The Cognitive Impact of Chronic Low-level Carbon Monoxide Exposure in Older Adults

Cheshire, Beth and Holland, Carol and Crawford, Trevor (2023) The Cognitive Impact of Chronic Low-level Carbon Monoxide Exposure in Older Adults. PhD thesis, Lancaster University.

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Abstract

Evidence of cognitive effects associated with low-level carbon monoxide (CO) is limited, but indicates neuropsychological impairments may follow exposure. Home exposure to low-level CO may be an unidentified cause of cognitive impairment that improved awareness could prevent. This thesis consists of a systematic literature review of acute low-level exposure, the development of data analysis methods and the cross-sectional and longitudinal study of the cognitive effects associated with chronic low-level exposure in older adults, a group identified as particularly vulnerable. Effects at a range of extremely low concentrations were analysed to determine thresholds of harm. Results indicated that the cognitive effects follow a trajectory that can be represented on a continuum, from extremely low-level exposure and positive effects through higher concentrations and negative impacts. The proposed continuum can account for reported negative effects, absence of effects, and trends towards positive impacts in different cognitive functions, by small variations in exposure concentration and duration, providing an explanation for inconsistent findings within the literature. This model increases theoretical understanding, bridging the knowledge gap between beneficial effects and CO toxicity. Findings indicate that particular areas of cognition are more vulnerable, and others more resilient, to CO. Analyses also revealed that the relationship between advancing age and specific cognitive functions was moderated by CO exposure, with greater exposure related to increased performance in younger older adults (59-74yrs) and decreased performance in old older adults (75-97yrs), suggesting that measures of frailty, rather than age alone, may be better indicators of CO vulnerability. The research makes a significant contribution to knowledge, proposing a theory that explains the cognitive effects of low-level CO exposure, which could ultimately be used in clinical settings to improve diagnosis and determine thresholds of harm. The analysis method presented provides an approach for future research that, in turn, may produce new evidence to underpin and inform exposure guidelines, policy, legislation and safety technology in order to keep those most vulnerable safe.