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.
Prisman
Eitan
E
Department of Anesthesiology, University Health Network, University of Toronto, Toronto, Canada.
Slessarev
Marat
M
Han
Jay
J
Poublanc
Julien
J
Mardimae
Alexandra
A
Crawley
Adrian
A
Fisher
Joseph
J
Mikulis
David
D
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