Influence of acute epinephrine infusion on endotoxin-induced parameters of heart rate variability: a randomized controlled trial

Non-invasive ventral cervical magnetoneurography as a proxy of in vivo lipopolysaccharide-induced inflammation

Maintenance of autonomic homeostasis is continuously calibrated by sensory fibers of the vagus nerve and sympathetic chain that convey compound action potentials (CAPs) to the central nervous system. Lipopolysaccharide (LPS) intravenous challenge reliably elicits a robust inflammatory response that can resemble systemic inflammation and acute endotoxemia. Here, we administered LPS intravenously in nine healthy subjects while recording ventral cervical magnetoneurography (vcMNG)-derived CAPs at the rostral Right Nodose Ganglion (RNG) and the caudal Right Carotid Artery (RCA) with optically pumped magnetometers (OPM). We observed vcMNG RNG and RCA neural firing rates that tracked changes in TNF-α levels in the systemic circulation. Further, endotype subgroups based on high and low IL-6 responders segregate RNG CAP frequency (at 30-120 min) and based on high and low IL-10 response discriminate RCA CAP frequency (at 0-30 min). These vcMNG tools may enhance understanding and management of the neuroimmune axis that can guide personalized treatment based on an individual's distinct endophenotype.

My Life in HRV Biofeedback Research

This paper reviews the published work of me along with my students and close colleagues on the topic of heart rate variability biofeedback (HRVB). It includes early research by Vaschillo documenting resonance characteristics of the baroreflex system that causes large oscillations in heart rate when breathing at resonance frequency, research on heart rate variability as a marker of parasympathetic stress response in asthma, and HRVB as a treatment for asthma and depression. Many questions about HRVB remain unresolved, and important questions for future research are listed.

Case report: Autonomic and endocrine response in the process of brain death in a child with hypoxic-ischemic brain injury

BACKGROUND

The causes of brain death include cerebral herniation and brainstem ischemia. Neuroendocrine failure or a series of autonomic nervous system disorders are clinically recognized in the transition to brain death among patients with critical brain injuries. An accurate evaluation of these physiologic instabilities and biomarkers is essential to assess the severity and prognosis of pediatric brain injury as well as to initiate supportive care. This case report presents a detailed evaluation of the autonomic nervous system and endocrine function during the transition to brain death in infantile hypoxic-ischemic brain injury by analyzing the heart rate variability and endocrine status.

CASE PRESENTATION

A 1-year-old previously healthy boy went into cardiac arrest after choking on a toy at home. Although spontaneous circulation returned 60 min after cardiopulmonary resuscitation, no cerebral activity or brainstem reflexes were observed after 18 hospital days. The heart rate variability was assessed by analyzing the generic electrocardiogram data. Rapid spikes or drops in the total power of the heart rate variability, accompanied by a cortisol surge, as well as an alternating surge of high- and low-frequency domain variables were detected in the process of brain death.

CONCLUSION

The heart rate variability assessment combined with endocrine provides a better understanding of the clinical course of patients undergoing brain death. It accurately detects the loss of brainstem function, which allows physicians to provide the appropriate supportive care.

Stress and the "extended" autonomic system

This review updates three key concepts of autonomic neuroscience-stress, the autonomic nervous system (ANS), and homeostasis. Hans Selye popularized stress as a scientific idea. He defined stress variously as a stereotyped response pattern, a state that evokes this pattern, or a stimulus that evokes the state. According to the "homeostat" theory stress is a condition where a comparator senses a discrepancy between sensed afferent input and a response algorithm, the integrated error signal eliciting specific patterns of altered effector outflows. Scientific advances since Langley's definition of the ANS have incited the proposal here of the "extended autonomic system," or EAS, for three reasons. (1) Several neuroendocrine systems are bound inextricably to Langley's ANS. The first to be described, by Cannon in the early 1900s, involves the hormone adrenaline, the main effector chemical of the sympathetic adrenergic system. Other neuroendocrine systems are the hypothalamic-pituitary-adrenocortical system, the arginine vasopressin system, and the renin-angiotensin-aldosterone system. (2) An evolving body of research links the ANS complexly with inflammatory/immune systems, including vagal anti-inflammatory and catecholamine-related inflammasomal components. (3) A hierarchical network of brain centers (the central autonomic network, CAN) regulates ANS outflows. Embedded within the CAN is the central stress system conceptualized by Chrousos and Gold. According to the allostasis concept, homeostatic input-output curves can be altered in an anticipatory, feed-forward manner; and prolonged or inappropriate allostatic adjustments increase wear-and-tear (allostatic load), resulting in chronic, stress-related, multi-system disorders. This review concludes with sections on clinical and therapeutic implications of the updated concepts offered here.

Wearable Patch Heart Rate Variability is An Early Marker of Systemic Inflammation During Experimental Human Endotoxemia

INTRODUCTION

Early diagnosis and treatment can reduce the risk of organ failure and mortality in systemic inflammatory conditions. Heart rate variability (HRV) has potential for early identification of the onset of systemic inflammation, as it may detect changes in sympathetic nervous system activity resulting from the developing inflammatory response before clinical signs appear. With the use of new methodologies, we investigated the onset and kinetics of HRV changes as well as several inflammatory parameters and symptoms during experimental human endotoxemia, a model of systemic inflammation in humans in vivo.

MATERIAL AND METHODS

Healthy volunteers were intravenously administered lipopolysaccharide (LPS, n = 15) or placebo (n = 15). HRV was determined using a wireless wearable device, and parameters low to high frequency (LF:HF) ratio, root mean square of the successive differences (RMSSD), and standard deviation of normal-to-normal R-R intervals (SDNN)were calculated through 1-min-rolling 6-minute windows. Plasma cytokine levels and flu-like symptoms and vital signs were serially assessed.

RESULTS

The increase in LF:HF ratio, reflecting sympathetic predominance, was more pronounced in the LPS group compared to the placebo group, with the difference becoming statistically significant 65 minutes following LPS administration (1.63 [1.42-1.83] vs. 1.28 [1.11-1.44], p = 0.005). Significant between-group differences in RMSSD and SDNN were observed from 127 and 140 minutes post-LPS administration onwards, respectively. Plasma cytokine levels showed significant between-group differences staring 60 minutes post-LPS. For symptom score, heart rate, temperature and diastolic blood pressure, significant differences compared with the placebo group were observed at 90, 118, 120, and 124 minutes post-LPS, respectively.

CONCLUSION

In a controlled human model of systemic inflammation, elevations in the LF:HF ratio followed very shortly after elevations in plasma cytokine levels and preceded onset of flu-like symptoms and alterations in vital signs. HRV may represent a promising non-invasive tool for early detection of a developing systemic inflammatory response.

The extended autonomic system, dyshomeostasis, and COVID-19

The pandemic viral illness COVID-19 is especially life-threatening in the elderly and in those with any of a variety of chronic medical conditions. This essay explores the possibility that the heightened risk may involve activation of the "extended autonomic system" (EAS). Traditionally, the autonomic nervous system has been viewed as consisting of the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. Over the past century, however, neuroendocrine and neuroimmune systems have come to the fore, justifying expansion of the meaning of "autonomic." Additional facets include the sympathetic adrenergic system, for which adrenaline is the key effector; the hypothalamic-pituitary-adrenocortical axis; arginine vasopressin (synonymous with anti-diuretic hormone); the renin-angiotensin-aldosterone system, with angiotensin II and aldosterone the main effectors; and cholinergic anti-inflammatory and sympathetic inflammasomal pathways. A hierarchical brain network-the "central autonomic network"-regulates these systems; embedded within it are components of the Chrousos/Gold "stress system." Acute, coordinated alterations in homeostatic settings (allostasis) can be crucial for surviving stressors such as traumatic hemorrhage, asphyxiation, and sepsis, which throughout human evolution have threatened homeostasis; however, intense or long-term EAS activation may cause harm. While required for appropriate responses in emergencies, EAS activation in the setting of chronically decreased homeostatic efficiencies (dyshomeostasis) may reduce thresholds for induction of destabilizing, lethal vicious cycles. Testable hypotheses derived from these concepts are that biomarkers of EAS activation correlate with clinical and pathophysiologic data and predict outcome in COVID-19 and that treatments targeting specific abnormalities identified in individual patients may be beneficial.

Effects of epinephrine on heart rate variability and cytokines in a rat sepsis model

Catecholamines have both anti-inflammatory and vasoactive properties. A decreased cardiac response to catecholamines has been associated with a high risk of death in sepsis and septic shock. The aim of this study was to investigate the effects of epinephrine (EPI) on heart rate variability (HRV) and autonomic balance, as well as cytokine levels, in a rat sepsis model. Thirty-six male Sprague-Dawley rats were assigned to 4 experimental groups and 2 control groups of 6 rats each. The rats in the experimental groups were inoculated with a lipopolysaccharide (LPS, endotoxin) to establish a sepsis model. Group A received only LPS; group B received LPS, antecedent EPI and the nonselective β-blocker propranolol; group C received LPS and antecedent EPI; and group D received LPS, antecedent EPI and the selective β1-blocker esmolol. One control group received EPI and the other received saline placebo. Heart rate variability (HRV) was analyzed and tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) levels were measured. Measurements were carried out at baseline, at 0 hour after EPI infusion, and at 0.5, 2, and 4 hours after LPS inoculation. There were significant differences in HRV and cytokine levels between the groups, indicating that LPS infusion caused autonomic imbalance. Antecedent EPI significantly decreased the level of TNF-α in group C compared with group A in which TNF-α level peaked at 2 hours and then declined. Propranolol (group B) but not esmolol (group D) administration resulted in elevated TNF-α levels, comparable to those observed in group A. In conclusion, antecedent administration of EPI in a rat sepsis model inhibits the production of TNF-α possibly via the β2-adrenoceptor.

Arrhythmia induction using isoproterenol or epinephrine during electrophysiology study for supraventricular tachycardia

BACKGROUND

Electrophysiology study (EPS) is an important part of the diagnosis and workup for supraventricular tachycardia (SVT). Provocative medications are used to induce arrhythmias, when they are not inducible at baseline. The most common medication is the β1-specific agonist, isoproterenol, but recent price increases have resulted in a shift toward the nonspecific agonist, epinephrine.

OBJECTIVE

We hypothesize that isoproterenol is a better induction agent for SVT during EPS than epinephrine.

METHODS

We created a retrospective cohort of 131 patients, who underwent EPS and required medication infusion with either isoproterenol or epinephrine for SVT induction. The primary outcome was arrhythmia induction.

RESULTS

Successful induction was achieved in 71% of isoproterenol cases and 53% of epinephrine cases (P = 0.020). Isoproterenol was significantly better than epinephrine for SVT induction during EPS (odds ratio [OR], 2.35; 95% confidence interval [CI], 1.14-4.85; P = 0.021). There was no difference in baseline variables or complications between the two groups. Other variables associated with successful arrhythmia induction included a longer procedure duration and atrioventricular nodal re-entry tachycardia as the clinical arrhythmia. In a multivariable model, isoproterenol remained significantly associated with successful induction (OR, 2.57; 95% CI, 1.002-6.59; P = 0.05).

CONCLUSIONS

Isoproterenol was significantly better than epinephrine for SVT arrhythmia induction. However, epinephrine was safe and successfully induced arrhythmias in the majority of patients who received it. Furthermore, when atropine was added in epinephrine-refractory cases, in a post hoc analysis there was no difference in arrhythmia induction between medications. Cost savings could thus be significant without compromising safety.

Proposed mechanisms of relative bradycardia

Relative bradycardia is the term used to describe the mechanism where there is dissociation between pulse and temperature. This finding is important to recognize since it may provide further insights into the potential underlying causes of disease. There is no known proposed mechanism to explain this phenomenon. We hypothesize that relative bradycardia is the central mechanism reflecting and influenced potentially by the direct pathogenic effect on the sinoatrial node as well as cross-talk between the autonomic nervous system and immune system. Cardiac pacemaker cells may act as a target for inflammatory cytokines leading to alteration in heart rate dynamics or their responsiveness to neurotransmitters during systemic inflammation. These factors account for the important role of how the host response to infectious and non-infectious causes influences the appearance of relative bradycardia. We propose several methods that may be useful to confirm the proposed theoretical framework to further enhance our understanding of this paradoxical phenomenon. This includes measuring, during the episode of relative bradycardia, proinflammatory and anti-inflammatory cytokines, monitoring heart rate variability (HRV), and assessing underlying comorbidities and outcomes in patients with the same disease.

Identification of cytokine-specific sensory neural signals by decoding murine vagus nerve activity

The nervous system maintains physiological homeostasis through reflex pathways that modulate organ function. This process begins when changes in the internal milieu (e.g., blood pressure, temperature, or pH) activate visceral sensory neurons that transmit action potentials along the vagus nerve to the brainstem. IL-1β and TNF, inflammatory cytokines produced by immune cells during infection and injury, and other inflammatory mediators have been implicated in activating sensory action potentials in the vagus nerve. However, it remains unclear whether neural responses encode cytokine-specific information. Here we develop methods to isolate and decode specific neural signals to discriminate between two different cytokines. Nerve impulses recorded from the vagus nerve of mice exposed to IL-1β and TNF were sorted into groups based on their shape and amplitude, and their respective firing rates were computed. This revealed sensory neural groups responding specifically to TNF and IL-1β in a dose-dependent manner. These cytokine-mediated responses were subsequently decoded using a Naive Bayes algorithm that discriminated between no exposure and exposures to IL-1β and TNF (mean successful identification rate 82.9 ± 17.8%, chance level 33%). Recordings obtained in IL-1 receptor-KO mice were devoid of IL-1β-related signals but retained their responses to TNF. Genetic ablation of TRPV1 neurons attenuated the vagus neural signals mediated by IL-1β, and distal lidocaine nerve block attenuated all vagus neural signals recorded. The results obtained in this study using the methodological framework suggest that cytokine-specific information is present in sensory neural signals within the vagus nerve.

Low-Dose Epinephrine Plus Tranexamic Acid Reduces Early Postoperative Blood Loss and Inflammatory Response: A Randomized Controlled Trial

BACKGROUND

The reductions of perioperative blood loss and inflammatory response are important in total knee arthroplasty. Tranexamic acid reduced blood loss and the inflammatory response in several studies. However, the effect of epinephrine administration plus tranexamic acid has not been intensively investigated, to our knowledge. In this study, we evaluated whether the combined administration of low-dose epinephrine plus tranexamic acid reduced perioperative blood loss or inflammatory response further compared with tranexamic acid alone.

METHODS

This randomized placebo-controlled trial consisted of 179 consecutive patients who underwent primary total knee arthroplasty. Patients were randomized into 3 interventions: Group IV received intravenous low-dose epinephrine plus tranexamic acid, Group TP received topical diluted epinephrine plus tranexamic acid, and Group CT received tranexamic acid alone. The primary outcome was perioperative blood loss on postoperative day 1. Secondary outcomes included perioperative blood loss on postoperative day 3, coagulation and fibrinolysis parameters (measured by thromboelastography), inflammatory cytokine levels, transfusion values (rate and volume), thromboembolic complications, length of hospital stay, wound score, range of motion, and Hospital for Special Surgery (HSS) score.

RESULTS

The mean calculated total blood loss (and standard deviation) in Group IV was 348.1 ± 158.2 mL on postoperative day 1 and 458.0 ± 183.4 mL on postoperative day 3, which were significantly reduced (p < 0.05) compared with Group TP at 420.5 ± 188.4 mL on postoperative day 1 and 531.1 ± 231.4 mL on postoperative day 3 and Group CT at 520.4 ± 228.4 mL on postoperative day 1 and 633.7 ± 237.3 mL on postoperative day 3. Intravenous low-dose epinephrine exhibited a net anti-inflammatory activity in total knee arthroplasty and did not induce an obvious hypercoagulable status. Transfusion values were significantly reduced (p < 0.05) in Group IV, but no significant differences were observed in the incidence of thromboembolic complications, wound score, range of motion, and HSS score among the 3 groups (p > 0.05).

CONCLUSIONS

The combined administration of low-dose epinephrine and tranexamic acid demonstrated an increased effect in reducing perioperative blood loss and the inflammatory response compared with tranexamic acid alone, with no apparent increased incidence of thromboembolic and other complications.

LEVEL OF EVIDENCE

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Effects of low-dose epinephrine on perioperative hemostasis and inflammatory reaction in major surgical operations: a randomized clinical trial

Essentials Blood loss and immune reaction are closely related to morbidity and recovery after surgery. We studied the effect of epinephrine plus tranexamic acid on blood loss and immune reaction. Epinephrine plus tranexamic acid reduced postoperative total blood loss and immune reaction. Epinephrine plus tranexamic acid did not increase the incidence of complications.

SUMMARY

Background Hemostasis, thrombosis and surgical stress-induced immune reactions are important for perioperative morbidity and recovery after major surgical operations. Objectives To evaluate the effects of combined administration of low-dose epinephrine (LDEPI) and tranexamic acid (TXA) on perioperative blood loss, thromboembolic complications and inflammatory responses in patients undergoing total hip arthroplasty (THA). Patients/Methods Patients scheduled for THA (n = 195) were randomized into three interventions: intravenous LDEPI plus TXA (group IV); topical diluted epinephrine plus TXA (group TP); and TXA alone as control (group CT). The primary outcome was perioperative blood loss on postoperative day (POD) 1. Secondary outcomes included perioperative blood loss on POD 3, intraoperative blood loss, volume of drainage, transfusion values, coagulation and fibrinolysis parameters, inflammatory cytokine levels, cases of thrombosis, intravenous fluid on the operation day, and length of hospital stay. Results The mean calculated amounts of total blood loss in groups IV, TP and CT were 631.2 mL, 760.5 mL, and 825.6 mL, respectively, on POD 1; treatment effects (differences) were 194.4 mL (95% confidence interval [CI] 146.7-242.0) and 65.0 mL (95% CI 17.4-112.7). Groups IV and TP had lower levels of proinflammatory cytokines (tumor necrosis factor-α and interleukin [IL]-1β) and higher levels of the anti-inflammatory cytokine IL-10, and showed faster development of coagulation and fibrinolysis (without change in peak levels), than group CT early postoperation. No differences were observed in transfusion, thromboembolic and other outcomes among the groups. Conclusion The combined administration of LDEPI and TXA was more effective in reducing perioperative blood loss and alleviating the inflammatory response than TXA alone, without increasing the incidence of thromboembolic and other complications.

Understanding Physiology in the Continuum: Integration of Information from Multiple -Omics Levels

In this paper, we discuss approaches for integrating biological information reflecting diverse physiologic levels. In particular, we explore statistical and model-based methods for integrating transcriptomic, proteomic and metabolomics data. Our case studies reflect responses to a systemic inflammatory stimulus and in response to an anti-inflammatory treatment. Our paper serves partly as a review of existing methods and partly as a means to demonstrate, using case studies related to human endotoxemia and response to methylprednisolone (MPL) treatment, how specific questions may require specific methods, thus emphasizing the non-uniqueness of the approaches. Finally, we explore novel ways for integrating -omics information with PKPD models, toward the development of more integrated pharmacology models.

Differential Patterns and Determinants of Cardiac Autonomic Nerve Dysfunction during Endotoxemia and Oral Fat Load in Humans

The autonomic nervous system (ANS) plays an important role in regulating the metabolic homeostasis and controlling immune function. ANS alterations can be detected by reduced heart rate variability (HRV) in conditions like diabetes and sepsis. We determined the effects of experimental conditions mimicking inflammation and hyperlipidemia on HRV and heart rate (HR) in relation to the immune, metabolic, and hormonal responses resulting from these interventions. Sixteen lean healthy subjects received intravenous (i.v.) low-dose endotoxin (lipopolysaccharide [LPS]), i.v. fat, oral fat, and i.v. glycerol (control) for 6 hours, during which immune, metabolic, hormonal, and five HRV parameters (pNN50, RMSSD, low-frequency (LF) and high-frequency (HF) power, and LF/HF ratio) were monitored and energy metabolism and insulin sensitivity (M-value) were assessed. LPS infusion induced an increase (AUC) in HR and LF/HF ratio and decline in pNN50 and RMSSD, while oral fat resulted in elevated HR and a transient (hours 1-2) decrease in pNN50, RMSSD, and HF power. During LPS infusion, ΔIL-1ra levels and ΔIL-1ra and ΔIL-1ß gene expression correlated positively with ΔLF/HF ratio and inversely with ΔRMSSD. During oral fat intake, ΔGLP-1 tended to correlate positively with ΔHR and inversely with ΔpNN50 and ΔRMSSD. Following LPS infusion, lipid oxidation correlated positively with HR and inversely with pNN50 and RMSSD, whereas HRV was not related to M-value. In conclusion, suppression of vagal tone and sympathetic predominance during endotoxemia are linked to anti-inflammatory processes and lipid oxidation but not to insulin resistance, while weaker HRV changes in relation to the GLP-1 response are noted during oral fat load.

Day-night variation in heart rate variability changes induced by endotoxaemia in healthy volunteers

BACKGROUND

Morbidity and mortality in response to sepsis may be dependent on clock time for the initiation of sepsis. Endotoxaemia, an experimental model for systemic inflammation, induces alterations in sympatico-vagal balance in the autonomic nervous system (ANS). The activity of sympathetic and parasympathetic activity can be estimated by measuring heart rate variability (HRV). Based on the intimate link between ANS and the inflammatory response, we hypothesized, that HRV changes seen during endotoxaemia would be different based on time of the day the endotoxaemia is initiated. We investigated day/night variation in endotoxaemia-induced changes in HRV.

METHODS

A randomized, crossover study with 12 healthy men (age 18-31) was conducted. Endotoxaemia were induced by lipopolysaccharide (LPS) endotoxin 0.3 ng/kg b.w. in two visits (day visit and night visit). At the day visit, endotoxaemia were induced at 12:00 h, and at the night visit it was induced at 24:00 h. Holter recordings were started 1 h before administration of LPS, and continued for 10 h. Time-domain and frequency-domain parameters of HRV were analysed.

RESULTS

A total of nine persons finished the study with valid recordings. Endotoxaemia at both night and day resulted in a significant depression in HRV parameters high-frequency power (HF), low-frequency power (LF), standard deviation of normal-to-normal (NN) intervals, root mean square of successive differences and proportion of NN50 divided by total number of NNs (P<0.001). The ratio LF/HF and mean heart rate significantly increased by endotoxaemia (P<0.001). At night-time endotoxaemia, a more pronounced depression of LF, HF and SDNN (P<0.01) and a more pronounced increase in the ratio of LF/HF and mean heart rate (P<0.01) occurred compared with day-time endotoxaemia.

CONCLUSION

Endotoxaemia induced changes in HRV exhibit a day-night difference. This difference may have clinical consequences in patients with sepsis.

A Double-Blinded Randomized Trial to Compare the Effectiveness of Minimally Invasive Procedures Using Patient-Reported Outcomes

BACKGROUND

The Institute of Medicine has included the comparison of minimally invasive surgical techniques in its research agenda. This study seeks to evaluate a model for the comparison of minimally invasive procedures using patient-reported outcomes.

STUDY DESIGN

A double-blinded randomized controlled trial (NCT01489436) was conducted. Baseline data were obtained, standardized anesthesia was induced, and patients were randomized to single-port (SP) or 4-port (FP) laparoscopic cholecystectomy. Perioperative care was standardized. The outcomes were pain (Visual Analog Scale) on postoperative day 1 (primary) and quality of life (Patient-Reported Outcomes Measures Information System and Linear Analog Self-Assessment), serum cytokines, and heart rate variability (secondary). Analysis was intention to treat. Using identical occlusive dressings, patients and the outcomes assessor remained blinded until postoperative day 2.

RESULTS

Fifty-five patients were randomized to each arm. There was no difference in demographics. Visual Analog Scale pain score on postoperative day 1 was significantly different from baseline in each group (SP: 1.6 ± 1.9 to 4.2 ± 2.4 vs FP: 1.8 ± 2.3 to 4.2 ± 2.2), but not different from each other (p = 0.83). Patients in the FP arm reported significantly less fatigue on postoperative day 7 than patients in the SP group (3.1 ± 2.1 vs 4.2 ± 2.2; p = 0.009). Fewer patients in the FP group required postoperative oral narcotics before discharge (40% vs 60%; p = 0.056). Cytokines levels and heart rate variability were similar between arms. In patients followed for >1 year, no difference in umbilical hernia rates was noted.

CONCLUSIONS

Early postoperative quality of life data captured differences in fatigue, indicating improved recovery after FP within a controlled trial. Physiologic measures were similar, suggesting that the differences between SP and FP are minimal.

A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability

Heart rate variability (HRV), the change in the time intervals between adjacent heartbeats, is an emergent property of interdependent regulatory systems that operate on different time scales to adapt to challenges and achieve optimal performance. This article briefly reviews neural regulation of the heart, and its basic anatomy, the cardiac cycle, and the sinoatrial and atrioventricular pacemakers. The cardiovascular regulation center in the medulla integrates sensory information and input from higher brain centers, and afferent cardiovascular system inputs to adjust heart rate and blood pressure via sympathetic and parasympathetic efferent pathways. This article reviews sympathetic and parasympathetic influences on the heart, and examines the interpretation of HRV and the association between reduced HRV, risk of disease and mortality, and the loss of regulatory capacity. This article also discusses the intrinsic cardiac nervous system and the heart-brain connection, through which afferent information can influence activity in the subcortical and frontocortical areas, and motor cortex. It also considers new perspectives on the putative underlying physiological mechanisms and properties of the ultra-low-frequency (ULF), very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) bands. Additionally, it reviews the most common time and frequency domain measurements as well as standardized data collection protocols. In its final section, this article integrates Porges' polyvagal theory, Thayer and colleagues' neurovisceral integration model, Lehrer et al.'s resonance frequency model, and the Institute of HeartMath's coherence model. The authors conclude that a coherent heart is not a metronome because its rhythms are characterized by both complexity and stability over longer time scales. Future research should expand understanding of how the heart and its intrinsic nervous system influence the brain.

Anti-inflammatory activity of iridoid and catechol derivatives from Eucommia ulmoides Oliver

Neuroinflammation and pro-inflammatory mediators play key roles in the pathogenesis of neurodegenerative diseases including stroke, which account for a significant burden of morbidity and mortality worldwide. Recently, the unsatisfactory pharmacotherapy and side effects of the drugs led to the development of alternative medicine for treating these diseases. Du Zhong (DZ), Eucommia ulmoides Oliver leaves, is a commonly used herb in the therapy of stroke in China. We hypothesize that the components from DZ inhibit neuroinflammation. In this study, DZ was extracted and the bioactive fractions with inhibitory effect on lipopolysaccharide (LPS)-stimulated nitric oxide (NO) production in BV-2 microglial cells were further separated using chromatography. Two purified bioactive compounds, genipin (compound C) and 4-(1,2-dimethoxyethyl)benzene-1,2-diol (compound F), were isolated and identified after spectroscopic analysis. The results showed that they inhibited LPS-stimulated NO and tumor necrosis factor-alpha (TNF-α) production. Genipin exerted its anti-inflammatory effects through PI3K/Akt signaling pathway, whereas compound F inhibited phosphorylation of p38 mitogen-activated protein kinase (MAPK). In conclusion, genipin and compound F have potential for developing into new drugs for treating neurodegenerative diseases.

Temporal metabolic profiling of plasma during endotoxemia in humans

Endotoxemia induced by the administration of low-dose lipopolysaccharide (LPS) to healthy human volunteers is a well-established experimental protocol and has served as a reproducible platform for investigating the responses to systemic inflammation. Because metabolic composition of a tissue or body fluid is uniquely altered by stimuli and provides information about the dominant regulatory mechanisms at various cellular processes, understanding the global metabolic response to systemic inflammation constitutes a major part in this investigation complementing the studies undertaken so far in both clinical and systems biology fields. This article communicates the first proof-of-principle metabonomic analysis, which comprised global biochemical profiles in human plasma samples from healthy subjects given intravenous endotoxin at 2 ng/kg. Concentrations of a total of 366 plasma biochemicals were determined in archived blood samples collected from 15 endotoxin-treated subjects at five time points within 24 h after treatment and compared with control samples collected from four saline-treated subjects. Principal component analysis within this data set determined the sixth hour as a critical time point separating development and recovery phases of the LPS-induced metabolic changes. Consensus clustering of the differential metabolites identified two distinct subsets of metabolites that displayed common coherent profiles with opposing directionality. The first group of metabolites, which were mostly associated with pathways related to lipid metabolism, was upregulated within the first 6 h and downregulated by the 24th hour following LPS administration. The second group of metabolites, in contrast, was first downregulated until the sixth hour, then upregulated. Metabolites in this group were predominantly amino acids or their derivatives. In summary, nontargeted biochemical profiling and unsupervised multivariate analyses highlighted the prominent roles of lipid and protein metabolism in regulating the response to systemic inflammation while also revealing their dynamics in opposite directions.

On heart rate variability and autonomic activity in homeostasis and in systemic inflammation

Analysis of heart rate variability (HRV) is a promising diagnostic technique due to the noninvasive nature of the measurements involved and established correlations with disease severity, particularly in inflammation-linked disorders. However, the complexities underlying the interpretation of HRV complicate understanding the mechanisms that cause variability. Despite this, such interpretations are often found in literature. In this paper we explored mathematical modeling of the relationship between the autonomic nervous system and the heart, incorporating basic mechanisms such as perturbing mean values of oscillating autonomic activities and saturating signal transduction pathways to explore their impacts on HRV. We focused our analysis on human endotoxemia, a well-established, controlled experimental model of systemic inflammation that provokes changes in HRV representative of acute stress. By contrasting modeling results with published experimental data and analyses, we found that even a simple model linking the autonomic nervous system and the heart confound the interpretation of HRV changes in human endotoxemia. Multiple plausible alternative hypotheses, encoded in a model-based framework, equally reconciled experimental results. In total, our work illustrates how conventional assumptions about the relationships between autonomic activity and frequency-domain HRV metrics break down, even in a simple model. This underscores the need for further experimental work towards unraveling the underlying mechanisms of autonomic dysfunction and HRV changes in systemic inflammation. Understanding the extent of information encoded in HRV signals is critical in appropriately analyzing prior and future studies.

Modeling physiologic variability in human endotoxemia

The control and management of inflammation is a key aspect of clinical care for critical illnesses such as sepsis. In an ideal reaction to injury, the inflammatory response provokes a strong enough response to heal the injury and then restores homeostasis. When inflammation becomes dysregulated, a persistent inflammatory state can lead to significant deleterious effects and clinical challenges. Thus, gaining a better biological understanding of the mechanisms driving the inflammatory response is of the utmost importance. In this review, we discuss our work with the late Stephen F. Lowry to investigate systemic inflammation through systems biology of human endotoxemia. We present our efforts in modeling the human endotoxemia response with a particular focus on physiologic variability. Through modeling, with a focus ultimately on translational applications, we obtain more fundamental understanding of relevant physiological processes. And by taking advantage of the information embedded in biological rhythms, ranging in time scale from high-frequency autonomic oscillations reflected in heart rate variability to circadian rhythms in inflammatory mediators, we gain insight into the underlying physiology.

Continuous enteral and parenteral feeding each reduces heart rate variability but differentially influences monocyte gene expression in humans

Enteral (EN) or parenteral (PN) nutrition is used to support critically ill patients until oral feeding resumes. Enteral nutrition is assumed preferable to PN, but the differential influence on immune function is not well defined. Autonomic nervous activity is known to influence innate immune responses, and we hypothesized that EN and PN could influence both autonomic signaling and gene activation in peripheral blood monocytes (PBMs). Ten subjects (aged 18-36 years) received continuous EN or PN for 72 h. Peripheral blood monocytes were isolated from whole blood before and after continuous feeding and were analyzed for gene expression using a microarray platform. Gene expression after feeding was compared from baseline and between groups. To measure autonomic outflow, subjects also underwent heart rate variability (HRV) monitoring during feeding. Time and frequency domain HRV data were compared between groups and five orally fed subjects for changes from baseline and changes over time. During continuous EN and PN, subjects exhibited declines in both time and frequency domain HRV parameters compared with baseline and with PO subjects, indicating a loss of vagal/parasympathetic tone. However, PN feeding had a much greater influence on PBM gene expression compared with baseline than EN, including genes important to innate immunity. Continuous EN and PN are both associated with decreasing vagal tone over time, yet contribute differently to PBM gene expression, in humans. These preliminary findings support assumptions that PN imposes a systemic inflammatory risk but also imply that continuous feeding, independent of route, may impart additional risk through different mechanisms.

Translational applications of evaluating physiologic variability in human endotoxemia

Dysregulation of the inflammatory response is a critical component of many clinically challenging disorders such as sepsis. Inflammation is a biological process designed to lead to healing and recovery, ultimately restoring homeostasis; however, the failure to fully achieve those beneficial results can leave a patient in a dangerous persistent inflammatory state. One of the primary challenges in developing novel therapies in this area is that inflammation is comprised of a complex network of interacting pathways. Here, we discuss our approaches towards addressing this problem through computational systems biology, with a particular focus on how the presence of biological rhythms and the disruption of these rhythms in inflammation may be applied in a translational context. By leveraging the information content embedded in physiologic variability, ranging in scale from oscillations in autonomic activity driving short-term heart rate variability to circadian rhythms in immunomodulatory hormones, there is significant potential to gain insight into the underlying physiology.

Experimental human endotoxemia: a model of the systemic inflammatory response syndrome?

BACKGROUND

The normal human intravenous endotoxin model has been used for more than 50 years. It was once considered a possible model of sepsis, but, because no infection is present, it is better described as a model of systemic inflammation. We demonstrate herein that at least three of four systemic inflammatory response syndrome (SIRS) criteria are achieved with the model.

METHODS

Otherwise healthy human volunteers were given Escherichia coli endotoxin 2 ng/kg intravenously. Vital signs were monitored, and blood samples were collected over time for assessment of white blood cells (WBCs), cytokines, counter-regulatory hormones, and monocyte receptors.

RESULTS

The means of three variables (core temperature, heart rate, WBC) met the SIRS criteria. Compared with baseline, cytokines were elevated acutely, with tumor necrosis factor-alpha (TNFα) exhibiting temporal primacy over the other cytokines. Counter-regulatory hormones (cortisol, epinephrine) also were elevated acutely. Finally, the monocyte cell-surface receptors cluster of differentiation molecule (CD) 11b and TNF receptor-II were elevated and decreased, respectively.

CONCLUSIONS

The experimental human endotoxin model satisfies SIRS criteria and probably is best described as a model of Toll-like receptor 4 agonist-induced systemic inflammation.

Influence of different breathing patterns on heart rate variability indices and reproducibility during experimental endotoxaemia in human subjects

HRV (heart rate variability) analysis is a widely employed method to assess cardiac autonomic nervous system activity. Accurate HRV measurement is critical to its value as a diagnostic and prognostic tool. Different breathing patterns may affect HRV, but results obtained under static conditions are conflicting. HRV indices decrease considerably during systemic inflammation evoked by experimental endotoxaemia, enabling the determination of the effects of different breathing patterns on HRV in a dynamic setting. We investigated the impact of different breathing patterns on short-term HRV measurements during experimental endotoxaemia. Furthermore, we assessed whether paced breathing improved HRV reproducibility. Twelve healthy male volunteers received an intravenous bolus (2 ng/kg of body weight) of endotoxin [LPS (lipopolysaccharide), derived from Escherichia coli O:113] on two occasions with an interval of 2 weeks. Five-minute HRV recordings were performed just prior to LPS administration and hourly thereafter until 8 h post-LPS. Three breathing protocols were employed every hour: (i) spontaneous breathing, (ii) metronome-guided breathing at the subject's normal respiratory rate ('paced') and (iii) metronome-guided breathing at 150% of the subject's normal respiratory rate ('mild hyperventilation'). LPS administration resulted in a sharp decrease in all of the HRV indices measured, which was similar during both LPS administrations. Neither paced breathing nor mild hyperventilation influenced HRV indices compared with spontaneous breathing. Paced breathing did not improve reproducibility as it did not exert a significant effect on intra-subject coefficients of variation and intra-class correlation coefficients (calculated between both visits). In conclusion, over a wide range of HRV magnitudes during experimental endotoxaemia, neither paced breathing nor mild hyperventilation affected HRV indices. Moreover, paced breathing did not result in a significant improvement in reproducibility. Therefore employing a paced breathing protocol is not required to obtain valid HRV data during endotoxaemia.

Immune, inflammatory and cardiovascular consequences of sleep restriction and recovery

In addition to its effects on cognitive function, compelling evidence links sleep loss to alterations in the neuroendocrine, immune and inflammatory systems with potential negative public-health ramifications. The evidence to suggest that shorter sleep is associated with detrimental health outcomes comes from both epidemiological and experimental sleep deprivation studies. This review will focus on the post-sleep deprivation and recovery changes in immune and inflammatory functions in well-controlled sleep restriction laboratory studies. The data obtained indicate non-specific activation of leukocyte populations and a state of low-level systemic inflammation after sleep loss. Furthermore, one night of recovery sleep does not allow full recovery of a number of these systemic immune and inflammatory markers. We will speculate on the mechanism(s) that link(s) sleep loss to these responses and to the progression of cardiovascular disease. The immune and inflammatory responses to chronic sleep restriction suggest that chronic exposure to reduced sleep (<6 h/day) and insufficient time for recovery sleep could have gradual deleterious effects, over years, on cardiovascular pathogenesis with a heightened risk in women and in night and shift workers. Finally, we will examine countermeasures, e.g., napping or sleep extension, which could improve the recovery processes, in terms of alertness and immune and inflammatory parameters, after sleep restriction.

A physiological model for autonomic heart rate regulation in human endotoxemia

The systemic inflammatory response syndrome often accompanies critical illnesses and can be an important cause of morbidity and mortality. Marked abnormalities in cardiovascular function accompany acute illnesses manifested as sustained tachyarrhythmias, which are but one component of systemic dysregulation. The realization that cardiac pacemaker activity is under control of the autonomic nervous system has promoted the analysis of heart rate (HR) variation for assessing autonomic activities. In acute illnesses, autonomic imbalance manifesting in part as parasympathetic attenuation is associated with increased morbidity in patients who manifest systemic inflammatory response syndrome phenotype. Driven by the premise that biological phenotypes emerge as the outcome of the coordinated action of network elements across the host, a multiscale model of human endotoxemia, as a prototype model of systemic inflammation in humans, is developed that quantifies critical aspects of the complex relationship between inflammation and autonomic HR regulation. In the present study, changes in HR response to acute injury, phenotypically expressed as tachycardia, are simulated as a result of autonomic imbalance that reflects sympathetic activity excess and parasympathetic attenuation. The proposed model assesses both the anti-inflammatory and cardiovascular effects of antecedent stresses upon the systemic inflammatory manifestations of human endotoxemia as well as a series of nonlinear inflammatory relevant scenarios. Such a modeling approach provides a comprehensive conceptual framework linking inflammation and physiological complexity via a multiscale model that may advance the translational potential of systems modeling in clinical research.

Modeling autonomic regulation of cardiac function and heart rate variability in human endotoxemia

Heart rate variability (HRV), the quantification of beat-to-beat variability, has been studied as a potential prognostic marker in inflammatory diseases such as sepsis. HRV normally reflects significant levels of variability in homeostasis, which can be lost under stress. Much effort has been placed in interpreting HRV from the perspective of quantitatively understanding how stressors alter HRV dynamics, but the molecular and cellular mechanisms that give rise to both homeostatic HRV and changes in HRV have received less focus. Here, we develop a mathematical model of human endotoxemia that incorporates the oscillatory signals giving rise to HRV and their signal transduction to the heart. Connections between processes at the cellular, molecular, and neural levels are quantitatively linked to HRV. Rhythmic signals representing autonomic oscillations and circadian rhythms converge to modulate the pattern of heartbeats, and the effects of these oscillators are diminished in the acute endotoxemia response. Based on the semimechanistic model developed herein, homeostatic and acute stress responses of HRV are studied in terms of these oscillatory signals. Understanding the loss of HRV in endotoxemia serves as a step toward understanding changes in HRV observed clinically through translational applications of systems biology based on the relationship between biological processes and clinical outcomes.

Voluntarily produced increases in heart rate variability modulate autonomic effects of endotoxin induced systemic inflammation: an exploratory study

Exposure of healthy people to lipopolysaccharide (LPS; endotoxin) produces a pro-inflammatory response, subjective symptoms, and decreased heart rate variability (HRV). Given the efficacy of HRV biofeedback (BF) for treating asthma, the large autonomic effects of HRV BF, and the link between vagus nerve activity and inflammation, we hypothesized that HRV BF would dampen the acute manifestations of systemic inflammation induced by LPS challenge. Healthy participants age 18-40 were randomly assigned to four-one-hour training sessions of either HRV BF (n = 6) or a control 15/min paced breathing condition (n = 5) prior to acute experimentally induced LPS exposure. Participants were coached to do the procedures for 10 min each at five hourly time points after LPS injection, and then 2 h later. Subjective symptoms, HRV parameters, and plasma cytokine levels were measured at each time point, 2 h afterward, and the following morning. Participants were able to perform the procedures both during four pre-exposure training sessions and while experiencing LPS-induced symptoms. The HRV BF group showed significant attenuation of the LPS-induced decline in HRV for the 6 h following LPS exposure, suggesting that HRV BF decreased autonomic dysfunction produced by LPS-induced inflammation. HRV BF also reduced symptoms of headache and eye sensitivity to light, but did not affect LPS-induced levels of pro-inflammatory cytokines or symptoms of nausea, muscle aches, or feverishness. Further evaluation of HRV BF appears to be warranted among patients with inflammatory conditions.

Relationship of basal heart rate variability to in vivo cytokine responses after endotoxin exposure

Autonomic inputs from the sympathetic and parasympathetic nervous systems, as measured by heart rate variability (HRV), have been reported to correlate to the severity injury and responses to infectious challenge among critically ill patients. In addition, parasympathetic/vagal activity has been shown experimentally to exert anti-inflammatory effects via attenuation of splanchnic tissue TNF-alpha production. We sought to define the influence of gender on HRV responses to in vivo endotoxin challenge in healthy humans and to determine if baseline HRV parameters correlated with endotoxin-mediated circulating cytokine responses. Young (<30 years of age), healthy subjects (n = 30) received endotoxin (2 ng/kg), and HRV and blood samples were obtained serially thereafter. Plasma cytokines were measured by enzyme-linked immunosorbent assay, and HRV parameters were determined by analysis of serial 5-min epochs of heart rate monitoring. In addition, calculation of multiscale entropy deriving from cardiac monitoring data was performed. The influence of factors such as gender, body mass index, and resting heart rate on HRV after endotoxin exposure was assessed. We found that gender, body mass index, or resting heart rate did not significantly alter the HRV response after endotoxin exposure. Using entropy analysis, we observed that females had significantly higher entropy values at 24 h after endotoxin exposure. Using a serially sampling protocol for cytokine determination, we found a significant correlation of several baseline HRV parameters (percentage of interval differences of successive interbeat intervals more than 50 ms, r = 0.42, P < 0.05; high-frequency variability, r = 0.4, P < 0.05; and low-frequency/high-frequency ratio, r = -0.43, P < 0.05) on TNF-alpha release after endotoxin exposure.

Multiscale model for the assessment of autonomic dysfunction in human endotoxemia

Severe injury and infection are associated with autonomic dysfunction. The realization that a dysregulation in autonomic function may predispose a host to excessive inflammatory processes has renewed interest in understanding the role of central nervous system (CNS) in modulating systemic inflammatory processes. Assessment of heart rate variability (HRV) has been used to evaluate systemic abnormalities and as a predictor of the severity of illness. Dissecting the relevance of neuroimmunomodulation in controlling inflammatory processes requires an understanding of the multiscale interplay between CNS and the immune response. A vital enabler in that respect is the development of a systems-based approach that integrates data across multiple scales, and models the emerging host response as the outcome of interactions of critical modules. Thus, a multiscale model of human endotoxemia, as a prototype model of systemic inflammation in humans, is proposed that integrates processes across the host from the cellular to the systemic host response level. At the cellular level interacting components are associated with elementary signaling pathways that propagate extracellular signals to the transcriptional response level. Further, essential modules associated with the neuroendocrine immune crosstalk are considered. Finally, at the systemic level, phenotypic expressions such as HRV are incorporated to assess systemic decomplexification indicative of the severity of the host response. Thus, the proposed work intends to associate acquired endocrine dysfunction with diminished HRV as a critical enabler for clarifying how cellular inflammatory processes and neural-based pathways mediate the links between patterns of autonomic control (HRV) and clinical outcomes.