Heart rate variability characteristics in a large group of active-duty marines and relationship to posttraumatic stress

Abstract

Objective: Heart rate variability (HRV), thought to reflect autonomic nervous system function, is lowered under conditions such as posttraumatic stress disorder (PTSD). The potential confounding effects of traumatic brain injury (TBI) and depression in the relationship between HRV and PTSD have not been elucidated in a large cohort of military service members. Here we describe HRV associations with stress disorder symptoms in a large study of Marines while accounting for well-known covariates of HRV and PTSD including TBI and depression.

Methods: Four battalions of male active-duty Marines (n = 2430) were assessed 1 to 2 months before a combat deployment. HRV was measured during a 5-minute rest. Depression and PTSD were assessed using the Beck Depression Inventory and Clinician-Administered PTSD Scale, respectively.

Results: When adjusting for covariates, including TBI, regression analyses showed that lower levels of high-frequency HRV were associated with a diagnosis of PTSD (β = -0.20, p = .035). Depression and PTSD severity were correlated (r = 0.49, p < .001); however, participants with PTSD but relatively low depression scores exhibited reduced high frequency compared with controls (p = .012). Marines with deployment experience (n = 1254) had lower HRV than did those with no experience (p = .033).

Conclusions: This cross-sectional analysis of a large cohort supports associations between PTSD and reduced HRV when accounting for TBI and depression symptoms. Future postdeployment assessments will be used to determine whether predeployment HRV can predict vulnerability and resilience to the serious psychological and physiological consequences of combat exposure.

Figure 1

Mean high frequency index (HF) in Marines with and without PTSD and depression or TBI, all cohorts combined. Note: Error bars are standard errors of the mean. Values in figure are back-transformed absolute HF means. Left Panel (A): * p < .050, PTSD only versus no PTSD/no depression in post-hoc comparison with transformed HF values as the dependent variable. Sample sizes are as follows: no PTSD and no depression n = 1965, PTSD only n = 248, depression only n = 124, PTSD and depression n = 64. “PTSD” refers to partial or full PTSD cases as determined by the CAPS. “Depression” refers to moderate/severe depression as determined by the BDI. Right Panel (B): * p < .050, main effect of PTSD versus no PTSD in ANOVA with transformed HF values as the dependent variable. Sample sizes are as follows: no PTSD and no TBI history n = 981, PTSD and no TBI history = n = 87, no PTSD and TBI history, n=1113, PTSD and TBI history n= 228. “PTSD” refers to partial or full PTSD cases as determined by the CAPS. History of TBI= self-reported history of a head injury accompanied by either loss of consciousness or altered mental status.

Figure 2

Mean high frequency index (HF) for no history of prior deployments versus prior deployment history in Marines with no PTSD, partial PTSD, and full PTSD, all cohorts combined. Note: Errors bars are standard errors of the mean. Values in figure are back-transformed absolute HF means. *p < .050 vs. No PTSD/No Prior Deployment group using ANCOVA with transformed HF values as the dependent variable and age as a covariate. Sample sizes are as follows: no PTSD and no prior deployment n = 1031, no PTSD and prior deployment n = 1063, partial PTSD and no prior deployment n = 80, partial PTSD and prior deployment n = 116, full PTSD and no prior deployment n = 51, full PTSD and prior deployment n = 68. See results for details.