Estimation of Left Ventricular Stroke Work for Rotary Left Ventricular Assist Devices.

Continuous monitoring of left ventricular stroke work (LVSW) may improve the medical management of patients with rotary left ventricular assist devices (LVAD). However, implantable pressure-volume sensors are limited by measurement drift and hemocompatibility. Instead, estimator algorithms derived from rotary LVAD signals may be a suitable alternative. An LVSW estimator algorithm was developed and evaluated in a range of in vitro and ex vivo cardiovascular conditions during full assist (closed aortic valve [AoV]) and partial assist (opening AoV) mode. For full assist, the LVSW estimator algorithm was based on LVAD flow, speed, and pump pressure head, whereas for partial assist, the LVSW estimator combined the full assist algorithm with an estimate of AoV flow. During full assist, the LVSW estimator demonstrated a good fit in vitro and ex vivo (R 2 : 0.97 and 0.86, respectively) with errors of ± 0.07 J. However, LVSW estimator performance was reduced during partial assist, with in vitro : R 2 : 0.88 and an error of ± 0.16 J and ex vivo : R 2 : 0.48 with errors of ± 0.11 J. Further investigations are required to improve the LVSW estimate with partial assist; however, this study demonstrated promising results for a continuous estimate of LVSW for rotary LVADs.

Surface Coatings for Rotary Ventricular Assist Devices: A Systematic Review.

Rotary ventricular assist devices (VADs) are frequently used to provide mechanical circulatory support to patients suffering from end-stage heart failure. Therefore, these devices and especially their pump impeller and housing components have stringent requirements on wear resistance and hemocompatibility. Various surface coatings have been investigated to improve the wear resistance or hemocompatibility of these devices. The aim of the present systematic review was to build a comprehensive understanding of these coatings and provide potential future research directions. A Boolean search for peer-reviewed studies was conducted in online databases (Web of Science, Scopus, PubMed, and ScienceDirect), and a preferred reporting items for systematic reviews and meta-analyses (PRISMA) process was followed for selecting relevant papers for analysis. A total of 45 of 527 publications were included for analysis. Eighteen coatings were reported to improve wear resistance or hemocompatibility of rotary VADs with the most common coatings being diamond-like carbon (DLC), 2-methacryloyloxyethyl phosphorylcholine (MPC), and heparin. Ninety-three percent of studies focused on hemocompatibility, whereas only 4% of studies focused on wear properties. Thirteen percent of studies investigated durability. This review provides readers with a systematic catalogue and critical review of surface coatings for rotary VADs. The review has identified that more comprehensive studies especially investigations on wear properties and durability are needed in future work.

Design and fabrication of a nerve-stretching device for in vivo mechanotransduction of peripheral nerve fibers.

The potential of peripheral nerves to regenerate under the effect of axial tensile forces was not previously extensively explored due to the lack of capabilities of translating ex vivo axonal stretch-growth to in vivo studies, until the development of a nerve stretcher. The nerve stretcher, which we have designed and manufactured recently, is a device that uses a controlled amount of axial tensile force (vacuum/negative gauge pressure) applied directly to a sectioned peripheral nerve in vivo to expedite nerve regrowth rate. Using this platform, a series of experiments was carried out to observe the effect of in vivo axial stretch on axonal lengthening. During these experiments, a few challenges necessitated redesigning the device like a sudden loss of stretching force due to vacuum leakage, erroneous feedback from vacuum sensor due to sensor drift, and inability to control and operate the device remotely. Here we present an improved design of the nerve stretcher along with its integration with a state-of-the-art online vacuum monitoring facility to control, collect, process, and visualize negative gauge pressure data in real-time.

Bridging larger gaps in peripheral nerves using neural prosthetics and physical therapeutic agents.

Peripheral nerve injuries are relatively common and can be caused by a variety of traumatic events such as motor vehicle accidents. They can lead to long-term disability, pain, and financial burden, and contribute to poor quality of life. In this review, we systematically analyze the contemporary literature on peripheral nerve gap management using nerve prostheses in conjunction with physical therapeutic agents. The use of nerve prostheses to assist nerve regeneration across large gaps (> 30 mm) has revolutionized neural surgery. The materials used for nerve prostheses have been greatly refined, making them suitable for repairing large nerve gaps. However, research on peripheral nerve gap management using nerve prostheses reports inconsistent functional outcomes, especially when prostheses are integrated with physical therapeutic agents, and thus warrants careful investigation. This review explores the effectiveness of nerve prostheses for bridging large nerve gaps and then addresses their use in combination with physical therapeutic agents.

Temperature Compensated Fibre Bragg Grating Pressure Sensor for Ventricular Assist Devices.

Rotary blood pumps may be used as ventricular assist devices (VADs) to support patients with end-stage heart failure-'rotary VADs'. Clinically, rotary VADs are operated at a constant speed which is set manually. Due to inadequate haemodynamic monitoring equipment outside of the hospital setting, device speed remains the same for weeks or months at a time, leaving clinicians in the dark, and patients vulnerable to harmful over- or under-pumping events. Therefore, it would be beneficial to have an implantable sensor which can measure blood pressure at the rotary VAD inlet or outlet and detect the onset of adverse events. In this study, a temperature compensated fibre Bragg grating (FBG) based strain sensor which can be incorporated into a VAD and used for continuous, real-time blood pressure monitoring is investigated. Error in the pressure reading between the developed and reference sensor occurred due to changes in temperature. A generalised linear model was used to compensate for temperature related error between 35-39º. Without temperature compensation, the mean error in the pressure reading over the desired range of -25 to 150 mmHg was approximately ±5 mmHg. The temperature compensated mean error over the same range was less than ±2 mmHg. The compensation technique was effective over a wide range of temperatures and pressures, demonstrating the potential of the sensor for continuous real-time blood pressure monitoring.

Rapid Speed Modulation of a Rotary Total Artificial Heart Impeller.

Unlike the earlier reciprocating volume displacement-type pumps, rotary blood pumps (RBPs) typically operate at a constant rotational speed and produce continuous outflow. When RBP technology is used in constructing a total artificial heart (TAH), the pressure waveform that the TAH produces is flat, without the rise and fall associated with a normal arterial pulse. Several studies have suggested that pulseless circulation may impair microcirculatory perfusion and the autoregulatory response and may contribute to adverse events such as gastrointestinal bleeding, arteriovenous malformations, and pump thrombosis. It may therefore be beneficial to attempt to reproduce pulsatile output, similar to that generated by the native heart, by rapidly modulating the speed of an RBP impeller. The choice of an appropriate speed profile and control strategy to generate physiologic waveforms while minimizing power consumption and blood trauma becomes a challenge. In this study, pump operation modes with six different speed profiles using the BiVACOR TAH were evaluated in vitro. These modes were compared with respect to: hemodynamic pulsatility, which was quantified as surplus hemodynamic energy (SHE); maximum rate of change of pressure (dP/dt); pulse power index; and motor power consumption as a function of pulse pressure. The results showed that the evaluated variables underwent different trends in response to changes in the speed profile shape. The findings indicated a possible trade-off between SHE levels and flow rate pulsatility related to the relative systolic duration in the speed profile. Furthermore, none of the evaluated measures was sufficient to fully characterize hemodynamic pulsatility.