Computational methods for parametric evaluation of the biventricular mechanics of direct cardiac compression.

Despite the increasing incidence of heart failure, advancements in mechanical circulatory support have become minimal. A new type of mechanical circulatory support, direct cardiac compression, is a novel support paradigm that involves a soft deformable cup around the ventricles, compressing it during systole. No group has yet investigated the biomechanical consequences of such an approach.

Muscle-Powered Counterpulsation for Untethered, Non-Blood-Contacting Cardiac Support: A Path to Destination Therapy.

Conventional long-term ventricular assist devices continue to be extremely problematic due to infections caused by percutaneous drivelines and thrombotic events associated with the use of blood-contacting surfaces. Here we describe a muscle-powered cardiac assist device that avoids both these problems by using an internal muscle energy converter to drive a non-blood-contacting extra-aortic balloon pump. The technology was developed previously in this lab and operates by converting the contractile energy of the latissimus dorsi muscle into hydraulic power that can be used, in principle, to drive any blood pump amenable to pulsatile actuation.

Computational Studies on the Effects of Applied Apical Torsion for Cardiac Assist on Regional Wall Mechanics.

Objective: Here we report the results of parametric computational simulations evaluating the biomechanical effects of applied apical torsion (AAT) on a patient-specific bi-ventricular failing heart model.

Methods: We examined the resulting effects on cardiac biomechanics with varying device coverage areas and applied rotation angles to determine the practical working limits of AAT on a dilated cardiomyopathy heart model.

Results: The largest maximum principal stresses and strains observed in the heart failure model were 80.

Left ventricular simulation of cardiac compression: Hemodynamics and regional mechanics.

Heart failure is a global epidemic. Left ventricular assist devices provide added cardiac output for severe cases but cause infection and thromboembolism. Proposed direct cardiac compression devices eliminate blood contacting surfaces, but no group has optimized the balance between hemodynamic benefit and excessive ventricular wall strains and stresses.

Ventricle-specific epicardial pressures as a means to optimize direct cardiac compression for circulatory support: A pilot study.

Direct cardiac compression (DCC) holds enormous potential as a safe and effective means to treat heart failure patients who require long-term, or even permanent, biventricular support. However, devices developed to date are not tuned to meet the individual compression requirements of the left and right ventricles, which can differ substantially. In this paper, a systematic study examining the relationship, range, and effect of independent pressures on the left and right epicardial surfaces of a passive human heart model was performed as a means to optimize cardiac output via DCC support.

Cardiac Assist Devices: Early Concepts, Current Technologies, and Future Innovations.

Congestive heart failure (CHF) is a debilitating condition that afflicts tens of millions of people worldwide and is responsible for more deaths each year than all cancers combined. Because donor hearts for transplantation are in short supply, a safe and durable means of mechanical circulatory support could extend the lives and reduce the suffering of millions. But while the profusion of blood pumps available to clinicians in 2019 tend to work extremely well in the short term (hours to weeks/months), every long-term cardiac assist device on the market today is limited by the same two problems: infections caused by percutaneous drivelines and thrombotic events associated with the use of blood-contacting surfaces.

Computational Parametric Studies Investigating the Global Hemodynamic Effects of Applied Apical Torsion for Cardiac Assist.

Healthy hearts have an inherent twisting motion that is caused by large changes in muscle fiber orientation across the myocardial wall and is believed to help lower wall stress and increase cardiac output. It was demonstrated that applied apical torsion (AAT) of the heart could potentially treat congestive heart failure (CHF) by improving hemodynamic function. We report the results of parametric computational experiments where the effects of using a torsional ventricular assist device (tVAD) to treat CHF were examined using a patient-specific bi-ventricular computational model.

Potential mechanisms for muscle-powered cardiac support.

Biomechanical actuation of an implanted ventricular assist device (VAD) is an attractive means of providing long-term circulatory support. Studies show that energy from electrically stimulated skeletal muscle can, in principle, be used to provide tether-free cardiac assistance without the need for percutaneous drivelines or bulky energy transmission hardware. A mechanical prosthesis designed to harness the contractile power of in situ skeletal muscle has been developed in this laboratory that collects energy from the latissimus dorsi muscle and transmits it in the form of hydraulic power.

In vivo performance of a muscle-powered drive system for implantable blood pumps.

A unique biomechanical implant has been developed to convert muscle power into hydraulic energy for the purpose of driving an implanted blood pump. This device, called a muscle energy converter (MEC), is designed to attach to the humeral insertion of the latissimus dorsi (LD) muscle, so that stimulated contractions cause a rotary cam to compress a fluid-filled bellows. Here we report results from the latest in a series of canine implant trials where the MEC was connected to an adjustable pressure load to measure power output and assess long-term function.

Effect of a flexible ventricular restraint device on cardiac remodeling after acute myocardial infarction.

The effects of a flexible ventricular restraint device on left ventricular (LV) dilatation and hypertrophy after transmural infarction are examined in an ovine model. Left ventricular remodeling and dilatation occurs after extensive myocardial infarction. A flexible ventricular restraint made from a nitinol mesh was evaluated in adult female sheep (n=14).

A femoral artery cannula that allows distal blood flow.

Objective: A femoral artery cannula is used for certain types of circulatory support but can cause ischemia, especially during prolonged perfusion. This study tests the function of a femoral cannula designed to allow proximal and distal blood flow.

Methods: Five pigs were used in the study.

Improved mechanism for capturing muscle power for circulatory support.

Although it is now understood that trained skeletal muscle can generate enough steady-state power to provide significant circulatory support, there are currently no means by which to tap this endogenous energy source to aid the failing heart. To that end, an implantable muscle energy converter (MEC) has been constructed and its function has been improved to optimize durability, anatomic fit, and mechanical efficiency. Bench tests show that MEC transmission losses average less than 10% of total work input and that about 85% of this muscle power is successfully transferred to the working fluid of the pump.

Catecholamines restore myocardial contractility in dilated cardiomyopathy at the expense of increased coronary blood flow and myocardial oxygen consumption (MvO2 cost of catecholamines in heart failure).

To investigate the metabolic cost of catecholamine use in heart failure, we administered intravenous dobutamine or norepinephrine to dogs with moderate and severe LV dysfunction until LV contractile function was restored to normal levels. Both drugs were associated with significant increases in myocardial O(2) consumption, increased coronary blood flow requirements and decreased myocardial mechanical efficiency. These mechanisms may contribute to the deleterious effects of catecholamines in heart failure.

Comparison of dog and pig models for testing substernal cardiac compression devices.

Subtle anatomic differences between species can be a critical consideration when determining whether a given animal model is appropriate for surgical research purposes, especially when testing biomechanical implants. This study compares the effectiveness of two common animal models (dogs and pigs) in testing a balloon based cardiac compression device designed for substernal placement. Pigs were used in acute studies using an infarction model of heart failure, whereas dogs were used in chronic experiments in which heart failure was induced via rapid pacing.

Improvement of sternal closure stability with reinforced steel wires.

Background: Sternal dehiscence occurs when steel wires pull through sternal bone. This study tests the hypothesis that closure stability can be improved by jacketing sternal wires with stainless steel coils, which distribute the force exerted on the bone over a larger area.

Methods: Midline sternotomies were performed in 6 human cadavers (4 male).

Capturing in situ skeletal muscle power for circulatory support: a new approach to device design.

Efforts to harness in situ skeletal muscle for circulatory support have been extensive, but implants designed to tap this power source have yet to meet the strict performance standards incumbent upon such devices. A fourth generation muscle energy converter (MEC4) is described that represents a significant departure from previous hydraulic muscle pump designs, all of which have assumed a long cylindrical profile. The MEC4, in contrast, features a puck shaped metallic bellows oriented so that its end fittings lie parallel to the chest wall.

Lower sternal reinforcement improves the stability of sternal closure.

Background: This study uses a mechanical testing system to evaluate three methods of sternal closure.

Methods: Twelve sternal replicas composed of a polyurethane foam bone analogue were divided in the midline and reapproximated using three stainless steel wire techniques: six simple wires (6S), six figure-of-eight wires (6F8), or seven simple wires (7S), which included an extra wire at the lower sternum. The closures were subjected to increasing lateral distraction from 0 to 400 Newtons (N) (1 N = 0.

Validation of a bone analog model for studies of sternal closure.

Background: The incidence of serious sternal wound complications may be reduced with improvements in closure methods. Biomechanical testing of median sternotomy closures in cadavers has proven useful but is limited by availability, high cost, and wide variations in the material properties of the sterna. This study tests whether artificial sterna can be used to replace whole cadavers in sternal closure testing.

Method for anchoring biomechanical implants to muscle tendon and chest wall.

Reliable tissue fixation is of fundamental importance to the successful development of muscle powered motor prostheses. This report describes a series of canine implant trials used to develop stable tissue-device interface mechanisms. Muscle pumps were fitted with prototype tendon and chest wall anchoring schemes and secured to the ribs and humeral insertion of latissimus dorsi (LD) muscles.