Posttraumatic stress disorder and impaired autonomic modulation in male twins

Abstract

Background: Posttraumatic stress disorder (PTSD) has been linked to increased morbidity. An inflexibility of the autonomic nervous system might be the underlying mechanism. We aimed to assess whether PTSD and combat trauma exposure are associated with lower heart rate variability (HRV), a measure of autonomic function and a predictor of death.

Methods: We measured HRV by power spectral analysis on 24-hour ambulatory electrocardiogram in 459 middle-aged veteran male twins. Combat trauma was assessed with the combat exposure scale, and current and remitted PTSD was assessed with the Structured Clinical Interview for Psychiatry Disorders. Mixed-effects regression models were used to test associations of PTSD and HRV between and within twin pairs.

Results: Of all twins, 211 had combat exposure, 31 had current PTSD, and 43 had remitted PTSD. Current PTSD was inversely associated with very-low-frequency and low-frequency HRV both in individual twins and within 20 pairs discordant for current PTSD. Twins with current PTSD had a 49% lower low-frequency HRV than their brothers without PTSD (p<.001). Remitted PTSD was not associated with HRV. Results were robust to adjustment for depression and other risk factors. Combat exposure was inversely associated with most HRV frequencies, but this association mostly diminished after adjustment for current PTSD.

Conclusion: In middle-aged veteran men, combat exposure and current PTSD are associated with measures of autonomic inflexibility previously shown to have prognostic significance. The negative health impact of combat exposure on autonomic function is mediated largely through PTSD and might reverse with remission of PTSD.

Figure 1

Adjusted Percent Difference in VLF, LF, and HF HRV Comparing Twins With and Without Current or Remitted PTSD Note: Adjusted for age, Baecke physical activity score, current/past smoking, lifetime history of hypertension, diabetes, low density lipoprotein cholesterol, antidepressant use, lifetime history of major depression, body mass index, and history of drug abuse. When examining remitted PTSD, models additionally adjusted for current PTSD. Abbreviations: VLF=very low frequency; LF=low frequency; HF=high frequency; MZ=monozygotic; DZ=dizygotic

Figure 2

Mean Natural Log VLF, LF, and HF HRV, According to CAPS and CES Ordinal Categories Abbreviations: CAPS=Clinically Administered PTSD Scale; CES=Combat Exposure Scale; VLF=very low frequency; LF=low frequency; HF=high frequency; ln=natural logarithm