Low-Level Carbon Monoxide Exposure Affects BOLD FMRI

Abstract

Blood Oxygen Level Dependent (BOLD) FMRI is a common technique for measuring brain activation that could be affected by low-level carbon monoxide (CO) exposure from e.g. smoking. This study aimed to probe the vulnerability of BOLD FMRI to CO and determine whether it constitutes a significant confound in neuroimaging and clinical trials. Low-level (6ppm exhaled) CO effects on BOLD signal were assessed in 12 healthy never-smokers on two separate experimental days (CO and air control). FMRI tasks were breath-holds (hypercapnia), visual stimulation and fingertapping. CO significantly dampened global BOLD FMRI signal during hypercapnia and visual cortex activation during visual stimulation. During fingertapping, CO reduced visual cortex activation but increased premotor cortex activation. Behavioural and physiological measures remained unchanged. We conclude that BOLD FMRI is vulnerable to CO, possibly through baseline increases in CBF, and suggest exercising caution when imaging populations exposed to elevated CO levels, e.g. with high smoking prevalence.