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Biomedical subjects

M B Wagner

Publications and source records attributed to M B Wagner.

At least 37 records · Page 2Linked to original sources
PubMed1996

Modeling triggered cardiac activity: an analysis of the interactions between potassium blockade, rhythm pauses, and cellular coupling.

It is known that under certain conditions, a combination of potassium channel blockade, sympathetic nervous activity, and pauses in sinus rhythm can increase the occurrence of cardiac arrhythmias. Although the arrhythmogenic interactions of these three factors are not completely understood, it is believed that the associated arrhythmias may be initiated by afterpotentials via a process that we refer to as propagated triggered activity. Using a two-cell computational model of ventricular action potential kinetics, we simulate nonuniform potassium blockade, sympathetic nervous activity, and pauses in sinus rhythm under conditions of hypokalemia. Under these conditions, the two-cell model suggests that (1) the arrhythmogenic interactions of potassium blockade and sympathetic nervous activity are highly dependent on heart rate; (2) triggered activity induced by potassium blockade would most likely occur during a pause in sinus rhythm; (3) during a sufficiently large pause in sinus rhythm, potassium blockade can induce triggered activity at normal levels of sympathetic activity; and (4) potassium blockade can increase the probability of triggered activity only if heart rate falls within a critical range. We also show that during pauses in sinus rhythm, two-cell triggering interactions between potassium blockade and sympathetic activity closely parallel the parametric displacement of the dynamic instability underlying the afterpotentials. Our results indicate that the behavior of the triggering mechanism studied here is consistent with that of pause-induced arrhythmias.

Action Potentials↗
PubMed1996

Ambulatory visits to hospital emergency departments. Patterns and reasons for use. 24 Hours in the ED Study Group.

OBJECTIVES: To characterize the reasons ambulatory patients use hospital emergency departments (EDs) for outpatient care and to determine the proportion of ED patients who initially are assessed as having nonurgent conditions, but subsequently are hospitalized. DESIGN: Cross-sectional survey during a single 24-hour period of time. SETTING: Fifty-six hospital EDs nationwide. PATIENTS OR OTHER PARTICIPANTS: Consecutive ambulatory patients presenting for care. Patents who arrived by ambulance were excluded. RESULTS: Of 6441 ambulatory patients (79 percent of all ED visits) who were eligible for study, interviews were obtained from 6187 (96 percent). A total of 5323 patients (86 percent) had clinical reasons or preferences for seeking care at an ED, including 2799 (45 percent) who thought they had an emergency or an urgent condition or were too sick to go elsewhere. Nineteen percent (n=1199) reported that they were sent to the ED by a health care professional. Patients with a regular clinician or with insurance cited similar reasons for seeking care at an ED. A total of 3062 patients (50 percent) cited 1 or more nonfinancial barriers to care as an important reason for coming to the ED, and 949 (15 percent) cited financial considerations. A total of 3045 patents (49 percent of ambulatory patients and 37 percent of total ED visits) were assessed at triage as having a nonurgent condition; 166 of them (5.5 percent; 95 percent confidence interval, 4.7 percent-6.3 percent) were admitted to the hospital. CONCLUSIONS: Most ambulatory patients seek care in an ED because of worrisome symptoms or nonfinancial barriers to care. Although many ambulatory patients appear to have nonurgent conditions based on triage classification, a small but disturbing percentage of nonurgent patients are hospitalized.

Adolescent↗
PubMed1996

Modulating L-type calcium current affects discontinuous cardiac action potential conduction.

We have used pairs of cardiac cells (i.e., one real guinea pig ventricular cell and a real-time simulation of a numerical model of a guinea pig ventricular cell) to evaluate the effects on action potential conduction of a variable coupling conductance in combination with agents that either increase or decrease the magnitude of the L-type calcium current. For the cell pairs studied, we applied a direct repetitive stimulation to the real cell, making it the "leader" cell of the cell pair. We have demonstrated that significant delays in action potential conduction for a cell pair can occur either with a decreased value of coupling conductance or with an asymmetry in size such that the follower cell is larger than the leader cell. In both conditions we have shown that isoproterenol, applied to the real cell at very low concentrations, can reversibly decrease the critical coupling conductance (below which action potential conduction fails) for a cell pair with fixed cell sizes, or, for a fixed value of coupling conductance, increase the maximum allowable asymmetry in cell size for successful conduction. For either of these effects, we were able to show that treatment of the real cell with BayK 8644, which more specifically increases the magnitude of the L-type calcium current, was able to mimic the actions of isoproterenol. Treatment of the leader cell of the cell pair (the real cell) with nifedipine, which selectively lowers the magnitude of the L-type calcium current, had effects opposite those of isoproterenol or BayK 8644. The actions of nifedipine, isoproterenol, and BayK 8644 are all limited to conditions in which the conduction delay is on the order of 5 ms or more, whether this delay is caused by limited coupling conductance or by asymmetry in size of the cells. This limitation is consistent with the time course of the L-type calcium current and suggests that the effects of calcium channel blockers or beta-adrenergic blocking drugs, in addition to being selective for regions of the heart that depend on the L-type calcium current for the upstroke of the action potential, would also be somewhat selective for regions of the heart that have discontinuous conduction, either normally or because of some pathological condition.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1996

Exercise participation in a frail elderly population.

A low-intensity exercise demonstration project was developed jointly by researchers, social service practitioners, and program participants to actively involve frail older people in their own health maintenance. This article describes this collaborative process and its impact on the success of the health promotion program, which was conducted at three senior centers serving a low-income, urban elderly population. Participants were predominantly sedentary women over age 70 with multiple chronic conditions. The program was conducted with peer leaders to facilitate its continuation after the research demonstration phase. In addition to positive health outcomes related to functional mobility, blood pressure maintenance, and overall well-being, this intervention was successful in sustaining active participation in regular physical activity through the use of peer leaders selected by the program participants. The planning, implementation, and outcomes of this project illustrate the benefits and challenges of combining research and practice perspectives in conducting health promotion interventions with older populations.

Black or African American↗
PubMed1996

Evaluation of a program for long-term treatment of Duchenne muscular dystrophy. Experience at the University Hospitals of Cleveland.

One hundred and forty-four boys who had Duchenne muscular dystrophy were managed at a single center between 1953 and 1994 and were followed for a mean of 8.9 years. The long duration of follow-up provided an opportunity to examine the effects of physical therapy and orthopaedic treatment on contractures of the lower extremities and on the duration of the ability to walk. Contractures of the lower extremities were controlled best when patients were managed with a combination of daily passive stretching exercises, prescribed periods of standing and walking, tenotomy of the Achilles tendon, posterior tibial-tendon transfer, and application of knee-ankle-foot orthoses. Approximately two years after bracing, the severity of the contracture of the heel cords was similar in the patients who had had an operation and those who had not. By the fourth year after bracing, however, the patients who had had an operation had less severe contractures than those who had had bracing alone. Five to seven years after the operation and bracing, control of contractures was still good, especially for the patients who had had posterior tibial-tendon transfer. Contracture of the knee was well controlled five to seven years after bracing in all patients who had had bracing, with or without an operation. The program enabled the patients who had been managed with bracing to walk until a mean age of 13.6 years. After loss of the ability to walk with bracing, the ability to stand continued for an additional two years with use of orthoses. The findings of the present study demonstrate the value of traditional methods of operative treatment and bracing for controlling contractures of the lower extremities in patients who have Duchenne muscular dystrophy and for prolonging their ability to walk.

Adolescent↗
PubMed1995

A model study of propagation of early afterdepolarizations.

Early afterdepolarizations (EAD's) are irregularities of the cardiac action potential that interrupt or retard repolarization. EAD's have been linked to the development of specific types of cardiac arrhythmias, however, the mechanism underlying the development of these arrhythmias remains unclear. We implemented a two-element kinetic model of the ventricular action potential to investigate a potentially arrhythmogenic form of triggered activity. By approximating EAD's by a sinusoidal driving force, we were able to study the effects of interelement coupling resistivity and sinusoidal frequency and amplitude on the triggering of action potentials. We demonstrated EAD's in a ventricular action potential model by altering the potassium and calcium channels to simulate experimental conditions under which EAD's occur. We also found that triggered activity depends critically on the frequency and amplitude of the driving force and also on the degree of cellular uncoupling between the elements. Our results suggest that triggered activity (due to EAD's) may be suppressed by drugs that improve coupling in unhealthy tissue, or ones that prevent EAD formation by inhibiting calcium channels.

Action Potentials↗
PubMed1994

Low-molecular weight heparin versus aspirin and dipyridamole after femoropopliteal bypass grafting.

Low-molecular weight heparin has theoretical advantages over aspirin and dipyridamole in maintaining vascular-graft patency by virtue of its better antithrombotic effect and antiproliferative activity on vascular, smooth-muscle cells. We tested the hypothesis that low-molecular weight heparin would be more effective than aspirin and dipyridamole in maintaining graft patency in patients undergoing femoropopliteal bypass grafting. Patients were randomised to receive either a daily injection of 2500 IU low-molecular weight heparin, or 300 mg aspirin with 100 mg dipyridamole 8 hourly for 3 months. 94 patients were randomised to low-molecular weight heparin and 106 to aspirin and dipyridamole. Patients were stratified according to indication for surgery and were followed up for 1 year. Kaplan-Meier estimate of graft patency showed 87% graft survival on low-molecular-weight heparin and 72% on aspirin and dipyridamole at 6 months. At 12 months, the respective figures were 78% and 64%. Stratified survival analysis showed that this benefit was confined to those having salvage surgery (log rank test p = 0.0006); for those having surgery for claudication there was no significant benefit. No major bleeding events occurred in either group. We conclude that low-molecular weight heparin is better than aspirin and dipyridamole in maintaining femoropopliteal-graft patency in patients with critical limb ischaemia undergoing salvage surgery. This treatment should have considerable cost benefits.

Adult↗
PubMed1994

Effects of simulated potassium blockade on the dynamics of triggered cardiac activity.

Under certain conditions, drugs that partially block transmembrane potassium currents in ventricular myocytes predispose patients to ventricular tachyarrhythmias. Although the precise mechanisms by which potassium blockade initiates tachyarrhythmias are unknown, it is believed that early afterdepolarizations (EADs) may play a role. Using the Luo-Rudy kinetic model of the ventricular action potential, we examine the effect of potassium blockade on the likelihood of observing triggered cardiac activity in a system of two coupled kinetic patches. We found that (i) phase 2 EADs are capable of triggering full action potentials in neighboring tissue if the patches are separated by a relatively large resistive barrier, and (ii) partial potassium blockade can either increase or decrease triggering probabilities depending on coupling resistivity. To understand the dynamic contribution of potassium blockade to triggered activity, the two-patch model is decomposed into two single patches. In one of the patches we compute the stability properties of simulated EADs (arising from phase 2 of the ventricular action potential) as a function of potassium blockade. The EAD stability properties are then related to the frequency-amplitude response of the neighboring patch. From the analysis of the decomposed system we found (iii) that increases in triggering probabilities brought about by potassium blockade may result from frequency and amplitude shifts of stable EAD oscillations. The first finding suggests a mechanism by which potassium blockade could induce EAD-triggered arrhythmias within the setting of chronic myocardial infarction. The second and third findings may partially explain why potassium blockade is antiarrhythmic in some patients, and proarrhythmic in others.

Action Potentials↗
PubMed1993

Incidence of hospital-acquired infection and length of hospital stay.

Two different measures of hospital-acquired infection (HAI), risk per discharge and incidence rate, were used to analyse the incidence of 225 primary HAIs detected in 3,090 patients in an 11-month survey. Longer hospital stay was associated with a greater risk of developing HAI, but the strength of the association was different for the two measures used. Day-specific incidence rates were found to vary, with a peak between the 14th and 19th days of hospitalisation. Similar patterns were observed when the data were stratified by age, sex and operation. Methods for calculating HAI should control for the length of hospital stay. Further studies are required to clarify the mechanisms that affect the temporal pattern of incidence of HAI observed with length of hospitalisation.

Adolescent↗
PubMed1993

Assessment of hand function in Duchenne muscular dystrophy.

Eighteen boys with Duchenne muscular dystrophy (DMD) were assessed for their ability to perform tasks involving wrist and hand function. Each subject was assessed using the Jebsen Test of Hand Function, range of motion measurements, and muscle strength tests. Writing and simulated page turning were performed successfully by boys in all age groups. Boys over age 15 had difficulty completing simulated feeding and picking up large and small objects. The muscle strength of the wrist extensors and the radial deviation range of motion at the wrist were found to be strongly correlated with six of the seven tasks assessed. These two clinical assessments appear to be good indicators of overall wrist and hand function. Life expectancy with DMD is increasing with advances in respiratory care making preservation of wrist and hand function, the major activity remaining with advanced disease, increasingly important.

Adolescent↗
PubMed1993

A study of the sexual behavior of teenagers in south Brazil.

A study of sexual behavior among teenagers was carried out in a random sample of 884 second degree school (high school) students of Porto Alegre (South Brazil) by means of a self-report questionnaire. The students' ages ranged from 13 to 22 years old, and 59% of them were females. The students believed themselves well-informed about physiologic phenomena involved in human reproduction (95.2%; 95% confidence interval (CI):93.5-96.5) and sexually transmitted diseases (STD) (82.1%; 95% CI:79.1-84.7). In addition, 42.4% (95% CI:39.0-45.8) said that they has had a sexual relationship. However, 51.5% (95% CI:45.9-57.0) did not use contraceptive precautions systematically, and 12% (95% CI:7.2-19.0) of girls had already undergone an abortion. Considering these results, it is important to stimulate programs for sexual education strictly focused on teenagers.

Adolescent↗
PubMed1990

A prevalence survey of nosocomial infection in a Brazilian hospital.

A study to determine the prevalence of hospital-acquired infection was undertaken in the Irmandade Santa Casa de Misericórdia de Porto Alegre Hospital in Brazil. The study was carried out in selected clinical areas of the hospital over a one-year period from 1987 to 1988. Of 397 patients surveyed, infections were present in 168 (42.3%); 53 (13.4%) were hospital acquired and 115 (29%) community acquired. The commonest infections involved the lower respiratory tract (30%), bacteraemias (24.4%) and the urinary tract (10%). A high prevalence of infection was encountered in the intensive care units.

Bacterial Infections↗
PubMed1990

[Demand of community health services in the periphery of a metropolitan area].

The content of 4,319 consultations in primary health care representing 7% of all consultations from March, 1985 to March, 1986 at the Murialdo Health Center, was analyzed. The health center is located in the outskirts of Porto Alegre, RS (Brazil). Woman represented 67% of the total demand. Most consultations were for children under 10 years of age (37%) and woman of childbearing age (21%). The first twenty reasons for the visit corresponded to 63% of the total, and the most common reason for visiting the health center was for renewal of prescriptions and/or ordering medication (9.3%). Of all the diagnoses, the first twenty accounted for 62% of the total number of patients and the most frequent were: hypertension (8.8%), upper respiratory tract infection (7.8%), and immunization (5.5%). Prescription and administration of medication were the most common actions performed. Referrals resulted in 7.3% of the visits. Of these, 5% were sent to other providers within the Murialdo service. Only 0.6% were referred for hospitalization. These findings, combined with others which describe aspects of morbimortality not easily measured in studies of spontaneous demand for medical services, should help in the planning of primary health care services and in the training of health personnel.

Brazil↗
PubMed1989

Duchenne muscular dystrophy: a study of wrist and hand function.

The wrist and hands of 18 Duchenne muscular dystrophy (DMD) patients were assessed for abnormalities. The subjects were divided into three groups by age. Flexion and ulnar deviation contractures of the wrist began in the youngest age group, 8-14 years. Other abnormalities, present in all age groups, included extrinsic and intrinsic digital muscle shortness, boutonniere and swan neck deformities, and hyperextension of the digital interphalangeal joints. Pain found with passive proximal interphalangeal joint flexion has not been reported previously. This study supports the importance of early assessment of the wrist and hand in DMD and suggests intervention techniques to possibly retard the deforming process.

Adolescent↗
PubMed1988

A comparison of four techniques to establish intraosseous infusion.

This study was designed to determine whether the success rate in establishing intraosseous infusion (IOI) varied with four different types of needles--standard hypodermic, spinal, bone marrow, and Turkel intraosseous infusion needle. Twenty-four second-year residents from various specialties, without prior training or experience in the technique, participated in the study. Each participant attempted to establish an intraosseous infusion in a randomly assigned limb of an anesthetized piglet, using each needle in a randomly assigned order. The overall success rate was 67.7%. Success ratios varied between needles: hypodermic 54%, spinal 75%, bone marrow 75%, and Turkel 67%. Utilizing Cochran's Q-test, there was no statistical difference in success rates between needle types. However, in cases where the resident was successful with all four needles, the average time to successful infusion was significantly less for bone marrow needles.

Animals↗
PubMed1986

Serial isokinetic evaluations used for a patient with scapuloperoneal muscular dystrophy. A case report.

This article reports the reversal of an atypical rapid decline in muscle strength experienced by a patient with scapuloperoneal muscular dystrophy by modulating his excessive daily physical activity. This process was aided by our monitoring the strength of the quadriceps femoris and hamstring muscles using an isokinetic dynamometer. Serial torque values for muscle strength were compared as the total daily physical activity was decreased systematically. The torque values for thigh muscle strength increased as the subject's total work load was decreased. A complete management program for neuromuscular patients should include specified amounts of daily physical activity, rest, and therapeutic exercise.

Adult↗