Non-linear Heart Rate and Blood Pressure Interaction in Response to Lower-Body Negative Pressure.

Ajay K Verma,Anita T Cote,Kouhyar Tavakolian,Andrew P Blaber,Da Xu,Nandu Goswami,Amanmeet Garg

doi:10.3389/fphys.2017.00767

Abstract

Early detection of hemorrhage remains an open problem. In this regard, blood pressure has been an ineffective measure of blood loss due to numerous compensatory mechanisms sustaining arterial blood pressure homeostasis. Here, we investigate the feasibility of causality detection in the heart rate and blood pressure interaction, a closed-loop control system, for early detection of hemorrhage. The hemorrhage was simulated via graded lower-body negative pressure (LBNP) from 0 to −40 mmHg. The research hypothesis was that a significant elevation of causal control in the direction of blood pressure to heart rate (i.e., baroreflex response) is an early indicator of central hypovolemia. Five minutes of continuous blood pressure and electrocardiogram (ECG) signals were acquired simultaneously from young, healthy participants (27 ± 1 years, N = 27) during each LBNP stage, from which heart rate (represented by RR interval), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were derived. The heart rate and blood pressure causal interaction (RR↔SBP and RR↔MAP) was studied during the last 3 min of each LBNP stage. At supine rest, the non-baroreflex arm (RR→SBP and RR→MAP) showed a significantly (p < 0.001) higher causal drive toward blood pressure regulation compared to the baroreflex arm (SBP→RR and MAP→RR). In response to moderate category hemorrhage (−30 mmHg LBNP), no change was observed in the traditional marker of blood loss i.e., pulse pressure (p = 0.10) along with the RR→SBP (p = 0.76), RR→MAP (p = 0.60), and SBP→RR (p = 0.07) causality compared to the resting stage. Contrarily, a significant elevation in the MAP→RR (p = 0.004) causality was observed. In accordance with our hypothesis, the outcomes of the research underscored the potential of compensatory baroreflex arm (MAP→RR) of the heart rate and blood pressure interaction toward differentiating a simulated moderate category hemorrhage from the resting stage. Therefore, monitoring baroreflex causality can have a clinical utility in making triage decisions to impede hemorrhage progression.

Highlights

Hemorrhage, a physiological condition resulting in central hypovolemia; owing to loss of blood from the circulation which leads to inadequate tissue perfusion (Schiller et al, 2017), is a major cause of death in soldiers and civilians following a trauma (Søreide et al, 2007; Evans et al, 2010; Eastridge et al, 2012; Rhee et al, 2014)
The current work studied the compensatory behavior responsible for blood pressure regulation with the progressing lower-body negative pressure (LBNP), of which the findings showcase the potential of causal heart rate and blood pressure interaction toward differentiating the severity of simulated hemorrhage
We demonstrated that nonbaroreflex causality dominates during resting stage followed by no significant (p > 0.05) change in response to the LBNP

Summary

Introduction

Hemorrhage, a physiological condition resulting in central hypovolemia; owing to loss of blood from the circulation which leads to inadequate tissue perfusion (Schiller et al, 2017), is a major cause of death in soldiers and civilians following a trauma (Søreide et al, 2007; Evans et al, 2010; Eastridge et al, 2012; Rhee et al, 2014). Reliance on arterial blood pressure as an early indicator of central blood loss has been ineffectual, due to various compensatory mechanisms maintaining arterial blood pressure homeostasis until the point of autonomic decompensation (Soller et al, 2008; Convertino et al, 2015). Blood pressure falls abruptly upon autonomic decompensation, followed by systemic hypotension, which, if not immediately compensated for, could result in tissue hypoperfusion (hemorrhagic shock; Victorino et al, 2003; Parks et al, 2006; Schiller et al, 2017). The quantification of compensatory mechanisms, corresponding to the maintenance of blood pressure homeostasis, could dispense paramount information pertaining to the progression of central hypovolemia (Nadler et al, 2014; Convertino et al, 2015, 2016; Janak et al, 2015)

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