Impact of right ventricular and pulmonary vascular characteristics on Impella hemodynamic support in biventricular heart failure: A simulation study.

BACKGROUND: Impella (Abiomed, Danvers, MA, USA) is a percutaneous ventricular assist device commonly used in cardiogenic shock, providing robust hemodynamic support, improving the systemic circulation, and relieving pulmonary congestion. Maintaining adequate left ventricular (LV) filling is essential for optimal hemodynamic support by Impella. This study aimed to investigate the impact of pulmonary vascular resistance (PVR) and right ventricular (RV) function on Impella-supported hemodynamics in severe biventricular failure using cardiovascular simulation. METHODS: We used Simulink® (Mathworks, Inc., Natick, MA, USA) for the simulation, incorporating pump performance of Impella CP determined using a mock circulatory loop. Both systemic and pulmonary circulation were modeled using a 5-element resistance-capacitance network. The four cardiac chambers were represented by time-varying elastance with unidirectional valves. In the scenario of severe LV dysfunction (LV end-systolic elastance set at a low level of 0.4 mmHg/mL), we compared the changes in right (RAP) and left atrial pressures (LAP), total systemic flow, and pressure-volume loop relationship at varying degrees of RV function, PVR, and Impella flow rate. RESULTS: The simulation results showed that under low PVR conditions, an increase in Impella flow rate slightly reduced RAP and LAP and increased total systemic flow, regardless of RV function. Under moderate RV dysfunction and high PVR conditions, an increase in Impella flow rate elevated RAP and excessively reduced LAP to induce LV suction, which limited the increase in total systemic flow. CONCLUSIONS: PVR is the primary determinant of stable and effective Impella hemodynamic support in patients with severe biventricular failure.

Novel closed-loop control system of dual rotary blood pumps in total artificial heart based on the circulatory equilibrium framework: a proof-of-concept in vivo study.

OBJECTIVE: Total artificial heart (TAH) using dual rotary blood pumps (RBPs) is a potential treatment for end-stage heart failure. A well-noted challenge with RBPs is their low sensitivity to preload, which can lead to venous congestion and ventricular suction. To address this issue, we have developed an innovative closed-loop control system of dual RBPs in TAH. This system emulates the Frank-Starling law of the heart in controlling RBPs while monitoring stressed blood volume (V) based on the circulatory equilibrium framework. We validated the system in in-vivo experiments. METHODS: In 9 anesthetized dogs, we prepared a TAH circuit using 2 centrifugal-type RBPs. We first investigated whether the flow and inlet atrial pressure in each RBP adhered to a logarithmic Frank-Starling curve. We then examined whether the RBP flows and atrial pressures were maintained stably during aortic occlusion (AO) and pulmonary cannula stenosis (PS), whether averaged flow of dual RBPs and bilateral atrial pressures were controlled to their predefined target values for a specific V, and whether this system could maintain the atrial pressures within predefined control ranges under significant changes in V. RESULTS: This system effectively emulated the logarithmic Frank-Starling curve. It robustly stabilized the flow and atrial pressures during AO and PS without venous congestion or ventricular suction, accurately achieved target values in averaged flow and atrial pressures, and efficaciously maintained these pressures within the control ranges. CONCLUSION: This system controls dual RBPs in TAH accurately and stably. SIGNIFICANCE: This system may accelerate clinical application of TAH with dual RBPs.

Computer-controlled closed-loop norepinephrine infusion system for automated control of mean arterial pressure in dogs under isoflurane-induced hypotension: a feasibility study.

Introduction: Intra-operative hypotension is a common complication of surgery under general anesthesia in dogs and humans. Computer-controlled closed-loop infusion systems of norepinephrine (NE) have been developed and clinically applied for automated optimization of arterial pressure (AP) and prevention of intra-operative hypotension in humans. This study aimed to develop a simple computer-controlled closed-loop infusion system of NE for the automated control of the mean arterial pressure (MAP) in dogs with isoflurane-induced hypotension and to validate the control of MAP by the developed system. Methods: NE was administered via the cephalic vein, whereas MAP was measured invasively by placing a catheter in the dorsal pedal artery. The proportional-integral-derivative (PID) controller in the negative feedback loop of the developed system titrated the infusion rate of NE to maintain the MAP at the target value of 60 mmHg. The titration was updated every 2 s. The performance of the developed system was evaluated in six laboratory Beagle dogs under general anesthesia with isoflurane. Results: In the six dogs, when the concentration [median (interquartile range)] of inhaled isoflurane was increased from 1.5 (1.5-1.5)% to 4 (4-4)% without activating the system, the MAP was lowered from 95 (91-99) to 41 (37-42) mmHg. In contrast, when the concentration was increased from 1.5 (1.0-1.5)% to 4 (4-4.8)% for a 30-min period and the system was simultaneously activated, the MAP was temporarily lowered from 92 (89-95) to 47 (43-49) mmHg but recovered to 58 (57-58) mmHg owing to the system-controlled infusion of NE. If the acceptable target range for MAP was defined as target MAP ±5 mmHg (55 ≤ MAP ≤65 mmHg), the percentage of time wherein the MAP was maintained within the acceptable range was 96 (89-100)% in the six dogs during the second half of the 30-min period (from 15 to 30 min after system activation). The median performance error, median absolute performance error, wobble, and divergence were - 2.9 (-4.7 to 1.9)%, 2.9 (2.0-4.7)%, 1.3 (0.8-1.8)%, and - 0.24 (-0.34 to -0.11)%·min-1, respectively. No adverse events were observed during the study period, and all dogs were extubated uneventfully. Conclusion: This system was able to titrate the NE infusion rates in an accurate and stable manner to maintain the MAP within the predetermined target range in dogs with isoflurane-induced hypotension. This system can be a potential tool in daily clinical practice for the care of companion dogs.

Effects of nitric oxide inhalation on pulmonary arterial impedance: differences between normal and pulmonary hypertension male rats.

Nitric oxide (NO) inhalation improves pulmonary hemodynamics in participants with pulmonary arterial hypertension (PAH). Although it can reduce pulmonary vascular resistance (PVR) in PAH, its impact on the dynamic mechanics of pulmonary arteries and its potential difference between control and participants with PAH remain unclear. PA impedance provides a comprehensive description of PA mechanics. With an arterial model, PA impedance can be parameterized into peripheral pulmonary resistance (Rp), arterial compliance (Cp), characteristic impedance of the proximal arteries (Zc), and transmission time from the main PA to the reflection site. This study investigated the effects of inhaled NO on PA impedance and its associated parameters in control and monocrotaline-induced pulmonary arterial hypertension (MCT-PAH) male rats (6/group). Measurements were obtained at baseline and during NO inhalation at 40 and 80 ppm. In both groups, NO inhalation decreased PVR and increased the left atrial pressure. Notably, its impact on PA impedance was frequency dependent, as revealed by reduced PA impedance modulus in the low-frequency range below 10 Hz, with little effect on the high-frequency range. Furthermore, NO inhalation attenuated Rp, increased Cp, and prolonged transmission time without affecting Zc. It reduced Rp more pronouncedly in MCT-PAH rats, whereas it increased Cp and delayed transmission time more effectively in control rats. In conclusion, the therapeutic effects of inhaled NO on PA impedance were frequency dependent and may differ between the control and MCT-PAH groups, suggesting that the effect on the mechanics differs depending on the pathological state.NEW & NOTEWORTHY Nitric oxide inhalation decreased pulmonary arterial impedance in the low-frequency range (<10 Hz) with little impact on the high-frequency range. It reduced peripheral pulmonary resistance more pronouncedly in pulmonary hypertension rats, whereas it increased arterial compliance and transmission time in control rats. Its effect on the mechanics of the pulmonary arteries may differ depending on the pathological status.

Donepezil attenuates progression of cardiovascular remodeling and improves prognosis in spontaneously hypertensive rats with chronic myocardial infarction.

The acetylcholinesterase inhibitor donepezil restores autonomic balance, reduces inflammation, and improves long-term survival in rats with chronic heart failure (CHF) following myocardial infarction (MI). As arterial hypertension is associated with a significant risk of cardiovascular death, we investigated the effectiveness of donepezil in treating CHF in spontaneously hypertensive rats (SHR). CHF was induced in SHR by inducing permanent MI. After 2 weeks, the surviving SHR were randomly assigned to sham-operated (SO), untreated (UT), or oral donepezil-treated (DT, 5 mg/kg/day) groups, and various vitals and parameters were monitored. After 7 weeks of treatment, heart rate and arterial hypertension reduced significantly in DT rats than in UT rats. Donepezil treatment improved 50-day survival (41% to 80%, P = 0.004); suppressed progression of cardiac hypertrophy, cardiac dysfunction (cardiac index: 133 ± 5 vs. 112 ± 5 ml/min/kg, P < 0.05; left ventricular end-diastolic pressure: 12 ± 3 vs. 22 ± 2 mmHg, P < 0.05; left ventricular +dp/dtmax: 5348 ± 338 vs. 4267 ± 114 mmHg/s, P < 0.05), systemic inflammation, and coronary artery remodeling (wall thickness: 26.3 ± 1.4 vs. 34.7 ± 0.7 µm, P < 0.01; media-to-lumen ratio: 3.70 ± 0.73 vs. 8.59 ± 0.84, P < 0.001); increased capillary density; and decreased plasma catecholamine, B-type natriuretic peptide, arginine vasopressin, and angiotensin II levels. Donepezil treatment attenuated cardiac and coronary artery remodeling, mitigated cardiac dysfunction, and significantly improved the prognosis of SHR with CHF.

The impact of ECPELLA on haemodynamics and global oxygen delivery: a comprehensive simulation of biventricular failure.

BACKGROUND: ECPELLA, a combination of veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) and Impella, a percutaneous left ventricular (LV) assist device, has emerged as a novel therapeutic option in patients with severe cardiogenic shock (CS). Since multiple cardiovascular and pump factors influence the haemodynamic effects of ECPELLA, optimising ECPELLA management remains challenging. In this study, we conducted a comprehensive simulation study of ECPELLA haemodynamics. We also simulated global oxygen delivery (DO2) under ECPELLA in severe CS and acute respiratory failure as a first step to incorporate global DO2 into our developed cardiovascular simulation. METHODS AND RESULTS: Both the systemic and pulmonary circulations were modelled using a 5-element resistance‒capacitance network. The four ventricles were represented by time-varying elastances with unidirectional valves. In the scenarios of severe LV dysfunction, biventricular dysfunction with normal pulmonary vascular resistance (PVR, 0.8 Wood units), and biventricular dysfunction with high PVR (6.0 Wood units), we compared the changes in haemodynamics, pressure-volume relationship (PV loop), and global DO2 under different VA-ECMO flows and Impella support levels. RESULTS: In the simulation, ECPELLA improved total systemic flow with a minimising biventricular pressure-volume loop, indicating biventricular unloading in normal PVR conditions. Meanwhile, increased Impella support level in high PVR conditions rendered the LV-PV loop smaller and induced LV suction in ECPELLA support conditions. The general trend of global DO2 was followed by the changes in total systemic flow. The addition of veno-venous ECMO (VV-ECMO) augmented the global DO2 increment under ECPELLA total support conditions. CONCLUSIONS: The optimal ECPELLA support increased total systemic flow and achieved both biventricular unloading. The VV-ECMO effectively improves global DO2 in total ECPELLA support conditions.

Inverse ESPVR Estimation with Singularity Avoidance via Constrained EDPVR Parameter Optimization.

Left ventricular end-systolic elastance Ees, as an index of cardiac contractility, can play a key role in continuous patient monitoring during cardiac treatment scenarios such as drug therapies. The clinical feasibility of Ees estimation remains challenging because most techniques have been built on left ventricular pressure and volume, which are difficult to measure or estimate in the regular ICU/CCU setting. The purpose of this paper is to propose and validate a novel approach to estimate Ees, which is independent of left ventricular pressure and volume. Our methods first derive an analytical representation of Ees as the inverse function of the gradient of the Frank-Starling Curve based on cardiac mechanics. Second, elucidating the mechanism of singularities in the inverse function, we derive multiple conditions in both end-systolic pressure-volume relationship (ESPVR) and end-diastolic pressure-volume relationship (EDPVR) parameters to avoid these singularities analytically. Third, we formulate a constrained nonlinear least squares problem to optimize both ESPVR and EDPVR parameters simultaneously to avoid singularities. The effectiveness of the proposed method in avoiding singularities was evaluated in an animal experiment. Compared to the conventional Ees estimation by linear regression, our proposed method reproduced in-vivo hemodynamics more accurately when simulating the estimated Ees variation during drug administration. Our method can be applied using the available data in the regular ICU/CCU setting. The improved clinical feasibility can support not only physicians' decision-making, including adjusting drug dosages in current clinical treatment, but also a closed-loop hemodynamic control system requiring accurate continuous Ees estimation.

Analytical Representation of Four-dimensional Hemodynamics for Drug Therapy Simulation in Acute Heart Failure Treatment.

Acute heart failure imperils multiple organs, including the heart. Elucidating the impact of drug therapies across this multidimensional hemodynamic system remains a challenge. This paper proposes a simulator that analyzes the impact of drug therapies on four dimensions of hemodynamics: left atrial pressure, cardiac output, mean arterial pressure, and myocardial oxygen consumption. To mathematically formulate hemodynamics, the analytical solutions of four-dimensional hemodynamics and the direction of its change are derived as functions of cardiovascular parameters: systemic vascular resistance, cardiac contractility, heart rate, and stressed blood volume. Furthermore, a drug library which represents the multi-dependency effect of drug therapies on cardiovascular parameters was identified in animal experiments. In evaluating the accuracy of our derived hemodynamic direction, the average angular error of predicted versus observed direction was 18.85[deg] after four different drug infusions for acute heart failure in animal experiments. Finally, the impact of drug therapies on four-dimensional hemodynamics was analyzed in three different simulation settings. One result showed that, even when drug therapies were simulated with simple rules according to the Forrester classification, the predicted direction of hemodynamic change matched the expected direction in more than 80% in 963 different AHF patient scenarios. Our developed simulator visualizes the impact of drug therapies on four-dimensional hemodynamics so intuitively that it can support clinicians' decision-making to protect multiple organs.

Acute effects of empagliflozin on open-loop baroreflex function and urinary glucose excretion in rats with chronic myocardial infarction.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have exerted cardioprotective effects in clinical trials, but underlying mechanisms are not fully understood. As mitigating sympathetic overactivity is of major clinical concern in the mechanisms of heart failure treatments, we examined the effects of modulation of glucose handling on baroreflex-mediated sympathetic nerve activity and arterial pressure regulations in rats with chronic myocardial infarction (n = 9). Repeated 11-min step input sequences were used for an open-loop analysis of the carotid sinus baroreflex. An SGLT2 inhibitor, empagliflozin, was intravenously administered (10 mg/kg) after the second sequence. Neither the baroreflex neural nor peripheral arc significantly changed during the last observation period (seventh and eighth sequences) compared with the baseline period although urinary glucose excretion increased from near 0 (0.0089 ± 0.0011 mg min-1 kg-1) to 1.91 ± 0.25 mg min-1 kg-1. Hence, empagliflozin does not acutely modulate the baroreflex regulations of sympathetic nerve activity and arterial pressure in this rat model of chronic myocardial infarction.

Impact of vericiguat on baroreflex-mediated sympathetic circulatory regulation: An open-loop analysis.

AIMS: To quantify in vivo the effects of the soluble guanylate cyclase (sGC) stimulator, vericiguat, on autonomic cardiovascular regulation in comparison with the nitric oxide (NO) donor, sodium nitroprusside. METHODS: In anesthetized Wistar-Kyoto rats, baroreflex-mediated changes in sympathetic nerve activity (SNA), arterial pressure (AP), central venous pressure (CVP), and aortic flow (AoF) were examined before and during the intravenous continuous administration (10 µg·kg-1·min-1) of vericiguat or sodium nitroprusside (n = 8 each). Systemic vascular resistance (SVR) was calculated as SVR = (AP-CVP) / AoF. RESULTS: Neither vericiguat nor sodium nitroprusside affected fitted parameters of the baroreflex-mediated SNA response. Both vericiguat and sodium nitroprusside decreased the AP mainly through their peripheral effects. Vericiguat halved the slope of the SNA-SVR relationship from 0.012 ± 0.002 to 0.006 ± 0.002 mmHg·min·mL-1·%-1 (P = 0.008), whereas sodium nitroprusside caused a near parallel downward shift in the SNA-SVR relationship with a reduction of the SVR intercept from 1.235 ± 0.187 to 0.851 ± 0.123 mmHg·min/mL (P = 0.008). CONCLUSION: Neither vericiguat nor sodium nitroprusside significantly affected the baroreflex-mediated SNA response. The vasodilative effect of vericiguat became greater toward high levels of SNA and AP, possibly reflecting the increased sGC sensitivity to endogenous NO. By contrast, the effect of sodium nitroprusside was more uniform over the range of SNA. These results help better understand cardiovascular effects of vericiguat.

Impact of neurally mediated antidiuretic effect relative to pressure diuresis during acute changes in sympathetic nerve activity.

We examined urine excretion during primary acute sympathetic activation (PASA) in anesthetized Wistar-Kyoto rats. Since arterial pressure (AP) changes with sympathetic nerve activity (SNA) during PASA, urine excretion reflects a neurally mediated antidiuretic effect combined with an effect of pressure diuresis. We hypothesized that preventing AP changes under PASA would enable the direct estimation of the neurally mediated antidiuretic effect alone. We changed the isolated carotid sinus pressure stepwise from 60 to 180 mmHg and compared the relationship of normalized urine flow (nUF, urine flow normalized by body weight) versus SNA between conditions allowing and preventing baroreflex-mediated changes in the mean AP. The slope of the SNA-nUF relationship was [Formula: see text]nUFvar = 0.444 ± 0.074 µL·min-1·kg-1·%-1 when the mean AP was variable, whereas it was [Formula: see text]nUFfix = -0.143 ± 0.032 µL·min-1·kg-1·%-1 when the mean AP was fixed at 100 mmHg (n = 7 rats). The slope associated with the effect of pressure diuresis alone, calculated as [Formula: see text]nUFvar - [Formula: see text]nUFfix, was 0.586 ± 0.105 µL·min-1·kg-1·%-1. Hence, the potency of the neurally mediated antidiuretic effect |[Formula: see text]nUFfix|/([Formula: see text]nUFvar - [Formula: see text]nUFfix) was 0.235 ± 0.014 relative to the effect of pressure diuresis under PASA. Our findings would aid an integrative understanding of the effects of renal hemodynamic and sympathetic modulations on urine output function.

A Novel Triple-Bladder Cuff Method for Blood Pressure Estimation Based on Pulse Wave Dynamics in Brachial Artery: Theoretical and Experimental Analyses.

OBJECTIVE: The objective of this study was to develop a novel triple-bladder cuff method for accurate and automated estimation of systolic (SBP) and diastolic (DBP) blood pressure and validate its reliability in animal experiments. METHODS: The cuff is composed of three bladders each measured one-third the width of a conventional BP cuff, which are designed to measure oscillatory pulsation at the proximal, middle, and distal segments of the upper arm. This structure allows evaluation of the pulse wave propagation in the brachial artery under the cuff. SBP is estimated (SBPe) by detecting resumption of systolic arterial flow based on statistical similarity in oscillatory pulse traces between the proximal and distal segments. DBP is estimated (DBPe) based on the relation between pulse wave velocity and transmural pressure at diastole in the brachial artery. In 7 anesthetized goats, we compared SBPe and DBPe to reference SBP and DBP, respectively, measured by an intra-arterial catheter. BP was perturbed by infusing nitroprusside or noradrenaline. RESULTS: SBP correlated strongly with SBPe in each animal [mean coefficient of determination (R2) = 0.98 ± 0.01]. Mean ± standard deviation of errors between SBP and SBPe was 0.0 ± 4.9 mmHg. DBP correlated strongly with DBPe in each animal (R2 = 0.96 ± 0.03). Mean ± standard deviation of errors between DBP and DBPe was 0.0 ± 6.3 mmHg. CONCLUSION: This method estimates SBP and DBP with acceptable accuracy. SIGNIFICANCE: Accurate and automated BP estimation by this method may potentially optimize antihypertensive treatment in patients with hypertension.

Dynamic accentuated antagonism of heart rate control during different levels of vagal nerve stimulation intensity in rats.

Accentuated antagonism refers to a phenomenon in which the vagal effect on heart rate (HR) is augmented by background sympathetic tone. The dynamic aspect of accentuated antagonism remains to be elucidated during different levels of vagal nerve stimulation (VNS) intensity. We performed VNS on anesthetized rats (n = 8) according to a binary white noise signal with a switching interval of 500 ms at three different stimulation rates (low-intensity: 0-10 Hz, moderate-intensity: 0-20 Hz, and high-intensity: 0-40 Hz). The transfer function from VNS to HR was estimated with and without concomitant tonic sympathetic nerve stimulation (SNS) at 5 Hz. The asymptotic low-frequency (LF) gain (in beats/min/Hz) of the transfer function increased with SNS regardless of the VNS rate [low-intensity: 3.93 ± 0.70 vs. 5.82 ± 0.65 (P = 0.021), moderate-intensity: 3.87 ± 0.62 vs. 5.36 ± 0.53 (P = 0.018), high-intensity: 4.77 ± 0.85 vs. 7.39 ± 1.36 (P = 0.011)]. Moreover, SNS slightly increased the ratio of high-frequency (HF) gain to the LF gain. These effects of SNS were canceled by the pretreatment of ivabradine, an inhibitor of hyperpolarization-activated cyclic nucleotide-gated channels, in another group of rats (n = 6). Although background sympathetic tone antagonizes the vagal effect on mean HR, it enables finer HR control by increasing the dynamic gain of the vagal HR transfer function regardless of VNS intensity. When interpreting the HF component of HR variability, the augmenting effect from background sympathetic tone needs to be considered.

Angiotensin II inhibition increases diuresis during acute sympathetic activation in intact and denervated kidneys in rats with chronic myocardial infarction.

We examined urine excretion during primary acute sympathetic activation (PASA) in Wistar-Kyoto rats with myocardial infarction (MI). The rats underwent unilateral renal denervation (RDN) 7 weeks after coronary artery ligation. 4-10 days later, an acute experiment was performed under anesthetized conditions (n = 8 rats). Isolated carotid sinus pressure was changed stepwise from 60 to 180 mmHg, and the relationship between the arterial pressure (AP) and the normalized urine flow (nUF, urine flow normalized by the body weight) was examined. After obtaining the control data, an angiotensin II type 1 receptor blocker telmisartan (2.5 mg/kg) was intravenously administered. The effects of RDN, telmisartan, and heart weight (biventricular weight) on the relationship between AP and nUF were examined using multiple regression analyses. Regarding the slope of nUF versus AP (nUFslope), the constant term of the regression was positive (0.315 ± 0.069 µL·min-1·kg-1·mmHg-1), indicating that nUF increased with AP. The heart weight had a negative effect on nUFslope (P < 0.05), suggesting that the severity of MI was associated with the impairment of urine excretion. Telmisartan increased nUFslope by 0.358 ± 0.080 µL·min-1·kg-1·mmHg-1 (P < 0.001), whereas RDN had no significant effect on this parameter. The results indicate that unilateral RDN was unable to abolish the effect of the renin-angiotensin system on urine excretion during PASA. Circulating or locally produced angiotensin II, rather than ongoing renal sympathetic nerve activity, played a dominant role in the impairment of urine excretion during PASA in rats with chronic MI.

Early donepezil monotherapy or combination with metoprolol significantly prevents subsequent chronic heart failure in rats with reperfused myocardial infarction.

Despite the presence of clinical guidelines recommending that ß-blocker treatment be initiated early after reperfused myocardial infarction (RMI), acute myocardial infarction remains a leading cause of chronic heart failure (CHF). In this study, we compared the effects of donepezil, metoprolol, and their combination on the progression of cardiac remodeling in rats with RMI. The animals were randomly assigned to untreated (UT), donepezil-treated (DT), metoprolol-treated (MT), and a combination of donepezil and metoprolol (DMT) groups. On day 8 after surgery, compared to the UT, the DT and DMT significantly improved myocardial salvage, owing to the suppression of macrophage infiltration and apoptosis. After the 10-week treatment, the DT and DMT exhibited decreased heart rate, reduced myocardial infarct size, attenuated cardiac dysfunction, and decreased plasma levels of brain natriuretic peptide and catecholamine, thereby preventing subsequent CHF. These results suggest that donepezil monotherapy or combined therapy with ß-blocker may be an alternative pharmacotherapy post-RMI.

Development of an automated closed-loop ß-blocker delivery system to stably reduce myocardial oxygen consumption without inducing circulatory collapse in a canine heart failure model: a proof of concept study.

Beta-blockers are well known to reduce myocardial oxygen consumption (MVO2) and improve the prognosis of heart failure (HF) patients. However, its negative chronotropic and inotropic effects limit their use in the acute phase of HF due to the risk of circulatory collapse. In this study, as a first step for a safe ß-blocker administration strategy, we aimed to develop and evaluate the feasibility of an automated ß-blocker administration system. We developed a system to monitor arterial pressure (AP), left atrial pressure (PLA), right atrial pressure, and cardiac output. Using negative feedback of hemodynamics, the system controls AP and PLA by administering landiolol (an ultra-short-acting ß-blocker), dextran, and furosemide. We applied the system for 60 min to 6 mongrel dogs with rapid pacing-induced HF. In all dogs, the system automatically adjusted the doses of the drugs. Mean AP and mean PLA were controlled within the acceptable ranges (AP within 5 mmHg below target; PLA within 2 mmHg above target) more than 95% of the time. Median absolute performance error was small for AP [median (interquartile range), 3.1% (2.2-3.8)] and PLA [3.6% (2.2-5.7)]. The system decreased MVO2 and PLA significantly. We demonstrated the feasibility of an automated ß-blocker administration system in a canine model of acute HF. The system controlled AP and PLA to avoid circulatory collapse, and reduced MVO2 significantly. As the system can help the management of patients with HF, further validations in larger samples and development for clinical applications are warranted.

A novel method of trans-esophageal Doppler cardiac output monitoring utilizing peripheral arterial pulse contour with/without machine learning approach.

Transesophageal Doppler (TED) velocity in the descending thoracic aorta (DA) is used to track changes in cardiac output (CO). However, CO tracking by this method is hampered by substantial change in aortic cross-sectional area (CSA) or proportionality between blood flow to the upper and lower body. To overcome this, we have developed a new method of TED CO monitoring. In this method, TED signal is obtained primarily from the aortic arch (AA). Using AA velocity signal, CO (COAA-CSA) is estimated by compensating changes in the aortic CSA with peripheral arterial pulse contour. When AA cannot be displayed properly or when the quality of AA velocity signal is unacceptable, our method estimates CO (CODA-ML) from DA velocity signal first by compensating changes in the aortic CSA, and by compensating changes in the blood flow proportionality through a machine learning of the relation between the CSA-adjusted CO and a reference CO (COref). In 12 anesthetized dogs, we compared COAA-CSA and CODA-ML with COref measured by an ascending aortic flow probe under diverse hemodynamic conditions (COref changed from 723 to 7316 ml·min-1). Between COAA-CSA and COref, concordance rate in the four-quadrant plot analysis was 96%, while angular concordance rate in the polar plot analysis was 91%. Between CODA-ML and COref, concordance rate was 93% and angular concordance rate was 94%. Both COAA-CSA and CODA-ML demonstrated "good to marginal" tracking ability of COref. In conclusion, our method may allow a robust and reliable tracking of CO during perioperative hemodynamic management.

Ivabradine increases the high frequency gain ratio in the vagal heart rate transfer function via an interaction with muscarinic potassium channels.

Muscarinic potassium channels (IK,ACh ) are thought to contribute to the high frequency (HF) dynamic heart rate (HR) response to vagal nerve stimulation (VNS) because they act faster than the pathway mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. However, the interactions between the two pathways have not yet been fully elucidated. We previously demonstrated that HCN channel blockade by ivabradine (IVA) increased the HF gain ratio of the transfer function from VNS to HR. To test the hypothesis that IVA increases the HF gain ratio via an interaction with IK,ACh , we examined the dynamic HR response to VNS under conditions of control (CNT), IK,ACh blockade by tertiapin-Q (TQ, 50 nM/kg), and TQ plus IVA (2 mg/kg) (TQ + IVA) in anesthetized rats (n = 8). In each condition, the right vagal nerve was stimulated for 10 min with binary white noise signals between 0-10, 0-20, and 0-40 Hz. On multiple regression analysis, the HF gain ratio positively correlated with the VNS rate with a coefficient of 1.691 ± 0.151 (×0.01) (p < 0.001). TQ had a negative effect on the HF gain ratio with a coefficient of -1.170 ± 0.214 (×0.01) (p < 0.001). IVA did not significantly increase the HF gain ratio in the presence of TQ. The HF gain ratio remained low under the TQ + IVA condition compared to controls. These results affirm that the IVA-induced increase in the HF gain ratio is dependent on the untethering of the hyperpolarizing effect of IK,ACh .

Ivabradine augments high-frequency dynamic gain of the heart rate response to low- and moderate-intensity vagal nerve stimulation under ß-blockade.

Our previous study indicated that intravenously administered ivabradine (IVA) augmented the dynamic heart rate (HR) response to moderate-intensity vagal nerve stimulation (VNS). Considering an accentuated antagonism, the results were somewhat paradoxical; i.e., the accentuated antagonism indicates that an activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels via the accumulation of intracellular cyclic adenosine monophosphate (cAMP) augments the HR response to VNS, whereas the inhibition of HCN channels by IVA also augmented the HR response to VNS. To remove the possible influence from the accentuated antagonism, we examined the effects of IVA on the dynamic vagal control of HR under ß-blockade. In anesthetized rats (n = 7), the right vagal nerve was stimulated for 10 min according to binary white noise signals between 0 and 10 Hz (V0-10), between 0 and 20 Hz (V0-20), and between 0 and 40 Hz (V0-40). The transfer function from VNS to HR was estimated. Under ß-blockade (propranolol, 2 mg/kg iv), IVA (2 mg/kg iv) did not augment the asymptotic low-frequency gain but increased the asymptotic high-frequency gain in V0-10 (0.53 ± 0.10 vs. 1.74 ± 0.40 beats/min/Hz, P < 0.01) and V0-20 (0.79 ± 0.14 vs. 2.06 ± 0.47 beats/min/Hz, P < 0.001). These changes, which were observed under a minimal influence from sympathetic background tone, may reflect an increased contribution of the acetylcholine-sensitive potassium channel (IK,ACh) pathway after IVA, because the HR control via the IK,ACh pathway is faster and acts in the frequency range higher than the cAMP-mediated pathway.NEW & NOTEWORTHY Since ivabradine (IVA) inhibits hyperpolarization-activated cyclic nucleotide-gated channels, interactions among the sympathetic effect, vagal effect, and IVA can occur in the control of heart rate (HR). To remove the sympathetic effect, we estimated the transfer function from vagal nerve stimulation to HR under ß-blockade in anesthetized rats. IVA augmented the high-frequency dynamic gain during low- and moderate-intensity vagal nerve stimulation. Untethering the hyperpolarizing effect of acetylcholine-sensitive potassium channels after IVA may be a possible underlying mechanism.

Quantitative assessment of the central versus peripheral effect of intravenous clonidine using baroreflex equilibrium diagrams.

Clonidine is a first-generation central antihypertensive that reduces sympathetic nerve activity (SNA). Although clonidine also exerts peripheral vasoconstriction, the extent to which this vasoconstriction offsets the centrally mediated arterial pressure (AP)-lowering effect remains unknown. In anesthetized rats (n = 8), we examined SNA and AP responses to stepwise changes in carotid sinus pressure under control conditions and after intravenous low-dose (2 µg/kg) and high-dose clonidine (5 µg/kg). In the baroreflex equilibrium diagram analysis, the operating-point AP under the control condition was 115.2 (108.5-127.7) mmHg [median (25th-75th percentile range)]. While the operating-point AP after low-dose clonidine was not significantly different with or without the peripheral effect, the operating-point AP after high-dose clonidine was higher with the peripheral effect than without [81.3 (76.2-98.2) mmHg vs. 70.7 (57.7-96.9), P < 0.05]. The vasoconstrictive effect of clonidine partly offset the centrally mediated AP-lowering effect after high-dose administration.