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Biomedical subjects

J Ross

Publications and source records attributed to J Ross.

At least 397 records · Page 22Linked to original sources
PubMed1990

Outlook after acute myocardial infarction in the very elderly compared with that in patients aged 65 to 75 years.

Little is known concerning late outcome and prognostic factors after acute myocardial infarction in the very elderly (greater than 75 years of age). Accordingly, this study compared the clinical course and mortality rate for up to 1 year in a large multicenter data base that included 702 patients greater than 75 years of age (mean +/- SD 81 +/- 4 years), with a less elderly subset of 1,321 patients between 65 and 75 years of age (mean 70 +/- 3 years). The postdischarge 1 year cardiac mortality rate was 17.6% for those greater than 75 years of age compared with 12.0% for patients between 65 and 75 years of age (p less than 0.01). There were differences in the prevalence of several factors, including female gender, history of angina pectoris, history of congestive heart failure, smoking habits and incidence of congestive heart failure during hospitalization. Multivariate analyses of predictors of cardiac death in hospital survivors selected different factors as important in the two age subgroups; age was selected in the 65 to 75 year age group but was not an independent predictor in the very elderly. The survival curves beginning at day 10 for patients 65 to 75 and in those greater than 75 years old were similar for up to 90 days but diverged later. In the very elderly, 63% of late cardiac deaths were sudden or due to new myocardial infarction, similar to the causes of 67% of deaths in the younger age group.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1990

Group treatment of exiled survivors of torture.

A model for time-limited group treatment of exiled survivors of torture is presented and the importance of placing such traumatic experiences in a sociopolitical context is emphasized. The model is illustrated by descriptions of work with a group made up of Central and South American refugees. Therapeutic techniques are proposed that focus on symptoms of torture-related post-traumatic stress disorder, allowing group members to attain gradual psychological reorganization.

Adaptation, Psychological↗
PubMed1990

Interactions of neural networks: models for distraction and concentration.

We present a model of neural group interactions, which are projections from one neural network (network B) of McCulloch-Pitts neurons connected via a Hebbian rule, to another network (network A) of the same structure. We first consider the case in which the projecting network B is in a pattern different from the initial attracting state of network A. A critical projecting strength lambda c is found such that for lambda below this value there exists a noise threshold sigma lambda corresponding to each lambda. For the case where lambda less than lambda c and the noise level sigma less than sigma lambda, there are two possible retrievals, with different probabilities: the initial attracting state of network A and the projecting pattern. If lambda less than lambda c and sigma greater than sigma lambda, stable states of network A disappear. In the case lambda greater than lambda c, network A is pulled out of its initial basin of attraction and into that of the projecting pattern. This analysis provides a model for distraction. Second-order interactions reduce the distraction. When the projecting network B is in the same pattern as the initial attracting state of network A, the projection acts as an external reinforcement, which enables network A to retrieve in highly noisy conditions. Sharp noise thresholds for nonzero retrievals are shown to be eliminated by the projection. Higher-order connectivity improves the retrieval ability of the network. The second case serves as a model of concentration. We discuss the model of distraction and concentration (i) in connection with common experience of expectation of recognition and (ii) in connection with recent T-maze experiments on infant rats; finally, we suggest a refined version of the Bruner-Potter experiment to test our prediction of the disappearance of hysteresis.

Animals↗
PubMed1990

Oscillations and chaos in neural networks: an exactly solvable model.

We consider a randomly diluted higher-order network with noise, consisting of McCulloch-Pitts neurons that interact by Hebbian-type connections. For this model, exact dynamical equations are derived and solved for both parallel and random sequential updating algorithms. For parallel dynamics, we find a rich spectrum of different behaviors including static retrieving and oscillatory and chaotic phenomena in different parts of the parameter space. The bifurcation parameters include first- and second-order neuronal interaction coefficients and a rescaled noise level, which represents the combined effects of the random synaptic dilution, interference between stored patterns, and additional background noise. We show that a marked difference in terms of the occurrence of oscillations or chaos exists between neural networks with parallel and random sequential dynamics.

Animals↗
PubMed1990

Synchronous neural networks of nonlinear threshold elements with hysteresis.

We use Hoffmann's suggestion [Hoffmann, G. W. (1986) J. Theor. Biol. 122, 33-67] of hysteresis in a single neuron level and determine its consequences in a synchronous network made of such neurons. We show that the overall retrieval ability in the presence of noise and the memory capacity of the network in the present model are better than in conventional models without such hysteresis. Second-order interaction further improves the retrieval ability of the network and causes hysteresis in the retrieval-noise curve for any arbitrary width of the bistable region. The convergence rate is increased by the hysteresis at high noise levels but is reduced by the hysteresis at low noise levels. Explicit formulae are given for calculations of average final convergence and noise threshold as functions of the width of the bistable region. There is neurophysiological evidence for hysteresis in single neurons, and we propose optical implementations of the present model by using ZnSe interference filters to test the predictions of the theory.

Animals↗
PubMed1990

Diabetic patients and beta-blockers after acute myocardial infarction.

Whether diabetic patients may benefit, compared with non-diabetic patients, from beta-blocker therapy following acute myocardial infarction was examined in a large multicentre cohort of 2024 patients, including 340 diabetics, 281 of whom survived hospitalization. One-year mortality following discharge was 17% for diabetics compared with 10% for non-diabetics (P less than 0.001). However, diabetics discharged on beta-blockers had a 1-year mortality of only 10%, compared with 23% for diabetics not on beta-blockers. In non-diabetics, mortality rates were 7% and 13% for those taking and not taking beta-blockers, respectively. Bias in patient selection for beta-blocker therapy might be responsible for the trends exhibited in our population since patients were not randomized to treatment. In diabetics, evidence of pulmonary congestion on X-ray was more prevalent than in non-diabetics; this appeared to be true both for patients taking beta-blockers and for those not taking beta-blockers. However, even in diabetics without evidence of pulmonary congestion on X-ray, 1-year mortality was 7% vs 17% for those with and without beta-blocker therapy, respectively (P less than 0.04). In multivariate analysis, beta-blocker use was an independent predictor of 1-year cardiac survival following hospital discharge for all diabetics, even those without evidence for pulmonary congestion on X-ray, but not for non-diabetics. These data suggest a beneficial effect, but a definitive answer regarding the benefit of beta-blockade in diabetic patients after acute myocardial infarction would require a prospective, randomized study.

Adrenergic beta-Antagonists↗
PubMed1990

Evaluating the clinical skills of foreign medical school graduates participating in an internship preparation program.

In the fall of 1986, the Ministry of Health of the province of Ontario, Canada, implemented a special 36-week internship preparation program for graduates of foreign medical schools. The program accepts 24 candidates per year and is offered at the five Ontario medical schools. At the time of this study, two cohorts of participants had completed the program. As part of the evaluation process, each participant was administered a battery of the same Objective Structured Clinical Examination-type test stations, prior to and on completion of the pre-internship experience. Repeating the same examination permitted investigation of the predictive and construct validities of the clinical skills tests, as well as the stability of the validity and high reliability estimates that emerged from the testing of the first cohort. The results provide convincing evidence of the testing approach's predictive and construct validity and reliability.

Clinical Competence↗
PubMed1990

Potent inflammatory properties in human skin of interleukin-1 alpha-like material isolated from normal skin.

Recombinant human interleukin 1 (IL-1) possesses potent inflammatory properties in both animal and human skin. However, IL-1-like material has been isolated from normal epidermal samples. In view of the uncertainty concerning the structure and biologic properties of human epidermal IL-1, heel stratum corneum, and chamber fluid samples from normal skin have been purified by successive reversed phase and anion exchange high-performance liquid chromatography (HPLC), and aliquots of each HPLC fraction tested for IL-1 activity in an EL-4 NOB-1 assay and for inflammatory activity by intradermal injection of autologous material. The results consistently indicated the presence of inflammatory quantities of IL-1 alpha-like material, which induced persistent erythema lasting at least 24 h, associated in 4-h biopsies with mixed dermal leukocyte infiltrates containing increased numbers of neutrophils, monocytes, and T helper cells. Biologically active quantities of IL-1 beta were not recovered following HPLC purification in most experiments. Analysis of heel stratum corneum extract also showed that the majority of the dilution-related IL-1 activity detected in the EL-4 NOB-1 bioassay was neutralized by IL-1 alpha but not IL-1 beta antiserum. These findings suggest that IL-1 alpha-like material is present in inflammatory amounts in normal human epidermis, and its release may represent a primary inflammatory mechanism in human skin.

Adult↗
PubMed1990

Changes of left ventricular diastolic function in exercising dogs without and with ischemia.

Left ventricular (LV) diastolic function in the absence and presence of regional ischemia was examined in eight conscious dogs chronically instrumented with ultrasonic devices for measuring LV wall thickness and volume. During treadmill exercise, ischemia was induced (hydraulic occluder) to produce less than 10% systolic wall thickening in the ischemic zone. LV filling was assessed by the peak filling rate (PFR), mean filling rates in the first and second halves of filling (mFR1 and mFR2), an early filling index from mitral valve opening to minimal diastolic pressure (PDm), and the percentage of atrial filling. Also, LV relaxation (tau) and wall thinning rates during isovolumetric relaxation and the first and second halves of the filling phase were assessed. During control exercise without ischemia, PDm decreased by 2.61 mm Hg (p less than 0.05) to -1.1 mm Hg and there was a downward shift of the entire LV diastolic pressure-volume (P-V) curve. The LV relaxation rate, PFR, mFR1, and mFR2 were enhanced. Early filling was increased by 116%, the percentage of atrial filling by 118%, and overall diastolic filling by 23% despite a 63% decrease in the filling period. During ischemic exercise, systolic function was depressed compared with the resting state, PDm increased by 4.84 mm Hg (p less than 0.005) associated with a pronounced rightward and upward shift of the early portion of the P-V curve. LV relaxation rate, PFR, and mFR1 were reduced, the early filling index fell sharply by 62% but percentage of atrial filling was unchanged, while overall diastolic filling decreased by 30%. The thinning rate of the control wall was enhanced, whereas that of ischemic wall was depressed. Multiple factors contributed to the markedly impaired early and overall diastolic LV filling during ischemia, including impaired systolic function, reduced relaxation rate, nonuniformity of wall motion, an upward shift of the early diastolic P-V curve, and absence of a compensatory increase in late diastolic filling.

Animals↗
PubMed1990

Intracoronary urokinase for intracoronary thrombus accumulation complicating percutaneous transluminal coronary angioplasty in acute ischemic syndromes.

Intracoronary urokinase was used to treat flow-limiting intracoronary thrombus accumulation that complicated successful percutaneous transluminal coronary angioplasty (PTCA) during acute ischemic syndromes in 48 patients who were followed up through the acute phase of their illness. The study group comprised 10 patients with unstable angina pectoris, 18 patients with an evolving acute myocardial infarction, and 20 patients with postinfarction angina. The initial mean percent coronary diameter stenosis for the entire population was 95 +/- 7% and decreased with initial PTCA to 41 +/- 20% (p less than 0.001), with improved corresponding coronary flow by Thrombolysis in Myocardial Infarction trial (TIMI) grade. However, thrombus accumulation then resulted in a significant increase in percent diameter stenosis to 83 +/- 17% (p less than 0.001); a corresponding significant reduction in coronary flow also occurred by TIMI grade. After administration of intracoronary urokinase (mean dose, 141,000 units; range, 100,000-250,000 units during an average period of 34 minutes), with additional PTCA, mean percent diameter stenosis significantly decreased to 34 +/- 17% (p less than 0.001); a correspondingly significant improvement in mean coronary flow by TIMI grade occurred to 2.9 +/- 0.2. Overall, the angiographic success rate was 90%. There were no ischemic events requiring repeat PTCA and no procedure-related myocardial infarctions or deaths before hospital discharge. One patient was referred for urgent coronary artery bypass graft surgery after a successful PTCA. Plasma fibrinogen levels were obtained in 15 patients, and in no patient was the level below normal for our laboratory.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Myocardial effects of selective alpha-adrenoceptor blockade during exercise in dogs.

To study the effect of selective alpha 1- or alpha 2-adrenergic blockade on the myocardial contractile and chronotropic response to exercise, 29 dogs were chronically instrumented with a sonomicrometer for measuring myocardial wall thickness and a micromanometer for measuring left ventricular pressure. During treadmill exercise, either the selective alpha 1-blocker prazosin (80 micrograms/kg, n = 12) or the alpha 2-blocker idazoxan (80 micrograms/kg, n = 8) was infused into the left atrium beginning 2-3 minutes after the onset of exercise. alpha 1-Adrenoceptor blockade, like alpha 2-adrenoceptor blockade, was found to cause significant increases in systolic wall thickening, thickening velocity, heart rate, and left ventricular contractility, indicating an increase in inotropic state that was comparable to that with alpha 2-adrenoceptor blockade. Preventing the decrease in aortic blood pressure after selective alpha 1-blockade by using either systemic angiotensin II infusion (n = 6) or inflation of an intra-aortic balloon (n = 6) did not prevent the observed increases in wall thickening, heart rate, and left ventricular contractility. In four of the dogs treated with prazosin, the norepinephrine concentration in the coronary sinus was found to more than double after alpha 1-blockade. beta-Adrenergic blockade (propranolol, 1.0 mg/kg) prevented the increased contractile and chronotropic state caused by alpha 1- or alpha 2-blockade. Selective alpha-adrenergic blockade during adrenergic activation by intravenous norepinephrine infusion, in contrast to exercise, had no effect on wall thickening, heart rate, or left ventricular contractility. These data indicate that selective alpha 1-adrenergic blockade, like selective alpha 2-adrenergic blockade, causes a significant augmentation of heart rate and left ventricular contractility in the dog during dynamic exercise. These data are consistent with the hypothesis that this occurs through a presynaptic disinhibition of neural norepinephrine release mediated by a prejunctional alpha 1-adrenoceptor.

Adrenergic alpha-Antagonists↗
PubMed1990

Topical vancomycin for the treatment of Staphylococcus epidermidis and methicillin-resistant Staphylococcus aureus conjunctivitis.

Staphylococcus aureus and Staphylococcus epidermidis are organisms that frequently cause conjunctivitis or blepharoconjunctivitis. We describe a patient with methicillin-resistant S. aureus and S. epidermidis conjunctivitis who was treated successfully using an extemporaneously prepared topical ophthalmic solution of vancomycin hydrochloride 31 mg/mL. Studies describing the preparation, stability, and comfort of this solution, as well as reports pertaining to efficacy, are reviewed. Controlled clinical trials evaluating the safety and efficacy of vancomycin ophthalmic solution have not yet been performed.

Administration, Topical↗
PubMed1990

Transfection of cytochrome P450 cDNAs into mammalian cells used in mutation and transformation assays.

The present work demonstrates that cDNAs coding for cytochrome P450 enzymes can be transfected into mammalian cells and expressed. In the present studies, two different cell systems were used for transfection: 10T1/2 cells which can be used to study initiation and promotion (Diamond, 1984) and AHH-1 cells which can be used to study mutation and clastogenesis (Crespi and Thilly, 1984, Crespi and Penman, 1989). Thus, a diversity of endpoints can be studied in cells which have increased metabolic capability. By increasing the metabolic capability of the target cell, the effects of nongenotoxic as well as genotoxic chemicals, can be examined in the appropriate in vitro systems. For example, the 10T1/2 cells can be treated with a nontransforming dose of an initiator followed by continuous treatment with a second chemical that requires cytochrome P450 specific metabolism to manifest its promoting activity. By this approach, greater insight into the role of chemical metabolism in the promotion process (and presumably other nongenotoxic effects) can be obtained. Additionally, the role of specific cytochrome P450s in the metabolism of different classes of carcinogens/drugs can be elucidated. A major advantage of having the metabolizing enzymes actually present in the target cell is that effects of chemicals can be studied in long-term, low-dose exposure protocols which will eliminate the acute toxic effects which are associated with many current protocols. Thus, more realistic environmental exposure conditions can be achieved by using these in vitro systems containing endogenous metabolism systems.

Animals↗
PubMed1990

A program for health behavior change in a preventive cardiology center.

The Preventive Cardiology Center at the University of California, San Diego, was designed to conduct training, service activities, and research related to behavioral modification of cardiovascular disease (CVD) risk. A primary aim is to train medical students and other health care professionals in the application of scientifically established methods of behavior change. This training takes place in the context of a behavior-change program for patients with CVD risk factors. Participants at increased risk for CVD and their families are recruited to the Preventive Cardiology Center. A comprehensive assessment of physiological and behavioral risk factors leads to the development of dietary and/or exercise behavior-change targets. A five-session group intervention instructs participants how to change health behaviors. Behavioral techniques included in the program include self-monitoring, goal-setting, social support, self-reward, self-talk, and problem solving. Students and others are trained through readings, videotapes, and coleading of intervention groups.

Academic Medical Centers↗
PubMed1989

Is there a true increase in myocardial stiffness with acute ischemia?

Based on experimental observations, an increase in intrinsic regional myocardial stiffness can be demonstrated during complete coronary occlusion at rest when there is dyskinesia. There is decreased chamber compliance as well during coronary occlusion, while the zero volume intercept of the ventricle in diastole is larger, changes that may relate in part to regional ultrastructural alterations at the sarcomere level. Postpacing studies suggest that decreased chamber compliance also occurs in that setting, but with an opposite shift upward of the diastolic pressure-volume relation, which may relate to reperfusion effects. The factors involved in such changes in stiffness undoubtedly are multiple, and also include delayed ventricular relaxation, which can be magnified at rapid heart rates, effects of nonuniformity, and possibly the timing of loading conditions during individual contractions. The relative influence of these multiple factors undoubtedly varies with the conditions and duration of acute ischemia.

Animals↗
PubMed1989

Downhill walking induces rapid shallow breathing.

To examine the effect of downhill walking a form of negative work on ventilation, we studied the exercise responses of 13 healthy subjects during uphill and downhill walking on a treadmill. Each test lasted 16 min and the peak work rate was 5.6 kph with either a positive or negative 14% grade. Throughout each test we recorded VO2, VE, f, VT, HR, systolic BP and Borg's rating of perceived exertion. At the target work rates of 5.6 kph +/- 14% grade, VO2 and VE were three times greater in uphill compared with downhill walking. However, in downhill walking, f was greater compared with uphill walking wherein VT approximated baseline values, reflecting rapid shallow breathing, and VT appeared to increase after reaching some critically-low level. These trends persisted when VO2 was held constant (p less than 0.01). HR and systolic BP increased and decreased with the positive and negative grade respectively. At a constant VO2 however, HR was significantly higher during downhill compared with horizontal walking (p less than 0.01) whereas systolic BP was not significantly different (p greater than 0.05). We conclude that there is a significant difference in the ventilatory responses between the two types of work performed on a treadmill. Specifically, downhill walking is associated with rapid shallow breathing which may be countered by a protective feedback mechanism at critically-low levels of VT.

Adult↗