Abstract
BackgroundPatients with a history of mild TBI (post-mTBI-patients) have an unexplained increase in long-term mortality which might be related to central autonomic dysregulation (CAD). We investigated whether standardized baroreflex-loading, induced by a Valsalva maneuver (VM), unveils CAD in otherwise healthy post-mTBI-patients.MethodsIn 29 healthy persons (31.3 ± 12.2 years; 9 women) and 25 post-mTBI-patients (35.0 ± 13.2 years, 7 women, 4–98 months post-injury), we monitored respiration (RESP), RR-intervals (RRI) and systolic blood pressure (BP) at rest and during three VMs. At rest, we calculated parameters of total autonomic modulation [RRI-coefficient-of-variation (CV), RRI-standard-deviation (RRI-SD), RRI-total-powers], of sympathetic [RRI-low-frequency-powers (LF), BP-LF-powers] and parasympathetic modulation [square-root-of-mean-squared-differences-of-successive-RRIs (RMSSD), RRI-high-frequency-powers (HF)], the index of sympatho-vagal balance (RRI LF/HF-ratios), and baroreflex sensitivity (BRS). We calculated Valsalva-ratios (VR) and times from lowest to highest RRIs after strain (VR-time) as indices of parasympathetic activation, intervals from highest systolic BP-values after strain-release to the time when systolic BP had fallen by 90 % of the differences between peak-phase-IV-BP and baseline-BP (90 %-BP-normalization-times), and velocities of BP-normalization (90 %-BP-normalization-velocities) as indices of sympathetic withdrawal.We compared patient- and control-parameters before and during VM (Mann-Whitney-U-tests or t-tests; significance: P < 0.05).ResultsAt rest, RRI-CVs, RRI-SDs, RRI-total-powers, RRI-LF-powers, BP-LF-powers, RRI-RMSSDs, RRI-HF-powers, and BRS were lower in patients than controls. During VMs, 90 %-BP-normalization-times were longer, and 90 %-BP-normalization-velocities were lower in patients than controls (P < 0.05).ConclusionsReduced autonomic modulation at rest and delayed BP-decrease after VM-induced baroreflex-loading indicate subtle CAD with altered baroreflex adjustment to challenge. More severe autonomic challenge might trigger more prominent cardiovascular dysregulation and thus contribute to increased mortality risk in post-mTBI-patients.
Highlights
IntroductionPatients with a history of mild Traumatic brain injuries (TBIs) (post-mild TBI (mTBI)-patients) have an unexplained increase in long-term mortality which might be related to central autonomic dysregulation (CAD)
Patients with a history of mild Traumatic brain injuries (TBIs) have an unexplained increase in long-term mortality which might be related to central autonomic dysregulation (CAD)
To further test our hypothesis that post-mild TBI (mTBI)-patients have a subtle dysfunction of central baroreflex structures that adjust efferent baroreflex responses, we evaluated in this study whether there is a generalized baroreflex dysregulation in post-mTBI-patients, i.e. whether baroreflex responses are altered in response to acute baroreceptor-unloading and in response to an acute increase in blood pressure (BP) requiring parasympathetic activation and sympathetic withdrawal
Summary
Patients with a history of mild TBI (post-mTBI-patients) have an unexplained increase in long-term mortality which might be related to central autonomic dysregulation (CAD). The authors observed an association between enduring emotional dysfunction [14], lowered levels of insulin-like growth factor [15] and reduced autonomic heart rate modulation after mild TBI. They concluded that altered cardiac autonomic modulation may predict and contribute to enduring emotional disorders after mild TBI [14, 15]
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