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Biomedical subjects

W W Muir

Publications and source records attributed to W W Muir.

At least 235 records · Page 13Linked to original sources
PubMed1976

Effects of training on resting and postexercise ECG in standardbred horses, using a standardized exercise test.

Five healthy, mature, previously trained Standardbred horses were given no exercise (left in a stall) for 4 months, then jogged (slow exercise) for 3 weeks, and placed in a 6-week training period. Cardiac variables were measured at the beginning of training and after 14, 20, 35, and 42 days of training before and at 10, 15, 20, 25, and 30 minutes after a 1.8-km (in 3:12 +/- 2 seconds) standard, submaximal exercise test on a deep 0.53-km track. There was no significant change during the 6-week conditioning period in the following variables at rest or at any of the times observed during recovery from test exercise: heart rate, PQ-interval, QRS-duration, QT-interval, and ratio of electrical systole to diastole. It appeared that measuring heart rate by electrocardiogram at rest and during recovery from execise is not of significance in evaluating the fitness in the previously trained adult horse.

Animals↗
PubMed1975

Ventilatory alterations in normal horses in response to changes in inspired oxygen and carbon dioxide.

The influence of various concentrations of CO2 and O2 in the inspired gases on minute volume (V), tidal volume (VT), and respiratory rate (breaths per min; BPM) was examined in nonanesthetized, nonsedated normal horses. The VT and BPM increased linearly in response to increases in inspired CO2 concentration and curvilinearly in response to decreases in inspired Os concentration. The V increased curvilinearly in response to both increases in inspired CO2 concentration and decreases in inspired O2 concentration.

Animals↗
PubMed1975

Effects of xylazine and acetylpromazine upon induced ventricular fibrillation in dogs anesthetized with thiamylal and halothane.

Ventricular arryhythmias including ventricular fibrillation were produced with epinephrine in dogs induced to an anesthetic state with thiamylal and maintained with halothane. In dogs given (premedicated) xylazine 20 minutes prior to anesthesia, ventricular arrhythmias, including ventricular fibrillation, were induced with much smaller doses of epinephrine than in nonpremedicated dogs. Dogs premedicated with acetylpromazine 20 minutes prior to anesthesia with thiamylal and halothane displayed protection from epinephrine-induced arrhythmias. Caution is advised from using xylazine in the presence of halothane if epinephrine is to be administered.

Anesthesia↗
PubMed1975

Effects of acetylpromazine on ventilatory variables in the horse.

The influence of breathing various concentrations of carbon dioxide and oxygen upon minute volume, tidal volume, and respiratory rate were examined in acetylpromazine-tranquilized horses. Responses in the horses before (control period) and after tranquilization were qualitatively similar to increases in carbon dioxide and to alterations in oxygen. The quantitative responses to these changes were less in tranquilized horses than in the same horses studied in the untranquilized state. Tranquilization had its most prominent effect upon respiratory rate in horses breathing room air.

Acepromazine↗
PubMed1975

Pulmonary arterial wedge pressures: blood gas tensions and pH in the resting horse.

Blood pressure recordings were made from right atrium, right ventricle, pulmonary trunk, and pulmonary arterial "wedge" positions in the standing, resting, adult horse. Similarly, comparisons were made of blood samples collected from these vascular positions, as well as from jugular vein and carotid artery. A consistently lower partial pressure of carbon dioxide and a greater partial pressure of oxygen and pH were found in blood samples from pulmonary arterial wedge than from carotid artery. A technique for safe and rapid collection of pulmonary trunk and pulmonary arterial wedge blood gases, pH, and pressure data, using a balloon-tipped flow-directed catheter, is described in the nonsedated, nontranquilized, resting, adult horse.

Animals↗
PubMed1975

Antiarrhythmic effects of diazepam during coronary artery occlusion in dogs.

The ventral interventricular branch of the left coronary artery was ligated in a 2-step operation in 10 dogs whose electrocardiograms and systemic arterial blood pressures were then monitored during the next 7 days. Monitoring was done in awake dogs given 1 mg of diazepam per kilogram of body weight (intravenously administered in 3 dogs and orally in 7). Because ventricualr ectopic activity was greatest during the interval of 10 to 48 hours after ligation, the antiarrhythmic activity of diazepam was recorded during this 38-hour interval. After administration of diazepam by either route, frequency of ventricular ectopic beats decreased from 98 to 80%. THIS REDUCTION BETAN IMMEDIATELY AFTER THE INTRAVENOUS ADMINISTRATION AND PERSISTED FOR ONLY 5 MINUTES; REDUCTION BEGAN APPROXIMATELY 1 HOUR AFTER THE ORAL ADMINISTRATION AND PERSISTED 4 TO 6 HOURS. Systemic arterial blood pressure decreased only after the intravenous administration. It is concluded that diazepam is effective in reducing the frequency of ventricular ectopic activity after occlusion of major branches of coronary arteries, that diazepam works independent of alterations in systemic arterial blood pressure, and that orally administered diazepam prolongs antiarrhythmic activity. Possibly, the adjuvants present in the parenteral form of diazepam reduce antiarrhythmic activity by being, themselves, arrhythmogenic.

Administration, Oral↗
PubMed1975

Arrhythmias in dogs associated with epinephrine and thiamylal anesthesia.

Sinus tachycardia bigeminy, ventricular rhythm, ventricular tachycardia, and ventricular fibrillation are produced by relatively small intravenous doses of epinephrine in nonanesthetized dogs and in dogs anesthetized with thiamylal sodium. Origin of the abnormal beat in coupled bigeminal rhythms generated from the bundle o of His or above. Increases in arterial blood pressure may predispose to arrhythmia formation during thiamylal anesthesia.

Anesthesia, Intravenous↗
PubMedDate not supplied

The effects of a hemoglobin-based oxygen carrier (HBOC-301) on left ventricular systolic function in anesthetized dogs.

OBJECTIVE: To evaluate the effects of a hemoglobin-based oxygen carrier (HBOC-301) on left ventricular preload, afterload, contractility, and ventriculo-arterial coupling in anesthetized dogs. STUDY DESIGN: A prospective experimental study. ANIMALS: Seven adult male dogs weighing 2.3 to 2.7 kg. METHODS: The study was performed on intact, closed-chest, chloralose-anesthetized dogs. Heart rate, left ventricular end-systolic and end-diastolic volume and pressure, cardiac output, stroke volume, blood resistivity, mean arterial pressure (MAP), dP/dtmax, end-systolic elastance (Ees), systemic vascular resistance (SVR), effective arterial elastance (Ea), left ventricular-arterial coupling (Ees/Ea), and myocardial oxygen consumption (MVO2) were determined during a 90-minute infusion of 30 mL/kg (20 mL/kg/h) of HBOC-301 and for 90 minutes thereafter. RESULTS: The administration of HBOC-301 significantly decreased packed cell volume, blood resistivity, heart rate, cardiac output, and dP/dtmax and significantly increased left ventricular end-diastolic and end-systolic pressure, MAP, and SVR. The Ea, Ees, Ees/Ea and MVO2 did not change. CONCLUSIONS: HBOC-301 produced insignificant changes in load independent indexes of cardiac performance (Ees, E, Ees/Ea) in anesthetized dogs. The collective directional changes in these variables, however, in conjunction with significant increases in SVR were most likely responsible for a decrease in cardiac output. Increases in SVR and the volume load (30 mL/kg) contributed to increases in left ventricular end-diastolic pressure. CLINICAL RELEVANCE: HBOC-301 infusion should be monitored and administered cautiously to dogs with poor ventricular function.

Anesthetics, Intravenous↗
PubMedDate not supplied

Effects of tricyclic antidepressant drugs on the electrophysiological properties of drug Purkinje fibers.

Microelectrode techniques were used to study the electrophysiologic effects of the tricyclic antidepressant (TCA) drugs imipramine , amitriptyline, doxepin, desipramine, protriptyline, and nortriptyline on isolated Tyrode's ([K +]o= 4.0 mM) superfused dog Purkinje fibers. Drug concentrations ranged from 10(-7) to 10(-5) M. TCA drug concentrations greater than 10(-6) M resulted in decreases in action potential amplitude, duration, and maximum slope of phase O (Vmax). Simultaneously with decreases in action potential duration, the effective refractory period decreased. In addition, the voltage time course of repolarization between proximally and distally recorded action potentials became less obvious. Imipramine, doxepin, protriptyline, and nortriptyline (10(-6), 10(-5) M) depressed membrane responsiveness. Superfusion of dog Purkinje fibers with 10(-5) M concentrations of TCA drugs resulted in conduction delay, postrepolarization refractoriness and, occasionally, total inexcitability. TCA drugs caused an increase in escape time and a decrease in spontaneous rate of spontaneously automatic Purkinje fibers equilibrated with epinephrine (10(-7) M) in 5 X 10(-5) M EDTA. Imipramine, doxepin, protriptyline, and nortriptyline abolished extra nondriven action potentials, and diminished oscillatory afterpotentials in dog Purkinje fibers exposed to toxic concentrations of ouabain (2 X 10(-7) M).

Action Potentials↗
PubMedDate not supplied

Electrophysiological effects of cyclic GMP on canine cardiac Purkinje fibers.

The effect of cyclic 3'5'-guanosine monophosphate (8-bromo-cGMP) on action potential characteristics was investigated. Standard microelectrode techniques were used to study the effects of 8-bromo-cGMP on canine cardiac Purkinje fibers in vitro. Canine Purkinje fiber tissue preparations were exposed to increasing concentrations of 8-bromo-cGMP (10(-6), 10(-5), 10(-4) M). The action potential duration at 50% (APD50) and 90% (APD90) repolarization, resting membrane potential (RMP), action potential amplitude (APA), rate of rise of phase 0 (Vmax), spontaneous rate (SR), escape time (ET), and effective refractory period (ERP) did not change at these concentrations of 8-bromo-cGMP. The effect of 8-bromo-cGMP on isoproterenol (10(-7) M) treated Purkinje fibers was tested. Predictably, isoproterenol shortened APD and ERP and increased SR. APD or ERP shortening was not affected by 8-bromo-cGMP, but the increase in SR produced by isoproterenol was prevented. Eleven of sixteen Purkinje fiber preparations treated with isoproterenol alone became spontaneously arrhythmic, whereas none of six treated with 8-bromo-cGMP and isoproterenol became arrhythmic (p less than 0.05). Slow-response action potentials elicited by potassium depolarization and catecholamines were abbreviated and eventually abolished by 8-bromo-cGMP. In conclusion, 8-bromo-cGMP has no effect on action potential characteristics in normally polarized canine Purkinje fibers but depressed slow response action potentials. The effects of isoproterenol on SR are antagonized and the production of arrhythmias in this model are prevented by 8-bromo-cGMP.

Action Potentials↗
PubMedDate not supplied

Antiarrhythmic effects of flecainide against canine ventricular arrhythmias induced by two-stage coronary ligation and halothane-epinephrine.

We studied the electrophysiologic effects of flecainide on noninfarcted and infarcted dog hearts and in dogs anesthetized with halothane and administered intravenous epinephrine. Flecainide demonstrated no effect on atrial conduction times, but significantly (p less than 0.05) increased ventricular conduction times in noninfarcted, infarcted, and halothane-epinephrine-exposed dog hearts. Atrial and ventricular effective refractory periods (ERPs) were significantly (p less than 0.05) increased by flecainide. The increase in ERP was more pronounced in infarcted than in noninfarcted dog hearts. Flecainide significantly (p less than 0.05) decreased the echo zone for two or more repetitive ventricular responses in infarcted dog hearts and eliminated all ventricular arrhythmias observed at 48 h after coronary artery ligation. The dose of epinephrine required to induce ventricular arrhythmias in dogs anesthetized with halothane was significantly increased (p less than 0.05) by flecainide. Acute intravenous administration of flecainide to dogs with infarcted hearts produced sinus arrest, transient third-degree heart block, inability to pace, right bundle branch block, and torsade des pointes. Our results provide evidence that flecainide produces its antiarrhythmic effects by increased ventricular ERP and ventricular conduction time. Caution is advised when administering flecainide to patients with previous history of myocardial infarction.

Animals↗
PubMedDate not supplied

Cardiovascular effects of intravenous sodium penicillin, sodium cefazolin, and sodium citrate in awake and anesthetized horses.

Sodium penicillin, sodium cefazolin, and sodium citrate were administered to six adult horses on separate occasions, when awake and during anesthesia. The order of administration was randomized and studies were separated by a minimum of 7 days. Arterial blood pressure decreased significantly (less than 0.05) from control 5 minutes after intravenous (IV) sodium penicillin in awake and anesthetized horses. Systolic arterial blood pressure remained significantly (less than 0.05) decreased 10 minutes after IV sodium penicillin in anesthetized horses. Sodium cefazolin and sodium citrate did not significantly affect any of the measured cardiovascular variables. Although the changes in arterial blood pressure were small (8-15 mm Hg), monitoring of arterial blood pressure is advised when sodium penicillin is administered IV to anesthetized horses.

Anesthesia, General↗
PubMedDate not supplied

Cardiorespiratory effects of the intravenous administration of tiletamine-zolazepam to cats.

The hemodynamic and respiratory effects of three doses (9.7, 15.8, and 23.7 mg/kg intravenous [IV]) of a 1:1 combination of tiletamine and zolazepam were studied after isoflurane anesthesia in cats instrumented for the recording of hemodynamic data. Systolic, mean, and diastolic arterial blood pressures were decreased 1 minute after drug administration but then increased above baseline with all three doses. Cardiac output was decreased briefly at 1 minute with the 15.8 and 23.7 mg/kg doses. The rate of development of left ventricular pressure and peripheral vascular resistance decreased at 1 minute but returned to baseline or above by 10 minutes. There were no significant changes in heart rate, central venous pressure, or left ventricular end diastolic pressure. The arterial pH and blood gas measurements reflected the development of respiratory acidosis after administration of 23.7 mg/kg. These results support the conclusions that tiletamine-zolazepam administered intravenously is a useful and comparatively safe anesthetic agent in the cat.

Anesthesia↗
PubMedDate not supplied

Cardiorespiratory effects of the intravenous administration of tiletamine-zolazepam to dogs.

The anesthetic, hemodynamic, and respiratory effects of an intravenously administered 1:1 combination of tiletamine and zolazepam were evaluated in dogs. Each dog received tiletamine-zolazepam (6.6, 13.2, 19.8 mg/kg) on two occasions, once when awake and a second time with residual isoflurane anesthesia while instrumented for the recording of hemodynamic data. Tiletamine-zolazepam administered to conscious dogs resulted in good, rapid induction of anesthesia. Time to sternal recumbency (recovery) was dose-dependent. Character of recovery tended to be better with the lower dose. Tiletamine-zolazepam caused significant increases in heart rate after all doses and significant increases in cardiac output after the two larger doses. All doses caused significant decreases in arterial blood pressure at 1 minute. Arterial blood pressures returned to baseline and then increased significantly above baseline values. The rate of development of left ventricular pressure was significantly decreased 1 minute after the two higher doses, returned to normal, and then was significantly increased above baseline for all doses. Peripheral vascular resistance increased transiently 1 minute after the 6.6 mg/kg dose. Peripheral vascular resistance decreased significantly after the 13.2 and 19.8 mg/kg doses. Minute ventilation was significantly decreased only after the 19.8 mg/kg dose.

Anesthesia, Intravenous↗
PubMedDate not supplied

Effects of acute hyperventilation on serum potassium in the dog.

The effects of increasing respiratory rates on arterial pH, PaCO2, HCO3, and potassium (K) were measured in normal anesthetized dogs. Hyperventilation resulted in increased pH, decreased PaCO2, decreased HCO3, and decreased K compared with those parameters in spontaneously breathing dogs. The changes were related quantitatively: each 10 mmHg decrease in PaCO2 was associated with a pH increase of 0.1, a HCO3 decrease of 2.0 mEq/L, and a K decrease of 0.4 mEq/L. There were no cardiac arrhythmias or clinical signs of hypokalemia. After termination of hyperventilation, serum K was slower to return to control values than PaCO2. The ratio of the duration of hyperventilation to the time required for return of serum K to control was 0.67.

Acid-Base Imbalance↗