ARMAX‐based Method Extends Knowledge of the Baroreflex

Abstract

IntroductionThe arterial baroreceptor‐heart rate reflex (baroreflex) is a key mechanism in regulating the cardiovascular system, and alterations in baroreceptor function are seen in many disease states, including heart failure, obesity and hypertension. Recent studies have identified impairment of the baroreflex early in the clinical course of hypertension. We propose a new and simple method for analyzing these alterations in baroreceptor function. The method is validated to describe dynamic relationships in causal systems with feedback, and in addition to the traditional estimate of baroreflex sensitivity (BRS) it adds information on two new valuable components of the reflex. Firstly, the average time for the baroreflex to reach its maximal effect on heart rate (HR) following a change in blood pressure (BP), and secondly, the average maximal change in HR produced by the baroreflex. This study aims to validate the method against a traditional method of estimating BRS in both healthy animals and in a verified model of diet‐induced obesity and hypertension.Methods48‐hour data series of continuous BP and HR recordings were collected with telemetry and used for analysis. 16‐weeks‐old SD rats on standard chow (n=11) served as healthy controls, while a similar group of rats on a high‐fat, high‐fructose (HFHC) diet from 4 weeks of age (n=6) constituted the obese hypertension model. An Autoregressive–moving‐average model with exogenous inputs (ARMAX)‐based algorithm was applied to the data series and compared with the α‐coefficient.ResultsThe ARMAX‐based method matched the traditional method, and interestingly when comparing the obese hypertension group with controls (body weight 531±27 vs. 458±19 g, p<0.05; mean arterial pressure 119±3 vs. 102±1 mmHg, p<0.05) the same degree of attenuation in BRS of ~50 % could be observed in the obese hypertensive group compared with controls with both methods (ARMAX: −0.08±0.01 vs. −0.15±0.01 Δbpm/heartbeat, p<0.05; α‐coefficient: 0.51±0.07 vs. 0.89±0.07 ms/mmHg, p<0.05). The ARMAX‐based method additionally demonstrated the maximal change in HR following a BP change to be reduced by ~50 % in the obese hypertensive group compared with controls (1.3±0.2 vs. −2.6±0.2 Δbpm, p<0.05), while the time until the maximal change in HR was reached was similar between groups.ConclusionThe ARMAX‐based method confirms traditional methods and presents an unbiased method of characterizing HR changes in response to changes in BP. The method further contributes to our understanding of the reflex by providing information on time to maximal change in HR as well as the degree of maximal change in HR. The presented algorithm can potentially be applied to other species including humans.Support or Funding InformationPregraduate Research Scholarship from The Danish Council for Independent Research, Grant from Fru Ruth König Petersens Foundation, Helge Peetz and Verner Peetz and Hustrus Scholarship.