Impairment of cardiopulmonary receptor sensitivity in the early phase of heart failure

Heart Rate Change as a Potential Digital Biomarker of Brain Death in Critically Ill Children With Acute Catastrophic Brain Injury

Bedside measurement of heart rate (HR) change (HRC) may provide an objective physiologic marker for when brain death (BD) may have occurred, and BD testing is indicated in children.

OBJECTIVES

To determine whether HRC, calculated using numeric HR measurements sampled every 5 seconds, can identify patients with BD among patients with catastrophic brain injury (CBI).

DESIGN SETTING AND PARTICIPANTS

Single-center, retrospective study (2008-2020) of critically ill children with acute CBI. Patients with CBI had a neurocritical care consultation, were admitted to an ICU, had acute neurologic injury on presentation or during hospitalization based on clinical and/or imaging findings, and died or survived with Glasgow Coma Scale (GCS) less than 13 at hospital discharge. Patients meeting BD criteria (BD group) were compared with those with cardiopulmonary death (CD group) or those who survived to discharge.

MAIN OUTCOMES AND MEASURES

HRC was calculated as the interquartile range of HR divided by median HR using 5-minute windows with 50% overlap for up to 5 days before death or end of recording. HRC was compared among the BD, CD, and survivor groups.

RESULTS

Of 96 patients with CBI (69% male, median age 4 years), 28 died (8 BD, 20 CD) and 20 survived (median GCS 9 at discharge). Within 24 hours before death, HRC was lower in BD compared with CD patients or survivors (0.01 vs 0.03 vs 0.04, p = 0.001). In BD patients, HRC decreased at least 1 day before death. HRC discriminated BD from CD patients and survivors with 90% sensitivity, 70% specificity, 44% positive predictive value, 96% negative predictive value (area under the receiver operating characteristic curve 0.88, 95% CI, 0.80-0.93).

CONCLUSIONS AND RELEVANCE

HRC is a novel digital biomarker that, with further validation, may be useful as a classifier for BD in the overall course of patients with CBI.

Cardiopulmonary Baroreflex Control of Renal Sympathetic Nerve Activity Is Impaired in Dogs With Left Ventricular Dysfunction

BACKGROUND

Activation of neurohormonal systems contributes to the progression of heart failure (HF). The mechanism(s) whereby these systems become activated is(are) not fully explained. We determined whether vagal cardiopulmonary baroreflex control of renal sympathetic nerve activity is abnormal in dogs with left ventricular (LV) dysfunction in the absence of clinical HF, and the relationship of abnormalities in baroreflexes to the development of the neurohumoral excitatory state.

METHODS

LV end-systolic and end-diastolic dimensions (echocardiography), arterial baroreflex sensitivity (slope of ΔRR/Δsystolic BP during phenylephrine or nitroglycerin bolus), and neurohumoral profiles (plasma norepinephrine, renin activity, and arginine vasopressin) were measured serially in conscious dogs (n=24) with progressive LV dysfunction due to rapid ventricular pacing. LV dimensions were used to define groups with mild, moderate, and marked LV dilatation (LVD; increase in LV end-diastolic volume <15%, 15-30%, and >30% of control, respectively). Changes in renal nerve activity (RNA) were recorded in response to increases in pulmonary capillary wedge pressure (PCWP) induced by volume infusion in anesthetized, sinoaortic-denervated dogs.

RESULTS

Cardiopulmonary baroreflex sensitivity (slope of %ΔRNA/ΔPCWP) for mild LVD (-17.8%/mmHg) was the same as controls (-17.7%/mmHg). However, the slopes of moderate (-5.8%/mmHg) and severe LVD (-1.9%/mmHg) were decreased significantly compared with controls (P < .05). Arterial baroreflex sensitivity was preserved at all stages of LVD. Plasma norepinephrine, renin activity, and arginine vasopressin remained unchanged after 4, 7, and 11 days of pacing.

CONCLUSIONS

Vagal cardiopulmonary baroreflex control of renal sympathetic nerve activity is blunted early in the development of LVD. These abnormalities precede neurohumoral excitation and abnormal arterial baroreflexes and become apparent when LV end-diastolic volume starts to increase.

Clinical evidence of autonomic dysfunction due to atrial fibrillation: implications for rhythm control strategy

PURPOSE

The role of the autonomic nervous system in the genesis of atrial fibrillation (AF) has been well studied; however, the converse remains poorly understood. Pulmonary veins (PV) contain receptors important in cardiac reflexes. Here, we evaluated reflex responses in patients with paroxysmal AF (PAF) to lower body negative pressure (LBNP).

METHODS

Thirty-four PAF patients (including 14 PAF patients post successful PV Isolation; PVI) were compared to 14 age and sex-matched controls. Mean arterial pressure (MAP), heart rate (HR), systemic vascular resistance index (SVRI), cardiac index (CI), and stroke volume index (SVI) were measured continuously during - 0, - 20, and - 40 mmHg LBNP. LBNP reduces venous return, deactivating atrial receptors, thereby eliciting a reflex increase in SVRI to maintain MAP.

RESULTS

AF patients have higher BMI than the controls (p = 0.02). In control subjects, LBNP did not alter MAP as SVRI increased. In PAF patients, LBNP resulted in a reduction in MAP (- 4.8%) with attenuated SVRI response (+ 4.2%) compared to controls (p < 0.05). However, in the post-PVI group, SVRI increase was similar to controls (p = 0.12) although that was insufficient to maintain MAP. In all patients, both reduction in SVI and CI and increase in HR were similar in response to LBNP.

CONCLUSIONS

This study provides novel clinical evidence of autonomic dysfunction in PAF patients. Successful PVI results in partial recovery of the cardiac reflex. Therefore, not only does autonomic disturbance predispose to AF but it is also a consequence of AF; potentially contributing to disease progression. This could help explain the dictum "AF begets AF."

High-intensity muscle metaboreflex activation attenuates cardiopulmonary baroreflex-mediated inhibition of muscle sympathetic nerve activity

Previous studies have shown that muscle sympathetic nerve activity (MSNA) is reduced during low- and mild-intensity dynamic leg exercise. It has been suggested that such inhibition is mediated by loading of the cardiopulmonary baroreceptors and that this effect is overridden by muscle metaboreflex activation with higher-intensity exercise. However, limited data are available regarding the interaction between the cardiopulmonary baroreflex and the muscle metaboreflex. Therefore, we tested the hypothesis that cardiopulmonary baroreflex-mediated inhibition of MSNA is attenuated during high-intensity muscle metaboreflex activation. In nine young men, MSNA (right peroneal nerve), mean arterial pressure (MAP), and thoracic impedance were recorded. Graded isolation of muscle metaboreflex activation was achieved via postexercise ischemia (PEI) following low (PEI-L)-, moderate (PEI-M)-, and high (PEI-H)-intensity isometric handgrip performed at 20, 30, and 40% maximum voluntary contraction, respectively. Lower-body positive pressure (LBPP, +10 Torr) was applied at rest and during PEI, to load the cardiopulmonary baroreceptors. Handgrip exercise elicited intensity-dependent increases in MSNA and MAP that were maintained during PEI, indicating a graded muscle metaboreflex activation. LBPP at rest significantly decreased MSNA burst frequency (BF: -36.7 ± 4.7%, mean ± SE, P < 0.05), whereas MAP was unchanged. When LBPP was applied during PEI, MSNA BF decreased significantly at PEI-L (-40.0 ± 9.2%, P < 0.05) and PEI-M (-27.0 ± 6.3%, P < 0.05), but not at PEI-H (+1.9 ± 7.1%, P > 0.05). These results suggest that low- and moderate-intensity muscle metaboreflex activation does not modulate the inhibition of MSNA by cardiopulmonary baroreceptor loading, whereas high-intensity metaboreflex activation can override cardiopulmonary baroreflex-mediated inhibition of sympathetic vasomotor outflow. NEW & NOTEWORTHY The interaction between the sympathoinhibitory influence of cardiopulmonary baroreflex and sympathoexcitatory effect of skeletal muscle metaboreflex is not completely understood. In the current study, light- to moderate-intensity muscle metaboreflex activation did not modulate the suppression of muscle sympathetic nerve activity by cardiopulmonary baroreceptor loading, whereas high-intensity muscle metaboreflex activation attenuated the cardiopulmonary baroreflex-mediated inhibition of muscle sympathetic nerve activity. These results provide important information concerning the neural reflex mechanisms regulating sympathetic vasomotor outflow during exercise.

Digitoxin improves cardiovascular autonomic control in rats with heart failure

The effects of chronic treatment with digitoxin on arterial baroreceptor sensitivity for heart rate (HR) and renal sympathetic nerve activity (rSNA) control, cardiopulmonary reflex, and autonomic HR control in an animal model of heart failure (HF) were evaluated. Wistar rats were treated with digitoxin, which was administered in their daily feed (1 mg/kg per day) for 60 days. The following 3 experimental groups were evaluated: sham, HF, and HF treated with digitoxin (HF + DIG). We observed an increase in rSNA in the HF group (190 ± 29 pps, n = 5) compared with the sham group (98 ± 14 pps, n = 5). Digitoxin treatment prevented an increase in rSNA (98 ± 14 pps, n = 7). Therefore, arterial baroreceptor sensitivity was decreased in the HF group (−1.24 ± 0.07 bpm/mm Hg, n = 8) compared with the sham group (−2.27 ± 0.23 bpm/mm Hg, n = 6). Digitoxin did not alter arterial baroreceptor sensitivity in the HF + DIG group. Finally, the HF group showed an increased low frequency band (LFb: 23 ± 5 ms2, n = 8) and a decreased high frequency band (HFb: 77 ± 5 ms2, n = 8) compared with the sham group (LFb: 14 ± 3 ms2; HFb: 86 ± 3 ms2, n = 9); the HF+DIG group exhibited normalized parameters (LFb: 15 ± 3 ms2; HFb: 85 ± 3 ms2, n = 9). In conclusion, the benefits of decreasing rSNA are not directly related to improvements in peripheral cardiovascular reflexes; such occurrences are due in part to changes in the central nuclei of the brain responsible for autonomic cardiovascular control.

Autonomous control of cardiovascular reactivity in patients with episodic and chronic forms of migraine

BACKGROUND

The autonomous cardiovascular control can contribute to progression of migraine. However, current data on cardiovascular reactivity in migraine, especially severe forms, are essentially contradictory. The main aim of this study was to compare the autonomous regulation of circulation in patients with episodic and chronic migraine and healthy subjects.

METHODS

Seventy three migraine patients (mean age 35 ± 10) including episodic migraine (51 patients, 4-14 headache days/months) and chronic migraine (22 patients, ≥15 headache days/month) along with age-match control (71 healthy voluntaries) were examined. The autonomic regulation of circulation was examined with the tilt-table test, a deep breathing and Valsalva Maneuver, handgrip test, cold-stress vasoconstriction, arterial baroreflex and blood pressure variability.

RESULTS

The changes in heart rate induced by deep breathing, Valsalva Maneuver, and blood pressure in tilt-table test in patients with migraine did not differ from the control group. In contrast, the values of cold-stress-vasoconstriction forearm blood-flow reactivity (p <0.001), the increase in diastolic blood pressure in handgrip test (p <0.001), mean blood pressure in the late stage of the second phase of Valsalva Maneuver (p <0.001) and blood pressure variability (p <0.005) were all higher in patients with migraine than in the control group.

CONCLUSION

Thus, both episodic and chronic migraine are associated with significant disturbances in autonomous control resulting in enhanced vascular reactivity whereas the cardiac regulation remains largely unchanged.

Impact of l-NAME on the cardiopulmonary reflex in cardiac hypertrophy

There is evidence that in cardiac failure, there is defective baroreceptor reflex control of sympathetic nerve activity. Often, cardiac failure is preceded by a state of cardiac hypertrophy in which there may be enhanced performance of the heart. This study investigated whether in two different models of cardiac hypertrophy, there was an increased contribution of nitric oxide (NO) to the low-pressure baroreceptor regulation of renal sympathetic nerve activity (RSNA) and nerve-dependent excretory function. Administration of a volume load, 0.25* body wt/min saline for 30 min, in normal rats decreased RSNA by 40* and increased urine flow by some 9-fold. Following nitro-l-arginine methyl ester (l-NAME) administration, 10 μg·kg−1·min−1 for 60 min, which had no effect on blood pressure, heart rate, or RSNA, the volume load-induced renal sympathoinhibitory and excretory responses were markedly enhanced. In cardiac hypertrophy states induced by 2 wk of isoprenaline/caffeine or 1 wk thyroxine administration, the volume challenge failed to suppress RSNA, and there were blunted increases in urine flow in the innervated kidneys, but following l-NAME infusion, the volume load decreased RSNA by 30–40* and increased urine flow by some 20-fold in the innervated kidneys, roughly to the same extent as observed in normal rats. These findings suggest that the blunted renal sympathoinhibition and nerve-dependent diuresis to the volume load in cardiac hypertrophy are related to a heightened production or activity of NO within either the afferent or central arms of the reflex.

Dissociation between reflex sympathetic and forearm vascular responses to lower body negative pressure in heart failure patients with coronary artery disease

Many heart failure (HF) patients exhibit paradoxical forearm vasodilation when central blood volume is reduced by lower body negative pressure (LBNP). We tested the hypothesis that this response results from reflex sympathetic withdrawal. We recorded simultaneously forearm blood flow, muscle sympathetic nerve activity (MSNA), and plasma norepinephrine (PNE) during four random applications of LBNP, -5, -10, -20, and -40 mmHg, in 12 men with HF (mean left ventricular ejection fraction = 24 + or - 2%) and 10 healthy, normal, age-matched men (N). Compared with N, MSNA burst frequency (P = 0.001) and PNE (P = 0.005) were significantly higher in the HF group, both at rest and during LBNP. As anticipated in N, LBNP -40 mmHg significantly increased MSNA (+14.2 + or - 2.5 bursts/min; P < 0.05) and PNE (+0.83 + or - 0.22 nmol/l; P < 0.05) and decreased forearm vascular conductance (FVC) (-11.7 + or - 3.2 ml.min(-1).mmHg(-1); P < 0.05). In the HF group, LBNP elicited similar increases in MSNA (+11.5 + or - 2.0; P < 0.05) and PNE (+0.85 + or - 0.12; P < 0.05), without affecting FVC significantly (-4.1 + or - 2.4; P = 0.01 vs. N, interaction P = 0.03). However, within the HF group, responses were bimodal: LBNP -40 mmHg increased MSNA in all subjects (P < 0.001), yet the six patients with nonischemic or dilated cardiomyopathy (DCM) exhibited significant vasoconstriction (decrease in FVC; P = 0.001), whereas the six patients with ischemic cardiomyopathy (ICM) exhibited significant vasodilation (increase in FVC; P < 0.02 vs. DCM and N; interaction P = 0.02). Cold pressor testing increased MSNA and decreased FVC in ICM (n = 4). Thus paradoxical forearm vasodilator responses to LBNP in HF are not mediated by reflex sympathetic withdrawal. ICM and DCM patients differ qualitatively in their vascular responses to hypotensive LBNP.

Current concepts of neurohormonal activation in heart failure: mediators and mechanisms

Neurohormonal activation is a commonly cited array of phenomena in the body's physiologic response to heart failure. Although various neurohormones and pharmacologic agents that moderate their pathophysiologic effects have been reviewed in the nursing literature, both the mechanisms of neurohormonal system activation and cellular and organ system effects have been described only in brief. Accordingly, this article reviews mechanisms of neurohormonal activation and describes cellular and cardiovascular effects of the (1) sympathetic nervous system, (2) renin-angiotensin-aldosterone system, (3) kallikrein-kininogen-kinin system, (4) vasopressinergic system, (5) natriuretic peptide systems, and (6) endothelin in the context of heart failure. This article implicitly details the physiologic basis for numerous current and potential future pharmacologic agents used in the management of heart failure. It is intended that this article be used as a reference for advanced clinical nursing practice, research, and education.

Left atrial remodelling contributes to the progression of asymptomatic left ventricular systolic dysfunction to chronic symptomatic heart failure

Systolic heart failure (HF) is a progressive disorder that often begins with asymptomatic left ventricular (LV) systolic dysfunction and culminates in symptoms from fluid overload and poor end-organ perfusion. The progression to symptomatic HF is accompanied by marked activation of neurohormonal and cytokine systems, as well as a series of adaptive LV anatomical and functional changes, collectively referred to as LV remodelling. However, the mechanisms underlying symptom appearance have not been delineated and the weight of experimental and clinical evidence suggests that the development of symptomatic HF occurs independently of the haemodynamic status of the patient. The left atrium is a muscular chamber strategically located between the left ventricle and the pulmonary circulation with important mechanical function (modulation of LV filling), which is closely coupled with its endocrine (atrial natriuretic peptide synthesis and secretion) and regulatory (contribution to the control of sympathetic activity and vasopressin release) functions. In this narrative review we provide evidence supporting the concept that left atrial dilation and systolic dysfunction (left atrial remodelling) contributes to the progression of asymptomatic LV dysfunction to chronic symptomatic systolic HF as it is a prerequisite for the development of the pulmonary congestion and marked neuronhormoral activity that characterize the symptomatic state.

The role of heart rate variability in prognosis for different modes of death in chronic heart failure

Classic risk factors for mortality due to chronic heart failure (CHF), such as low left ventricular ejection fraction, NYHA functional stage, and increased heart rate perform well in the prediction of death from pump failure. The prediction of sudden cardiac death (SCD) remains somewhat problematic. Numerous studies have analyzed the potential contribution heart rate variability (HRV) can make to risk assessment in CHF. The aim of this review was to summarize the literature and identify the role HRV might play in identifying mode of death, as well as overall mortality risk. In studies where all-cause mortality or cardiac events were the clinical end point(s), global and slow oscillatory measures of HRV were the strongest risk predictors. In the fewer studies that used SCD as an end point, the strongest risk factors were HRV measures of short-term oscillations and sympathovagal interaction. We concluded from these findings that different HRV measurements predict different modes of death in CHF.Additionally, further studies using short-term analysis of HRV and non-linear analyses are warranted. Furthermore, studies with multiple end points, which clearly delineate pump failure from SCD, may be useful to identify more clearly the role HRV measures can play in the prediction of SCD.

Effect of pimobendan on cardiopulmonary baroreflex control of sympathetic nerve activity in healthy young men

In order to determine the effect of pimobendan on sympathetic nerve activity and cardiopulmonary baroreflex (CPB), electrocardiogram, direct arterial pressure, central venous pressure (CVP) and cardiac output were recorded along with muscle sympathetic nerve activity (MSNA) in 8 healthy young men. CPB function was evaluated before and 60 min after oral administration of 5 mg pimobendan using the response of MSNA to lower body negative pressure (LBNP) of -5 and -10 mm Hg. The same protocol also was performed during handgrip exercise. Cardiac index, MSNA increased and CVP decreased significantly (p<0.01, respectively), but arterial pressure and heart rate unchanged after pimobendan administration. During LBNP, CVP decreased and MSNA increased significantly. CPB sensitivity was augmented from 5.53+/-0.75 to 8.59+/-0.78 burst incidence/mm Hg after pimobendan administration (p<0.01). Pimobendan did not alter the percentage increase of MSNA during handgrip exercise. In conclusion, pimobendan induces an increase in basal sympathetic nerve activity by decreasing CVP and augmenting CPB sensitivity without changing arterial pressure in healthy young men.

Noninvasive assessment of cardiac output

Improved outcome from shock depends on early detection and correction of circulatory abnormalities. Global cardiac output and oxygen delivery must be adequate and distributed appropriately to meet metabolic demands to prevent the development of multiple organ system dysfunction, prolonged morbidity, and death. Circulatory assessment using standard monitors gives incomplete and sometimes misleading information. This article focuses on the available and emerging technologies that emphasize assessment of blood flow and regional tissue oxygenation.

Pressure and time dependence of the cardiopulmonary reflex response in patients with hypertensive cardiomyopathy

The first minutes of the time course of cardiopulmonary reflex control evoked by lower body negative pressure (LBNP) in patients with hypertensive cardiomyopathy have not been investigated in detail. We studied 15 hypertensive patients with left ventricular dysfunction (LVD) and 15 matched normal controls to observe the time course response of the forearm vascular resistance (FVR) during 3 min of LBNP at -10, -15, and -40 mmHg in unloading the cardiopulmonary receptors. Analysis of the average of 3-min intervals of FVR showed a blunted response of the LVD patients at -10 mmHg (P = 0.03), but a similar response in both groups at -15 and -40 mmHg. However, using a minute-to-minute analysis of the FVR at -15 and -40 mmHg, we observed a similar response in both groups at the 1st min, but a marked decrease of FVR in the LVD group at the 3rd min of LBNP at -15 mmHg (P = 0.017), and -40 mmHg (P = 0.004). Plasma norepinephrine levels were analyzed as another neurohumoral measurement of cardiopulmonary receptor response to LBNP, and showed a blunted response in the LVD group at -10 (P = 0.013), -15 (P = 0.032) and -40 mmHg (P = 0.004). We concluded that the cardiopulmonary reflex response in patients with hypertensive cardiomyopathy is blunted at lower levels of LBNP. However, at higher levels, the cardiopulmonary reflex has a normal initial response that decreases progressively with time. As a consequence of the time-dependent response, the cardiopulmonary reflex response should be measured over small intervals of time in clinical studies.

Neural control of renal function

The renal nerves are the communication link between the central nervous system and the kidney. In response to multiple peripheral and central inputs, efferent renal sympathetic nerve activity is altered so as to convey information to the major structural and functional components of the kidney, the vessels, glomeruli, and tubules, each of which is innervated. At the level of each of these individual components, information transfer occurs via interaction of the neurotransmitter released at the sympathetic nerve terminal-neuroeffector junction with specific postjunctional receptors coupled to defined intracellular signaling and effector systems. In response to normal physiological stimuli, changes in efferent renal sympathetic nerve activity contribute importantly to homeostatic regulation of renal blood flow, glomerular filtration rate, renal tubular epithelial cell solute and water transport, and hormonal release. Afferent input from sensory receptors located in the kidney participates in this reflex control system via renorenal reflexes that enable total renal function to be self-regulated and balanced between the two kidneys. In pathophysiological conditions, abnormal regulation of efferent renal sympathetic nerve activity contributes significantly to the associated abnormalities of renal function which, in turn, are of importance in the pathogenesis of the disease.