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OBJECTIVES: To examine the independent association between heart rate variability (HRV), a marker of cardiac autonomic function, and cognitive impairment. DESIGN: Cross-sectional analysis of baseline data from Women's Health and Aging Study I. SETTING: Urban community in Baltimore, Maryland. PARTICIPANTS: A subset of 311 physically disabled, community-dwelling women aged 65 and older whose HRV data were obtained. MEASUREMENTS: Reduced HRV was defined as the lowest quartile of each of several HRV measures exploring time and frequency domains and compared with the remaining three quartiles. Cognitive impairment was defined as a Mini-Mental State Examination score less than 24. Multiple logistic regression was used to model the independent relationship between reduced HRV and prevalent cognitive impairment. RESULTS: The age-, education-, and race-adjusted prevalence of cognitive impairment was higher in those with reduced HRV than in those with nonreduced HRV. After adjusting for relevant demographic and clinical characteristics, participants with reduced HRV were significantly more likely than those with nonreduced HRV to have cognitive impairment; these findings were consistent across different HRV indices. In particular, reduced high-frequency power, indicative of decreased parasympathetic activity, was associated with 6.7 times greater odds of cognitive impairment (95% confidence interval=2.27–20.0). CONCLUSION: Cardiac autonomic dysfunction, particularly decreased parasympathetic activity, was independently associated with cognitive impairment in older disabled women in the community. This finding may improve understanding of the pathophysiological basis of cognitive impairment. The potential role of HRV as a cause or consequence of cognitive impairment needs to be elucidated in future studies. [ABSTRACT FROM AUTHOR]