Endotoxemia causes central downregulation of sympathetic vasomotor tone in healthy humans

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.

Suppression by central adenosine A3 receptors of the cholinergic defense against cardiovascular aberrations of sepsis: role of PI3K/MAPKs/NFκB signaling

Introduction: Despite the established role of peripheral adenosine receptors in sepsis-induced organ dysfunction, little or no data is available on the interaction of central adenosine receptors with sepsis. The current study tested the hypothesis that central adenosine A3 receptors (A3ARs) modulate the cardiovascular aberrations and neuroinflammation triggered by sepsis and their counteraction by the cholinergic antiinflammatory pathway. Methods: Sepsis was induced by cecal ligation and puncture (CLP) in rats pre-instrumented with femoral and intracisternal (i.c.) catheters for hemodynamic monitoring and central drug administration, respectively. Results: The CLP-induced hypotension, reduction in overall heart rate variability (HRV) and sympathovagal imbalance towards parasympathetic predominance were abolished by i.v. nicotine (100 μg/kg) or i.c. VUF5574 (A3AR antagonist, 2 µg/rat). In addition, the selective A3AR agonist, 3-iodobenzyl-5'-N-methylcarboxamidoadenosine IB-MECA, 4 µg/rat, i.c.) exaggerated the hypotension and cardiac autonomic dysfunction induced by sepsis and opposed the favorable nicotine actions against these septic manifestations. Immunohistochemically, IB-MECA abolished the nicotine-mediated downregulation of NFκB and NOX2 expression in rostral ventrolateral medullary areas (RVLM) of brainstem of septic rats. The inhibitory actions of IB-MECA on nicotine responses disappeared after i.c. administration of PD98059 (MAPK-ERK inhibitor), SP600125 (MAPK-JNK inhibitor) or wortmannin (PI3K inhibitor). Moreover, infliximab (TNFα inhibitor) eliminated the IB-MECA-induced rises in RVLM-NFκB expression and falls in HRV, but not blood pressure. Conclusion: Central PI3K/MAPKs pathway mediates the A3AR counteraction of cholinergic defenses against cardiovascular and neuroinflammatory aberrations in sepsis.

Vascular Responses to Acute Induced Inflammation With Aging: Does Fitness Matter?

Acute inflammation impairs vascular function in an age-dependent manner and affects cardiovascular event risk. Regular aerobic exercise preserves vascular function with aging and potentially modifies how acute inflammation affects the vasculature. We hypothesize high cardiorespiratory fitness may accompany greater arterial responsiveness post-acute inflammation in older adults.

Intranasal orexin A modulates sympathetic vascular tone - a pilot study in healthy male humans

INTRODUCTION

Previous research suggests that the neuropeptide orexin A contributes to sympathetic blood pressure (BP) control inasmuch as hypothalamic injection of orexin A increases sympathetic vasomotor tone and arterial BP in rodents. In humans with narcolepsy, a disorder associated with loss of orexin-producing neurons, vasoconstrictive muscle sympathetic nerve activity (MSNA) is reduced. Since intranasally administered oligopeptides like orexin are known to modulate brain function, we investigated the effect of intranasal orexin A on vascular sympathetic baroreflex function in healthy humans.

METHODS

In a balanced, double-blind cross-over study, orexin A (500 nmol) and placebo, respectively, were intranasally administered to 10 lean healthy males (age, 25.8±4.6 years). MSNA was assessed microneurographically before and 30-45 minutes after either substance administration. Additionally, baroreflex was challenged via graded infusions of vasoactive drugs before and after substance administration. Baroreflex function was defined as the correlation of BP with MSNA and heart rate.

RESULTS

Intranasal orexin A compared to placebo induced a significant increase in resting MSNA from prior to post administration (Δ-burst rate, orexin A vs. placebo: +5.8±0.8 vs. +2.1±0.6; p=0.007; total activity (169±11.5% vs. 115±5.0%; p=0.002). BP, heart rate and sympathovagal balance to the heart, as represented by HRV, as well as baroreflex sensitivity during the vasoactive challenge were not altered.

CONCLUSION

Intranasally administered orexin A acutely induced vasoconstrictory sympathoactivation in healthy male humans. This result suggests that orexin A mediates upward resetting of the vascular baroreflex setpoint at centers superordinate to the mere baroreflex-feedback-loop.

The role of lactate in sepsis and COVID-19: Perspective from contracting skeletal muscle metabolism

NEW FINDINGS

What is the topic of this review? Lactate is considered an important substrate for mitochondria in the muscles, heart and brain during exercise and is the main gluconeogenetic precursor in the liver and kidneys. In this light, we review the (patho)physiology of lactate metabolism in sepsis and coronavirus disease 2019 (COVID-19). What advances does it highlight? Elevated blood lactate is strongly associated with mortality in septic patients. Lactate seems unrelated to tissue hypoxia but is likely to reflect mitochondrial dysfunction and high adrenergic stimulation. Patients with severe COVID-19 exhibit near-normal blood lactate, indicating preserved mitochondrial function, despite a systemic hyperinflammatory state similar to sepsis.

ABSTRACT

In critically ill patients, elevated plasma lactate is often interpreted as a sign of organ hypoperfusion and/or tissue hypoxia. This view on lactate is likely to have been influenced by the pioneering exercise physiologists around 1920. August Krogh identified an oxygen deficit at the onset of exercise that was later related to an oxygen 'debt' and lactate accumulation by A. V. Hill. Lactate is considered to be the main gluconeogenetic precursor in the liver and kidneys during submaximal exercise, but hepatic elimination is attenuated by splanchnic vasoconstriction during high-intensity exercise, causing an exponential increase in blood lactate. With the development of stable isotope tracers, lactate has become established as an important energy source for muscle, brain and heart tissue, where it is used for mitochondrial respiration. Plasma lactate > 4 mM is strongly associated with mortality in septic shock, with no direct link between lactate release and tissue hypoxia. Herein, we provide evidence for mitochondrial dysfunction and adrenergic stimulation as explanations for the sepsis-induced hyperlactataemia. Despite profound hypoxaemia and intense work of breathing, patients with severe coronavirus disease 2019 (COVID-19) rarely exhibit hyperlactataemia (> 2.5 mM), while presenting a systemic hyperinflammatory state much like sepsis. However, lactate dehydrogenase, which controls the formation of lactate, is markedly elevated in plasma and strongly associated with mortality in severe COVID-19. We briefly review the potential mechanisms of the lactate dehydrogenase elevation in COVID-19 and its relationship to lactate metabolism based on mechanisms established in contracting skeletal muscle and the acute respiratory distress syndrome.

The autonomic nervous system in septic shock and its role as a future therapeutic target: a narrative review

The autonomic nervous system (ANS) regulates the cardiovascular system. A growing body of experimental and clinical evidence confirms significant dysfunction of this regulation during sepsis and septic shock. Clinical guidelines do not currently include any evaluation of ANS function during the resuscitation phase of septic shock despite the fact that the severity and persistence of ANS dysfunction are correlated with worse clinical outcomes. In the critical care setting, the clinical use of ANS-related hemodynamic indices is currently limited to preliminary investigations trying to predict and anticipate imminent clinical deterioration. In this review, we discuss the evidence supporting the concept that, in septic shock, restoration of ANS-mediated control of the cardiovascular system or alleviation of the clinical consequences induced by its dysfunction (e.g., excessive tachycardia, etc.), may be an important therapeutic goal, in combination with traditional resuscitation targets. Recent studies, which have used standard and advanced monitoring methods and mathematical models to investigate the ANS-mediated mechanisms of physiological regulation, have shown the feasibility and importance of monitoring ANS hemodynamic indices at the bedside, based on the acquisition of simple signals, such as heart rate and arterial blood pressure fluctuations. During the early phase of septic shock, experimental and/or clinical studies have shown the efficacy of negative-chronotropic agents (i.e., beta-blockers or ivabradine) in controlling persistent tachycardia despite adequate resuscitation. Central α-2 agonists have been shown to prevent peripheral adrenergic receptor desensitization by reducing catecholamine exposure. Whether these new therapeutic approaches can safely improve clinical outcomes remains to be confirmed in larger clinical trials. New technological solutions are now available to non-invasively modulate ANS outflow, such as transcutaneous vagal stimulation, with initial pre-clinical studies showing promising results and paving the way for ANS modulation to be considered as a new potential therapeutic target in patients with septic shock.

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

A physiological model of the inflammatory-thermal-pain-cardiovascular interactions during an endotoxin challenge

KEY POINTS

Inflammation in response to bacterial endotoxin challenge impacts physiological functions, including cardiovascular, thermal and pain dynamics, although the mechanisms are poorly understood. We develop an innovative mathematical model incorporating interaction pathways between inflammation and physiological processes observed in response to an endotoxin challenge. We calibrate the model to individual data from 20 subjects in an experimental study of the human inflammatory and physiological responses to endotoxin, and we validate the model against human data from an independent study. Using the model to simulate patient responses to different treatment modalities reveals that a multimodal treatment combining several therapeutic strategies gives the best recovery outcome.

ABSTRACT

Uncontrolled, excessive production of pro-inflammatory mediators from immune cells and traumatized tissues can cause systemic inflammatory conditions such as sepsis, one of the ten leading causes of death in the USA, and one of the three leading causes of death in the intensive care unit. Understanding how inflammation affects physiological processes, including cardiovascular, thermal and pain dynamics, can improve a patient's chance of recovery after an inflammatory event caused by surgery or a severe infection. Although the effects of the autonomic response on the inflammatory system are well-known, knowledge about the reverse interaction is lacking. The present study develops a mathematical model analyzing the inflammatory system's interactions with thermal, pain and cardiovascular dynamics in response to a bacterial endotoxin challenge. We calibrate the model with individual data from an experimental study of the inflammatory and physiological responses to a one-time administration of endotoxin in 20 healthy young men and validate it against data from an independent endotoxin study. We use simulation to explore how various treatments help patients exposed to a sustained pathological input. The treatments explored include bacterial endotoxin adsorption, antipyretics and vasopressors, as well as combinations of these. Our findings suggest that the most favourable recovery outcome is achieved by a multimodal strategy, combining all three interventions to simultaneously remove endotoxin from the body and alleviate symptoms caused by the immune system as it fights the infection.

Intranasal oxytocin has sympathoexcitatory effects on vascular tone in healthy males

Oxytocin appears to be involved in the neuroendocrine regulation of sympathetic blood pressure (BP) homeostasis. In animals, intracerebral administration of oxytocin induces BP-relevant sympathetic activation. In humans, central nervous effects of oxytocin on BP regulation remain unclear. Intranasal administration supposedly delivers oligopeptides such as oxytocin directly to the brain. We investigated the effects of intranasal oxytocin on sympathetic vascular baroreflex function in humans using microneurographic techniques. In a balanced, double-blind crossover design, oxytocin or placebo was administered intranasally to 12 lean, healthy males (age 25 ± 4 yr). Muscle sympathetic nerve activity (MSNA) was assessed microneurographically before (presubstance), 30-45 min (postsubstance I), and 105-120 min (postsubstance II) after oxytocin administration. Baroreflex was challenged via graded infusions of vasoactive drugs, and correlation of BP with MSNA and heart rate (HR) defined baroreflex function. Experiments were conducted in the afternoon after a 5-h fasting period. After oxytocin, resting MSNA (burst rate and total activity) showed significant net increases from pre to postsubstance II compared with placebo [Δincrease = +4.3 ± 1.2 (oxytocin) vs. +2.2 ± 1.4 bursts/min (placebo), ANOVA; P < 0.05; total activity = 184 ± 11.5% (oxytocin) vs. 121 ± 14.3% (placebo), ANOVA; P = 0.01). This was combined with a small but significant net increase in resting diastolic BP, whereas systolic and mean arterial BP or HR as well as baroreflex sensitivity at vasoactive drug challenge were not altered. Intranasally administered oxytocin induced vasoconstrictory sympathoactivation in healthy male humans. The concomitant increase of diastolic BP was most likely attributable to increased vascular tone. This suggests oxytocin-mediated upward resetting of the vascular baroreflex set point at centers superordinate to the mere baroreflex-feedback loop.

Sympathetic nerves control bacterial clearance

A neural reflex mediated by the splanchnic sympathetic nerves regulates systemic inflammation in negative feedback fashion, but its consequences for host responses to live infection are unknown. To test this, conscious instrumented sheep were infected intravenously with live E. coli bacteria and followed for 48 h. A month previously, animals had undergone either bilateral splanchnic nerve section or a sham operation. As established for rodents, sheep with cut splanchnic nerves mounted a stronger systemic inflammatory response: higher blood levels of tumor necrosis factor alpha and interleukin-6 but lower levels of the anti-inflammatory cytokine interleukin-10, compared with sham-operated animals. Sequential blood cultures revealed that most sham-operated sheep maintained high circulating levels of live E. coli throughout the 48-h study period, while all sheep without splanchnic nerves rapidly cleared their bacteraemia and recovered clinically. The sympathetic inflammatory reflex evidently has a profound influence on the clearance of systemic bacterial infection.

A Whole-Body Mathematical Model of Sepsis Progression and Treatment Designed in the BioGears Physiology Engine

Sepsis is a debilitating condition associated with a high mortality rate that greatly strains hospital resources. Though advances have been made in improving sepsis diagnosis and treatment, our understanding of the disease is far from complete. Mathematical modeling of sepsis has the potential to explore underlying biological mechanisms and patient phenotypes that contribute to variability in septic patient outcomes. We developed a comprehensive, whole-body mathematical model of sepsis pathophysiology using the BioGears Engine, a robust open-source virtual human modeling project. We describe the development of a sepsis model and the physiologic response within the BioGears framework. We then define and simulate scenarios that compare sepsis treatment regimens. As such, we demonstrate the utility of this model as a tool to augment sepsis research and as a training platform to educate medical staff.

GHRH-mediated GH release is associated with sympathoactivation and baroreflex resetting: a microneurographic study in healthy humans

Previous research suggested substantial interactions of growth hormone (GH) and sympathetic nervous activity. This cross talk can be presumed both during physiological (e.g., slow-wave sleep) and pathological conditions of GH release. However, microneurographic studies of muscle sympathetic nerve activity (MSNA) and assessment of baroreflex function during acute GH-releasing hormone (GHRH)-mediated GH release were not conducted so far. In a balanced, double-blind crossover design, GHRH or placebo (normal saline) were intravenously administered to 11 healthy male volunteers. MSNA was assessed microneurographically and correlated with blood pressure (BP) and heart rate (HR) at rest before (pre-) and 30-45 (post-I) and 105-120 min (post-II) after respective injections. Additionally, baroreflex function was assessed via graded infusion of vasoactive drugs. GHRH increased GH serum levels as intended. Resting MSNA showed significant net increases of both burst rate and total activity from pre- to post-I and post-II following GHRH injections compared with placebo (ANOVA for treatment and time, burst rate: P = 0.028; total activity: P = 0.045), whereas BP and HR were not altered. ANCOVA revealed that the dependent variable MSNA was not affected by the independent variables mean arterial BP (MAP) or HR (MAP: P = 0.006; HR: P = 0.003). Baroreflex sensitivity at baroreflex challenge was not altered. GHRH-mediated GH release is associated with a significant sympathoactivation at central nervous sites superordinate to the simple baroreflex feedback loop because GH induced a baroreflex resetting without altering baroreflex sensitivity.

Lactic Acid Inhibits Lipopolysaccharide-Induced Mast Cell Function by Limiting Glycolysis and ATP Availability

Sepsis has a well-studied inflammatory phase, with a less-understood secondary immunosuppressive phase. Elevated blood lactate and slow lactate clearance are associated with mortality; however, regulatory roles are unknown. We hypothesized that lactic acid (LA) contributes to the late phase and is not solely a consequence of bacterial infection. No studies have examined LA effects in sepsis models in vivo or a mechanism by which it suppresses LPS-induced activation in vitro. Because mast cells can be activated systemically and contribute to sepsis, we examined LA effects on the mast cell response to LPS. LA significantly suppressed LPS-induced cytokine production and NF-κB transcriptional activity in mouse bone marrow-derived mast cells and cytokine production in peritoneal mast cells. Suppression was MCT-1 dependent and reproducible with sodium lactate or formic acid. Further, LA significantly suppressed cytokine induction following LPS-induced endotoxemia in mice. Because glycolysis is linked to inflammation and LA is a byproduct of this process, we examined changes in glucose metabolism. LA treatment reduced glucose uptake and lactate export during LPS stimulation. LA effects were mimicked by glycolytic inhibitors and reversed by increasing ATP availability. These results indicate that glycolytic suppression and ATP production are necessary and sufficient for LA effects. Our work suggests that enhancing glycolysis and ATP production could improve immune function, counteracting LA suppressive effects in the immunosuppressive phase of sepsis.

Effect of pre-operative methylprednisolone on orthostatic hypotension during early mobilization after total hip arthroplasty

BACKGROUND

Orthostatic hypotension (OH) and intolerance (OI) are common after total hip arthroplasty (THA) and may delay early mobilization. The pathology of OH and OI includes a dysregulated post-operative vasopressor response, by a hitherto unknown mechanism. We hypothesized that OI could be related to the inflammatory stress response which is inhibited by steroid administration. Consequently, this study evaluated the effect of a pre-operative high-dose methylprednisolone on OH and OI early after THA.

METHODS

Randomized, double-blind, placebo-controlled study in 59 patients undergoing elective unilateral THA with spinal anesthesia and a standardized multimodal analgesic regime. Patients were allocated (1 : 1) to pre-operative intravenous (IV) methylprednisolone (MP) 125 mg or isotonic saline (C). OH, OI and cardiovascular responses to sitting and standing were evaluated using a standardized mobilization protocol pre-operatively, 6, and 24 h after surgery. Systolic and diastolic arterial pressure and heart rate were measured non-invasively (Nexfin^® ). The systemic inflammation was monitored by the C-reactive protein (CRP) response.

RESULTS

At 6 h post-operatively, 11 (38%) versus 11 (37%) patients had OH in group MP and group C, respectively (RR 1.02 (0.60 to 1.75; P = 1.00)), whereas OI was present in 9 (31%) versus 13 (43%) patients (RR 0.76 (0.42 to 1.36; P = 0.42)), respectively. At 24 h post-operatively, the prevalence of OH and OI did not differ between groups, though CRP levels were significantly reduced in group MP (P < 0.001).

CONCLUSION

Pre-operative administration of 125 mg methylprednisolone IV did not reduce OH or OI compared with placebo despite a reduced inflammatory response.

A novel heart rate variability based risk prediction model for septic patients presenting to the emergency department

A quick, objective, non-invasive means of identifying high-risk septic patients in the emergency department (ED) can improve hospital outcomes through early, appropriate management. Heart rate variability (HRV) analysis has been correlated with mortality in critically ill patients. We aimed to develop a Singapore ED sepsis (SEDS) predictive model to assess the risk of 30-day in-hospital mortality in septic patients presenting to the ED. We used demographics, vital signs, and HRV parameters in model building and compared it with the modified early warning score (MEWS), national early warning score (NEWS), and quick sequential organ failure assessment (qSOFA) score.Adult patients clinically suspected to have sepsis in the ED and who met the systemic inflammatory response syndrome (SIRS) criteria were included. Routine triage electrocardiogram segments were used to obtain HRV variables. The primary endpoint was 30-day in-hospital mortality. Multivariate logistic regression was used to derive the SEDS model. MEWS, NEWS, and qSOFA (initial and worst measurements) scores were computed. Receiver operating characteristic (ROC) analysis was used to evaluate their predictive performances.Of the 214 patients included in this study, 40 (18.7%) met the primary endpoint. The SEDS model comprises of 5 components (age, respiratory rate, systolic blood pressure, mean RR interval, and detrended fluctuation analysis α2) and performed with an area under the ROC curve (AUC) of 0.78 (95% confidence interval [CI]: 0.72-0.86), compared with 0.65 (95% CI: 0.56-0.74), 0.70 (95% CI: 0.61-0.79), 0.70 (95% CI: 0.62-0.79), 0.56 (95% CI: 0.46-0.66) by qSOFA (initial), qSOFA (worst), NEWS, and MEWS, respectively.HRV analysis is a useful component in mortality risk prediction for septic patients presenting to the ED.

Activation of central GABAB receptors offsets the cyclosporine counteraction of endotoxic cardiovascular outcomes in conscious rats

We have previously shown that cyclosporine (CSA) counteracts cardiovascular manifestations induced by endotoxemia (lipopolysaccharide, LPS) such as hypotension and cardiac autonomic dysfunction in conscious rats. In this study, we investigated whether the facilitation of central γ-amino butyric acid (GABA) neurotransmission blunts these favorable influences of CSA. The LPS-CSA interaction was determined in the absence and presence of drugs that activate GABA_A or GABA_B receptors or elevate synaptic GABA levels in the central nervous system. The consequent i.v. administration of CSA (10 mg/kg) blunted the LPS-evoked hypotension, tachycardia, and reductions in time- and frequency-domain indices of heart rate variability (measures of cardiac autonomic control) evoked by LPS (10 mg/kg i.v.). The ability of CSA to reverse the LPS effects disappeared in rats treated intracisternally (i.c.) with baclofen (selective GABA_B agonist, 2 μg/rat) but not muscimol (selective GABA_A agonist, 1 μg/rat), indicating a preferential compromising action for central GABA_B receptors on the advantageous effects of CSA. Moreover, the improvement by CSA of LPS-evoked cardiovascular derangements was also eliminated after concurrent i.c. administration of vigabatrin (GABA transaminase inhibitor, 200 μg/rat) or tiagabine (GABA reuptake inhibitor, 100 μg/rat). These results demonstrate that the activation of central GABA_B receptors either directly via baclofen or indirectly following interventions that boost GABA levels in central synapses counterbalances the rectifying action of CSA on endotoxemia.

Sympathetic cardiac function in early sepsis: Noninvasive evaluation with [123I]-meta-iodobenzylguanidine (123I-MIBG) in vivo SPECT imaging

BACKGROUND

Sympathetic system abnormalities have been reported in sepsis-related cardiac dysfunction. The present study aimed at evaluating the potential of the norepinephrine radiolabeled analogue [123I]-meta-iodobenzylguanidine (123I-MIBG) for the noninvasive assessment of modifications in cardiac sympathetic activity occurring in lipopolysaccharide (LPS)-induced experimental acute sepsis by single-photon emission computed tomographic imaging (SPECT).

METHODS AND RESULTS

Sepsis was induced in male Wistar rats by intraperitoneal injection of 10 mg·kg-1 lipopolysaccharide (n = 16), whereas control animals (n = 7) were injected with vehicle (NaCl 0.9%). Echocardiography in LPS-injected animals (n = 8) demonstrated systolic and diastolic cardiac dysfunction. 123I-MIBG was injected 1 hour after LPS or vehicle administration (n = 8 and 7, respectively), and in vivo SPECT imaging was performed early and late (20 and 180 minutes) after tracer injection prior to animal euthanasia and ex vivo assessment of 123I-MIBG biodistribution. Global and 17-segment SPECT image analysis indicated that early 123I-MIBG activity was not affected by LPS treatment, whereas late cardiac tracer activity was significantly decreased in LPS-treated animals. Consequently, the cardiac washout of 123I-MIBG was significantly higher in LPS-treated (63.3% ± 4.0%) than that in control animals (56.7% ± 5.8%) (P < .05).

CONCLUSION

Sepsis-induced modifications in cardiac sympathetic nervous system activity were evidenced by noninvasive in vivo 123I-MIBG SPECT imaging.

Central GABAA receptors are involved in inflammatory and cardiovascular consequences of endotoxemia in conscious rats

γ-Aminobutyric acid (GABA), the principal brain inhibitory neurotransmitter, modulates inflammatory and neurodegenerative disease. Here, we tested the hypothesis that central GABAergic neurotransmission mediates the detrimental inflammatory, hemodynamic, and cardiac autonomic actions of endotoxemia. The effects of drugs that block GABA receptors or interfere with GABA uptake or degradation on blood pressure (BP), heart rate (HR), and HR variability (HRV) responses elicited by i.v. lipopolysaccharide (LPS) were assessed in conscious rats. The hypotensive effect of LPS (10 mg/kg) was blunted after intracisternal (i.c.) administration of bicuculline (GABAA receptor antagonist) or saclofen (GABAB receptor antagonist). By contrast, the concomitant LPS-evoked tachycardia and decreases in time domain and frequency domain indices of HRV (measures of cardiac autonomic control) were abolished upon treatment with bicuculline but not saclofen. Increases in serum tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) caused by LPS disappeared in the presence of bicuculline or saclofen, whereas LPS-evoked increases in serum nitric oxide metabolites (NOx) were counteracted by bicuculline only. None of the endotoxemia effects was altered in rats treated with i.c. tiagabine (GABA reuptake inhibitor) or vigabatrin (GABA transaminase inhibitor). These data suggest a major role for central GABAA receptors in the inflammatory and cardiovascular effects of endotoxemia.

Oral Midodrine Hydrochloride for Prevention of Orthostatic Hypotension during Early Mobilization after Hip Arthroplasty

Background

Early postoperative mobilization is essential for rapid recovery but may be impaired by orthostatic intolerance (OI) and orthostatic hypotension (OH), which are highly prevalent after major surgery. Pathogenic mechanisms include an insufficient postoperative vasopressor response. The oral α-1 agonist midodrine hydrochloride increases vascular resistance, and the authors hypothesized that midodrine would reduce the prevalence of OH during mobilization 6 h after total hip arthroplasty relative to placebo.

Methods

This double-blind, randomized trial allocated 120 patients 18 yr or older and scheduled for total hip arthroplasty under spinal anesthesia to either 5 mg midodrine hydrochloride or placebo orally 1 h before mobilization at 6 and 24 h postoperatively. The primary outcome was the prevalence of OH (decrease in systolic or diastolic arterial pressures of &gt; 20 or 10 mmHg, respectively) during mobilization 6 h after surgery. Secondary outcomes were OI and hemodynamic responses to mobilization at 6 and 24 h.

Results

At 6 h, 14 (25%; 95% CI, 14 to 38%) versus 23 (39.7%; 95% CI, 27 to 53%) patients had OH in the midodrine and placebo group, respectively, relative risk 0.63 (0.36 to 1.10; P = 0.095), whereas OI was present in 15 (25.0%; 15 to 38%) versus 22 (37.3%; 25 to 51%) patients, relative risk 0.68 (0.39 to 1.18; P = 0.165). At 24 h, OI and OH prevalence did not differ between groups.

Conclusions

Preemptive use of oral 5 mg midodrine did not significantly reduce the prevalence of OH during early postoperative mobilization compared with placebo. However, further studies on dose and timing are warranted since midodrine is effective in chronic OH conditions.

Decreased heart rate variability responses during early postoperative mobilization--an observational study

BACKGROUND

Intact orthostatic blood pressure regulation is essential for early mobilization after surgery. However, postoperative orthostatic hypotension and intolerance (OI) may delay early ambulation. The mechanisms of postoperative OI include impaired vasopressor responses relating to postoperative autonomic dysfunction. Thus, based on a previous study on haemodynamic responses during mobilization before and after elective total hip arthroplasty (THA), we performed secondary analyses of heart rate variability (HRV) and aimed to identify possible abnormal postoperative autonomic responses in relation to postural change.

METHODS

A standardized mobilization protocol before, 6 and 24 h after surgery was performed in 23 patients scheduled for elective THA. Beat-to-beat arterial blood pressure was measured by photoplethysmography and HRV was derived from pulse wave interbeat intervals and analysed in the time and frequency domain as well as by non-linear analysis using sample entropy

RESULTS

Before surgery, arterial pressures and HR increased upon standing, while HRV low (LF) and high frequency (HF) components remained unchanged. At 6 and 24 h after surgery, resting total HRV power, sample entropy and postural responses in arterial pressures decreased compared to preoperative conditions. During standing HF variation increased by 16.7 (95 % CI 8.0-25.0) normalized units (nu) at 6 h and 10.7 (2.0-19.4) nu at 24 h compared to the preoperative evaluation. At 24 h the LF/HF ratio decreased from 1.8 (1.2-2.6) nu when supine to 1.2 (0.8-1.8) nu when standing.

CONCLUSIONS

This study observed postoperative autonomic cardiovascular dysregulation that may contribute to limited HRV responses during early postoperative mobilization.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01089946.

Dynamic cerebral autoregulation to induced blood pressure changes in human experimental and clinical sepsis

Previous studies have demonstrated that dynamic cerebral autoregulation to spontaneous fluctuations in blood pressure is enhanced following lipopolysaccharide (LPS) infusion, a human experimental model of early sepsis, whereas by contrast it is impaired in patients with severe sepsis or septic shock. In this study, we hypothesized that this pattern of response would be identical during induced changes in blood pressure. Dynamic cerebral autoregulation was assessed in nine healthy volunteers and six septic patients. The healthy volunteers underwent a 4-h intravenous infusion of LPS (total dose: 2 ng kg^-1 ). Mean arterial blood pressure (MAP, arterial transducer) and middle cerebral artery blood flow velocity (MCAv, transcranial Doppler ultrasound) were recorded continuously during thigh-cuff deflation-induced changes in MAP for the determination of a modified rate of regulation (RoR). This was performed before and after LPS infusion in healthy volunteers, and within 72 h following clinical diagnosis of sepsis in patients. In healthy volunteers, thigh-cuff deflation caused a MAP reduction of 16 (13-20) % at baseline and 18 (16-20) % after LPS, while the MAP reduction was 12 (11-13) % in patients (P<0·05 versus volunteers at baseline; P<0·01 versus volunteers after LPS). The corresponding RoR values increased from 0·46 (0·31-0·49) s^-1 at baseline to 0·58 (0·36-0·74) s^-1 after LPS (P<0·05) in healthy volunteers, whereas they were similar to values observed in patients [0·43 (0·36-0·52) s^-1 ; P = 0·91 versus baseline; P = 0·14 versus LPS]. While our findings support the concept that dynamic cerebral autoregulation is enhanced during the very early stages of sepsis, they remain inconclusive with regard to more advanced stages of disease, because thigh-cuff deflation failed to induce sufficient MAP reductions in patients.

Modulation of voltage-gated Ca2+ channels by G protein-coupled receptors in celiac-mesenteric ganglion neurons of septic rats

Septic shock, the most severe complication associated with sepsis, is manifested by tissue hypoperfusion due, in part, to cardiovascular and autonomic dysfunction. In many cases, the splanchnic circulation becomes vasoplegic. The celiac-superior mesenteric ganglion (CSMG) sympathetic neurons provide the main autonomic input to these vessels. We used the cecal ligation puncture (CLP) model, which closely mimics the hemodynamic and metabolic disturbances observed in septic patients, to examine the properties and modulation of Ca²⁺ channels by G protein-coupled receptors in acutely dissociated rat CSMG neurons. Voltage-clamp studies 48 hr post-sepsis revealed that the Ca²⁺ current density in CMSG neurons from septic rats was significantly lower than those isolated from sham control rats. This reduction coincided with a significant increase in membrane surface area and a negligible increase in Ca²⁺ current amplitude. Possible explanations for these findings include either cell swelling or neurite outgrowth enhancement of CSMG neurons from septic rats. Additionally, a significant rightward shift of the concentration-response relationship for the norepinephrine (NE)-mediated Ca²⁺ current inhibition was observed in CSMG neurons from septic rats. Testing for the presence of opioid receptor subtypes in CSMG neurons, showed that mu opioid receptors were present in ~70% of CSMG, while NOP opioid receptors were found in all CSMG neurons tested. The pharmacological profile for both opioid receptor subtypes was not significantly affected by sepsis. Further, the Ca²⁺ current modulation by propionate, an agonist for the free fatty acid receptors GPR41 and GPR43, was not altered by sepsis. Overall, our findings suggest that CSMG function is affected by sepsis via changes in cell size and α2-adrenergic receptor-mediated Ca²⁺ channel modulation.

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.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

Calcium-overloaded sympathetic preganglionic neurons in a case of severe sepsis with anorexia nervosa

Aim

We aimed to show the status of intracellular elements in sympathetic preganglionic neurons in an autopsy case of a 55‐year‐old woman with severe sepsis and cardiac dysfunction with anorexia nervosa.

Methods

Our methods include a case report and pathological examinations of autopsied tissues using synchrotron‐generated microbeam X‐ray fluorescence analysis.

Results

A case report of severe sepsis and myocardial dysfunction. The patient had sudden short cardiac arrest without arrhythmia and sequelae, and echocardiogram showed negative inotropic change. The X‐ray fluorescence analysis of autopsied tissues indicated an unusually high concentration of cytosolic calcium in sympathetic preganglionic neurons. However, there were no significant pathological findings of damage in the heart or the cardiovascular autonomic nuclei in the central nervous system.

Conclusion

The data indicate that dysfunction of the sympathetic preganglionic neurons exists in a patient of severe sepsis and cardiac dysfunction with anorexia nervosa.

Early identification and management of patients with severe sepsis and septic shock in the emergency department

Severe sepsis and septic shock have great relevance to Emergency Medicine physicians because of their high prevalence, morbidity, and mortality. Treatment is time-sensitive, depends on early identification risk stratification, and has the potential to significantly improve patient outcomes. In this article, we review the pathophysiology of, and evidence basis for, the emergency department management of severe sepsis and septic shock.

Role of prostaglandins in determining the increased cardiac sympathetic nerve activity in ovine sepsis

Effective treatment of sepsis remains a significant challenge in intensive care units. During sepsis, there is widespread activation of the sympathetic nervous system, which is thought to have both beneficial and detrimental effects. The sympathoexcitation is thought to be partly due to the developing hypotension, but may also be a response to the inflammatory mediators released. Thus, we investigated whether intracarotid infusion of prostaglandin E2 (PGE2) induced similar cardiovascular changes to those caused by intravenous infusion of Escherichia coli in sheep and whether inhibition of prostaglandin synthesis, with the nonselective cyclooxygenase inhibitor indomethacin, administered at 2 and 8 h after the onset of sepsis, reduced sympathetic nerve activity (SNA), and heart rate (HR). Studies were performed in conscious sheep instrumented to measure mean arterial pressure (MAP), HR, cardiac SNA (CSNA), and renal SNA (RSNA). Intracarotid infusion of PGE2 (50 ng·kg−1·min−1) increased temperature, CSNA, and HR, but not MAP or RSNA. Sepsis, induced by infusion of E. coli, increased CSNA, but caused an initial, transient inhibition of RSNA. At 2 h of sepsis, indomethacin (1.25 mg/kg bolus) increased MAP and caused reflex decreases in HR and CSNA. After 8 h of sepsis, indomethacin did not alter MAP, but reduced CSNA and HR, without altering baroreflex control. These findings indicate an important role for prostaglandins in mediating the increase in CSNA and HR during the development of hyperdynamic sepsis, whereas prostaglandins do not have a major role in determining the early changes in RSNA.

Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans

Excessive or persistent proinflammatory cytokine production plays a central role in autoimmune diseases. Acute activation of the sympathetic nervous system attenuates the innate immune response. However, both the autonomic nervous system and innate immune system are regarded as systems that cannot be voluntarily influenced. Herein, we evaluated the effects of a training program on the autonomic nervous system and innate immune response. Healthy volunteers were randomized to either the intervention (n = 12) or control group (n = 12). Subjects in the intervention group were trained for 10 d in meditation (third eye meditation), breathing techniques (i.a., cyclic hyperventilation followed by breath retention), and exposure to cold (i.a., immersions in ice cold water). The control group was not trained. Subsequently, all subjects underwent experimental endotoxemia (i.v. administration of 2 ng/kg Escherichia coli endotoxin). In the intervention group, practicing the learned techniques resulted in intermittent respiratory alkalosis and hypoxia resulting in profoundly increased plasma epinephrine levels. In the intervention group, plasma levels of the anti-inflammatory cytokine IL-10 increased more rapidly after endotoxin administration, correlated strongly with preceding epinephrine levels, and were higher. Levels of proinflammatory mediators TNF-α, IL-6, and IL-8 were lower in the intervention group and correlated negatively with IL-10 levels. Finally, flu-like symptoms were lower in the intervention group. In conclusion, we demonstrate that voluntary activation of the sympathetic nervous system results in epinephrine release and subsequent suppression of the innate immune response in humans in vivo. These results could have important implications for the treatment of conditions associated with excessive or persistent inflammation, such as autoimmune diseases.

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.

Impaired chemoreflex sensitivity during septic shock induced by cecal ligation and perforation

In this study, we sought to determine the effects produced by cecal ligation and perforation (CLP) on the autonomic responses to the activation of peripheral chemoreflexes in conscious rats. The peripheral chemoreflex was activated with potassium cyanide (KCN; 40 μg·(0.1 mL)(-1); intravenous injection (i.v.)) in male Wistar rats 3, 6, 12, and 24 h after CLP or sham surgery. The mean arterial pressure (MAP), heart rate (HR), and respiratory frequency (fR) were recorded simultaneously. CLP surgery reduced the baseline MAP when compared with the sham animals. In the animals of the sham group, the autonomic responses to KCN produced increases in MAP and fR as well as a decrease in HR. However, 12 and 24 h after CLP surgery, the autonomic responses to KCN were attenuated. The restoration of MAP by i.v. injected l-NAME or phenylephrine did not restore the autonomic response to KCN in rats subjected to CLP. These data show that septic shock induced by CLP compromised the autonomic responses to peripheral chemoreflex activation in conscious rats, suggesting that an important regulatory mechanism is impaired during the course of this condition.

Infusion of Escherichia coli lipopolysaccharide toxin in rats produces an early and severe impairment of baroreflex function in absence of blood pressure changes

The assessment of baroreflex function since the first appearance of endotoxemia is important because the arterial baroreflex should exert a protective role during sepsis. Nevertheless, contrasting results were previously reported. This could be due to the hemodynamic instability characterizing this condition that may per se interfere with reflex cardiovascular adjustments. The aim of our study was therefore to study the baroreflex function (a) since the very beginning of infusion of Escherichia coli lipopolysaccharide (LPS) toxin and (b) in absence of the unloading effect produced by a decrease in blood pressure. Lipopolysaccharide was infused in 10 rats for 20 min at the infusion rate of 0.05 mg · kg · min. Blood pressure was continuously measured before, during, and after infusion, and the baroreflex function was evaluated analyzing spontaneous fluctuations of systolic blood pressure and pulse interval by the sequence and transfer-function techniques. Plasma concentrations of inflammatory (interleukin 6, tumor necrosis factor α) and anti-inflammatory (interleukin 10) cytokines were measured in other eight rats, similarly instrumented, four of which receiving the same LPS infusion. We found that blood pressure levels did not change with the infusion of LPS, whereas inflammatory cytokines increased significantly. The baroreflex sensitivity was significantly reduced 10 min after the beginning of LPS infusion, reached values about half those at baseline within 15 min after the start of infusion, and remained significantly low after the end of infusion. In conclusion, we documented that septic shock inducing LPS infusion is responsible for a very rapid impairment of the baroreflex function, independent from the level of blood pressure.

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.

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.

The influence of concentration/meditation on autonomic nervous system activity and the innate immune response: a case study

OBJECTIVE

In this case study, we describe the effects of a particular individual's concentration/meditation technique on autonomic nervous system activity and the innate immune response. The study participant holds several world records with regard to tolerating extreme cold and claims that he can influence his autonomic nervous system and thereby his innate immune response.

METHODS

The individual's ex vivo cytokine response (stimulation of peripheral blood mononuclear cells with lipopolysaccharide [LPS]) was determined before and after an 80-minute full-body ice immersion during which the individual practiced his concentration/meditation technique. Furthermore, the individual's in vivo innate immune response was studied while practicing his concentration/mediation technique during human endotoxemia (intravenous administration of 2 ng/kg LPS). The results from the endotoxemia experiment were compared with a historical cohort of 112 individuals who participated in endotoxemia experiments in our institution.

RESULTS

The ex vivo proinflammatory and anti-inflammatory cytokine response was greatly attenuated by concentration/meditation during ice immersion, accompanied by high levels of cortisol. In the endotoxemia experiment, concentration/meditation resulted in increased circulating concentrations of catecholamines, and plasma cortisol concentrations were higher than in any of the previously studied participants. The individual's in vivo cytokine response and clinical symptoms after LPS administration were remarkably low compared with previously studied participants.

CONCLUSIONS

The concentration/meditation technique used by this particular individual seems to evoke a controlled stress response. This response is characterized by sympathetic nervous system activation and subsequent catecholamine/cortisol release, which seems to attenuate the innate immune response.

Naturally occurring hypothermia is more advantageous than fever in severe forms of lipopolysaccharide- and Escherichia coli-induced systemic inflammation

The natural switch from fever to hypothermia observed in the most severe cases of systemic inflammation is a phenomenon that continues to puzzle clinicians and scientists. The present study was the first to evaluate in direct experiments how the development of hypothermia vs. fever during severe forms of systemic inflammation impacts the pathophysiology of this malady and mortality rates in rats. Following administration of bacterial lipopolysaccharide (LPS; 5 or 18 mg/kg) or of a clinical Escherichia coli isolate (5 × 10(9) or 1 × 10(10) CFU/kg), hypothermia developed in rats exposed to a mildly cool environment, but not in rats exposed to a warm environment; only fever was revealed in the warm environment. Development of hypothermia instead of fever suppressed endotoxemia in E. coli-infected rats, but not in LPS-injected rats. The infiltration of the lungs by neutrophils was similarly suppressed in E. coli-infected rats of the hypothermic group. These potentially beneficial effects came with costs, as hypothermia increased bacterial burden in the liver. Furthermore, the hypotensive responses to LPS or E. coli were exaggerated in rats of the hypothermic group. This exaggeration, however, occurred independently of changes in inflammatory cytokines and prostaglandins. Despite possible costs, development of hypothermia lessened abdominal organ dysfunction and reduced overall mortality rates in both the E. coli and LPS models. By demonstrating that naturally occurring hypothermia is more advantageous than fever in severe forms of aseptic (LPS-induced) or septic (E. coli-induced) systemic inflammation, this study provides new grounds for the management of this deadly condition.

Ghrelin modulates baroreflex-regulation of sympathetic vasomotor tone in healthy humans

Ghrelin, a neuropeptide originally known for its growth hormone-releasing and orexigenic properties, exerts important pleiotropic effects on the cardiovascular system. Growing evidence suggests that these effects are mediated by the sympathetic nervous system. The present study aimed at elucidating the acute effect of ghrelin on sympathetic outflow to the muscle vascular bed (muscle sympathetic nerve activity, MSNA) and on baroreflex-mediated arterial blood pressure (BP) regulation in healthy humans. In a randomized double-blind cross-over design, 12 lean young men were treated with a single dose of either ghrelin 2 μg/kg iv or placebo (isotonic saline). MSNA, heart rate (HR), and BP were recorded continuously from 30 min before until 90 min after substance administration. Sensitivity of arterial baroreflex was repeatedly tested by injection of vasoactive substances based on the modified Oxford protocol. Early, i.e., during the initial 30 min after ghrelin injection, BP significantly decreased together with a transient increase of MSNA and HR. In the course of the experiment (>30 min), BP approached placebo level, while MSNA and HR were significantly lower compared with placebo. The sensitivity of vascular arterial baroreflex significantly increased at 30-60 min after intravenous ghrelin compared with placebo, while HR response to vasoactive drugs was unaltered. Our findings suggest two distinct phases of ghrelin action: In the immediate phase, BP is decreased presumably due to its vasodilating effects, which trigger baroreflex-mediated counter-regulation with increases of HR and MSNA. In the delayed phase, central nervous sympathetic activity is suppressed, accompanied by an increase of baroreflex sensitivity.

The effects of brain injury on heart rate variability and the innate immune response in critically ill patients

Brain injury and its related increased intracranial pressure (ICP) may lead to increased vagus nerve activity and the subsequent suppression of innate immunity via the cholinergic anti-inflammatory pathway. This may explain the observed increased susceptibility to infection in these patients. In the present study, we investigated the association between brain injury, vagus nerve activity, and innate immunity. We determined heart rate variability (HRV) as a measure of vagus nerve activity, plasma cytokines, and cytokine production of ex vivo lipopolysaccharide-stimulated whole blood in the first 4 days of admission to the neurological intensive care unit (ICU) in 34 patients with various forms of brain damage. HRV, immune parameters, and the correlations between these measures were analyzed in the entire group of patients and in subgroups of patients with conditions associated with high (intracranial hemorrhage [ICH]) and normal ICP (subarachnoid hemorrhage [SAH] with an extraventricular drain alleviating ICP). Healthy volunteers were used for comparison. HRV total spectral power and ex vivo-stimulated cytokine production were severely depressed in patients compared with healthy volunteers (p<0.05). Furthermore, HRV analysis showed that normalized units of high-frequency power (HFnu, corresponding with vagus nerve activity) was higher, and the low-frequency:high-frequency ratio (LF:HF, corresponding with sympathovagal balance) was lower in patients compared to healthy volunteers (p<0.05). HFnu correlated inversely with ex vivo-stimulated tumor necrosis factor-α (TNF-α) production (r=-0.22, p=0.025). The most pronounced suppression of ex vivo-stimulated cytokine production was observed in the ICH group. Furthermore, in ICH patients, HFnu correlated strongly with lower plasma TNF-α levels (r=-0.73, p=0.002). Our data suggest that brain injury, and especially conditions associated with increased ICP, is associated with vagus nerve-mediated immune suppression.

Spontaneous fluctuations in the peripheral photoplethysmographic waveform: roles of arterial pressure and muscle sympathetic nerve activity

Assessment of spontaneous slow waves in the peripheral blood volume using the photoplethysmogram (PPG) has shown potential clinical value, but the physiological correlates of these fluctuations have not been fully elucidated. This study addressed the contribution of arterial pressure and muscle sympathetic nerve activity (MSNA) in beat-to-beat PPG variability in resting humans under spontaneous breathing conditions. Peripheral PPG waveforms were measured from the fingertip, earlobe, and toe in young and healthy individuals (n = 13), together with the arterial pressure waveform, electrocardiogram, respiration, and direct measurement of MSNA by microneurography. Cross-spectral coherence analysis revealed that among the PPG waveforms, low-frequency fluctuations (0.04-0.15 Hz) in the ear PPG had the highest coherence with arterial pressure (0.71 ± 0.15) and MSNA (0.44 ± 0.18, with a peak of 0.71 ± 0.16 at 0.10 ± 0.03 Hz). The normalized midfrequency powers (0.08-0.15 Hz), with an emphasis on the 0.1-Hz region, were positively correlated between MSNA and the ear PPG (r = 0.77, P = 0.002). Finger and toe PPGs had lower coherence with arterial pressure (0.35 ± 0.10 and 0.30 ± 0.11, respectively) and MSNA (0.33 ± 0.10 and 0.26 ± 0.10, respectively) in the LF band but displayed higher coherence between themselves (0.54 ± 0.09) compared with the ear (P < 0.001), which may suggest the dominance of regional vasomotor activities and a common sympathetic influence in the glabrous skin. These findings highlight the differential mechanisms governing PPG waveform fluctuations across different body sites. Spontaneous PPG variability in the ear includes a major contribution from arterial pressure and MSNA, which may provide a rationale for its clinical utility.

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.

Effect of acute ozone induced airway inflammation on human sympathetic nerve traffic: a randomized, placebo controlled, crossover study

Background

Ozone concentrations in ambient air are related to cardiopulmonary perturbations in the aging population. Increased central sympathetic nerve activity induced by local airway inflammation may be one possible mechanism.

Methodology/Principal Findings

To elucidate this issue further, we performed a randomized, double-blind, cross-over study, including 14 healthy subjects (3 females, age 22–47 years), who underwent a 3 h exposure with intermittent exercise to either ozone (250 ppb) or clean air. Induced sputum was collected 3 h after exposure. Nineteen to 22 hours after exposure, we recorded ECG, finger blood pressure, brachial blood pressure, respiration, cardiac output, and muscle sympathetic nerve activity (MSNA) at rest, during deep breathing, maximum-inspiratory breath hold, and a Valsalva maneuver. While the ozone exposure induced the expected airway inflammation, as indicated by a significant increase in sputum neutrophils, we did not detect a significant estimated treatment effect adjusted for period on cardiovascular measurements. Resting heart rate (clean air: 59±2, ozone 60±2 bpm), blood pressure (clean air: 121±3/71±2 mmHg; ozone: 121±2/71±2 mmHg), cardiac output (clean air: 7.42±0.29 mmHg; ozone: 7.98±0.60 l/min), and plasma norepinephrine levels (clean air: 213±21 pg/ml; ozone: 202±16 pg/ml), were similar on both study days. No difference of resting MSNA was observed between ozone and air exposure (air: 23±2, ozone: 23±2 bursts/min). Maximum MSNA obtained at the end of apnea (air: 44±4, ozone: 48±4 bursts/min) and during the phase II of the Valsalva maneuver (air: 64±5, ozone: 57±6 bursts/min) was similar.

Conclusions/Significance

Our study suggests that acute ozone-induced airway inflammation does not increase resting sympathetic nerve traffic in healthy subjects, an observation that is relevant for environmental health. However, we can not exclude that chronic airway inflammation may contribute to sympathetic activation.

Autonomic dysfunction in older people

The autonomic nervous system comprises the sympathetic, parasympathetic and enteric nervous systems and plays an integral role in homeostasis. This includes cardiovascular and temperature control, glucose metabolism, gastrointestinal and reproductive function and increasing evidence to support its involvement in the inflammatory response to infection and cancer. Ageing is associated with autonomic dysfunction, and many clinical syndromes associated with older adults are due to inadequate autonomic responses to physiological stressors. The aim of this review is to explore the relationship between autonomic dysfunction and ageing illustrated with examples of maladaptive autonomic responses in a variety of different clinical syndromes including an exploration of autonomic cellular changes. Appropriate investigation and management strategies are outlined, recognizing the fine balance needed to improve symptoms without creating further medical complications.

The role of vasoactive agents in the resuscitation of microvascular perfusion and tissue oxygenation in critically ill patients

Purpose

The clinical use of vasoactive drugs is not only intended to improve systemic hemodynamic variables, but ultimately to attenuate derangements in organ perfusion and oxygenation during shock. This review aims (1) to discuss basic physiology with respect to manipulating vascular tone and its effect on the microcirculation, and (2) to provide an overview of available clinical data on the relation between vasoactive drugs and organ perfusion, with specific attention paid to recent developments that have enabled direct in vivo observation of the microcirculation and concepts that have originated from it.

Methods

A MedLine search was conducted for clinical articles in the English language over the last 15 years pertainig to shock, sepsis, organ failure, or critically ill patients in combination with vasoactive drugs and specific variables of organ perfusion/oxygenation (e.g., tonometry, indocyanine clearance, laser Doppler, and sidestream dark field imaging).

Results

Eighty original papers evaluating the specific relationship between organ perfusion/oxygenation and the use of vasoactive drugs were identified and are discussed in light of physiological theory of vasomotor tone.

Conclusions

Solid clinical data in support of the idea that increasing blood pressure in shock improves microcirculatory perfusion/oxygenation seem to be lacking, and such a concept might not be in line with physiological theory of microcirculation as a low-pressure vascular compartment. In septic shock no beneficial effect on microcirculatory perfusion above a mean arterial pressure of 65 mmHg has been reported, but a wide range in inter-individual effect seems to exist. Whether improvement of microcirculatory perfusion is associated with better patient outcome remains to be elucidated.

Circulating white blood cell count and measures of adipose tissue inflammation predict higher 24-h energy expenditure

OBJECTIVE

Energy expenditure (EE) and measures of inflammation increase with adiposity, and this obesity-induced chronic and subclinical inflammation was extensively reported to be a cause of insulin resistance. However, whether subclinical inflammation has a role in increasing EE, which may be at the cost of developing insulin resistance, is not clear.

METHODS

We investigated the association between circulating white blood cell count (WBC) in a population of Native Americans (n=243) with measurement of EE in a respiratory chamber, and in a subset of the same population (n=34), with gene expression measures of inflammation in subcutaneous abdominal adipose tissue (SAAT). All subjects were healthy on oral glucose tolerance test. Statistically, nonnormally distributed variables were logarithmically transformed before analyses to approximate normal distributions.

RESULTS

WBC was associated with 24-h EE adjusted for age, sex, fat-free mass, and fat mass (r=0.13, P=0.04). In SAAT, tumor necrosis factor-alpha (TNF-alpha), shown as log10-transformed TNF-alpha (r=0.36, P=0.05), and plasminogen activator inhibitor-1 (PAI-1), shown as log10-transformed PAI-1 (lPAI-1; r=0.41, P=0.02), expressions were also positively correlated with adjusted 24-h EE. lPAI-1 was also correlated with adjusted sleep EE (r=0.34, P=0.07).

CONCLUSIONS

In conclusion, circulating markers of inflammation (WBC) and markers of inflammation within adipose tissue (TNF-alpha and PAI-1) are positively associated with EE, indicating a role of chronic subclinical inflammation in the regulation of metabolic rate.