Changes in CBF/CMRO 2 coupling with graded visual stimuli are modulated by baseline perfusion

The BOLD fMRI response depends on multiple physiological factors, in particular, the ratio of fractional changes in CBF and CMRO2, defined as n. Meaningful comparisons of BOLD responses between stimulus conditions rely upon a constant n, which may not be the case. The BOLD and CBF responses to 4 visual contrast levels were measured in 9 subjects during normocapnia and hypercapnia. We found larger BOLD responses during hypercapnia, suggesting altered CBF/CMRO2 coupling dynamics. These data show BOLD changes that are consistent with varying n values across contrast, and which are modulated further by changes in baseline physiology.

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