A versatile microprocessor-based multichannel stimulator for skeletal muscle cardiac assist

Optimal assist strategy exploration for a direct assist device under stress‒strain dynamics

OBJECTIVES

The aim of this paper is to introduce a new assist strategy for a direct assist device that can enhance the heart's pumping efficiency and decrease the chances of myocardial injury in contrast to the conventional assist strategy.

METHODS

We established a finite element model of a biventricular heart, divided the ventricles into several regions, and applied pressure to each region separately in order to identify the primary and secondary assist areas. Then combined and tested these areas to obtain the optimal assist strategy.

RESULTS

The results indicate that our method exhibits an assist efficiency approximately ten times higher than that of the traditional assist method. Additionally, the stress distribution in the ventricles is more uniform after assistance.

CONCLUSIONS

In summary, this approach can result in a more homogenous stress distribution within the heart while also minimizing the contact area with it, which can reduce the incidence of allergic reactions and the likelihood of myocardial injury.

An IC-based controllable stimulator for respiratory muscle stimulation investigations

Functional Electrical Stimulation can be used to restore motor functions loss consecutive to spinal cord injury, such as respiratory deficiency due to paralysis of ventilatory muscles. This paper presents a fully configurable IC-centered stimulator designed to investigate muscle stimulation paradigms. It provides 8 current stimulation channels with high-voltage compliance and real-time operation capabilities, to enable a wide range of FES applications. The stimulator can be used in a standalone mode, or within a closed-loop setup. Primary in vivo results show successful drive of respiratory muscles stimulation using a computer-based dedicated controller.

INVESTIGATION OF SHAPE MEMORY ALLOY SPRING ELASTIC COEFFICIENT BASED ON VARYING APPLIED CURRENTS IN A CARDIAC ASSIST DEVICE

This paper analyses the mechanical properties of shape memory alloy (SMA) springs based on different electric currents applied in a cardiac assist device (CAD). Experimental results show that when the input drive current is constant, the SMA spring is equivalent to a tension spring with determined elastic coefficient that increases with the current. Based on our experiments, the theoretical maximum recovery force produced by SMA can be obtained through this input current. The phase transformation of SMA from austenite to martensite is able to be controlled by the drive current instead of the surface temperature of SMA. In addition, this experiment designed a cardiac supporting device composed of eight SMA springs, and used a saline bag to simulate human heart. The peak pressure inside the saline bag produced by this device was 17.4% of the normal heart systolic pressure. Our results can provide further support for the research of advanced CAD.

A VERSATILE LABVIEW-BASED TOOLBOX DESIGN AND MAN-MACHINE INTERFACE FOR THE ELECTRICAL STIMULATION SYSTEM

This article introduces the modification of a self-developed prototype electrical stimulator. In addition, we describe our new design of a versatile and user-friendly toolbox based on the LabVIEW environment that will enable clinical users and physicians to easily go on to further applications and research. The prototype electrical stimulator is based on the digital signal processor, and the drive stage of the previous model has also been improved by using a modified constant-current circuit. Moreover, we use LabVIEW to implement the man-machine interface and to develop a user-friendly toolbox. This system is versatile and feasible from the viewpoint of the hardware and software designs. With the virtual instrument in the toolbox, the man-machine interface is easy for users to implement and helpful in their further research. Furthermore, this toolbox includes many units and parameters, such as waveform types, currents, stimulation time, and others. The system can be considered a versatile and full-featured stimulator for various applications, with its high flexibility in stimulation patterns and multi-channel designs. The proposed system can produce suitable electrical stimulation by tuning the parameters in the interface. The procedure described above can also be implemented in man-machine interfaces for different research purposes.

Continuous-waveform constant-current isolated physiological stimulator

We have developed an isolated continuous-waveform constant-current physiological stimulator that is powered and controlled by universal serial bus (USB) interface. The stimulator is composed of a custom printed circuit board (PCB), 16-MHz MSP430F2618 microcontroller with two integrated 12-bit digital to analog converters (DAC0, DAC1), high-speed H-Bridge, voltage-controlled current source (VCCS), isolated USB communication and power circuitry, two isolated transistor-transistor logic (TTL) inputs, and a serial 16 × 2 character liquid crystal display. The stimulators are designed to produce current stimuli in the range of ±15 mA indefinitely using a 20V source and to be used in ex vivo cardiac experiments, but they are suitable for use in a wide variety of research or student experiments that require precision control of continuous waveforms or synchronization with external events. The device was designed with customization in mind and has features that allow it to be integrated into current and future experimental setups. Dual TTL inputs allow replacement by two or more traditional stimulators in common experimental configurations. The MSP430 software is written in C++ and compiled with IAR Embedded Workbench 5.20.2. A control program written in C++ runs on a Windows personal computer and has a graphical user interface that allows the user to control all aspects of the device.

Universal serial bus powered and controlled isolated constant-current physiological stimulator

We have developed a compact, isolated, physiological, constant-current stimulator that is powered and controlled by a universal serial bus (USB) interface. The stimulator is designed to be used in ex vivo cardiac experiments but is suitable for a wide variety of settings. The cost and features compare very favorably with commercial stimulators usually used in research and student laboratories. In addition to being USB powered, other novel aspects of our stimulator include the ability to produce large currents, up to 100 mA through a typical 1 kOmega load, by means of a single high-voltage dc-to-dc converter; user-specified variable period, magnitude, and duration of complex monophasic or biphasic sequences; and easy integration via hardware or software into existing experimental setups.

Amplitude modulation drive to rectangular-plate linear ultrasonic motors with vibrators dimensions 8 mm x 2.16 mm X 1 mm

In this paper, to exploit the contribution from not only the stators but also from other parts of miniature ultrasonic motors, an amplitude modulation drive is proposed to drive a miniature linear ultrasonic motor consisting of two rectangular piezoelectric ceramic plates. Using finite-element software, the first longitudinal and second lateral-bending frequencies of the vibrator are shown to be very close when its dimensions are 8 mm x 2.16 mm x 1 mm. So one single frequency power should be able to drive the motor. However, in practice the motor is found to be hard to move with a single frequency power because of its small vibration amplitudes and big frequency difference between its longitudinal and bending resonance, which is induced by the boundary condition variation. To drive the motor effectively, an amplitude modulation drive is used by superimposing two signals with nearly the same frequencies, around the resonant frequency of the vibrators of the linear motor. When the amplitude modulation frequency is close to the resonant frequency of the vibrator's surroundings, experimental results show that the linear motor can move back and forward with a maximum thrust force (over 0.016 N) and a maximum velocity (over 50 mm/s).

A Closed-Loop Electrical Stimulation System for Cardiac Cell Cultures

An integrated electrical stimulation and recording system was designed for closed-loop control and analysis of cardiac cultures on planar microelectrode arrays. Stimulated action potentials from HL-1 clonal myocyte cultures were digitized, stimulation artifacts were removed using nulling and filtering methods, and analysis was performed to determine stimulation efficacy in real time. Results of this analysis were used to determine future stimulation waveform parameters such as polarity, amplitude, pulse duration, and rate or pattern. Algorithms were designed utilizing real-time analysis and control to maintain a desired electrophysiological response of the culture, such as an arbitrary capture fraction value. This paper presents the hardware and software design of the stimulus pulse circuitry, artifact extraction, analysis, and control components of the system. Applications of this technology include the study of cardiac cell physiology, improving the speed and accuracy of traditional open-loop stimulation protocols, pharmacological screening, and improving the performance of biosensors based on sensing electrical activity in cardiac cultures.

Aortomyoplasty: hemodynamics and comparison to the intraaortic balloon pump

BACKGROUND

Aortomyoplasty (AMP), a procedure in which the latissimus dorsi muscle (LDM) is wrapped around the aorta and stimulated during diastole, is a potential method of chronic counterpulsation. Counterpulsation by the intraaortic balloon pump (IABP) is a proven treatment for ischemic coronary syndrome and heart failure but cannot be used chronically. This study examined the long-term potential of a unique AMP configuration and compared its performance to the IABP.

MATERIALS AND METHODS

AMP was done using a wringer configuration (AMP-W) in nine dogs. Six and 12 months later, acute hemodynamic augmentation was evaluated by measuring differences in mean diastolic aortic pressure (mDAP), peak left ventricular pressure (pLVP), and the endocardial viability ratio (EVR) between stimulated and unstimulated beats.

RESULTS

The diastolic augmentation obtained by AMP-W at 6 months and by AMP-W and IABP at 12 months was statistically significant. Additionally, the enhancements in EVR (16.1 +/- 4.3%), mDAP (8.6 +/- 2.5%), and pLVP (-1.8 +/- 1.0%) at 6 months were similar to those in EVR (19.1 +/- 5.2%), mDAP (13.1 +/- 3.6%), and pLVP (-0.8 +/- 1.3%) at 12 months. Most importantly, the augmentation obtained by AMP-W at 12 months was similar to that of the IABP: EVR (17.1 +/- 5.9%), mDAP (13.4 +/- 6.7%), and pLVP (-1.5 +/- 0.8%).

CONCLUSIONS

AMP-W is a safe, robust procedure, capable of providing counterpulsation equivalent to the IABP, 12 months following surgery. The potential for AMP-W to offer chronic counterpulsation and to benefit the ischemic heart should be investigated further.

Circulatory benefits of diastolic counterpulsation in an ischemic heart failure model after aortomyoplasty

OBJECTIVE

Aortomyoplasty is an experimental surgical procedure in which the latissimus dorsi muscle is wrapped around the thoracic aorta and stimulated to contract during diastole, providing diastolic counterpulsation. We hypothesized that aortomyoplasty could improve cardiac function in a chronic ischemic heart failure model, similar to the improvement seen with the intra-aortic balloon pump.

METHODS

Six dogs (25-30 kg) successfully underwent aortomyoplasty followed by serial coronary microembolization. Ejection fraction decreased from 63.5% to 36.5%. Two weeks after the final microembolization, the muscle was conditioned for 4 months to achieve fatigue resistance. One year after aortomyoplasty, hemodynamic studies during 1 hour of aortomyoplasty and 1 hour of intra-aortic balloon counterpulsation determined mean diastolic aortic pressure, peak left ventricular pressure, and endocardial viability ratio for assisted and unassisted beats. Cardiac output, stroke volume, and parameters of cardiac function were also measured.

RESULTS

Endocardial viability ratio increased by 23.8% +/- 7.9% (P =.001) with aortomyoplasty counterpulsation and by 22.7% +/- 12.9% (P =.021) with the intra-aortic balloon pump. Both aortomyoplasty and the intra-aortic balloon pump significantly increased mean diastolic aortic pressure and reduced peak left ventricular pressure. Improvements in cardiac function with aortomyoplasty and the intra-aortic balloon pump were similar. Cardiac output increased from 2.61 +/- 0.88 to 3.07 +/- 1.06 L/min (P =.006), and index of afterload decreased from 5.4 +/- 1.4 to 4.8 +/- 1.4 mm Hg/mL (P =.02) during 1 hour of aortomyoplasty counterpulsation.

CONCLUSION

One year after the procedure, aortomyoplasty counterpulsation provided diastolic augmentation and improved cardiac performance similar to the improvement provided by the intra-aortic balloon pump in a chronic ischemic heart failure model. Aortomyoplasty has the potential to benefit patients with ischemic heart disease refractory to current therapies.

Re-animation of muscle flaps for improved function in dynamic myoplasty

The authors report on a series of experiments designed to produce a skeletal muscle contraction functional for dynamic myoplasties. Conventional stimulation techniques recruit all or most of the muscle fibers simultaneously and with maximal strength. This approach has limitations in free dynamic muscle flap transfers that require the muscle to contract immediately after transfer and before re-innervation. Sequential stimulation of segments of the transferred muscle provides a means of producing non-fatiguing contractions of the muscle in the presence or absence of innervation. The muscles studied were the canine gracilis, and all experiments were acute studies in anesthetized animals. Comparison of conventional and sequential segmental neuromuscular stimulation revealed an increase in muscle fatigue resistance and muscle blood flow with the new approach. This approach offers the opportunity for development of physiologically animated tissue and broadening the abilities of reconstructive surgeons in the repair of functional defects.

Increased coronary artery blood flow with aortomyoplasty in chronic heart failure

BACKGROUND

We hypothesized that diastolic counter-pulsation using aortomyoplasty will increase coronary blood flow.

METHODS

In dogs (n = 6, 20 to 25 kg), the left latissimus dorsi muscle was isolated, wrapped around the descending thoracic aorta, and conditioned by chronic electrical stimulation. Heart failure was induced by rapid ventricular pacing. In a terminal study, left ventricular and aortic pressures, and blood flow in the left anterior descending coronary artery and descending aorta were measured. The endocardial-viability ratio was calculated.

RESULTS

Aortomyoplasty increased mean diastolic aortic pressure (70 +/- 5 to 75 +/- 5 mm Hg, p < 0.05) and reduced peak left ventricular pressure (86 +/- 4 to 84 +/- 4 mm Hg, p < 0.05), leading to a 16% increase in endocardial-viability ratio (1.29 +/- 0.05 to 1.49 +/- 0.05, p < 0.05). Coronary blood flow was increased by 15% (8.2 +/- 1.5 to 9.4 +/- 1.6 mL/min, p < 0.05). During muscle contraction, 2.7 +/- 0.5 mL was ejected from the wrapped aortic segment.

CONCLUSIONS

These data demonstrate that aortomyoplasty provides successful diastolic counterpulsation after muscle conditioning and heart failure.

Design of low-cost general purpose microcontroller based neuromuscular stimulator

In this study, a general purpose, low-cost, programmable, portable and high performance stimulator is designed and implemented. For this purpose, a microcontroller is used in the design of the stimulator. The duty cycle and amplitude of the designed system can be controlled using a keyboard. The performance test of the system has shown that the results are reliable. The overall system can be used as the neuromuscular stimulator under safe conditions.