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Biomedical subjects

G F Tyers

Publications and source records attributed to G F Tyers.

At least 127 records · Page 7Linked to original sources
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

Diagnostic and therapeutic challenges following the cytologic diagnosis of in situ carcinoma of the lung.

Clinical challenges associated with the cytologic detection of eight cases of occult pulmonary carcinoma are presented. The pulmonary lesions were successfully localized and resected in three of six cases encountered since the availability of flexible fiberoptic bronchoscopy and selective bronchial brushing. Two of the resected neoplasms were unequivocally in situ, while preoperative radiotherapy precluded accurate pathologic determination of invasiveness in the third. The reported experience with unequivocal in situ bronchogenic carcinoma localized and treated surgically prior to invasion through the basement membrane now totals 17 cases (15 previously reported). Forty-four additional cases (43 previously reported) have been localized and resected following early invasion. From this group totaling 61 occult carcinomas, only two patients (3 percent) are known to have died of pulmonary carcinoma during a followup ranging from 2 to 20 years.

Adenocarcinoma↗
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↗
PubMed1975

Effect of stimulation site on ventricular threshold in dogs with heart block.

Ventricular pacing thresholds were measured in barbiturate-anesthetized dogs with complete heart block using an oscilloscope and current probe. All electrode and physiologic variables were carefully controlled in order to compare the effects of stimulus duration and site of ventricular threshold energy requirements. Left ventricular intramyocardial stimulation, at all stimulus durations under 5 msec., required less current and energy, and at all stimulus durations under 2 msec. less voltage, than either right ventricular endocardial or right ventricular intramyocardial stimulation. Chronaxy and polarization losses were lowest and impedance highest with left ventricular intramyocardial stimulation. The two right ventricular sites were almost equivalent electrically. Earlier studies which reported lower thresholds with endocardial stimulation than with intramyocardial stimulation were biased in favor of the endocardial site by lack of control of electrode variables including: material, configuration, cross-sectional area, and epicardial versus intramyocardial location.

Animals↗
PubMed1975

Isolated heart perfusion techniques for rapid screening of myocardial preservation methods. Anoxia versus ischemia.

Isolated nonworking and working heart preparations are described and recent modifications that increase their reliability and scope are reviewed. Isolated perfused tissues are superior to other models for screening myocardial preservation techniques. The metabolic and functional differences between anoxia and ischemia are stressed, myocardial glycolysis is reviewed, and from basic studies potentially fruitful avenues for investigation of myocardial preservation techniques are outlined. Better application of available knowledge of myocardial metabolism could further reduce the risks of cardiac operation.

Animals↗
PubMed1975

Metabolic arrest of the ischemic heart.

Procaine, hypocalcemia, magnesium, fluoride, adrenochrome, and tetrodotoxin have been used to induce metabolic arrest of the heart and increase its tolerance to ischemia. Prolonged periods of ischemic cardiac arrest without measurable deterioration of cardiac function are possible. The application of these techniques in the repair of intracardiac lesions deserves further study.

Adenosine Triphosphate↗