Combat injury and limb amputation moderate the association between mental health and sympathetic activity

BACKGROUND Combat-related traumatic injury (CRTI) can increase sympathetic nervous system (SNS) activity, with poor mental health possibly worsening this effect. Increased SNS activity is associated with CVD risk. We examined the ADVANCE cohort to assess whether the effect of mental health on sympathetic activity differs in injured servicemen with and without associated limb loss and a frequency-matched uninjured group. METHODS The primary outcome was the SNS index (SNSi) measured via a single-lead 5-min electrocardiogram recording and analysed in Kubios software. The exposure variables were mental health (generalised anxiety/depression/Post-Traumatic Stress Disorder; PTSD) measured from self-report questionnaires. The interaction between mental health and CRTI with and without limb loss and its effect on the SNSi was analysed using linear regression models, adjusted for confounders. RESULTS A total of 974 participants [median age 37 years, n = 469 injured (n = 133 amputees), n = 505 uninjured, time-from-injury/deployment = 11.5 years] were included. The effects of mental health severity on SNSi for the uninjured group and those injured with and without limb loss were negligible and inconclusive for generalised anxiety and depression, and small for PTSD. The effect of PTSD [coefficient 0.021 (95%CI 0.002, 0.039)] was found to be greater in those injured with limb loss compared to the uninjured group. CONCLUSIONS The effects of poorer mental health on SNSi were greater in those injured with limb loss compared to demographically similar personnel without such injuries. This highlights the need to introduce interventions targeted at restoring autonomic balance, especially in injured servicemen with limb loss and poor mental health.