the duration was ≥4 min. This study highlights the need for consistent methodological approaches. ABSTRACT: Cerebrovascular reactivity to carbon dioxide (CVR) is a common functional test to assess brain vascular health, though conflicting age and fitness effects have been reported. Studies have used different CO2 stimulus durations to induce CVR and extracted data from different time points for analysis. Therefore, this study examined whether these differences alter CVR and explain conflicting findings. Eighteen healthy volunteers (24 ± 5 years) inhaled CO2 for four stimulus durations (1, 2, 4 and 5 min) of 5% CO2 (in air) via the open-circuit Douglas bag method, in a randomized order. CVR data were derived from transcranial Doppler (TCD) measures of middle cerebral artery blood velocity (MCAv), with concurrent ventilatory sensitivity to the CO2 stimulus ( V ̇ E , C O 2 ). Repeated measures ANOVAs compared CVR and V ̇ E , C O 2 measures between stimulus durations and steady-state time points. An effect of stimulus duration was observed (P = 0.002, η² = 0.140), with 1 min (P = 0.010) and 2 min (P < 0.001) differing from 4 min, and 2 min differing from 5 min (P = 0.019) durations. V ̇ E , C O 2 sensitivity increased ∼3-fold from 1 min to 4 and 5 min durations (P < 0.001, η² = 0.485). CVRs calculated from different steady-state time points within each stimulus duration were different (P < 0.001, η² = 0.454), specifically for 4 min (P = 0.001) and 5 min (P < 0.001), but not 2 min stimulus durations (P = 0.273). These findings demonstrate that methodological differences alter the CVR measure.
Authors: Olivia Sobczyk; Jorn Fierstra; Lakshmikumar Venkatraghavan; Julien Poublanc; James Duffin; Joseph A Fisher; David J Mikulis Journal: Front Physiol Date: 2021-07-07 Impact factor: 4.566
Authors: Gabriele Gratton; Samuel R Weaver; Claire V Burley; Kathy A Low; Edward L Maclin; Paul W Johns; Quang S Pham; Samuel J E Lucas; Monica Fabiani; Catarina Rendeiro Journal: Sci Rep Date: 2020-11-24 Impact factor: 4.379
Authors: Claire V Burley; Susan T Francis; Kate N Thomas; Anna C Whittaker; Samuel J E Lucas; Karen J Mullinger Journal: Front Physiol Date: 2021-04-12 Impact factor: 4.566
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