Pressure-volume loops in clinical research: a contemporary view

Validation of Dynamic 3D MRI for Urodynamics Assessment Using an Anatomically Realistic In Vitro Model of the Bladder

Lowery urinary tract symptoms (LUTS) affect a large majority of the aging population. 3D Dynamic MRI shows promise as a noninvasive diagnostic tool that can assess bladder anatomy and function (urodynamics) while overcoming challenges associated with current urodynamic assessment methods. However, validation of this technique remains an unmet need. In this study, an anatomically realistic, bladder-mimicking in vitro flow model was created and used to systematically benchmark 3D dynamic MRI performance using a highly controllable syringe pump. Time-resolved volumes of the synthetic bladder model were obtained during simulated filling and voiding events and used to calculate volumetric flowrate. During MRI acquisitions, pressure during each event was recorded and used to create PV loops for work assessment. Error between control and MRI-derived volume for voiding and filling events exhibited 3.36% and 4.66% differences, respectively. A slight increase in average error was observed for MRI-derived flowrate when compared to the control flowrate (4.90% and 7.67% for voiding and filling, respectively). Overall, average error in segmented volumes increased with decreasing volume flowrate. Pressure drops were observed during voiding. Pressure increased during filling. Enhanced validation of novel 3D MRI urodynamics is achieved by using high-resolution PIV for visualizing and quantifying velocity inside the bladder model, which is not currently possible with 3D Dynamic MRI.

Application of Cardiovascular Physiology to the Critically Ill Patient

OBJECTIVES

To use the ventricular pressure-volume relationship and time-varying elastance model to provide a foundation for understanding cardiovascular physiology and pathophysiology, interpreting advanced hemodynamic monitoring, and for illustrating the physiologic basis and hemodynamic effects of therapeutic interventions. We will build on this foundation by using a cardiovascular simulator to illustrate the application of these principles in the care of patients with severe sepsis, cardiogenic shock, and acute mechanical circulatory support.

DATA SOURCES

Publications relevant to the discussion of the time-varying elastance model, cardiogenic shock, and sepsis were retrieved from MEDLINE. Supporting evidence was also retrieved from MEDLINE when indicated.

STUDY SELECTION, DATA EXTRACTION, AND SYNTHESIS

Data from relevant publications were reviewed and applied as indicated.

CONCLUSIONS

The ventricular pressure-volume relationship and time-varying elastance model provide a foundation for understanding cardiovascular physiology and pathophysiology. We have built on this foundation by using a cardiovascular simulator to illustrate the application of these important principles and have demonstrated how complex pathophysiologic abnormalities alter clinical parameters used by the clinician at the bedside.

Trans-aortic Valvular Ejection Fraction for Monitoring Recovery of Patients with Ventricular Systolic Heart Failure

Durable mechanical circulatory support in the form of left ventricular (LV) assist device (LVAD) therapy is increasingly considered in the context of the recovery of native cardiac function. Progressive improvement in LV function may facilitate LVAD explantation and a resultant reduction in device-related risk. However, ascertaining LV recovery remains a challenge. In this study, we investigated the use of trans-aortic valvular flow rate and trans-LVAD flow rate to assess native LV systolic function using a well-established lumped parameter model of the mechanically assisted LV with pre-existing systolic dysfunction. Trans-aortic valvular ejection fraction (TAVEF) was specifically found to characterize the preload-independent contractility of the LV. It demonstrated excellent sensitivity to simulated pharmacodynamic stress tests and volume infusion tests. TAVEF may prove to be useful in the ascertainment of LV recovery in LVAD-supported LVs with pre-existing LV systolic dysfunction.

A Platform for Assessing Cellular Contractile Function Based on Magnetic Manipulation of Magnetoresponsive Hydrogel Films

Despite significant advancements in in vitro cardiac modeling approaches, researchers still lack the capacity to obtain in vitro measurements of a key indicator of cardiac function: contractility, or stroke volume under specific loading conditions-defined as the pressures to which the heart is subjected prior to and during contraction. This work puts forward a platform that creates this capability, by providing a means of dynamically controlling loading conditions in vitro. This dynamic tissue loading platform consists of a thin magnetoresponsive hydrogel cantilever on which 2D engineered myocardial tissue is cultured. Exposing the cantilever to an external magnetic field-generated by positioning magnets at a controlled distance from the cantilever-causes the hydrogel film to stretch, creating tissue load. Next, cell contraction is induced through electrical stimulation, and the force of the contraction is recorded, by measuring the cantilever's deflection. Force-length-based measurements of contractility are then derived, comparable to clinical measurements. In an illustrative application, the platform is used to measure contractility both in untreated myocardial tissue and in tissue exposed to an inotropic agent. Clear differences are observed between conditions, suggesting that the proposed platform has significant potential to provide clinically relevant measurements of contractility.

Quantification of cardiac pumping mechanics in TAVI patients: A pilot study utilizing minimally invasive method for pressure-volume analysis

The ventriculo-arterial coupling (VAC) and left ventricle (LV) mechanics are crucial and play an important role in the pathophysiology of aortic stenosis (AS). The pressure-volume (PV) analysis is a powerful tool to study VAC and LV mechanics. We proposed a novel minimally-invasive method for PV analysis in patients with severe AS receiving transcatheter aortic valve implantation (TAVI). Patients with severe AS were prospectively enrolled in a single center. LV pressure and cardiac output were recorded before and after TAVI. We constructed the PV loop for analysis by analyzing LV pressure and the assumed flow. 26 patients were included for final analysis. The effective arterial elastance (Ea) decreased after TAVI (3.7 ± 1.3 vs. 2.9 ± 1.1 mmHg/mL, p < 0.0001). The LV end-systolic elastance (Ees) did not change immediately after TAVI (2.4 ± 1.3 vs. 2.6 ± 1.1 mmHg/mL, p = 0.3670). The Ea/Ees improved after TAVI (1.8 ± 0.8 vs. 1.2 ± 0.4, p < 0.0001), demonstrating an immediate improvement of VAC. The stroke work (SW) did not change (7669.6 ± 1913.8 vs. 7626.2 ± 2546.9, p = 0.9330), but the pressure-volume area (PVA) decreased (14469.0 ± 4974.1 vs. 12177.4 ± 4499.9, p = 0.0374) after TAVI. The SW/PVA increased after TAVI (0.55 ± 0.12 vs. 0.63 ± 0.08, p < 0.0001) representing an improvement of LV efficiency. We proposed a novel minimally invasive method for PV analysis in patients with severe AS receiving TAVI. The VAC and LV efficiency improved immediately after TAVI.

Feasibility of CMR Imaging during Biventricular Pacing: Comparison with Invasive Measurement as a Pathway towards a Novel Optimization Strategy

OBJECTIVES

This prospective pilot study assessed the feasibility of cardiovascular magnetic resonance (CMR) imaging during biventricular (BIV) pacing in patients with a CMR conditional cardiac resynchronization therapy defibrillator (CRT-D) and compared the results with invasive volume measurements.

METHODS

Ten CRT-D patients underwent CMR imaging prior to device implantation (baseline) and six weeks after device implantation, including CRT-on and CRT-off modes. Left ventricular (LV) function, volumes, and strain measurements of LV dyssynchrony and dyscoordination were assessed. Invasive pressure-volume measurements were performed, matching the CRT settings used during CMR.

RESULTS

Post-implantation imaging enabled reliable cine assessment, but showed artefacts on late gadolinium enhancement images. After six weeks of CRT, significant reverse remodeling was observed, with a 22.7 ± 11% reduction in LV end-systolic volume during intrinsic rhythm (CRT-off). During CRT-on, the LV ejection fraction significantly improved from 27.4 ± 5.9% to 32.2 ± 8.7% (p < 0.01), and the strain assessment showed the abolition of the left bundle branch block contraction pattern. Invasively measured and CMR-assessed LV hemodynamics during BIV pacing were significantly associated.

CONCLUSIONS

Post-CRT implantation CMR assessing acute LV pump function is feasible and provides important insights into the effects of BIV pacing on cardiac function and contraction patterns. LV assessment during CMR may constitute a future CRT optimization strategy.

The Role of the Vasculature in Heart Failure

The contribution of the vasculature in the development and progression of heart failure (HF) syndromes is poorly understood and often neglected. Incorporating both arterial and venous systems, the vasculature plays a significant role in the regulation of blood flow throughout the body in meeting its metabolic requirements. A deterioration or imbalance between the cardiac and vascular interaction can precipitate acute decompensated HF in both preserved and reduced ejection fraction phenotypes. This is characterised by the increasingly recognised concept of ventricular-arterial coupling: a well-balanced relationship between ventricular and vascular stiffness, which has major implications in HF. Often, the cause of decompensation is unknown, with international guidelines mainly centred on arrhythmia, infection, acute coronary syndrome and its mechanical complications as common causes of decompensation; the vascular component is often underrecognised. A better understanding of the vascular contribution in cardiovascular failure can improve risk stratification, earlier diagnosis and facilitate earlier optimal treatment. This review focuses on the role of the vasculature by integrating the concepts of ventricular-arterial coupling, arterial stiffness and venous return in a failing heart.

Clinical Applications of Pressure-Volume Assessment in Congenital Heart Disease

Ventricular pressure-volume (PV) loops offer unique insights into cardiovascular mechanics. PV loops can be instrumental in improving our understanding of various congenital heart diseases, including single ventricular physiology, heart failure, and pulmonary hypertension, as well as guiding therapeutic interventions. This review focuses on the theoretical and practical foundations for the acquisition and interpretation of PV loops in congenital heart disease and discusses their clinical applications.

Diastolic dysfunction, hypertrophy and hypertension ventricular-arterial uncoupling treatment

The aim of the study was to evaluate hypertension treatment effects on mechanical efficiency of the cardiovascular system and cardiac reverse remodeling in hypertensive patients. This is an observational prospective study, consecutive hypertension patients. Left ventricle mass index measured by Devereux 2D method and diastolic function following the Guidelines from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. Left ventricular end systolic elastance (Ees) was measured by Guarracino calculator, the effective arterial elastance (Ea) and ventricular-arterial coupling (VAC) measured by Sunagawa et al. single beat method adapted by Chen et al. in human ventricles. The sample was analyzed in quartiles (Q) according to VAC. Follow-up 2 years. In total, 288 patients, mean age 56.3 ± 12.5 years and 168 patients (58.3%) males. VAC increased from 0.303 ± 0.07 to 0.54 ± 0.25 (p < 0.005) in Q1 mainly due to a reduction in Ees from 5.25 ± 2.3 to 3.68 ± 0.25 mmHg/ml (p < 0.01), while Ea increased from 1.5 ± 0.53 to 1.64 ± 0.56 mmHg/ml (p = NS). The frequency of LVH was reduced from 31.9 to 10.8% in Q1 (p < 0.025). The frequency of normal diastolic function increased from 75 to 94.6% (p < 0.01) in Q1, from 78.7 to 100% in Q2 (p < 0.005), from 87.1 to 100% (p < 0.025) in Q3 and from 88.7 to 100% (0,025) in Q4. Patients with the worst ventricular-arterial uncoupling were the most benefited from hypertension treatment. Regression of left ventricular hypertrophy was observed only in the group of patients with the worst ventricular-arterial uncoupling, while improvement in diastolic function was demonstrated in all quartiles of patients.

Ventricular-Arterial Uncoupling and Hypertension Mediated Diastolic Dysfunction

INTRODUCTION

The increase in the pulsatile component of left ventricle afterload is suspected to cause a mismatch between the left ventricle (LV) and the vascular tree.

AIM

To demonstrate that ventricular-arterial uncoupling is frequently present in the development of LV hypertrophy (H) and diastolic dysfunction (DD) in hypertension (HBP).

METHODS

Observational study, HBP patients with ejection fraction > 54%. Conventional 2D echocardiography and tissue Doppler performed following imaging guidelines. LV end systolic elastance (Ees), the effective arterial elastance (Ea), and ventricular-arterial coupling (VAC) measured by Chen single beat method.

RESULTS

288 patients, mean age 56.3 ± 12.5 years and 168 patients (58.3%) males. Mean LV mass index was 87.2 ± 20.4 grs/m² and frequency of LVH 20.1% (58 patients). The mean VAC was 0.54 ± 9.23. LV Stroke volume, stroke work and systolic stress were 46.2 ± 10.3 cc/m², 91.4 ± 22.2 g-min/m², and 57 ± 14.6 dynes/cm² in quartile 1, and 33.5 ± 6.6 cc/m², 65.5 ± 15.2 g-min/m², and 77.8 ± 17.1 dynes/cm², in quartile 4, respectively (p < 0.001). Peripheral resistance index was 3349 ± 1072 and 4410 ± 1143 dynes*s/cm-5/m² quartiles 1 vs. 4 (p < 0.005). The frequency of LVH was 31.9% in quartile 1 and 11.3% in quartile 4 (p < 0.005) and LVH or DD was 37.5% and 12.7%, respectively (p < 0.001).

CONCLUSIONS

Stroke volume and stroke work were significantly increased while systolic stress and peripheral resistance index were significantly reduced in patients with worst VAC. Ventricular-arterial uncoupling is mostly caused by an increase in Ees rather than by an elevation of Ea. LVH or DD are more frequent in the worst cases of ventricular-arterial uncoupling.

One step closer to myocardial physiology: From PV loop analysis to state-of-the-art myocardial imaging

Recent advances in cardiac imaging have revitalized the assessment of fundamental physiological concepts. In the field of cardiac physiology, invasive measurements with pressure-volume (PV) loops have served as the gold standard methodology for the characterization of left ventricular (LV) function. From PV loop data, fundamental aspects of LV chamber function are derived such as work, efficiency, stiffness and contractility. However, the parametrization of these aspects is limited because of the need for invasive procedures. Through the utilization of recent advances in echocardiography, magnetic resonance imaging and positron emission tomography, it has become increasingly feasible to quantify these fundamental aspects of LV function non-invasively. Importantly, state-of-the-art imaging technology enables direct assessment of myocardial performance, thereby extending functional assessment from the net function of the LV chamber, as is done with PV loops, to the myocardium itself. With a strong coupling to underlying myocardial physiology, imaging measurements of myocardial work, efficiency, stiffness and contractility could represent the next generation of functional parameters. The purpose of this review is to discuss how the new imaging parameters of myocardial work, efficiency, stiffness and contractility can bring cardiac physiologists, researchers and clinicians alike one step closer to underlying myocardial physiology.

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.

Heterogeneity of Cardiovascular Response to Standardized Sepsis Resuscitation

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Disturbed ventricular-arterial coupling and increased left atrial stiffness in a patient with heart failure with preserved ejection fraction and hyperaldosteronism: a case report

Background

Aldosterone is involved in almost all parts of the cardiovascular system. Hyperaldosteronism causes arterial hypertension and might predispose to stroke, atrial fibrillation, and heart failure.

Case summary

A 60-year-old obese woman with long-standing hypertension, hypokalaemia, and shortness of breath was admitted to our hospital. Hypertension was caused by primary hyperaldosteronism due to an adenoma of the adrenal gland. Detailed transthoracic echocardiography revealed diastolic dysfunction, disturbed ventricular–arterial interaction, and atrial compliance resulting in heart failure with preserved ejection fraction (HFPEF). Three months of aldosterone antagonist treatment improved ventricular–arterial coupling, while left ventricular diastolic and atrial dysfunction remained unchanged.

Discussion

Presumably, hyperaldosteronism is the reason for HFPEF in this case. Standard criteria to diagnose HFPEF include clinical symptoms of heart failure and an ejection fraction (EF) >50% as well as echocardiographically or invasively assessed elevated filling pressures. Single beat pressure-volume analysis gives insights on the pathophysiology of increased filling pressures, showing in our case diastolic dysfunction as well as disturbed ventricular–arterial interaction. Three months of aldosterone antagonist treatment reduced blood pressure with concomitant improvement of ventricular–arterial interaction, thereby reducing stroke work while stroke volume remained nearly unchanged. Diastolic dysfunction and increased atrial stiffness were unaltered.

Assessing Right Ventricular Function in the Perioperative Setting, Part II: What About Catheters?

An-depth assessment of right ventricular function is important in a many perioperative settings. After exploring 2-dimensional echo-based evaluation, other proposed monitoring modalities are discussed. Pressure-based methods of right ventricular appraisal is discussed. Flow-based assessment is reviewed. An overview of the state of current right ventricular 3-dimensional echocardiography and its potential to construct clinical pressure-volume loops in conjunction with pressure measurements is provided. An overview of right ventricular assessment modalities that do not rely on 2-dimensional echocardiography is discussed. Tailored selection of monitoring modalities can be of great benefit for the perioperative physician. Integrating modalities offers optimal estimations of right ventricular function.

Predictive value of left ventricular diastolic chamber stiffness in patients with severe aortic stenosis undergoing aortic valve replacement

Aims

Despite improvements in cardiac haemodynamics and symptoms, long-term mortality remains increased in some patients after aortic valve replacement (AVR). Limited data exist on the prognostic role of left ventricular (LV) chamber stiffening in these patients.

Methods and results

We performed a retrospective analysis in 1893 patients with severe aortic stenosis (AS) referred for AVR. LV end-diastolic pressure–volume relations (EDPVR, P = αV^β) were reconstructed from echocardiographic measurements of end-diastolic volumes and estimates of end-diastolic pressure (EDP). The impact of EDPVR-derived LV chamber stiffness (CS30, at 30 mmHg EDP) on all-cause mortality after AVR was evaluated. Mean age was 76 ± 10 years, 39% were females, and ejection fraction (EF) was 61 ± 12%. The mean LV chamber stiffness (CS30) was 2.2 ± 1.3 mmHg/mL. A total of 877 (46%) patients had high LV stiffness (CS30 &gt;2 mmHg/mL). In these patients, the EDPVR curves were steeper and shifted leftwards, indicating higher stiffness at all pressure levels. These patients were slightly older, more often female, and had more prevalent comorbidities compared to patients with low stiffness. At follow-up [median 4.2 (interquartile range 2.8–6.3) years; 675 deaths], a higher CS30 was associated with lower survival (hazard ratio: 2.7 for severe vs. mild LV stiffening; P &lt; 0.0001), both in patients with normal or reduced EF. At multivariate analysis, CS30 remained an independent predictor, even after adjusting for age, sex, comorbidities, EF, LV remodelling, and diastolic dysfunction.

Conclusion

Higher preoperative LV chamber stiffening in patients with severe AS is associated with poorer outcome despite successful AVR.

Impaired Baroreflex Function in an Ovine Model of Chronic Heart Failure Induced by Multiple Coronary Microembolizations

Testing new therapies in heart failure (HF) requires a chronic stable model of HF in large animals. Microembolization of the coronary arteries has been used to model HF previously; however, neural control has not been previously explored in this model. Thus the aim of this study was to further characterize neural control in this model of HF. HF was induced by infusion of microspheres (45 micron; 1.3 ml) into the proximal left coronary artery or left descending coronary arteries, with three sequential embolizations over 3 weeks. Twelve to 14 weeks after the final embolization, and when ejection fraction had decreased below 45%, animals were instrumented to record blood pressure and heart rate. Baroreflex control of heart rate was investigated in conscious animals. Additionally, pressure-volume loops were constructed under anesthesia. Embolization-induced HF was associated with a decrease in mean arterial pressure (67 ± 2 vs. 85 ± 4 mmHg, p < 0.05), an increase in heart rate (108 ± 4 vs. 94 ± 4 bpm, p < 0.05), and a significant increase in left ventricular end-diastolic pressure (11.4 ± 2 vs. 6.2 ± 1 mmHg, p < 0.01). Under conscious conditions, there was a significant decrease in the gain (-8.2 ± 2 vs. -4.1 ± 1 beats/min/mmHg, p < 0.05) as well as the lower plateau of the baroreflex in HF compared to control animals. HF was also associated with significantly increased respiratory rate (107 ± 4 vs. 87 ± 4 breaths/min, p < 0.01) and incidence of apneas (520 ± 24 vs. 191 ± 8 apnea periods >4 s, p < 0.05), compared to control sheep. The microembolization model of heart failure is associated with an increase in left ventricular end-diastolic pressure, impaired cardiac function, and altered baroreflex control of the heart. These findings suggest this chronic model of HF is appropriate to use for investigating interventions aimed at improving neural control in HF.

Cardiovascular determinants of resuscitation from sepsis and septic shock

BACKGROUND

We hypothesized that the cardiovascular responses to Surviving Sepsis Guidelines (SSG)-defined resuscitation are predictable based on the cardiovascular state.

METHODS

Fifty-five septic patients treated by SSG were studied before and after volume expansion (VE), and if needed norepinephrine (NE) and dobutamine. We measured mean arterial pressure (MAP), cardiac index (CI), and right atrial pressure (Pra) and calculated pulse pressure and stroke volume variation (PPV and SVV), dynamic arterial elastance (Ea_dyn), arterial elastance (Ea) and left ventricular (LV) end-systolic elastance (Ees), Ees/Ea (VAC), LV ejection efficiency (LVeff), mean systemic pressure analogue (Pmsa), venous return pressure gradient (Pvr), and cardiac performance (Eh), using standard formulae.

RESULTS

All patients were hypotensive (MAP 56.8 ± 3.1 mmHg) and tachycardic (113.1 ± 7.5 beat min^-1), with increased lactate levels (lactate = 5.0 ± 4.2 mmol L^-1) with a worsened VAC. CI was variable but > 2 L min^-1 M^-2 in 74%. Twenty-eight-day mortality was 48% and associated with admission lactate, blood urea nitrogen (BUN), and creatinine levels but not cardiovascular state. In all patients, both MAP and CI improved following VE, as well as cardiac contractility (Ees). Fluid administration improved Pra, Pmsa, and Pvr in all patients, whereas both HR and Ea decreased after VE, thus normalizing VAC. CI increases were proportional to baseline PPV and SVV. CI increases proportionally decreased PPV and SVV. VE increased MAP > 65 mmHg in 35/55 patients. MAP responders had higher PPV, SVV, and Ea_dyn than non-responders. NE was given to 20/55 patients in septic shock, but increased MAP > 65 mmHg in only 12. NE increased Ea, Ea_dyn, Pra, Pmsa, and VAC while decreasing HR, PPV, SVV, and LVeff. MAP responders had higher pre-NE Ees and lower VAC. Dobutamine was given to 6/8 patients who remained hypotensive following NE. It increased Ees, MAP, CI, and LVeff, while decreasing HR, Pra, and VAC. At all times and all steps of the protocol, CI changes were proportional to Pvr changes independent of treatment.

CONCLUSIONS

The cardiovascular response to SSG-based resuscitation is highly heterogeneous but predictable from pre-treatment measures of cardiovascular state.

Finite state machine implementation for left ventricle modeling and control

Background

Simulation of a left ventricle has become a critical facet of evaluating therapies and operations that interact with cardiac performance. The ability to simulate a wide range of possible conditions, changes in cardiac performance, and production of nuisances at transition points enables evaluation of precision medicine concepts that are designed to function through this spectrum. Ventricle models have historically been based on biomechanical analysis, with model architectures constituted of continuous states and not conducive to deterministic processing. Producing a finite-state machine governance of a left ventricle model would enable a broad range of applications: physiological controller development, experimental left ventricle control, and high throughput simulations of left ventricle function.

Methods

A method for simulating left ventricular pressure-volume control utilizing a preload, afterload, and contractility sensitive computational model is shown. This approach uses a logic-based conditional finite state machine based on the four pressure-volume phases that describe left ventricular function. This was executed with a physical system hydraulic model using MathWorks’ Simulink^® and Stateflow tools.

Results

The approach developed is capable of simulating changes in preload, afterload, and contractility in time based on a patient’s preload analysis. Six pressure–volume loop simulations are presented to include a base-line, preload change only, afterload change only, contractility change only, a clinical control, and heart failure with normal ejection fraction. All simulations produced an error of less than 1 mmHg and 1 mL of the absolute difference between the desired and simulated pressure and volume set points. The acceptable performance of the fixed-timestep architecture in the finite state machine allows for deployment to deterministic systems, such as experimental systems for validation.

Conclusions

The proposed approach allows for personalized data, revealed through an individualized clinical pressure–volume analysis, to be simulated in silico. The computational model architecture enables this control structure to be executed on deterministic systems that govern experimental left ventricles. This provides a mock circulatory system with the ability to investigate the pathophysiology for a specific individual by replicating the exact pressure–volume relationship defined by their left ventricular functionality; as well as perform predictive analysis regarding changes in preload, afterload, and contractility in time.

Left ventricular pumping during the transition-adaptation sequence in preterm infants: impact of the patent ductus arteriosus

BackgroundPostnatally, the immature left ventricle (LV) is subjected to high systemic afterload. Hypothesizing that LV pumping would change during transition-adaptation, we analyzed the LV in preterm infants (GA≤32+6), clinically stable or with a hemodynamically significant patent ductus arteriosus (hPDA) by applying a pump model.MethodsPumping was characterized by E_A (effective arterial elastance, reflecting afterload), E_ES (end-systolic LV elastance, reflecting contractility), E_A/E_ES coupling ratios, descriptive E_A:E_ES relations, and E_A/E_ES graphs. Data calculated from echocardiography and blood pressure were analyzed by diagnosis (S group: clinically stable, no hPDA, n=122; hPDA group, n=53) and by periods (early transition: days of life 1-3; late transition: 4-7; and adaptation: 8-30).ResultsS group: LV pumping was characterized by an increased E_A/E_ES coupling ratio of 0.65 secondary to low E_ES in early transition, a tandem rise of both E_A and E_ES in late transition, and an E_A/E_ES coupling ratio of 0.45 secondary to high E_ES in adaptation; hPDA group: time-trend analyses showed significantly lower E_A (P<0.0001) and E_ES (P=0.006). Therefore, LV pumping was characterized by a lower E_A/E_ES coupling ratio (P=0.088) throughout transition-adaptation.ConclusionsIn stable infants, facing high afterload, the immature LV, enhanced by the physiological PDA, increases its contractility. In hPDA, facing low afterload, the overloaded immature LV exhibits a consistently lower contractility.

A Physical Heart Failure Simulation System Utilizing the Total Artificial Heart and Modified Donovan Mock Circulation

With the growth and diversity of mechanical circulatory support (MCS) systems entering clinical use, a need exists for a robust mock circulation system capable of reliably emulating and reproducing physiologic as well as pathophysiologic states for use in MCS training and inter-device comparison. We report on the development of such a platform utilizing the SynCardia Total Artificial Heart and a modified Donovan Mock Circulation System, capable of being driven at normal and reduced output. With this platform, clinically relevant heart failure hemodynamics could be reliably reproduced as evidenced by elevated left atrial pressure (+112%), reduced aortic flow (-12.6%), blunted Starling-like behavior, and increased afterload sensitivity when compared with normal function. Similarly, pressure-volume relationships demonstrated enhanced sensitivity to afterload and decreased Starling-like behavior in the heart failure model. Lastly, the platform was configured to allow the easy addition of a left ventricular assist device (HeartMate II at 9600 RPM), which upon insertion resulted in improvement of hemodynamics. The present configuration has the potential to serve as a viable system for training and research, aimed at fostering safe and effective MCS device use.

Mimicking the cardiac cycle in intact cardiomyocytes using diastolic and systolic force clamps; measuring power output

Aims

A single isolated cardiomyocyte is the smallest functional unit of the heart. Yet, all single isolated cardiomyocyte experiments have been limited by the lack of proper methods that could reproduce a physiological cardiac cycle. We aimed to investigate the contractile properties of a single cardiomyocyte that correctly mimic the cardiac cycle.

Methods and results

By adjusting the parameters of the feedback loop, using a suitably engineered feedback system and recording the developed force and the length of a single rat cardiomyocyte during contraction and relaxation, we were able to construct force–length (FL) relations analogous to the pressure–volume (PV) relations at the whole heart level. From the cardiac loop graphs, we obtained, for the first time, the power generated by one single cardiomyocyte.

Conclusion

Here, we introduce a new approach that by combining mechanics, electronics, and a new type optical force transducer can measure the FL relationship of a single isolated cardiomyocyte undergoing a mechanical loop that mimics the PV cycle of a beating heart.

Model based non-invasive estimation of PV loop from echocardiography

We introduce a model-based approach for the non-invasive estimation of patient specific, left ventricular PV loops. A lumped parameter circulation model is used, composed of the pulmonary venous circulation, left atrium, left ventricle and the systemic circulation. A fully automated parameter estimation framework is introduced for model personalization, composed of two sequential steps: first, a series of parameters are computed directly, and, next, a fully automatic optimization-based calibration method is employed to iteratively estimate the values of the remaining parameters. The proposed methodology is first evaluated for three healthy volunteers: a perfect agreement is obtained between the computed quantities and the clinical measurements. Additionally, for an initial validation of the methodology, we computed the PV loop for a patient with mild aortic valve regurgitation and compared the results against the invasively determined quantities: there is a close agreement between the time-varying LV and aortic pressures, time-varying LV volumes, and PV loops.

Acute effects of intravenous dronedarone on electrocardiograms, hemodynamics and cardiac functions in anesthetized dogs

Dronedarone is a class III antiarrhythmic that has been used for management of atrial fibrillation in humans, but limited information was found in dogs. The objective of this study was to determine the acute effects of escalating concentrations of dronedarone on electrocardiograms (ECG), hemodynamics and cardiac mechanics in healthy dogs. A total of 7 beagle dogs were anesthetized with isoflurane and instrumented to obtain lead II ECG, pressures at ascending aorta, right atrium, pulmonary artery and left ventricle, and left ventricular pressure-volume relationship. Five dogs were given vehicle and followed by escalating doses of dronedarone (0.5, 1.0 and 2.5 mg/kg, 15 min for each dose), and two dogs were used as a vehicle-treated control. All parameters were measured at 15 min after the end of each dose. The results showed that all parameters in vehicle-treated dogs were unaltered. Dronedarone at 2.5 mg/kg significantly lengthened PQ interval (P<0.01), reduced cardiac output (P<0.01) and increased systemic vascular resistance (P<0.01). Dronedarone produced negative inotropy assessed by significantly lowered end-systolic pressure-volume relationship, preload recruitable stroke work, contractility index and dP/dtmax. It also impaired diastolic function by significantly increased end-diastolic pressure-volume relationship, tau and dP/dtmin. These results suggested that acute effects of dronedarone produced negative dromotropy, inotropy and lusitropy in anesthetized dogs. Care should be taken when given dronedarone to dogs, especially when the patients have impaired cardiac function.

The Living Heart Project: A robust and integrative simulator for human heart function

The heart is not only our most vital, but also our most complex organ: Precisely controlled by the interplay of electrical and mechanical fields, it consists of four chambers and four valves, which act in concert to regulate its filling, ejection, and overall pump function. While numerous computational models exist to study either the electrical or the mechanical response of its individual chambers, the integrative electro-mechanical response of the whole heart remains poorly understood. Here we present a proof-of-concept simulator for a four-chamber human heart model created from computer topography and magnetic resonance images. We illustrate the governing equations of excitation-contraction coupling and discretize them using a single, unified finite element environment. To illustrate the basic features of our model, we visualize the electrical potential and the mechanical deformation across the human heart throughout its cardiac cycle. To compare our simulation against common metrics of cardiac function, we extract the pressure-volume relationship and show that it agrees well with clinical observations. Our prototype model allows us to explore and understand the key features, physics, and technologies to create an integrative, predictive model of the living human heart. Ultimately, our simulator will open opportunities to probe landscapes of clinical parameters, and guide device design and treatment planning in cardiac diseases such as stenosis, regurgitation, or prolapse of the aortic, pulmonary, tricuspid, or mitral valve.

Ventriculo-arterial coupling in children with Still's murmur

Still's murmur is the most common innocent heart murmur in children and considered flow related; however, so far the cause of the murmur has not yet been fully explained. Assessment of the hemodynamic ventriculo‐arterial interaction and the proportional anatomical dimensions of the left ventricle and the aortic root were the objective for this study. This case–control study was conducted at the Division of Pediatric Cardiology, Vienna Medical University, including healthy children with and without Still's murmur. To assess ventriculo‐arterial interaction, the model of ventriculo‐arterial coupling (VAC) was applied. The model describes the interaction between the left ventricle (left ventricular contractility, E_LV) and the arterial system (effective arterial elastance, E_A) by the VAC ratio E_A/E_LV. The parameters E_A and E_LV can be derived from M‐mode echocardiography thereby allowing a noninvasive pressure–volume analysis. Outcomes comprised VAC ratio and diameters of both the aortic root (AOD) and the left ventricle in end diastole (LVED) and end systole (LVES) as well as their relative proportions, ejection fraction (EF), stroke volume (SV), blood pressure (BP), and heart rate (HR). Forty‐three healthy children with Still's murmur (mean age 5.2 years) and 42 healthy children without murmur (mean age 5.8 years) participated in this study. Children with Still's murmur had a significantly lower VAC ratio E_A/E_LV (0.5 ± 0.13 vs. 0.59 ± 0.15; P < 0.005), a significantly higher EF% (67.1 ± 5.8 vs. 63.3 ± 5.6; P < 0.005, P < 0.01), and a larger SV per kg bodyweight (1.84 ± 0.33 vs. 1.68 ± 0.38; P < 0.05) than controls. BP, HR, and diameters of AOD, LVED, and LVES as well as their relative anatomic proportions did not differ between children with Still's murmur and controls. Still's murmur seems to be generated by a subtle alteration in ventriculo‐arterial coupling in healthy children. This result can be translated to parents, as they may be informed that their child's innocent murmur is caused by a more “lively interplay between the heart and the aorta.”

So far, the physiology of Still's murmur has not yet been defined. This study is the first to describe a significant difference in ventriculo‐arterial coupling in healthy children with and without Still's murmur.

Systolic heart failure and cardiac resynchronization therapy: a focus on diastole

Conflicting data exist about the effects of cardiac resynchronization therapy (CRT) on diastolic function (DF). Aim of the study was to assess if and how CRT affects DF in systolic heart failure patients. We also investigated potential relations between CRT-induced left ventricular changes and the composite clinical endpoint of progressive heart failure and cardiac death over 3 years follow-up. 119 CRT patients underwent clinical evaluation and echocardiography before CRT and 4 months later. DF was quantified by transmitral velocities [E/A waves, deceleration time (DT), E/DT], early diastolic mitral annulus velocity (E'), E/E' ratio and 2-D speckle tracking strain rate during isovolumetric relaxation (IVR, SRivr). End-diastolic pressure-volume relationship (EDPVR) was also assessed noninvasively using a single-beat method. Overall stiffness was quantified by ventricular stiffness (Klv) normalized to end-diastolic volume (EDV). New York Heart Association class improved at 4 months (from 2.7 ± 0.7 to 1.9 ± 0.6, p < 0.001) as did ventricular filling (E/DT from 0.48 ± 0.29 to 0.39 ± 0.31 cm/s(2), p = 0.01). In contrast, relaxation (E', SRivr) and filling pressures (E/E', E/SRivr) did not change. Slope of EDPVR did not change with CRT. Such finding, together with an unmodified Klv/EDV and a 7 ± 18 % reduction in EDV (p = 0.001), suggested reverse remodelling towards a smaller equilibrium volume. Finally, end-systolic LV volume decreased from 147 ± 59 to 125 ± 52 ml and ejection fraction increased from 0.26 ± 0.07 to 0.32 ± 0.09 (both p < 0.001). Using a Cox regression model we found that only changes (Δ) in diastolic, but not systolic indexes, correlated with the composite clinical endpoint, with increments in ΔEDV20 and ΔE/DT, single or combined, greatly increasing risk of heart failure and/or cardiac death (p = 0.003). Ventricular reverse remodelling, together with improvement in ventricular filling, rather than improvements of systolic function, predict clinical prognosis long-term post-CRT.