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Biomedical subjects

A Tonkin

Publications and source records attributed to A Tonkin.

17 recordsLinked to original sources
PubMed1992

Aging and susceptibility to drug-induced orthostatic hypotension.

OBJECTIVE: To test the hypothesis that the short-term effect of transbuccal nitroglycerin (glyceryl trinitrate, 0.0625 to 1.5 mg) on orthostatic cardiovascular responses would predict the effect of a diuretic (5 mg bendroflumethiazide daily for 1 week), particularly in elderly subjects who may be at higher risk for orthostatic hypotension. METHODS: This was a randomized crossover study. Participants were 17 elderly (age range, 63 to 84 years) and 15 younger (age range, 19 to 35 years) healthy ambulant volunteers. Interventions and measures of outcome included blood pressure (BP; in millimeters of mercury) and heart rate (HR; in beats per minute) changes with standing, which were measured before administration of medication and after each drug treatment. RESULTS: Subjects in the elderly and younger groups had different BP and HR changes (mean percentage change) at 1 minute after standing in all three study phases (unmedicated, elderly: BP, -4%/+1%; HR, +12%; young: BP, +2%/+12%; HR, +27%; p = 0.06 for BP, p less than 0.01 for HR; bendroflumethiazide, elderly: BP, -9%/-3%; HR, +17%; young: BP, +1%/+11%; HR, +33%; p less than 0.05 for all; nitroglycerin (0.25 mg), elderly: BP, -15%/-12%; HR, +21%; young: BP, -6%/+7%; HR, +38%; p less than 0.05 for all). The incremental orthostatic effects of the two drugs were similar in the two age groups and were positively correlated (r = 0.65, p less than 0.001) in individual subjects. CONCLUSIONS: Individual susceptibility to drug-induced orthostatic hypotension depends on a combination of the age-related unmedicated orthostatic response and the additional drug effect, which is independent of age. The BP response to standing after administration of nitroglycerin may be useful in predicting the effect of other drugs known to influence orthostatic BP control.

Administration, Oral↗
PubMed1991

A randomised study of outcomes in a defined group of acutely ill elderly patients managed in a geriatric assessment unit or a general medical unit.

The aim of this study was to identify differences in the medical management and clinical outcome in a group of elderly patients admitted to a designated geriatric assessment unit (GAU) or to two general medical units (GMUs). A prospective randomised controlled trial was undertaken in 267 patients aged 70 years and over (mean age = 78.3 years). Following discharge from hospital, patients were followed up at three monthly intervals for a total of 12 months. At the time of discharge, no significant differences were found in inpatient management, length of stay, mortality rates, discharge rates to institutional care or utilisation of community services in patients admitted to the GAU and the GMUs. Similarly, no significant differences were found at three, six, nine, and 12 month follow up in case fatality, activities of daily living indices, mental health status, rates of institutional referral and the level of community service support in patients admitted to the GAU and the GMUs studied. These findings do not show any advantage for the unselected 70+ acutely ill elderly patient who is admitted to a designated geriatric assessment unit rather than to a general medical unit. Therefore, an admission policy to GAU, based solely on age 70+ is medically inappropriate and cost-inefficient. Evidence from other sources suggests that an age cohort of acutely admitted patients beyond 80 years may well have returned more optimistic findings for the GAU. In future, GAUs will require a more selective admission policy to maximise the benefits of their rehabilitative and interdisciplinary approach.

Acute Disease↗
PubMed1990

Single oral dose pharmacokinetics of erythromycin and roxithromycin and the effects of chronic dosing.

Roxithromycin is a semisynthetic macrolide antibiotic having similar in vitro antibacterial profile and potency to erythromycin but possibly greater in vivo potency. The single and multiple oral dose pharmacokinetics of roxithromycin and erythromycin were studied in 12 healthy volunteers. Plasma concentrations of the two compounds were measured by a sensitive and specific high-performance liquid chromatographic method using electrochemical detection. After single doses, roxithromycin 150 mg gave a Cmax 3.3-fold higher and an area under the curve (AUC) 16.2-fold higher than erythromycin 250 mg. The half-life for roxithromycin was 12.42 +/- 3.94 h compared with 1.53 +/- 0.42 h for erythromycin. On multiple dosing, the AUC over a dosing interval for erythromycin (250 mg, six hourly doses) was increased 2.3-fold compared with the single dose, whereas that for roxithromycin (150 mg, 12 hourly) was decreased by 25.4%. Because of these opposing changes during chronic dosing, the average plasma roxithromycin concentration over the dosing interval was 2.6-fold higher than that for erythromycin, which was a smaller excess than would have been predicted from the single dose data. The results suggest that roxithromycin exerts less inducing and inhibiting effects on human cytochrome P450 than erythromycin. Roxithromycin has a favorable pharmacokinetic profile suitable for twice daily dosing and may have a lower potential than erythromycin for cytochrome P450-mediated drug interactions.

Adolescent↗
PubMed1989

Results of cardiopulmonary resuscitation in adult patients managed in a teaching hospital: clinical outcome and implications.

OBJECTIVE: To assess the impact and clinical implications of therapeutic strategies for managing sudden cardiac arrest in a teaching hospital. METHOD: A prospective audit of the results of out-of-hospital and in-hospital cardiac arrest. RESULTS: Compared with other studies, our results for resuscitation of out-of-hospital cardiac arrest were poor, only 5% of patients being discharged. This probably relates to the inability to revert ventricular tachycardia or ventricular fibrillation promptly by defibrillation. Improving access to defibrillation at the scene of cardiac arrest could improve the results of out-of-hospital cardiac arrest. In contrast, among patients with in-hospital cardiac arrest. In contrast, among patients with in-hospital cardiac arrest, 14% of patients in monitored wards, and 24% of patients in unmonitored wards, were discharged (P less than 0.05). When cardiac arrest is not associated with acute myocardial infarction, survivors require thorough investigation and treatment to prevent recurrence.

Adult↗
PubMed1988

Direct identification of parameters in a mathematical model describing conduction through the atrioventricular node.

Function of the atrioventricular node is assessed during intracardiac electrophysiology study by relating the output intervals A2H2 and H1H2 to the input A1A2, where A and H are, respectively, atrial and His bundle electrograms recorded by catheter. The H1H2 curves have been previously deduced from a model describing the A2H2 curves. Because of presence in a few cases of different behaviour of A2H2 and H1H2, this study aimed to establish a more suitable model of H1H2 independently of A2H2 for the particular case of a single transmission pathway. The two models were compared by calculation of standard error of the estimate. As a first approximation, the deduced model may be sufficient. However, the standard error of the estimate was less with the direct algorithm, which is therefore the more suitable for further development, particularly for recognition and modelling of conduction over multiple pathways through the atrioventricular node.

Adult↗
PubMed1987

Ventricular standstill complicating cardiac catheterization.

A patient is described in this paper who developed repeated episodes of ventricular standstill during left heart catheterization. The patient had a resting pattern of right bundle branch block with left anterior fascicular block; subsequent electrophysiology study was normal. Ventricular standstill during catheterization was apparently due to catheter-related trauma of His bundle connections.

Aged↗
PubMed1986

A comprehensive model describing conduction through the atrioventricular node.

An algorithm which models conduction over two conduction pathways through the atrioventricular (AV) node has been derived and tested. Output from the node has been previously related to input, the coupling intervals of extrastimuli introduced during programmed atrial stimulation. An exponential model of conduction in a single pathway was used with the general form: A2 H2 = K1 + K2 exp (-A1 A2/K3) with K1, K2, K3 parameters The algorithm for identification of dual pathways minimised residual sums of squares from two such functions. Potential 'bifurcation' points were selected by significant deviation of the computed single curve of best fit. The algorithm was tested using data obtained during electrophysiology study. Three trials of programmed stimulation were performed in 15 patients after pacing at 100 bpm. Computations using the model suggested single and dual functions (and therefore pathways) respectively in 19 and 25 of 44 trials. An electrophysiologist independently examining the data usually agreed (83% of trials). As the reasons for discordance were minor the model was reasonably verified.

Adolescent↗
PubMed1985

Comparison of exponential and hyperbolic models of conduction through the atrioventricular node.

Conduction through the atrioventricular node (AVN) is assessed during electrophysiology study by relating the output to the input generated by an atrial extrastimulus. This extrastimulus scans electrical diastole of the heart to enable output to be plotted against input. Using this technique, we compared two mathematical models of the AVN, a rectangular hyperbola and a decaying exponential, respectively. The models were compared in 40 curves from 32 patients with only one AVN transmission pathway. Standard errors of the estimate were usually (25/40 trials) less with the exponential model, suggesting this the preferred algorithm for further development.

Adolescent↗
PubMed1985

Examination of an exponential model of conduction through the human atrioventricular node.

The atrioventricular node (AVN) has been modeled by relating output (A2H2 or H1H2) to input (A1A2) where A and H are atrial and His bundle electrograms during fixed rate atrial pacing (A1A1) or with an extrastimulus (A2). (Formula: see text) This study examined this model in 61 nonselected patients, specifically for AVN (in)stability and the possibility of multiple pathways. After programmed atrial stimulation at two basic cycle lengths of 600 ms and 462 ms, A1H1, A2H2 and H1H2 were digitized and plotted as a function of A1A2. Seven of 104 trials were rejected as SD. A1H1 was greater than 15 ms, suggesting AVN instability. Another 26 and 34 plots, respectively, of A2H2 and H1H2 were rejected because of inadequate data. In the remainder, goodness of fit of the single exponentials was tested statistically in three ways: R2, the runs test, and the Kendall rank coefficient test. Results were compared with an electrophysiologist who examined plots for one or more pathways (either discontinuous curves or slope change in a continuous curve). Single exponentials were successfully fitted (by runs test) in 44/71 and 34/63 of A2H2 and H1H2 plots, respectively, usually in accordance with the cardiologist. Discordance between computations and the cardiologist could be attributed to data scatter and lack of a sufficiently rigid stimulation protocol. The identification of bifurcation points in the presence of multiple pathways, particularly when manifest as a change in slope (approximately 6% of trials) rather than discontinuity of plots (approximately 20% of trials) remains an outstanding problem.

Adolescent↗
PubMed1979

Sick sinus syndrome and AV node re-entry.

A 69-year-old man presented with recurrent palpitations since childhood. Electrophysiology studies performed on two separate occasions revealed the combination of sick sinus syndrome and AV node re-entrant tachycardia. The case is reported because it illustrates marked temporal variability in the electrophysiological properties of the dual AV node pathways, and also deleterious effects of verapamil on sinoatrial node function.

Aged↗
PubMed1979

Complications of defibrillation with permanent pacemaker in situ.

A permanent demand pacing generator was implanted in the right deltopectoral fossa with unipolar transvenous lead advanced to the right ventricle. Implant and subsequent pacing parameters were normal. Five days later an emergency DC cardioversion was performed with one paddle 2 inches from the generator. Cardioversion was followed by failure of QRS-sensing and, at immediate explant, rise in stimulation threshold. The pulse generator showed end-of-life characteristics. The patient died 4 days following replacement of the generator and lead. At autopsy, right ventricular infarction was found, presumably relating to current discharge along the lead. Pacemaker analysis showed damage to the protection zener diode and oscillator integrated circuit of the generator during cardioversion.

Aged↗