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Biomedical subjects

K S Tan

Publications and source records attributed to K S Tan.

68 records · Page 4Linked to original sources
PubMed1977

Cardiac pathology of transvenous pacemakers in dogs.

Transvenous right ventricular pacemaker catheters were implanted in 18 mongrel dogs for periods of 2 to 18 months (average 4.9 months). Heart block was produced in 15 of these dogs by injection of 37 per cent formaldehyde into the interatrial septum. In the other three dogs which served as controls, no heart block was produced and no electrical stimulation was applied to the implanted catheters. After the animals had been put to death, gross and microscopic examination of the hearts revealed four categories of morphological changes: (1) connective tissue sheath formation around the catheters, (2) endocardial papillary thickening, (3) interatrial septal changes, and (4) myocardial damage. Changes 1, 2, and 4 occurred in one or more intracardiac locations in all 18 dogs. Change 3 occurred only in the 15 dogs in which heart block was produced. The most striking histologic findings were areas of cartilagenous metaplasia in endocardium an underlying myocardium and areas of marked cellular proliferation of the endocardial cells both in the endothelium and underlying stroma. Chronic implantation of transvenous intracardiac pacemaker catheters in dogs consistently produces morphologic changes which may interfere with cardiac and pacemaker function and may hinder attempts to remove nonfunctional or unneeded catheter electrodes. The changes observed appear to be related to the presence of foreign material per se and not external electrical stimulation of the heart.

Animals↗
PubMed1975

Interaction of aortic and carotid sinus baroreceptors: effect of activation times.

Changes in pulse-wave velocity were simulated by changing the relative timing between aortic and carotid sinus barorecptor activity in anesthetized rabbits and dogs. In the rabbit, electrical stimulation was used to vary the timing; in the dog, it was also varied by perfusing the carotid sinuses with externally generated pressure pulses that could be triggered in any portion of the cardiac cycle. Changing the relative delay between aortic and carotid sinsus nerve stimulation did not result in variations of blood pressure or heart rate in the rabbit. Varing the time of electrical stimulation of the carotid sinus nerve caused at most 5 mmHg change of blood pressure in the dog. Delay-related heart-rate changes could be usually observed only when the stimulus consisted of short, high-intensity bursts. When the carotid sinus was externally perfused with pulses of pressure, only one out of five dogs showed delay-related variations in blood pressure (3mmHg) and heart rate (6 beats/min). It is concluded that variations in pulse-wave velocity are unlikely to play a significant role in acute cardiovascular control.

Animals↗
PubMedDate not supplied

Reversal of diabetes by syngeneic transplantation of a radiation-induced rat insulinoma.

The growth and metabolic effects of a radiation-induced rat insulinoma were examined after subcutaneous subscapular transplantation into normal and streptozotocin diabetic NEDH rats. Streptozotocin diabetic rats exhibited hyperglycaemia, hypoinsulinaemia, impaired glucose tolerance without an insulin response, polyuria, polydipsia, hyperphagia and weight loss. Transplantation of tumour fragments gradually improved the physical and metabolic state over the following 3 weeks. Coincident with a progressive rise in plasma insulin between 10 and 17 days, the diabetic rats gained weight and reduced their food intake. The rats remained hyperglycaemic during this time, but developed hypoglycaemia with marked hyperinsulinaemia by 24 days. Furthermore, plasma glucose and insulin concentrations were not increased by an intraperitoneal glucose challenge, indicating greatly accelerated glucose clearance. Both the streptozotocin-treated and normal insulinoma-bearing rats incurred a fatal hypoglycaemic coma by 28-33 days after transplantation. Final body weights, tumour weights and concentrations of glucose and insulin were similar in the two groups. This study demonstrates reversal of streptozotocin diabetes by insulinoma transplantation. The hyperglycaemia and the accompanying diabetic environment did not modify tumour growth and development.

Adenoma, Islet Cell↗
PubMedDate not supplied

Walkie-talkies and cellular telephones: the hazards of electromagnetic interference in hospitals.

This article presents an overview of the effects of electromagnetic interference (EMI) on medical devices, with emphasis on portable telecommunication devices. In addition, the authors discuss existing voluntary national and international standards and policies governing the use of cellular telephones and walkie-talkies in hospitals, possible solutions to the susceptibility of medical devices to EMI, and recommendations to lessen EMI's potentially hazardous effects.

Canada↗
PubMedDate not supplied

Effects of a wireless local area network (LAN) system, a telemetry system, and electrosurgical devices on medical devices in a hospital environment.

Concerns have been raised about interference of wireless local area network (LAN) systems and telemetry systems with medical devices in hospitals. The authors have investigated the susceptibility of 65 electromedical devices to a wireless LAN system and a telemetry system in preselected areas of a hospital. Testing was based on the American National Standards Institute Standard C63.18. The wireless LAN system operated at 2.42 GHz with an output power of 100 mW. The telemetry system operated at 466 MHz with an output power of 4 mW. Of the 65 devices tested, only two hand-held Doppler units, a Mini Doppler Model D900 (Huntleigh Healthcare Ltd) and a Ultrasonic Doppler Model 811 (Parks Medical Electronics, Inc.), were affected by the LAN system. Placed within 10 cm of the LAN system in standby mode, both units emitted periodic high-pitched beating sounds, which could be misinterpreted as normal beating sounds from the patient. These changed to random static noise during data transmission by the LAN. Under normal conditions of use, a LAN system would never be placed this close to a medical device. The quality of data transmission from the LAN system changed from "good" to "acceptable" in the colonoscopy room. This deterioration in transmission quality could have been caused by the lead shielding in the room. Electrosurgical devices operating at 0.5 to 1 MHz did not affect the LAN system at distances up to 3 m. None of the devices was affected by the telemetry system. These findings suggest that wireless LAN systems and telemetry systems can be acceptable for use in hospitals. Nevertheless, other systems should be tested on potentially susceptible devices by the hospital before use.

Artifacts↗
PubMedDate not supplied

Threshold of sensation for 60-Hz leakage current: results of a survey.

Canadian regulations have set a limit of 100 microA on leakage currents permitted to flow from patient-applied parts of an electromedical device under single-fault conditions, while international standards, such as International Electrotechnical Commission (IEC) 601-1, have set the limit of 500 microA under the same conditions. Canadian agencies have suggested that national standards for electromedical devices should harmonize with widely used international standards by increasing the leakage current limit to 500 microA. The authors investigated the question of whether 500 microA would compromise safety, or would be unpleasant or painful for the patient. A survey was conducted on the reactions of 95 adult volunteers to 60-Hz alternating currents ranging from 10 to 500 microA applied through typical ECG electrodes to determine the level at which these volunteers felt a distinctly uncomfortable or painful sensation. Results of this survey confirm that 500 microA currents are more than sufficient to induce pain in healthy adult volunteers, and that currents greater than 100 microA can evoke a definite sensation. Based on these findings, the authors recommend that the maximum allowable leakage current for patient-applied parts under single-fault conditions should not exceed 100 microA.

Adult↗
PubMedDate not supplied

Effects of diet-induced ketosis in rats with hypoglycaemia due to a serially transplantable insulinoma.

In view of the ability of ketones to partially replace glucose as an alternative fuel in the brain, the potential protective effects of diet-induced ketosis were examined in male NEDH rats with hypoglycaemia due to a serially transplantable radiation-induced insulinoma. Ketosis was induced by daily oral administration of medium chain triglycerides to normal rats and to insulinoma-bearing rats 1 day after subcutaneous subscapular implantation of tumours fragments. All rats treated with medium chain triglycerides became ketotic within 72 hours, and plasma 3-hydroxybutyrate concentrations remained 5-10 fold elevated at 24 days. Untreated insulinoma-bearing rats became moderately hyperinsuliaemic and hypoglycaemic by 17 days, with the later manifestation of more marked hyperinsulineamia (21.6 +/- 0.8 ng/ml, mean +/- SEM) severe hypoglycaemia (1.5 +/- 0.1 mmol/l) and death by 24-28 (26 +/- 1) days. Induction and maintenance of hyperketonaemia did not affect the development of hyperinsulineamia, hypoglycaemia or the exaggerated fall of plasma glucose produced by an 8 hour fast in these rats. However by day 21, the severity of hypoglycaemia was greater in insulinoma-bearing rats receiving medium chain triglycerides, culminating in accelerated death by 22-25 (23 +/- 1) days and an accompanying 50% decrease in final tumour weight. These results demonstrate that induction of ketosis in the face of marked hyperinsulinaemia did not afford protection against the profound hypoglycaemia produced by a serially transplantable rat insulinoma.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Temperature distribution beneath pediatric electrosurgical dispersive electrodes: a model study.

Concerns have been raised about the safety and the thermal performances of commercially available electrosurgical dispersive electrodes. A model system was designed to simulate the thermal effects observed in humans. The following critical factors affecting the thermal performances of pediatric electrodes were investigated: the intensity and duration of the applied current, the electrical resistivity of the test medium, the contact interface area between the electrode and the test medium, and the water content of the adhesive gel of the electrode. The maximum temperature rises (delta Tm) under the electrodes were 0.6 +/- 0.1 degrees C, 2.8 +/- 0.2 degrees C, and 5.2 +/- 0.3 degrees C when 60 s of 1 A, 2 A, and 3 A currents, respectively, were applied. delta Tm increased linearly with the increase of the duration of applied current and the resistivities of the test medium. When dispersive electrodes with reduced areas or reduction of water content of the adhesive gel of the electrodes were used, delta Tm increased with the areas or the water contents decreased. The currents and durations used in this study were in excess of those routinely used in electrosurgery. The study confirmed that the maximum temperature increase under the electrode is inversely proportional to the square of the perimeter of the electrode, rather than the square of the surface area. The test methods described can be used to evaluate the thermal performances of other electrosurgical dispersive electrodes. Monitoring the impedance at the interface between the dispersive electrode and the tissue in contact would reduce the risk of burns.

Child↗