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Biomedical subjects

R R Brownlee

Publications and source records attributed to R R Brownlee.

15 recordsLinked to original sources
PubMed1979

Myocardial stimulation impedance: the effects of electrode, physiological, and stimulus variables.

With exposed metal at the electrode tissue interface (8 mm2, 28 mm2, 57 mm2), myocardial threshold stimulation impedance increased as pulse duration was lengthened, with left ventricular intramyocardial stimulation, and with the smaller surface area electrode. An 0.5 mm2 differential-current-density electrode, which eliminated direct metal-to-tissue contact at the electrode-myocardial interface, was associated with notably higher impedances than each of the three metal tip electrodes and did not show increasing impedance levels with changes in pulse duration, confirming the minimization of polarization energy losses with this device. The majority of electrode, electrode tissue interface, and myocardial variables that are characterized by high threshold stimulation impedance are associated with low threshold energy requirements for pacing and reduced pacemaker power source drain. No accurate information about sensing impedances can be derived from current knowledge of pacing impedance.

Acid-Base Imbalance↗
PubMed1978

Current status of pacemaker power sources.

After years during which pacers of very similar design and capabilities were provided by a small number of manufactures, many different lithium, halogen, rechargeable, and nuclear power sources are now available. The variety of chemistries, methods of construction, and sealing techniques used in the batteries of the different manufacturers is almost unlimited. This has made it necessary for physicians who implant and follow pacer to acquire a general knowledge of the field if they are to make an informed choice of pacemaker power source for implantation and if they are to manage recalls with a minimum of patient and physician trauma. More experience is required before it can be definitely determined which of the new pacer power sources will prove superior, but when coupled with well-designed, hermetically sealed pulse generators, all are capable of providing continuous pacing for at least 5 years and the 10-year pacemaker is now a probability.

Animals↗
PubMed1976

Rechargeable silver-modified mercuric oxide-zinc cell for cardiac pacemakers.

Tests were conducted on rechargeable mercury-zinc pacemaker batteries under simulated and actual biologic conditions, using a variety of discharge rates and charging schedules. In tests on 96 cells at a 6.4 milliampere (ma) discharge, recharging once every 15 months of simulated pacing at a 25 microampere (mua) drain, the earliest cell failure occurred after an equivalent of 50 years of pacing. The mean pacing equivalent for all 96 cells was more than 140 years. In 6.4 ma discharge tests on 24 cells, recharging once every 8 days of simulated pacing, only 1 cell in 24 failed after an equivalent of more than 500 years of pacing (actual time 2 years). In tests on 13 cells pacing at a 200 mua drain without recharging, the simulated mean duration of pacing before total discharge was 4.8 years. Seven other cells at a 200 mua drain with periodic recharging continue to function normally after more than 7 years of actual time, simulating 56 years of pacing at a 25 mua drain. Cardiac pacemakers using the rechargeable mercury-zinc cell have been implanted in animals for more than 2 1/2 years and in patients for more than 1 year with all units continuing to function satisfactorily. It has been demonstrated unequivocally that a rechargeable mercury-zinc pacemaker will function continuously for more than 4 years without recharging and that periodic recharging will extend pacing life far beyond that predicted for lithium and nuclear primary power sources.

Animals↗
PubMed1976

Chronic testing of a pacemaker that needs recharging only once every four years.

Since 1967, three series of rechargeable single-cell silver-mercuric oxide-zinc pacemakers have been implanted in dogs with complete heart block. The five nonhermetic units in series 1 failed after less than or equal to 18 months, primarily due to prototype cell deficiencies, although one cell functioned for eight years. The six units in series II contained improved cells, but failed due to gradual transepoxy fluid absorption after less than or equal to 31 months. All rechargeable cells were salvaged and dried, and, seven years after their manufacture, they continue to power pacing circuits. Series III now totals 20 doubly hermetically sealed units, tested for up to three years (total more than 300 months or 26 years), with no pacemaker failures. Accelerated tests indicate a minimum life of more than 50 years. A clinical trial is in progress.

Animals↗
PubMed1976

Failure of demand pacing with small surface area electrodes.

As pacemaker electrode myocardial contact area is reduced, the energy required to stimulate the heart decreases; but the effect of surface area on an electrode's ability to transmit R-wave potentials has not been well documented. Endocardial and intramyocardial R-wave potentials were measured in ten dogs with seven commercially available pacemaker electrodes of different surface area. With a load impedance of 1000 ohms, there was a direct correlation between surface area and the R-wave potentials measured. The amplitude of the R-wave that resulted from conduction from the heart to the sensor via the electrode system decreased with decreasing surface area. A similar direct correlation was seen between the R-wave potentials measured and the threshold current and energy requirements. With the present trend toward utilization of small surface area electrodes to reduce pacemaker cell drain, care must be taken to optimize pacemaker circuit impedance if sensing problems are to be avoided.

Animals↗
PubMed1976

Two to three years of failure-free testing of a rechargeable pacemaker in experimental complete heart block.

Six hermetically sealed single cell rechargeable mercury-zinc pacemakers (B.T.) that will run continuously for over 4 years between rechargings have paced dogs with complete heart block for from 2 to 3 years. To maintain full cell capacity (over 1,000 mA hours) requires recharging for from 2-3 min/day to 60 to 80 hr once every 4 years, with any variation between these extremes being acceptable. Six realtime bench tests continue after over 7 years and accelerated tests have simulated a minimum of 50 years continuous pacing. Battery voltage is assessed by direct telemetry, eliminating the risk of patient intrinsic rhythm-pacemaker competition which is present with all current indirect (stimulation rate change) battery assessment techniques. The B.T. is an excellent 4-5 year primary pacemaker, fully rechargeable after several 4 year periods of battery rundown. A clinical test series has been initiated.

Animals↗
PubMed1976

The non-hermetically sealed pacemaker myth, or, Navy-Ribicoff 22,000-FDA-Weinberger o.

Although the Secretary of Health, Education and Welfare recently stated that hermetic sealing of all implanted cardiac pacemakers, as recommended by the Navy in 1969, is inadvisable, several small manufacturers are already marketing hermetically sealed devices (CPI, Pacesetter), all of the over 600 nuclear pacers implanted to date have been hermetically sealed, and belatedly the major manufacturers are developing hermetically sealed units. Total hermetic sealing of all implantable electronic devices has been technically feasible for years, and it is essential that device legislation include mandatory encapsulation standards.

Biomedical Engineering↗
PubMedDate not supplied

Advances in ventricular synchronous demand cardiac pacemakers.

New ventricular synchronous demand (VVT) pacemaker functions have been developed that provide improved performance in electromagnetic interference (EMI) environments and improved sensing of ventricular premature contractions. All previous ventricular synchronous pacemakers had an inherent design conflict between choosing the optimal (relatively long) input refractory interval needed for limiting the maximum pulse delivery rate and choosing the optimal (relatively short) input refractory interval (sensing dead time) following either a sensed or paced cardiac contraction. The necessary compromise resulted in a device that in the presence of EMI, stimulated at a rate (approximately 150 ppm) which was dangerously fast for certain patients, yet was insensitive to early poststimulation (400 to 500 msec) premature ventricular contractions, resulting in a risk of T-wave stimulation. Partly because of these deficiencies, the VVT function has not been widely employed by the medical profession: instead, the ventricular inhibited (VVI) pacemaker has evolved as the treatment of choice for the cardiac patient with intermittent heart block, even though total inhibition by certain EMI radiators is a potentially serious problem. New VVT structures have been developed that allow control separation of the maximum EMI discharge rate and the sensing refractory interval by employing independent input and output refractory intervals. New low-power digital devices provide building blocks applicable to the developed architectures.

Arrhythmias, Cardiac↗
PubMedDate not supplied

Improved waveform generator and cardiac simulator for sensitivity testing of ventricular programmed pulse generator.

The need for an easily generated, simulated QRS complex to facilitate preimplantation sensitivity testing of ventricular programmed pacemakers has led to the adoption of the sine squared waveform as the standard test pulse, by the Pacemaker Standards Subcommitte of the Association for the Advancement of Medical Instrumentation (AAMI). A simple circuit is presented that provides an accurate sine squared pulse with easily adjustable pulse width (base frequency). A suggested circuit for incorporating this sine squared pulse generator into a complete pacemaker test waveform generator/cardiac simulator is also presented.

Electronics↗