PubMed Health⌕ Search

Biomedical subjects

R C Wesley

Publications and source records attributed to R C Wesley.

At least 19 recordsLinked to original sources
PubMed1997

Effects of adenosine infusion on renal function, plasma ANP and ADH concentrations and central hemodynamics in anesthetized pigs.

1. The effect of high-dose adenosine administration on atrial natriuretic peptide (ANP) and antidiuretic hormone (ADH) release is not completely understood, and data concerning the effect of adenosine on renal and systemic hemodynamics in the pig are lacking. Measurements of central hemodynamics, renal blood flow and urine production were made in anesthetized pigs during infusion of adenosine. The relationship between these parameters and the plasma concentrations of ANP, ADH and renal renin production was examined. 2. Adenosine infusion at the rate of 140 mg/kg per minute resulted in a significant decrease in systolic, diastolic and mean arterial blood pressure as well as pulmonary arterial pressure. However, cardiac output and renal blood flow remained unchanged during adenosine infusion. Likewise, heart rate remained unchanged until the end of infusion when it increased significantly, Plasma ANP and ADH concentrations increased significantly within 30 min after adenosine infusion, reaching peak levels at 30 to 60 min. However, despite the significant decrease in arterial blood pressure, renal renin production did not change significantly. 3. The adenosine-induced rise in ANP, which is normally released by atrial stretch, may represent a direct effect of adenosine on the cardiac myocytes. The increase in ADH may be a result of decreased arterial blood pressure triggering stimulatory signals from the aortic arch and carotid body receptors to hypothalamic-pituitary sites of ADH production/release. Urine flow decreased dramatically within 30 min of adenosine infusion. Thus adenosine infusion at the given rate led to marked reduction in systemic and pulmonary arterial pressures without significant change in cardiac output, heart rate and renal blood flow. This was associated with a marked increase in plasma ANP and ADH levels with no significant change in renal renin production despite a marked reduction in arterial blood pressure. 4. Maintenance of renal blood flow despite marked reduction in perfusion pressure suggests that, at high doses, adenosine induces renal vasodilation in pigs as opposed to a combined afferent and efferent vasoconstriction known to occur under different experimental conditions.

Adenosine↗
PubMed1996

Efficacy of intravenous ibutilide for rapid termination of atrial fibrillation and atrial flutter: a dose-response study.

OBJECTIVES: Currently available antiarrhythmic drugs have limited efficacy for short-term, rapid termination of atrial fibrillation and atrial flutter. BACKGROUND: Ibutilide fumarate is an investigational class III antiarrhythmic agent that prolongs repolarization by increasing the slow inward sodium current and by blocking the delayed rectifier current. It can be administered intravenously and has a rapid onset of electrophysiologic effects. METHODS: The efficacy and safety of ibutilide were studied in 200 patients with atrial flutter > 3 h in duration or atrial fibrillation 3 h to 90 days in duration. Patients were randomized to receive a single intravenous dose of placebo or an infusion of ibutilide fumarate at 0.005, 0.010, 0.015 or 0.025 mg/kg body weight over 10 min. Conversion was defined as termination of the atrial arrhythmia during or within 60 min after infusion. Forty-one patients received placebo and 159 received ibutilide (0.005 mg/kg [n = 41], 0.010 mg/kg [n = 40], 0.015 mg/kg [n = 38] or 0.025 mg/kg [n = 40]). RESULTS: The arrhythmia terminated in 34% of drug-treated patients. The rates of successful arrhythmia termination were 3% for placebo and 12%, 33%, 45% and 46%, respectively, for 0.005-, 0.010-, 0.015- and 0.025-mg/kg ibutilide. The placebo and 0.005-mg/kg ibutilide groups had lower success rates than all other dose groups (p < 0.05). The mean time to termination of the arrhythmia was 19 min (range 3 to 70) from the start of infusion. Successful arrhythmia termination was not affected by enlarged left atrial diameter, decreased ejection fraction, presence of valvular heart disease or the use of concomitant medications (beta-adrenergic blocking agents, calcium channel blocking agents or digoxin). Arrhythmia termination was not predicted by the magnitude of corrected QT interval prolongation but was associated with a shorter duration of atrial arrhythmia. The most frequent adverse events in ibutilide-treated patients were sustained and nonsustained polymorphic ventricular tachycardia (3.6%). All patients with sustained polymorphic ventricular tachycardia were successfully treated with direct current cardioversion and had no recurrence. The occurrence of proarrhythmia did not correlate with ibutilide plasma concentration. CONCLUSIONS: These data demonstrate that ibutilide is able to rapidly terminate atrial fibrillation and atrial flutter.

Aged↗
PubMed1994

Automated precision current delivery: an alternative method for cardiac defibrillation.

Substantial evidence suggests that the current associated with the discharge is a more precise predictor of defibrillation success than is the total energy of the discharge. However, virtually all commercially available defibrillators are calibrated in terms of energy. This article describes an alternative type of experimental defibrillator, which provides a precisely controlled current throughout the discharge waveform, independent of the load presented to the discharge electrodes (or "paddles"). The discharge current waveform is designed to have the classical critically damped sinusoid waveform, identical to that of the traditional energy-based defibrillator when it is properly matched with its ideal load (the heart/thorax combination). The techniques used to obtain a controlled current discharge are discussed in addition to special operational features.

Automation↗
PubMed1993

Changes in renal vein, renal surface, and urine oxygen tension during hypoxia in pigs.

To determine whether ureteral urine oxygen tension could serve as a monitor of renal hypoxia and its relationship to other renal O2 tension parameters, we simultaneously measured femoral artery (PaO2), renal vein (PrvO2), renal surface (PrsO2), and ureteral urine (PuO2) oxygen tensions in 8 anesthetized pigs while incrementally decreasing the inspired oxygen concentration (FiO2) from 21% to 12%. Renal artery blood flow, measured by transit time ultrasound, renal oxygen consumption, and thermodilution cardiac output, was constant. Changes in PaO2, PrvO2, PrsO2, and PuO2 caused by decreasing FiO2 were evaluated by one-way analysis of variance. The relationships between PuO2 and the other O2 tension parameters were evaluated by correlation coefficient and linear regression statistics. Of six possible O2 decrements (combinations of 3, 6, and 9%), only PrvO2 significantly decreased with all six decrements. PuO2 decreased when FiO2 decreased 6% or more. PuO2 is not a sensitive indicator of systemic hypoxia. Under constant renal perfusion and oxygen consumption, PuO2 had a correlation coefficient of 0.80 and a regression equation of PuO2 = 0.84 (PrvO2) + 11.6, with PrvO2. PuO2 is related to PrvO2 when renal perfusion is constant.

Animals↗
PubMed1993

Effect of selective A1 adenosine receptor antagonism of postdefibrillation cardiovascular depression: evidence for an antiadrenergic role of endogenous adenosine.

OBJECTIVE: The aim was to examine the effect of a selective A1 adenosine receptor antagonist (N-0861) on postdefibrillation cardiovascular depression to determine whether antagonist mediated enhanced postdefibrillation haemodynamic recovery is due to reversal of the antiadrenergic action of adenosine, an A1 receptor mediated effect. METHODS: Halothane-nitrous oxide anaesthetised Duroc pigs of either sex, weight 22-25 kg, were subjected to sequential episodes of induced ventricular fibrillation lasting either 15 s (terminated by a suprathreshold shock at 60-70 A) or 35 s (subjected to a subthreshold shock at 20 A followed by a suprathreshold shock at 60-70 A) during intravenous placebo infusion (n = 10), N-0861 infusion (0.1 mg.kg-1.min-1, n = 10), and N-0861 infusion plus propranolol (2 mg.kg-1, n = 6). RESULTS: N-0861 significantly enhanced immediate postdefibrillation electrophysiological and haemodynamic recovery compared to placebo for ventricular fibrillation episodes lasting 35 s. Over the first 15 s postdefibrillation, N-0861 significantly (p < 0.05) shortened mean cycle length by 55%, increased mean arterial pressure by 33%, and increased the first derivative of left ventricular pressure (an indirect measure of cardiac contractility) by 100% compared to placebo. At 60 s postdefibrillation, when other variables were equal, the first derivative of left ventricular pressure in the presence of N-0861 remained 26% greater than placebo. This effect was completely antagonised by propranolol. CONCLUSIONS: (1) Cardiac contractility in the immediate postdefibrillation period is suppressed by the antiadrenergic action of endogenous adenosine. (2) Selective A1 adenosine receptor antagonism can markedly enhance postdefibrillation contractility. (3) These results support an antiadrenergic role of endogenous adenosine under pathophysiological conditions.

Adenine↗
PubMed1993

Transepicardial defibrillation dose response: current versus energy.

In pentobarbital-anesthetized dogs, we compared the relative efficacy of current versus energy in applying the dose response method in transcardiac defibrillation. Damped sinusoidal shocks via epicardial patches were administered by a custom defibrillator permitting precise current delivery. Following the establishment of an initial estimated defibrillation threshold for energy and current, the dose response method was performed with regard to either energy defibrillation threshold (group E, n = 8) or current defibrillation threshold (group C, n = 8). Two sequential sets (I, II) of shocks (21 shocks each) were delivered in random order at each of seven doses: 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 1.45 x defibrillation threshold. Data were subjected to nonlinear logistic regression analysis. There were no significant differences between sets I and II in either groups E or C for resistance or for raw and normalized values associated with 50% and 80% success expressed as energy, current, or voltage. Correlation coefficients (r) associated with nonlinear logistic regression analysis were significantly different for normalized current and energy for group E (0.70 +/- 11 and 0.71 +/- 12) compared to group C (0.86 +/- 0.60 and 0.88 +/- 0.06). The difference, however, could be explained by a significantly narrower range of normalized current values tested in group E (0.79 to 1.31) versus group C (0.54 to 1.46). Thus, when resistance does not change, transcardiac current offers limited advantage over energy when applying a dose response method. The efficacy of nonlinear logistic regression analysis depends upon an adequate dose range.

Animals↗
PubMed1993

Ibutilide: enhanced defibrillation via plateau sodium current activation.

Reductions in current and energy requirements for defibrillation have previously been ascribed to type III antiarrhythmic agents that block outward potassium conductance. This study investigated the effect on defibrillation of ibutilide, a type III antiarrhythmic agent that prolongs action potential duration by activating the sodium component of the plateau inward current. Pentobarbital-anesthetized dogs were subjected to serial episodes of ventricular fibrillation lasting 10 s. In protocol I, current and energy defibrillation requirements were determined via an interactive approach after bolus injections of saline placebo and ibutilide (0.1 mg/kg i.v.). In protocol II, a current dose-response method was utilized in which four shocks each at current doses of 0.7, 0.8, 0.9, and 1.0 x an estimated defibrillation threshold were administered before and after ibutilide (0.075 mg/kg bolus; 0.00125 mg.kg-1 x min-1 i.v.). In protocol I, current and energy values associated with defibrillation measured 10.9 +/- 4.5 A and 16.0 +/- 11.9 J for ibutilide compared with 14.1 +/- 5.6 A and 27.7 +/- 17.7 J for placebo, respectively (n = 9, P < 0.005). In protocol II, ibutilide significantly shifted the current doses associated with 50% successful defibrillation from 14.8 +/- 3.7 to 8.9 +/- 2.0 A (n = 6, P < 0.05). Eight of 15 animals given ibutilide exhibited one or more episodes of spontaneous defibrillation. Ibutilide significantly (P < 0.05) increased ventricular effective refractory period (+23.4%), and both preventricular fibrillation and postdefibrillation monophasic action potential duration at 90% repolarization (+21.7% and +23.3%, n = 9, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Intravenous adenosine: a noninvasive diagnostic test for sick sinus syndrome.

Adenosine has a well established negative chronotropic effect on the sinoatrial node. The most widely utilized test of sinus node function remains the sinus node recovery time (SNRT), which generally requires catheterization. We compared the effect of adenosine (150 mcg/kg IV) on the lengthening of sinus cycle length (ADO:SCL) in 12 control patients (group I) and in 11 patients with clinical sick sinus syndrome (SSS) (group II), eight of whom had undergone prior permanent pacemaker implantation. Using 675 msec as an abnormal result indicating sinus node dysfunction (two standard deviations above the mean value established in controls), ADO:SCL had a sensitivity and specificity of 64% and 100%, which were equal to that observed for the corrected sinus node recovery time (CSNRT) (abnormal value > or = 550 msec). There was a significant difference in the CSNRT between group I (304 +/- 149 msec) and group II (1,199 +/- 916 msec, P = 0.003). There was no significant difference in ADO:SCL between groups I (256 +/- 210 msec) and group II (1,213 +/- 1,719 msec, P = 0.069); however, there was substantial overlap between patients exhibiting an abnormal ADO:SCL and CSNRT. As such, a significant difference in ADO:SCL was evident between group II patients (1,784 +/- 1,950 msec, n = 7) exhibiting an abnormal CSNRT and group I patients, P = 0.014. In conclusion, ADO:SCL has the same sensitivity and specificity for sinus node dysfunction as compared to the CSNRT. Intravenous adenosine may prove to be a useful noninvasive test to assess the need for permanent pacemaker implantation.

Adenosine↗
PubMed1991

Reconsiderations of the routine and preferential use of lidocaine in the emergent treatment of ventricular arrhythmias.

OBJECTIVE: Despite a history of widespread use, the utility of lidocaine as an antiarrhythmic and antifibrillatory agent is questionable. The objective of this article is to examine the theoretical basis for the use of lidocaine in light of recent experimental and clinical data. This article reviews the effects of lidocaine on: a) ventricular arrhythmias under ischemic and nonischemic conditions; b) the energy and current requirements for defibrillation; and c) the propensity for asystole during cardiac arrest. DESIGN: A contemporary review of the literature. FINDINGS: There appears to be a theoretical basis for the use of lidocaine in treating ventricular arrhythmias secondary to acute ischemia largely based on voltage- and pH-dependent binding and inactivation of sodium channels by lidocaine under ischemic conditions. However, clinical and experimental data failed to establish enhanced survival following prophylactic treatment for acute ischemic events or when treatment is administered during cardiac arrest. Moreover, there are no data supporting the use of lidocaine in treating sustained and life-threatening ventricular arrhythmias in the absence of acute ischemia. Experimental data demonstrate that lidocaine can reduce countershock efficacy, i.e., increase the current and energy requirements for defibrillation. Experimental and clinical data suggest that the administration of lidocaine increases the propensity for asystole during cardiac arrest. CONCLUSIONS: While lidocaine may possess an antifibrillatory effect under experimental conditions, the clinical relevance of such an effect is questionable. If cardiac arrest occurs, lidocaine has limited utility and may be deleterious secondary to diminished countershock efficacy or lidocaine-induced asystole. Reconsideration of the use of lidocaine should be included in future guidelines for management of cardiac arrest.

Arrhythmias, Cardiac↗
PubMed1991

Limitations of the countershock dose response: a study of transthoracic current.

Dose response assessment of countershock efficacy has been widely determined with respect to energy but not current. The purpose of this study was to examine the utility of the dose response method in a current-based model of transthoracic defibrillation (pentobarbital anesthetized dogs, n = 8). Ventricular fibrillation induction lasting 15 seconds was separated by 5-minute intervals. Current defibrillation threshold (DFT; the lowest current that successfully defibrillated) was determined by decreasing current on successive trials. Energy DFT equaled the energy value of the corresponding current DFT. Subsequent data were expressed in normalized terms with each DFT assigned a normalized value of 1.00. Three shocks were delivered in random order at each of seven normalized current nodes (total of 21 shocks): 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 2.00 x DFT (early testing). Randomization was repeated, and a second set of 21 trials were performed (late testing). Composite plots were made relating normalized current and energy to the percent successful defibrillation. The dose response expressed in normalized energy demonstrated an overall shift to the left compared to current. The difference was significant at every node value below the estimated DFT. Ninety percent of successful trials with respect to current and energy occurred at or above 0.85 DFT and 0.55 DFT, respectively. Significant changes in impedance occurred between early testing (60 +/- 6 ohms) and late testing (47 +/- 5 ohms), n = 8, mean +/- SD. Current, compared to energy, is a more accurate parameter in the dose response assessment of transthoracic defibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Ventricular tachycardia during routine treadmill testing. Risk and prognosis.

Exercise-induced ventricular tachycardia during exercise testing is considered to increase risk during testing. Moreover, exercise-induced ventricular tachycardia has been considered to confer a poor prognosis although this has not been specifically studied. On a retrospective review of 3351 patients who had undergone routine clinical exercise testing between September 1984 and June 1989, we identified 55 patients with exercise-induced ventricular tachycardia. The mean follow-up was 26 months (range, 2 to 58 months). Fifty patients had nonsustained ventricular tachycardia during exercise testing and one of these patients died due to congestive heart failure during the follow-up period. Five patients had sustained ventricular tachycardia during exercise testing and one died suddenly 7 months after the test. Ventricular tachycardia was reproduced in only two of the 29 patients who underwent repeated exercise testing. Ventricular tachycardia during routine clinical exercise testing occurred rarely (prevalence of 1.5%) and was not associated with complications during testing. The total mortality in the exercise-induced ventricular tachycardia group (3.6%) was not significantly different from the mortality in the entire population (5.1%). Nonsustained ventricular tachycardia occurring during clinical exercise testing is not an independent marker of a poor prognosis.

Adult↗
PubMed1990

Effect of continuous intra-aortic balloon inflation in canine open chest cardiopulmonary resuscitation.

In a canine model of open chest CPR, the effect of continuous intra-aortic balloon (IAB) inflation on cerebral and myocardial perfusion was investigated utilizing hemodynamic and radioactive microsphere techniques of assessing regional blood flow. Compared to deflation, IAB inflation augmented the following variables, expressed as percentage of prearrest control: aortic systolic (50% to 71%) and aortic diastolic (40% to 58%) pressures during 30-sec inflations; and epicardial blood flow (BF) (44% to 57%), mesocardial BF (40% to 56%), endocardial BF (36% to 50%), carotid BF (32% to 51%), and cerebral BF (67% to 88%) during inflations of greater than 150 sec. IAB inflation had no effect on right atrial pressure; thus, estimated cerebral and myocardial perfusion gradients were augmented. IAB inflation may prove to be a beneficial adjunct to open chest CPR.

Animals↗
PubMed1990

Nature of defibrillation: determinism versus probabilism.

The gradual transitions that are found between unsuccessful and successful shock strengths in percent success or dose-response curves suggest that defibrillation is a probabilistic phenomenon. This concept appears to be reinforced by the fact that a frequency distribution is observed in defibrillation threshold data and that a dose-response relationship is also obtained by integration of the frequency distribution. The purpose of this study was to investigate whether a deterministic threshold model (based on experimental results) could produce 1) gradual transitions in dose-response curves, and 2) a threshold frequency distribution for individual subjects. In the experimental phase of the study, a linear deterministic relationship was found between transthoracic threshold current and defibrillation episode number (other variables held constant) in pentobarbital-anesthetized dogs. The correlation coefficient for each dog was between 0.77 and 0.98 (P less than 0.01), and both positive and negative slopes were found. Based on these results, threshold current was modeled for computer simulation as a linear function of episode number. The model was thus purely deterministic with no random variability. For each simulated experiment, several parameters were varied: order of shocks (increment, decrement, random order), slope of threshold function, and percent error of the initial threshold. Several hundred computer simulations were performed to determine the effect of varying these parameters. In all cases, threshold-frequency distributions and sigmoidal dose-response curves with gradual transitions were produced. The results of this investigation demonstrate that the apparent probabilistic behavior of defibrillation can be produced by a deterministic relationship.

Animals↗
PubMed1989

Patient response to variations in denture technique. Part VII: Twenty-year patient status.

Sixty-four patients were originally treated with complete dentures. Two different techniques, complex and standard, were used with 32 patients assigned to each group. Patients were recalled for their 20th year recall and 34 of the original 64 patients returned. Of those 34 patients, 26 patients were still wearing their original dentures. All 26 patients were judged by three project clinicians to have clinically acceptable dentures. In addition, all but two stated that their dentures were clinically acceptable. Neither of these patients were unhappy with fit, but with the esthetics. One patient had worn his denture teeth by pipe smoking and the other had bleached the pink out of her denture bases. The remaining eight patients who still participate in the project have had modifications in their original dentures or have had new dentures constructed.

Adult↗