Comparison of the effects of independently-controlled end-tidal PCO 2 and PO2 on Blood Oxygen Level-Dependent (BOLD) MRI

Abstract

Purpose: To assess the effect of changes in end-tidal partial pressure of O2 (PETO2) on cerebrovascular reactivity (CVR) estimated from changes in blood oxygen level-dependent (BOLD) signal during cyclic changes in end-tidal partial pressure of CO2 (PETCO2). Materials and Methods: BOLD response to fixed cyclic step changes in PETCO2 (range = 30.4-48.8 mmHg) and PETO2 (range = 100.6-444.0 mmHg) was studied in four healthy volunteers. Results: The BOLD reactivity to PETCO 2 and PETO2 were 0.283 (0.188-0.379) (median, range) and 0.004 (0.003-0.006)%/mmHg, respectively, in the whole brain; 0.438 (0.382-0.614) vs. 0.006 (0.004-0.009)%/mmHg, respectively, in the gray matter; and 0.075 (0.065-0.093) vs. 0.002 (0.001-0.002)%/mmHg, respectively, in the white matter. Conclusion: The BOLD reactivity to PETO2 was much smaller than that to PETCO2. However, BOLD reactivity can be significantly distorted by CO2-induced changes in PETO2. We conclude that PETO 2 should be carefully controlled during studies that use BOLD reactivity as an indicator of CVR. © 2007 Wiley-Liss, Inc.