Valsalva maneuver unveils central baroreflex dysfunction with altered blood pressure control in persons with a history of mild traumatic brain injury

Abstract

Background: 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). We investigated whether standardized baroreflex-loading, induced by a Valsalva maneuver (VM), unveils CAD in otherwise healthy post-mTBI-patients.

Methods: In 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).

Results: At 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).

Conclusions: Reduced 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.

Keywords: Baroreflex dysfunction; Blood pressure overshoot; Central autonomic network; Mild traumatic brain injury; Sympathetic dysregulation; Valsalva maneuver.

Fig. 1

Time-series of systolic blood pressure (BPsys) and heart rate (HR) during the Valsalva maneuver. For a healthy participant and a post-mTBI-patient, the double-headed arrows indicate the intervals from the highest systolic blood pressure (BPsys) value after strain to the time when BPsys had fallen by 90 % of the difference between peak-phase-IV BPsys and baseline BPsys, i.e. the 90 %-blood-pressure-normalization-time. “Start” and “stop” refer to the beginning and release of expiratory strain during the Valsalva maneuver

Fig. 2

The 90 %-blood-pressure-normalization-times and 90 %-blood-pressure-normalization-velocities in healthy controls and post-mTBI-patients. The 90 % normalization-times of systolic blood pressure (BPsys), i.e. the intervals from the highest BPsys-values after VM strain-release to the times when BPsys had fallen by 90 % of the differences between peak-phase-IV BPsys and baseline BPsys, were longer in the 25 patients with a history of mild TBI than in the healthy participants. The 90 %-blood-pressure-normalization-velocities, i.e. the differences between peak-phase-IV BPsys and BPsys at the moment of the 90 %-BP-normalization-time, divided by the 90 %-BP-normalization-times, were lower in the post-mTBI-patients than in the healthy participants. Data are presented as box plots. The line in the middle of the box represents the median (50th percentile), the top of the box represents the upper quartile (75th percentile), the bottom of the box represents the lower quartile (25th percentile), and the end of the whiskers represent the highest and lowest values that are not extreme values or outliers. Grey boxes illustrate results in healthy participants; white boxes with vertical lines illustrate results in the 25 patients with a history of mild TBI