Search PubMed⌕ Search

Biomedical subjects

J R Stewart

Publications and source records attributed to J R Stewart.

At least 91 records · Page 5Linked to original sources
PubMed1990

Cardiac surgery in patients age 80 years or older.

Between February 1978 and August 1989, forty patients aged 80 years or older underwent cardiac surgery at this institution. Patient age varied from 80 to 87 years (mean, 82.4 years). Operative indications were angina pectoris or congestive heart failure. Twenty-eight patients underwent coronary artery bypass (CAB) alone and 12 underwent valve replacement(s) with or without CAB. The operative mortality rate was 10%. Postoperative hospitalization averaged 14 days. There were three late cardiac deaths at 13, 36, and 48 months after operation and one late noncardiac death. Thirty-two survivors have been followed from 1 to 86 months (mean, 20 months). All experienced sustained improvement in functional status and minimal late morbidity. All survivors remained in NYHA class 1 or 2. Cardiac surgical procedures in patients older than 80 years can be performed with increased but acceptable mortality and morbidity rates. Most patients achieve sustained symptomatic improvement and excellent long-term survival.

Aged↗
PubMed1989

Advances in the role of minerals in immunobiology.

Immunology and our understanding of its various cells, immunoglobulins and lymphokines are recent events that date from the work of Pasteur and Metchnikoff in the late nineteenth century. Experimental evidence has shown the importance of adequate dietary protein and vitamins. The present review examines past and recent experimental evidence for the role of minerals in the functioning of the immune system. Included is in vivo and in vitro information on the macrominerals; calcium and magnesium, the micro-(trace) minerals; iron, zinc, copper, and selenium as they affect various components of the immune system. The effects of gold as either gold-thiomaleate or gold-thioglucose on selenium is also reviewed.

Animals↗
PubMed1989

Estimating the effects over time of alcohol on injury severity.

Estimates of the effect of blood alcohol on injury severity obtained through studies of patients at clinical facilities have been found to be quite different from those estimated through the analysis of highway accident data. Several factors have been suggested to account for these differences, including consideration of the relative frequencies of alcohol-involved and alcohol-free drivers who were killed at the scene or who died before reaching a treatment facility. More generally, the nature of the way that the effect of alcohol varies as a function of time from injury may play a important role. In this paper information from highway accident data was combined with time of death information from state medical examiner files to yield estimates of the function P(T), the probability that an injured driver dies at the time T or later from an injury occurring at T = 0, for classes of crash-involved drivers with differing blood alcohol concentrations. Other factors also considered in the analyses included measures of crash severity, driver age, and restraint use. Elevated blood alcohol was consistently found to be associated with shorter survival times.

Accidents, Traffic↗
PubMed1989

Ten years' experience with the Senning operation for transposition of the great arteries: physiological results and late follow-up.

We report our results in 93 consecutive infants and children who underwent atrial repair of simple transposition of the great arteries using the Senning operation between February 1978 and February 1988. Mean age at operation was 5.6 +/- 6.3 months (range, 1 week to 4 years); 60 were less than 6 months old. There were 65 boys and 28 girls. Operative mortality was 5.4%, and there has been 1 late death. Average follow-up is 45.1 months with 39 followed more than 3 years and 25 followed more than 5 years. Postoperative cardiac catheterization was performed in 43 patients. Right ventricular ejection fraction at rest averaged 0.50 +/- 0.09 and was normal in 26 patients. Response of right ventricular ejection fraction to afterload stress was abnormal in 12 of 14 patients tested. Right ventricular ejection fraction increased normally during exercise in 6 patients, but was abnormal in 15. Mild tricuspid regurgitation was noted in 10 patients. Mild obstruction of the superior vena cava was noted in 4 patients. Baffle leak requiring reoperation occurred in 1 patient. Seventy-two of 80 patients are in sinus rhythm by latest electrocardiogram. Postoperative electrophysiological studies were performed in 34 patients and Holter monitoring was performed in 22. A major arrhythmia occurred in 8 patients: 3 required a pacemaker for junctional rhythm or sinus node dysfunction, 2 have symptomatic or inducible supraventricular tachycardia, 2 have junctional rhythm, and 1 has sick sinus syndrome. Eight additional patients have delayed sinus node recovery time. At last follow-up, 78 children (97.5%) are in New York Heart Association functional class I, and 2 (2.5%) are in class II.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1989

Electron arc therapy: design, implementation and evaluation of a dynamic multi-vane collimator system.

Innovative techniques in motion control technology have been applied to the design and implementation of a portable computer-controlled multi-vane collimator for use in electron arc therapy. The collimator, consisting of 18 independently controlled vanes, is inserted into the standard accessory mount assembly of a linear accelerator, in the same fashion as standard field shaping blocks. Power is supplied to the collimator vane motors via a self-contained battery system. The range of motion of the vanes, symmetrically mounted nine on each side, provides a variable aperture width projected to isocenter of 2 cm minimum to 8 cm maximum. The projected length of the aperture at isocenter is 38 cm. The transition time between vane positions is less than 1 second, corresponding to gantry movement of less than 1 degree. The movement of each of the 18 vanes is monitored and controlled by six individually addressed three axis processors that are shielded from the electron beam. A table of collimator vane positions versus gantry angle, as determined by dose optimization calculations, is stored in a data file. The desired collimator vane position corresponding to the current arc segment is conveyed from the control console to each vane controller via packets within a token passing network. Communication between the computer in the console area and the vane controllers is accomplished through encoded infra-red pulse transmission, eliminating the need for additional communication lines between the console and the accelerator. This dynamic collimator offers improved dose uniformity while simplifying the delivery of electron arc therapy.

Electronics, Medical↗
PubMed1989

Optimization of electron arc therapy doses by multi-vane collimator control.

Retrospective computer simulations, based on clinical treatment planning data available from over 50 patients treated by electron arc radiotherapy to the chestwall following mastectomy, show that a dramatic improvement in dose uniformity can, in many clinical situations, be achieved by dynamic shaping of the electron arc collimator, under computer control, as a function of gantry angle and distance superior or inferior to the central plane. The greatest improvement in dose uniformity is seen in calculational planes in which the patient contour has the greatest departure from a circular shape. Dosimetric studies demonstrate this improvement. Indicators for use of variable-width multi-vane electron arc collimators include the following: (1) Mechanical constraints of the therapy equipment may limit the placement of isocenter to an inadequate depth which causes large variation in the SSD around the arc; (2) Out of the central plane, the shape of the chest wall may change dramatically across the limits of the arc, creating large variations in the dose distribution; (3) Clinical definition of the treatment surface to include surgical scars or other at-risk volume may create an irregularly shaped treatment surface, thereby changing the fraction of the arc included in the treatment surface from one plane to the next. Electron arc collimator shape determines both the dose rate and the electron arc beam profile. Both the dose rate and the beam profile must be included in the integration of dose to a point within the arc. The dose to a point within the arc can be modified by as much as a factor of 1.5 to 2.0 by increasing the collimator width from 3 cm to 7 cm. A multi-vane collimator allows these changes to be made in each specific plane to compensate for changes in patient contour.

Breast Neoplasms↗
PubMed1989

The physical effects of lightning injury.

Several thousand lightning-related injuries occur each year in the United States resulting in nearly 600 deaths. Most incidents involve individual victims; group lightning strikes are rare. Ten soldiers were simultaneously injured in a group lightning strike while on training maneuvers at Fort Benning. Georgia. No deaths or loss of consciousness occurred, although two of the soldiers had amnesia for the event. All of the soldiers were hospitalized and observed for potential lightning-related complications. Ninety percent of the soldiers had first-degree skin burns, and all had focal muscular tenderness. Seventy percent had transient ST segment elevation that resolved. Fifty percent developed creatinine kinase (muscular component) elevation, but none developed myoglobinuria or acute renal failure. No patient had creatinine kinase (myocardial component) elevation. Transient hypertension and tinnitus were noted in 40% and 20%, respectively. No compartment syndromes or ocular manifestations developed. All 10 soldiers recovered uneventfully and returned to full active duty.

Adolescent↗
PubMed1989

Pharmacokinetics of superoxide dismutase during hypothermic cardiopulmonary bypass.

We evaluated the plasma elimination of recombinant human superoxide dismutase (rHSOD) when given before reperfusion in an experimental canine model of global hypothermic myocardial ischemia. Adult mongrel dogs were placed on cardiopulmonary bypass, and core temperature was reduced to 25 degrees C. Hypothermic global myocardial ischemia was maintained for 90 minutes with intermittent crystalloid cardioplegic solution. Five minutes before reperfusion, rHSOD was administered via the pump oxygenator as a bolus injection. Plasma rHSOD levels were measured at 0, 3, 5, 10, 20, 30, 60, and 120 minutes after injection. Animals were rewarmed and weaned from bypass. Three experimental groups received either 4, 8, or 16 mg/kg rHSOD. Based on previously reported dose-response data, we conclude that desirable peak serum concentrations are achieved with 16 mg/kg rHSOD. In the setting of hypothermic cardiopulmonary bypass and global myocardial ischemia, single bolus administration of rHSOD before reperfusion is an effective method due to the prolonged serum half-life.

Animals↗
PubMed1988

Electron arc therapy: chest wall irradiation of breast cancer patients.

From 1980 to October 1985 we treated 45 breast cancer patients with electron arc therapy. This technique was used in situations where optimal treatment with fixed photon or electron beams was technically difficult: long scars, recurrent tumor extending across midline or to the posterior thorax, or marked variation in depth of target tissue. Forty-four patients were treated following mastectomy: 35 electively because of high risk of local failure, and 9 following local recurrence. One patient with advanced local regional disease was treated primarily. The target volume boundaries on the chest wall were defined by a foam lined cerrobend cast which rested on the patient during treatment, functioning as a tertiary collimator. A variable width secondary collimator was used to account for changes in the radius of the thorax from superior to inferior border. All patients had computerized tomography performed to determine Internal Mammary Chain depth and chest wall thickness. Electron energies were selected based on these thicknesses and often variable energies over different segments of the arc were used. The chest wall and regional node areas were irradiated to 45 Gy-50 Gy in 5-6 weeks by this technique. The supraclavicular and upper axillary nodes were treated by a direct anterior photon field abutted to the superior edge of the electron arc field. Follow-up is from 10-73 months with a median of 50 months. No major complications were observed. Acute and late effects and local control are comparable to standard chest wall irradiation. The disadvantages of this technique are that the preparation of the tertiary field defining cast and CT treatment planning are labor intensive and expensive. The advantage is that for specific clinical situations large areas of chest wall with marked topographical variation can be optimally, homogeneously irradiated while sparing normal uninvolved tissues.

Adult↗
PubMed1988

Surgical treatment of acute traumatic tear of the thoracic aorta.

Acute traumatic tear of the thoracic aorta is a severe injury with a high mortality rate. This condition requires expeditious evaluation and prompt surgical intervention in order to improve patient survival. The experience at the authors' institution from 1971 to 1987 includes 41 patients who sustained acute traumatic tear of the thoracic aorta and reached the hospital alive. The purpose of the study was to evaluate the surgical management of this injury with regards to mortality rate and the incidence of spinal cord injury. Five patients died from exsanguination before definitive repair could be undertaken. Thirty-six patients had repair of traumatic aortic tear in the area of the isthmus. Nine patients were operated upon with the clamp and sew technique, 20 patients had a heparin-bonded shunt placed, and seven patients were treated by repair with cardiopulmonary bypass. There were five operative deaths that were not related to the technique employed. Two patients without preoperative evidence of spinal cord injury developed paraparesis. No patient had postoperative paraplegia. Despite rapid transport, expeditious evaluation, and emergency thoracotomy, some patients die from exsanguination prior to definitive repair. Even with the provision of distal aortic perfusion during clamping, the risk of spinal cord injury is not eliminated.

Adolescent↗
PubMed1988

Discrimination of anterograde from retrograde atrial electrograms for physiologic pacing.

The morphology of bipolar electrograms recorded in the right atrium was examined in nine patients in an attempt to discriminate retrograde from anterograde atrial signals to an extent that would be useful for physiologic pacing. Peak-to-peak amplitude, duration, square root of energy (energy), maximum slew rate, mean slew rate, and polarity were examined in the time domain. Maximum frequency, half-power frequency, Fourier amplitude peak, and frequency of peak were measured in the frequency domain. There was a significant difference between anterograde and retrograde signals for all variables related to amplitude; these variables are peak-to-peak amplitude, energy, Fourier amplitude peak, maximum slew rate and mean slew rate. In seven of nine patients there was at least one variable sufficiently discriminating to insure reliable detection of anterograde signals while systematically rejecting retrograde signals. However, no individual variable was able to effect this discrimination in more than four patients and at least three variables were needed for all seven patients: maximum frequency, one of either energy and Fourier amplitude peak, and one of either frequency of peak or half-power frequency (six possible combinations). Thus, although differences between anterograde and retrograde atrial activity can be demonstrated in most patients, no single parameter displays sufficient discriminating power to facilitate physiologic pacing in patients exhibiting retrograde activity.

Atrial Function↗
PubMed1988

Complexing activity of 2,3-dimercapto-1-propanesulfonate and its disulfide auto-oxidation product in rat kidney.

The complexing activity of 2,3-dimercapto-1-propanesulfonate (DMPS) was examined in vivo and in the isolated perfused rat kidney. Intravenous infusions of the sulfhydryl form of DMPS into rats pretreated with HgCl2 resulted in a dose-dependent increase in the urinary excretion of mercury and a decrease in the retention of mercury in kidney. A 120-min infusion of 2 mg sulfhydryl DMPS.min-1.kg body wt-1 resulted in excretion of 76% of the mercury body burden of which greater than 90% was removed from kidney. The disulfide auto-oxidation product of DMPS significantly increased the urinary excretion of mercury in the rat, but its effect was less than that of an equivalent dose of sulfhydryl DMPS. The presence of disulfide DMPS or 3:1 mixtures of sulfhydryl DMPS and disulfide DMPS in the perfusate increased the excretion of mercury and induced a loss of mercury from the cortex and outer medulla in the isolated perfused rat kidney. Thus both the disulfide and sulfhydryl forms of DMPS can act directly on the kidney to accelerate the excretion of mercury. This is consistent with previous observations of the ability of the kidney to reduce disulfide DMPS to sulfhydryl DMPS.

Animals↗
PubMed1987

Occurrence of exercise-induced and spontaneous wide complex tachycardia during therapy with flecainide for complex ventricular arrhythmias: a probable proarrhythmic effect.

Flecainide acetate, a new antiarrhythmic agent, possesses favorable pharmacokinetic and hemodynamic properties and demonstrates highly favorable antiarrhythmic activity in patients with ventricular arrhythmias. However, the proarrhythmic potential of flecainide deserves further evaluation. In 7 (13%) of 55 consecutive patients treated with oral flecainide, 200 to 600 mg/day, for complex ventricular arrhythmias (including sustained ventricular tachycardia in 14), we observed the appearance of new or more sustained exercise-induced (five patients) or spontaneous (two patients) wide complex tachycardia. The mechanism of wide complex tachycardia appeared to be ventricular tachycardia in all seven. In our series, episodes were self-remitting or successfully treated. In four patients, wide complex tachycardia did not recur during exercise testing during alternative antiarrhythmic therapy (three patients) or no antiarrhythmic therapy (one patient). These observations raise the possibility of flecainide-related proarrhythmia, manifested as an increased propensity to exercise (activity)-induced wide complex tachycardia, which was not reliably predicted by results of Holter recordings or programmed electrical stimulation. Patients with complex ventricular arrhythmias beginning long-term treatment with oral flecainide should be considered for treadmill exercise testing together with ambulatory monitoring as part of the initial assessment of drug efficacy.

Adult↗