Article

The CO2 stimulus duration and steady-state time point used for data extraction alters the cerebrovascular reactivity outcome measure

Citation

Burley CV, Lucas RAI, Whittaker AC, Mullinger K & Lucas SJE (2020) The CO2 stimulus duration and steady-state time point used for data extraction alters the cerebrovascular reactivity outcome measure. Experimental Physiology, 105 (5), pp. 893-903. https://doi.org/10.1113/EP087883

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 CO 2 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 CO ± 2 for four stimulus durations (1, 2, 4 and 5 min) of 5% CO 2 (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 CO 2 stimulus (̇ V E,CO 2). Repeated measures ANOVAs compared CVR and ̇ V E,CO 2 measures between stimulus durations and steady-state time points. An effect of stimulus duration was observed (P = 0.002, í µí¼‚ 2 = = 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 CO , 2 sensitivity increased ∼3-fold from 1 min to 4 and 5 min durations (P < 0.001, í µí¼‚ 2 = 0.485). CVRs calculated from different steady-state time points within each stimulus duration were different (P < 0.001, í µí¼‚ 2 = = 0.454), specifically for 4 min (P 0.001) and 5 min (P P < 0.001), but not 2 min stimulus durations (= 0.273). These findings demonstrate that methodological differences alter the CVR measure.

Keywords
cerebrovascular reactivity; CO2 stimulus; transcranial Doppler

Journal
Experimental Physiology: Volume 105, Issue 5

StatusPublished
FundersUniversity of Birmingham and The Physiological Society
Publication date01/05/2020
Publication date online21/02/2020
Date accepted by journal19/02/2020
URLhttp://hdl.handle.net/1893/31157
ISSN0958-0670
eISSN1469-445X