The inverse and non-linear association between central augmentation index and heart rate variability in a cohort of male British combat personnel- findings from the ADVANCE study.

Purpose: The central augmentation index (cAIx) is an indirect measure of arterial stiffness. The influence of heart rate variability (HRV) on cAIx remains unexplored in a military cohort and was the aim of this analysis.

Method: The first follow-up data from the ArmeD serVices trAuma rehabilitatioN outComE (ADVANCE) study were analysed. Participants were male British servicemen who served in Afghanistan (2003-2014) and were divided into two groups at recruitment: injured (who sustained severe combat injury) and uninjured. The uninjured were frequency-matched to the injured by age, rank, role-in-theatre and deployment. HRV was reported as root-mean-square-of-successive-differences (RMSSD) using a five-minute single-lead electrocardiogram. The cAIx was measured using pulse waveform analysis and was adjusted for heart rate at 60 beats/minute (cAIx@60). Effect modification by injury was assessed via interaction analysis. Linear models reported the association between RMSSD (HRV) and cAIx@60 adjusting for a priori confounders.

Results: 1052 participants (injured n = 526; uninjured 526; median age at follow-up 37.4 years) were examined. Effect modification by injury was not statistically significant; therefore, was adjusted for along with other confounders. RMSSD and cAIx@60 exhibited a moderate inverse correlation (-0.40; p < 0.001). The association between natural log-transformed RMSSD (LnRMSSD) and cAIx@60 was non-linear and statistically significant, suggesting that a 10% decrease in LnRMSSD would be associated with 0.30% increase in cAIx@60.

Conclusion: Lower RMSSD (HRV) is associated with an increase in cAIx@60, independent of injury status and other traditional cardiovascular risk factors. The efficacy of positive HRV modification on cardiovascular risk in military populations needs to be examined.