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Biomedical subjects

M Sweeney

Publications and source records attributed to M Sweeney.

At least 73 records · Page 4Linked to original sources
PubMed1989

Improved low energy defibrillation efficacy in man with the use of a biphasic truncated exponential waveform.

The standard implantable defibrillator waveform is a truncated exponential of approximately 6 msec duration. This study compares the defibrillation efficacy of a standard monophasic truncated exponential to a biphasic 12 msec truncated exponential waveform in 21 patients undergoing automatic implantable cardioverter defibrillator (AICD) surgery. For the biphasic waveform, the polarity was reversed and remaining capacitor voltage was attenuated by 75% after 6 msec. Two hundred thirty episodes of VF were induced with 115 "matched pairs" of monophasic and biphasic waveforms of identical initial capacitor voltages given over a range from 70 to 600 V (0.35 to 25.7 joules). The biphasic waveform was superior to the monophasic waveform (p less than 0.006), especially for "low energy" defibrillation. For initial voltages less than 200 V, the percent successful defibrillation was 28% for the monophasic waveform versus 64% for the biphasic waveform and from 200 to 290 V (energies less than 6.4 joules) it was 45% versus 69%. There was no difference in the two waveforms in time to the first QRS complex or in the blood pressure following defibrillation. This study shows that a 12 msec biphasic truncated exponential is superior to a 6 msec monophasic waveform for defibrillation in man, especially at energies less than 6.4 joules. The waveform can be achieved in an implanted device without any increase in capacitor size or in battery energy consumption.

Electric Countershock↗
PubMed1989

Patch tests demonstrating immune (antibody and cell-mediated) reactions to foods.

For decades food allergists have sought a simple, inexpensive test for food allergy. Intradermal tests of aqueous material have not proved reliable. When positive, they are probably only 10% accurate. The newer laboratory tests for food allergy are expensive and highly sophisticated. They are impractical for use in the laboratories of practicing allergists with whom individuals with a potential food allergy are most liable to consult. The RAST is capable of identifying only Type I of the Gell-Coombs' reaction classification. Since 1980, a patch test of individual foods suspended in dimethylsulfoxide has been used as a screen for sensitivity to foods. Controlled clinical studies suggest this might prove to be a valuable test for food allergy. Immune studies appear to confirm the accuracy and reliability of this inexpensive test. No systemic reactions have been observed in the 400 patients tested indicating it to be a safe procedure.

Antibody Formation↗
PubMed1989

Efficacy of metabolic support with glucose-insulin-potassium for left ventricular pump failure after aortocoronary bypass surgery.

Refractory pump failure after cardiopulmonary bypass carries a high mortality. To assess the effectiveness of metabolic support for the heart in patients with refractory heart failure after hypothermic ischemic arrest for aortocoronary bypass surgery, we randomly assigned 22 patients to receive either intravenous glucose (50%), insulin (80 units/I), and potassium (100 meq/l) (GIK) infused at a rate of 1 ml/kg/hr for up to 48 hours or glucose (5%) and NaCl (0.225%) infused at the same rate (control). All patients required inotropic drug support, received intra-aortic balloon pump assistance, and had an initial mean cardiac index (CI) of 2.5 l/min/m2. At 12 and 24 hours, CI had risen significantly in the GIK but not in the control group (3.6 and 3.4 l/min/m2 vs. 2.5 and 2.7 l/min/m2, p less than 0.005). Time on the intra-aortic balloon pump (39 vs. 61 hours) and requirements for inotropic drug support were also significantly less in the GIK compared with the control group. Although the number of patients was relatively small, the GIK group also showed a trend for improved long-term survival: at 60 days after surgery, there were 10 of 11 survivors in the GIK-treated group compared with seven of 11 survivors in the control group. Although the exact mechanism for the beneficial effects of GIK on myocardial contractility remains to be elucidated, we conclude that GIK is safe and effective in the treatment of refractory left ventricular failure after aortocoronary bypass surgery.

Aged↗
PubMed1988

5-Hydroxytryptamine releases adenosine from primary afferent nerve terminals in the spinal cord.

5-Hydroxytryptamine (serotonin, 5-HT) increased the release of endogenous adenosine from dorsal, but not ventral, spinal cord synaptosomes. This release was reduced by (i) the 5-HT receptor antagonist methysergide, (ii) removal of Ca2+ from the medium, (iii) inhibition of ecto-5'-nucleotidase and (iv) capsaicin pretreatment. These data suggest that activation of 5-HT receptors on primary afferent terminals releases a nucleotide which is converted extracellularly to adenosine. This adenosine may contribute to the spinal antinociceptive effect of 5-HT.

Adenosine↗
PubMed1987

Norplant contraceptive implants: rods versus capsules.

Norplant contraceptive implants are silastic implants containing levonorgestrel. When placed subcutaneously in the medial aspect of the upper arm, they release low levels of levonorgestrel in a constant manner over an extended period of time. Comparative studies of two silastic rods versus six capsules containing levonorgestrel were studied in 250 subjects for 4,464 months of use. Only one pregnancy occurred during the study. Side effect patterns were similar in both groups; the major side effect being irregular uterine bleeding. The bleeding, however, was well tolerated by subjects in both groups and discontinuation rate was very low. The two-rod system offers the advantages of easier insertion technique and shorter insertion time as well as ease of removal as compared to the six-capsule system. Norplant contraceptive implants offer a highly effective means of contraception which is particularly suited for women who are concerned about failure and compliance with oral contraceptives. This type of contraception should become well accepted, not only in underdeveloped countries, but in developed countries as well.

Adolescent↗
PubMed1984

The management of paroxysmal tachycardias using the Cybertach-60.

The Cybertach-60 is a bipolar multiprogrammable pacemaker designed for the automatic detection and termination of reentrant tachycardias using bursts of rapid pacing. From August 1979 to March 1984 in the U.S.A., 143 patients received the device; 91 for supraventricular and 52 for ventricular tachycardia. After a mean follow-up period of 1.8 years, 82% of patients with supraventricular tachycardia remain alive with the implanted pacemaker providing the principal therapy for the arrhythmia. Of those patients with ventricular tachycardia, 30 (58%) remain alive (mean follow-up 1.1 years) and use the device for tachycardia termination. In this group there were 18 patient deaths: 14 documented and not sudden; 4 sudden and not documented. None of the 14 documented deaths were a result of arrhythmia or pacemaker activity. The Cybertach-60 has proved to be effective in the long-term management of patients with reentrant rhythms, particularly supraventricular tachycardia.

Atrioventricular Node↗
PubMed1983

Tachyarrhythmias associated with programmable automatic atrial antitachycardia pacemakers.

A multiprogrammable automatic antitachycardia pacemaker (Cybertach-60), connected to a tined "J" wire electrode, was positioned in the right atrial appendage in three patients with recurrent supraventricular tachycardia (SVT). Mechanisms of SVT included atrioventricular (AV) nodal reentry (two patients) and reciprocating tachycardia using an accessory pathway (one patient). Indications for implantation included frequent symptomatic episodes, multiple drug failures, and reproducible termination of the arrhythmia by the automatic pacemaker during electrophysiologic studies. Following discharge, multiple episodes of pacemaker malfunction were recorded. The three types of malfunction included: undersensing with induction of SVT by a single atrial premature depolarization, oversensing of extraneous electromechanical potentials triggering burst pacing which initiated SVT, and inappropriate burst pacing in response to sinus tachycardia with and without initiation of SVT. Treatment with a beta-blocking agent prevented pacemaker triggering by sinus tachycardia, and replacement of the electrode catheter resolved pacemaker triggering by electromechanical potentials. One patient required removal of the pacemaker because undersensing could not be corrected by repositioning the atrial electrode. This report illustrates three potential complications that may result with either normal or faulty sensing when employing automatic atrial antitachycardia pacemakers for control of SVT. It also stresses the importance of careful electrophysiologic evaluation before implantation and meticulous follow-up after implantation.

Adult↗
PubMed1975

Incidental appendicectomy with laparotomy for trauma.

Incidental appendicectomy was performed in 83 of 206 patients undergoing laparotomy for abdominal trauma. No organs were injured in 42 per cent of the appendicectomy patients and in 17 per cent of the non-appendicetomy patients, thus making comparison between the groups unreliable. While the incidence of intestinal perforation was 21 per cent in the appendicectomy patients, the rate of wound infection was only 7 per cent. One complication (pelvic abscess) was possibly attributable to incidental appendicetomy. Since males below the age of 50 face a significant risk of future appendicitis and represent the majority of patients with abdominal trauma, it may be advisable to perform incidental appendicectomy with laparotomy for trauma in such patients. Specific indications for incidental appendicectomy during laparotomy for trauma are suggested.

Abdominal Injuries↗
PubMedDate not supplied

The release of mercury from dental amalgam and potential neurotoxicological effects.

OBJECTIVES: The aim of this study was to estimate the amount of mercury released into both air and saliva from fresh and aged, abraded amalgam discs and then investigate neurotoxic effects of inorganic mercury upon sensory neuronal cultures. METHODS: An air-tight chamber was constructed to allow the combined estimation of mercury species released from amalgam pellets. The level released into air and saliva from both freshly packed and aged-abraded amalgam pellets was assessed. Dorsal root ganglia cultures from male CBA mice were exposed to 1 and 10 microM mercuric chloride concentrations. The effects of this were assessed by means of morphology, adhesion, size and immunocytochemistry. RESULTS: The mercury released into air from dry fresh amalgam was low and less than the recommended industrial exposure limit for mercury. However, covering the discs with saliva reduced air-mercury levels by 46-56% and there was a statistically significant difference in the air-mercury levels recorded (p=0.013-0.048). The mercury released into air from dry abraded amalgam was shown to be above the recommended industrial limit. Coating the abraded amalgam discs with saliva reduced the mercury by 66-72% with the levels recorded being significantly lower (p<0.001). The level of total mercury within the saliva was found to be highly variable. Little change was noted in the neuronal cultures treated with 1 microM mercuric chloride. However, the cultures exposed to high level (10 microM) mercuric chloride showed cells that became rounded and clumped together indicating pathological change. CONCLUSIONS: Amalgam placement appears to present minimal mercury exposure risk. To reduce the amount of mercury released into air, however, amalgam should be polished in a moist atmosphere with high volume aspiration. The neurotoxic effect of mercury appears to be related to concentration, as only in the cultures treated with 10 microM mercuric chloride showed striking qualitative and quantitative cellular changes.

Air↗