Abstract
OBJECTIVE—Heart rate variability (HRV), a measure of autonomic function, has been associated with cognitive function, but studies are conflicting. Previous studies have also not controlled for familial and genetic influences. METHODS—We performed power spectral analysis on 24-hour ambulatory ECG’s in 416 middle-aged male twins from the Vietnam Era Twin Registry. Memory and learning were measured by verbal and visual selective reminding tests (SRT). Mixed-effect regression models were used to calculate associations between and within twin pairs, while adjusting for covariates. RESULTS—The mean age (SD) was 55 (2.9) years. A statistically significant positive association was found between measures of HRV and verbal, but not visual, SRT scores. The most statistically significant unadjusted association was found between very low frequency (VLF) HRV and verbal total recall SRT, such that each logarithm of increase in VLF was associated with an increased verbal SRT score of 4.85 points (p=0.002). The association persisted despite adjustment for demographic and cardiovascular risk factors, and after accounting for familial, and genetic factors by comparing twins within pairs. A significant interaction was found between posttraumatic stress disorder (PTSD) and HRV, such that total power and ultra low frequency were associated with SRT in twins (n=362) without PTSD, but not in those with PTSD.