Biomedical subjects

T Mussivand

Publications and source records attributed to T Mussivand.

At least 19 recordsLinked to original sources

PubMed1997

Wireless monitoring and control for implantable rotary blood pumps.

A wireless biotelemetry system for the transfer of digital data through intact skin and tissue has been developed to provide a safe and noninvasive means of communication between implanted medical devices and the outside of the body. The system utilizes 2 miniature infrared transmitter/receiver modules. Data are transmitted through intact skin and subcutaneous tissue on an 890 nm infrared carrier signal. The system has been evaluated in human cadavers and during in vivo implantation of artificial hearts and ventricular assist devices for durations of up to 96 h. Acceptable data transfer (error rate < 10(-5)) through a typical tissue thickness of 5-25 mm has been demonstrated. The ability to monitor and control a device from a remote site using public communication systems such as telephone lines and asynchronous transfer mode (ATM) systems has also been demonstrated. Design optimization is currently ongoing in preparation for clinical utilization with artificial heart systems and other implantable devices (such as rotary blood pumps).

Animals↗

PubMed1996

A remotely controlled and powered artificial heart pump.

An intrathoracic pulsatile artificial heart pump has been developed. Transcutaneous energy transfer and biotelemetry systems provide continuous power and remote monitoring and control, with no percutaneous connections required. The electrohydraulic system can be used either as a ventricular assist device or with modifications as a total artificial heart. The device uses a unidirectional axial flow pump coupled with a pressure activated one-way valve to allow hydraulic fluid to passively return to the volume displacement chamber during diastole. The transcutaneous energy transfer system provides power to the device and recharges the implantable battery pack. A wearable external controller and external battery pack provide the patient enhanced mobility and thus an improved quality of life. The biotelemetry system allows control and monitoring of the device after implantation, as well as an added capability to monitor and control the device remotely over public communication lines. Early prototypes have functioned failure free for up to 3 years in vitro. The device has sustained circulation in vivo for up to 4 days. Design optimization is continuing, and chronic in vivo evaluation is planned.

Animals↗

PubMed1996

Transcutaneous energy transfer with voltage regulation for rotary blood pumps.

Rotary blood pumps often require a constant operating voltage. To meet this requirement and to eliminate the need for percutaneous leads, a voltage-regulated transcutaneous energy transfer (TET) system has been developed. Voltage regulation is achieved by using a transcutaneous infrared feedback control loop operating on a 890 nanometer (nm) wavelength. In vitro testing of the system developed has shown that output voltage can be maintained to within 0.2 V of nominal (14.5 V) for delivered powers up to 50 watts (W) and coil separations of between 3 and 10 mm. Power transfer efficiencies were determined to be from 68% to 72% over the tested range of coil separations and output currents from 1.5 to 3.6 amperes (A). This system has demonstrated acceptable performance in regulating output voltage while transferring power inductively without using percutaneous connections. By integrating this type of TET system with an implanted rotary blood pump, the quality of life for the device recipient could be improved.

Energy Transfer↗

PubMed1995

Assessment of the cytotoxicity of the photosensitizing drug BPD verteporfin using human vascular smooth muscle cells in culture.

Photosensitizing drugs are selectively taken up by lipid-rich lesions such as atheromatous plaque which when exposed to light render the drugs cytotoxic. However, skin photosensitivity which persists for many weeks is a significant side effect. We investigated the cytotoxicity of a new photosensitizing drug, the benzoporphyrin derivative BPD verteporfin (Quadra Logic Technologies), which does not have this deleterious side effect. Vascular smooth muscle cells (VSMC) from normal human mammary and diseased human coronary arteries were grown in culture from explants and characterized with respect to their growth rates. The sensitivity to BPD with and without light was assessed by measuring viability after treatment. The lethal dose of drug for 50% viability loss (LD50) for BPD with light was approximately 12.5 ng/ml for mammary artery, with 52 +/- 8% cell survival (n = 6). The coronary artery VSMC from all patient sources, although differing significantly in growth rate, had a survival of 44 +/- 6% (n = 12) at the same concentration of BPD used for the mammary artery SMC (p = NS). Our results established the LD50 for BPD using human arterial sources of SMC and showed that the growth rates of the cells did not affect the cytotoxicity of the drug.

Cell Survival↗

PubMed1994

Comparison of rechargeable lithium and nickel/cadmium battery cells for implantable circulatory support devices.

Size and weight constraints are critical areas in the design of implantable medical devices. For this reason, a study of different rechargeable lithium and nickel/cadmium (Ni/Cd) battery cell types was undertaken to determine which cell type, when assembled into a multicell battery pack, would provide the smallest and lightest power source for implantation. The discharge rate and cycle life characteristics of 2 different rectangular prismatic Ni/Cd cells and 5 different rechargeable lithium cells were determined at 37 degrees C by charge/discharge cycling, the cells using a constant discharge load of 0.87 A. Using the observed discharge rate and cycle life characteristics of the cells, along with the desired performance criteria of 30 min operating time at the end of a 1-year implant period, the projected weight and volume of the various 12-V battery packs were determined. These results showed that one of the rectangular prismatic Ni/Cd cells would yield the smallest (53 ml) and lightest (189 g) 12-V battery pack that met the performance criteria specified. The results also indicate that, for applications requiring long implant times, cycle life can be more important in the selection of cells for a small, lightweight battery pack than specific energy or energy density.

Cadmium↗

PubMed1993

Can disturbed brain microcirculation cause Alzheimer's disease?

Recent ultrastructural studies demonstrate characteristic and extensive angio-architectural distortions of cerebral capillaries in Alzheimer's brains. Alzheimer's disease subjects additionally show reduced cerebral blood flow (CBF), glucose metabolism and oxygen utilization which appear inversely proportional to the disease severity. These findings led us to develop a hypothetical model which appears consistent with the pathogenesis and progression of AD. During ageing, brain capillaries (site of the blood-brain barrier) may undergo progressive degeneration caused by amyloid deposits, thickened basement membrane, cerebral atrophy, reduced vessel elasticity, or genetic predisposition. When these structural abnormalities of the brain microvasculature begin to interfere with basic laws of fluid dynamics, haemorheological compromise will result in cerebral capillary resistance, high blood viscosity, abnormal flow patterns, and changes in shear stress and shear rate in vessel walls. The net effect is chronic 'disturbed' blood flow to the brain that impairs the delivery of essential nutrients, particularly oxygen and glucose, to cerebral neurons. As ischaemic-sensitive neurons lower their oxidative phosphorylation and ATP production to subfunctional levels, they release a diffusible glial mitogen that directly stimulates reactive astrocytosis. These reactive glia differ significantly from normal glia because they proliferate mostly in response to brain injury and can spread to unaffected tissue. It has been suggested that amyloid precursor protein (APP) may be expressed from reactive glia following neuronal injury thus providing the nidus of plaque formation. As brain tissue space is invaded by reactive glia and microglia, neuronal cytoskeletal damage can result in neurofibrillary tangles.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1993

Transcutaneous energy transfer system performance evaluation.

A transcutaneous energy transfer (TET) system has been developed to power implantable devices such as artificial hearts, defibrillators, and electrical stimulators. Transcutaneous coupling of power to these implanted devices remains a favorable alternative as percutaneous lines are avoided in order to eliminate the potential of infection and allow patient mobility. In vitro, in vivo, ex vivo, and human cadaver studies of the electrohydraulic ventricular assist device TET have demonstrated that power can be transmitted over a range of skin thicknesses of 3-15 mm and can tolerate radial misalignments of up to 20 mm. Sensitivity to coil separation and radial misalignment variations has been addressed by the development of an auto-tuning TET. The system has only a 10% attenuation in secondary coil voltage when metallic objects are in contact with the primary coil. The system has demonstrated a power transfer efficiency of 60-80% for power demands from 5 to 70 W. The TET secondary coil will provide an output voltage of 10-25 V for current demands from 0.5 to 4.0 A. TET chronic studies in porcine models have demonstrated no adverse effect to the tissue when up to 40 W of power can be delivered to an implanted load without the tissue-contacting surface of the coil exceeding 42 degrees C. In conclusion, the TET is a feasible alternative for tether-free power transmission.

Cadaver↗

PubMed1989

Development of compliance chamber diaphragms with reduced permeability.

The implantable ventricular assist systems currently undergoing clinical readiness testing shuttle the displaced gas between the non-blood side of the pumping diaphragm and an elastic chamber generally called a "compliance chamber" or variable volume device. The movement of the stored gas allows the pump to fill and empty without compression or expansion of the gas behind the pump diaphragm. The material used for the construction of compliance chambers should be fatigue resistant to withstand the 63 million flexes per year of the blood pump. The material should also be biocompatible and highly impervious to gases. Significant diffusion of gases from the compliance system necessitates external make-up gases to somehow be added to the internal system. Material selection is complicated by the fact that most fatigue-resistant elastomers also have high gas permeability. In order to solve this problem, bilayer compliance chambers have been developed using biocompatible and fatigue-resistant polyolefin rubber comolded with relatively impervious butyl rubber.

Assisted Circulation↗

PubMedDate not supplied

In vitro and in vivo performance evaluation of a totally implantable electrohydraulic left ventricular assist system.

The biolized electrohydraulic left ventricle assist devices were tested in 14 calves with an average survival time of 162 days and as long as 250 days without the use of anticoagulants. In vitro, the system pumped 4.1 L/min at a low 4.8 mmHg fill pressure with a mean afterload of 100 mmHg and rate of 46 bpm. A flow rate of 13.5 L/min was observed at 155 bpm and 110 mmHg afterload. Motor frequency and current increased with increasing flow rate (162 Hz, 0.67 amp at 2.5 L/min; 484 Hz, 2.43 amp at 13.5 L/min). Flow rate did not change significantly with afterload pressure. The complete system was implanted in a 100 kg calf. Synchronization of the blood pump with the natural heart was demonstrated at heart rates of 85 to 167 bpm. The synchronized flow rate varied from 6 to 10.5 L/min despite the considerable heart rate changes and stroke variations. The system hemodynamic performances were acceptable and met NIH requirements.

Animals↗

PubMedDate not supplied

New crisscross-shaped port design for universal serial pumps.

The long range goal is the development of a clinically useful, implantable, skeletal muscle powered cardiac assist device (MCAD). To accomplish this goal, two criteria must be met: good anatomic fit, and antithrombogenicity. Because of the relative locations of the latissimus dorsi (LD) muscle and aorta, there are two possible port arrangements: "crisscrossed" (C design), in which the ports are crossed to anastomotic sites, and "prong" shaped (P design), in which no crossover takes place. The purpose of this paper is to determine which of these designs is best from a fluid dynamic perspective, and hence has the best possibility for low thrombogenicity. Flow visualization (FV) techniques were used during two pumping conditions in a mock loop: worst case (MCAD off) and best case (MCAD driven optimally). Results of the MCAD off tests showed that both designs required immediate actuation (for example, an IABP console). However, FV studies under optimal conditions indicated superiority of the C design, most likely due to kinetic energy-induced rotary motion combined with a minimal interport distance. It is concluded that the C design provides ideal flow dynamics, even in valveless pumps, and also has application to valved devices.

Counterpulsation↗

PubMedDate not supplied

Electrohydraulic ventricular assist device development.

An electrohydraulic ventricular assist device has been developed. An axial flow pump driven by a brushless DC motor provides actuation. Energy is supplied by internal Ni/Cd batteries and by external Ag/Zn batteries, both rechargeable. Electromagnetic induction is used to pass energy through the skin with a transcutaneous energy transfer (TET) system. Physiologic control, battery management, motor commutation, and communication functions are performed by a surface mount internal controller. An infrared data link within the TET coils provides bidirectional communication between the external and internal controllers. A computer model was developed to predict system performance. The dimensions are 180 mm x 116 mm x 40 mm. An in vitro system pumped 5.7 L/min at 10 mmHg inflow and 100 mmHg outflow pressure. The internal battery can provide the projected energy requirements for 40 min after 540 charge/discharge cycles, and the external battery is capable of 4 hr of operation after 150 cycles. The TET system can deliver 60 W of power and exceeds 80% efficiency between 15 and 30 W. The device configuration is based on human cadaver and intraoperative fit trials. The device is being modified for calf implantation by redirecting the blood ports, increasing the output, and incorporating the internal controller in the unified device base.

Animals↗

PubMedDate not supplied

A transcutaneous energy and information transfer system for implanted medical devices.

During the last four decades there has been a rapid increase in the development and usage of medical devices. Currently, there are more than 500,000 devices on the market and 25,000 new devices enter the market each year. Many medical devices are now designed to be implantable (pacemakers, defibrillators, circulatory assist devices, artificial hearts, cochlear implants, neuromuscular stimulators, biosensors, etc.). Almost all of the active devices (those that perform work) and many of the passive devices (those that do not perform work) require a source of power. In addition, these devices need to be monitored and controlled, which can be accomplished by utilizing remote communication methods. A transcutaneous energy transfer system combined with a remote communications system has been developed and evaluated in vitro and in vivo (bovine, porcine, and human cadaver experiments). The energy transfer system can deliver up to 60 W with power transfer efficiencies between 60 and 83%. An automatically tuned, resonant frequency tracking method is used to obtain optimum power transfer over a range of operating conditions. The remote communications system can transfer digital data bidirectionally through intact skin at rates up to 9600 baud. The system transmits information by frequency modulating an 890 nm infrared carrier signal. The system has demonstrated satisfactory performance during multicenter evaluation with ventricular assist and total artificial heart devices. Design improvements have been identified, which will be implemented to produce an optimized system for energy transfer to and remote communications with various implantable medical devices.

Animals↗

PubMedDate not supplied

Assessment of reused catheters.

Demands for health care cost containment have prompted the assessment of recycling medical devices, including catheters. The investigation of catheter reuse for effectiveness and safety began at the University of Ottawa Heart Institute in early 1994. This report provides the preliminary results from this ongoing assessment on the feasibility of catheter reuse. Burst tests were conducted to detect changes in catheter mechanical integrity. Scanning electron microscopy (SEM) was performed to assess surface changes and protein deposition after use and the subsequent cleaning process. Results of burst testing showed no significant difference in burst patterns or burst pressures between single use and unused catheters. Surface differences were observed between used and unused catheters. SEM studies detected physical changes such as scratches, gouges, cuts, and deposits on the used catheters. Unused balloon surfaces appeared to be clean and uniform compared to used ones. Residue and cracking were identified on other used devices. In conclusion, the methods used can assess various effects of recycling. A blind study of large samples of used catheters is planned to establish statistically the level and variance of structural damage to catheters during typical use.

Catheterization↗

PubMedDate not supplied

Evolution of an electrohydraulic ventricular assist device through in vivo testing. The EVAD Team.

A totally implantable intrathoracic electrohydraulic ventricular assist device has been developed at the University of Ottawa Heart Institute. In vivo testing has been instrumental in its progressive development. A total of 15 experiments (4 acute, 11 performance) have been performed using male calves (62-117 kg). Data from the acute experiments, human fit trials, fluid dynamic studies, and hydraulic/energy efficiency analyses formed the basis for the development of a compact, single piece ventricular assist device called the Unified System in which the volume displacement chamber, motor, and blood chamber are housed within a compact 600 cc, 740 g unit. The performance experiments indicated that the unified system could support calves for periods up to 96 hr. The mean postoperative cardiac output was 7.1 +/- 0.7 L/ min (range = 4.9-11), mean blood pressure was 99.7 +/- 5.8 mmHg, and mean pulmonary artery pressure was 32.1 +/- 1.2 mmHg. The operative technique for intrathoracic implantation has been developed. The major problems encountered were of respiratory failure, improved by device repositioning in the calf; decreased blood inflow to the device that was improved by cannula redesign; circuit board fracture corrected by design modification; and a power supply problem that was limited to a single unit. The preliminary experiments have helped in the design modifications of the Unified System. The improved version of the system will undergo formal performance, reliability, and chronic in vivo testing before human implantation.

Animals↗

PubMedDate not supplied

Electrohydraulic ventricular assist device development.

A 64 ml (effective stroke volume) in vitro electrohydraulic ventricular assist device (VAD) prototype has been built. The energy converter is an axial flow pump driven by a brushless direct current (DC) motor. Systole begins as silicone oil is pumped from the volume displacement chamber (VDC) into the ventricle, displacing the flexing diaphragm separating the oil and the blood. In diastole, the motor reverses, providing active filling by pumping oil from the ventricle into the VDC. The surface mount electronic internal controller provides motor commutator, energy management, telemetry, and physiologic control functions. Energy is supplied externally by either a 12 V DC power supply or a 12 V DC rechargeable battery and is transmitted through the skin by a transcutaneous energy transformer (TET). Energy can also be supplied by a 12 V DC rechargeable internal battery. Bidirectional infrared telemetry is used to transmit information between the internal and external controllers.

Blood Pressure↗

PubMedDate not supplied

Flow visualization in an artificial heart using diffuse and planar laser lighting.

The purpose of the study was to characterize flow properties within a clinical pusher plate type artificial heart. Dual camera video tape and synchronized still photographs were used to study flow patterns. Diffused light and a planar laser source provided illumination. The laser light was turned into a plane of light with a thickness varying from 0.1 to 10 mm, and magnesium oxide and Amberlite particles were used as tracers. Qualitative and quantitative analyses were performed by the examination and digitization of flow patterns. Inflow, outflow, pneumatic drive and after-load pressure, diaphragm motion, cardiac output, and heart rate were measured and recorded. An electrical circuit was developed to synchronize pump diaphragm motion with captured images of flow trajectories. Trajectories were then digitized, and velocities, turbulence, and shear stresses were calculated. As the result of these experiments, disturbed, recirculating, and stagnation zones were identified and global and local turbulence values were determined. Simultaneous turbulence, stasis, recirculation, and laminar flow patterns were observed during most phases of the pumping cycle. Velocities obtained varied from 2 cm/sec to 145 cm/sec; total local shear stresses of 12 to 897 dynes/cm2 were seen.

Blood Flow Velocity↗

PubMedDate not supplied

The effect of pulsatile power loads on nickel/cadmium battery cells for mechanical circulatory support devices.

A number of portable medical devices, including the implantable ventricular assist device, demand fluctuating or pulsatile power from their batteries. Therefore, a study was undertaken to determine the effects of these pulsatile discharge loads on the cycle life and operating time of rectangular prismatic nickel/cadmium battery cells. The battery cells were charge/discharge cycled at 37 degrees C using either a pulsatile discharge load of 10.0 or 11.25 W (average) or a nonpulsatile discharge load equivalent to the average of the pulsatile loads. The tests showed that the pulsatile discharged cells gave significantly less operating time throughout their cycle life, by a mean of 3 +/- 3-8 +/- 2 min on each cycle (ie, 8 +/- 8-18 +/- 5%), compared to the cells under equivalent nonpulsatile discharge loads. The tests also showed that the pulsatile discharged cells had significantly shorter cycle lives, by 61-97 cycles (11-17%), than the nonpulsatile discharged cells. The results show that, under the test conditions of this study, pulsatile discharge loads reduce the cycle lives and operating times of rectangular prismatic nickel/cadmium battery cells, compared to cells discharged under nonpulsatile loads of equivalent average power.

Cadmium↗

PubMedDate not supplied

Device reliability.

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Artificial Organs↗