Comparison of the effects of independently-controlled end-tidal PCO(2) and PO(2) on blood oxygen level-dependent (BOLD) MRI.
OBJECTIVE
To assess the effect of changes in end-tidal partial pressure of O(2) (PETO(2)) on cerebrovascular reactivity (CVR) estimated from changes in blood oxygen level-dependent (BOLD) signal during cyclic changes in end-tidal partial pressure of CO(2) (PETCO(2)).


METHODS
BOLD response to fixed cyclic step changes in PETCO(2) (range = 30.4-48.8 mmHg) and PETO(2) (range = 100.6-444.0 mmHg) was studied in four healthy volunteers.


RESULTS
The BOLD reactivity to PETCO(2) and PETO(2) 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.


CONCLUSIONS
The BOLD reactivity to PETO(2) was much smaller than that to PETCO(2). However, BOLD reactivity can be significantly distorted by CO(2)-induced changes in PETO(2). We conclude that PETO(2) should be carefully controlled during studies that use BOLD reactivity as an indicator of CVR.
Department of Anesthesiology, University Health Network, University of Toronto, Toronto, Canada.
Eitan
E
Prisman
Marat
M
Slessarev
Jay
J
Han
Julien
J
Poublanc
Alexandra
A
Mardimae
Adrian
A
Crawley
Joseph
J
Fisher
David
D
Mikulis
D000328:Adult; D001921:Brain / Q000098:blood supply*; D001931:Brain Mapping / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood*; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D013990:Tidal Volume
D002245:Carbon Dioxide; D010100:Oxygen