Delayed effect of blood pressure fluctuations on heart rate in patients with end-stage kidney disease

Dynamical interaction between heart rate and blood pressure of end-stage renal disease patients evaluated by cross recurrence plot diagonal analysis

The assessment of spontaneous variability of blood pressure and heart rate is based on specific physiological hypotheses about dynamic features, for example, the baroreflex modulation of heart rate over time in daily life. Usually, arterial baroreflex control of heart rate is explored without delays between blood pressure and heart rate data points, within a narrow range of values, excluding the analysis of saturation regions or low-threshold changes. In this work, we examine the dynamic interactions between systolic blood pressure (SBP) and interbeat interval (IBI), in 15-min length time series and for the first time using the analysis of diagonals derived from a cross-recurrence plots in healthy persons and end-stage renal disease (ESRD) patients. We found that ESRD patients have stronger intermittent dynamical interactions between IBI and SBP, but they lose most of the dynamical interactions. Although healthy subjects exhibit a continuously changing order of precedence between IBI and SBP at different lags, ESRD patients preserve this changing order of precedence only for lags >0 beats.NEW & NOTEWORTHY This study is the first to compare the time-variant pattern of systolic blood pressure (SBP) and interbeat interval (IBI) coupling between ESRD patients and healthy volunteers through the analysis of diagonal in cross-recurrence plots, and in the face of an orthostatic challenge. Our results demonstrated alternant interactions on the order of precedence (IBI → SBP or SBP→ IBI) at different time delays. This pattern is different in resting position and during active standing for the two groups studied, and interestingly, some association patterns are lost in ESRD patients. These patterns of alternant interactions on the order of precedence could be related to autonomic neural activities and cardiovascular synchronization at different scales both in time and space. This could reflect physiological adaptive flexibility of cardiovascular regulation. Losing some association patterns in ESRD may be the result of chronic adjustments of many physiological mechanisms (including chronic sympathetic hyperactivity), which could increase cardiovascular vulnerability to hemodynamic challenges.

A method for assessment of the dynamic response of the arterial baroreflex

AIM

The baroreflex is a key mechanism in cardiovascular regulation, and alterations in baroreceptor function are seen in many diseases, including heart failure, obesity and hypertension. We propose a new method for analysing baroreceptor function from continuous blood pressure (BP) and heart rate (HR) in both health and disease.

METHODS

Forty-eight-hour data series of BP and HR were collected with telemetry. Sprague Dawley rats on standard chow (n = 11) served as controls, while rats on a high-fat, high-fructose (HFHC) diet (n = 6) constituted the obese-hypertensive model. A third group of rats underwent autonomic blockade (n = 6). An autoregressive-moving-average with exogenous inputs (ARMAX) model was applied to the data and compared with the α-coefficient.

RESULTS

Autonomic blockade caused a significant reduction in the strength of the baroreflex as estimated by ARMAX [ARMAX- baroreflex sensitivity (BRS)] -0.03 ± 0.01 vs. -0.19 ± 0.04 bpm heartbeat^-1) . Both methods showed a ~50% reduction in BRS in the obese-hypertensive group compared with control (body weight 531 ± 27 vs. 458 ± 19 g, P < 0.05; mean arterial pressure 119 ± 3 vs. 102 ± 1 mmHg, P < 0.05; ARMAX-BRS -0.08 ± 0.01 vs. -0.15 ± 0.01 bpm heartbeat^-1 , P < 0.05; α-coefficient BRS 0.51 ± 0.07 vs. 0.89 ± 0.07 ms mmHg^-1 , P < 0.05). The ARMAX method additionally showed the open-loop gain of the baroreflex to be reduced by ~50% in the obese-hypertensive group (-2.3 ± 0.3 vs. -4.1 ± 0.3 bpm, P < 0.05), while the rate constant was similar between groups.

CONCLUSION

The ARMAX model represents an efficient method for estimating several aspects of the baroreflex. The open-loop gain of the baroreflex was attenuated in obese-hypertensive rats compared with control, while the time response was similar. The algorithm can be applied to other species including humans.

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

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.