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Biomedical subjects

W W Muir

Publications and source records attributed to W W Muir.

At least 217 records · Page 12Linked to original sources
PubMed1979

Hemodynamic and respiratory effects of xylazine-morphine sulfate in horses.

The cardiopulmonary effects of two xylazine-morphine sulfate drug combinations (mixtures) given IV were evaluated in horses. In horses given xylazine (0.66 mg/kg of body weight) and morphine sulfate (0.12 mg/kv) IV (experiment 1), there were significant (P less than 0.05) decreases in heart rate, cardiac output, and respiratory rate. Central venous pressure was significantly (P less than 0.05) increased. Arterial and pulmonary arterial blood pressures increased significantly (P less than 0.05) but transiently. Arterial blood gas tensions (PaCO2 and PaO2) and pH remained unchanged. In the horses given xylazine (0.66 mg/kg) and morphine sulfate (0.66 mg/kg) IV (experiment 2), the responses were qualitatively similar to those of experiment 1 horses, excluding lessened heart rate which was not significant). Horses in both experiments remained stationary and did not attempt to kick or strike for the duration of the experiment. Objective (trained personnel) and semiquantitative assessments of the analgesia in the horses during experiment 1 and those during experiment 2 indicated marked improvement in analgesia in the latter experiment.

Animals↗
PubMed1978

Effects of atropine on cardiac rate and rhythm in dogs.

Changes in cardiac rate and rhythm were determined in atropinized dogs prior to, during, and after anesthetic induction with thiamylal sodium and maintenance with 1% halothane in 50% nitrous oxide and 50% oxygen. The incidence of cardiac dysrhythmias and sinus tachycardia was significantly higher prior to and after anesthetic induction in dogs given atropine, compared with dogs not atropinized. Second-degree atrioventricular block was the most frequent dysrhythmia prior to anesthetic induction in atropinized dogs. Most cardiac dysrhythmias were detected during the anesthetic induction and early maintenance periods. The most common dysrhythmias during these periods were unifocal ventricular premature depolarizations and ventricular bigeminy.

Anesthesia, Inhalation↗
PubMed1978

Cardiac dysrhythmias associated with gastric dilatation-volvulus in the dog.

Of 16 dogs treated medically and surgically for gastric dilatation-volvulus, 11 developed electrocardiographic evidence of ventricular dysrhythmias. Seven of these dogs had ventricular dysrhythmias for the first time during their hospitalization after surgery. The ventricular dysrhythmias included ventricular premature depolarizations, slow ventricular rhythms, paroxysmal ventricular tachycardia, ventricular tachycardia, and multifocal ventricular tachycardia. Two of these dogs had electrocardiographic evidence of atrial premature depolarizations at the time of hospitalization. Treatment with lidocaine hydrochloride or procainamide hydrochloride was successful in reestablishing sinus rhythm in 9 of the 11 dogs with ventricular dysrhythmias.

Animals↗
PubMed1978

Echocardiography in swine.

Twelve clinically normal pigs were anesthetized with fentanyl citrate and sodium pentobarbital and placed in left lateral recumbency. M-mode echograms were recorded from the area of the 4th intercostal space with a 3.5 mmHz transducer. Changes in the internal minor axis diameter %deltaD were measured at 44.8 +/- 3.3 cm. An index of contractility (Vcf) was 1.12 +/- 0.16 cm/s. The caudal wall thickness dimension measured 0.61 +/- 0.04 cm and the aortic root dimension was 1.9 +/- 0.11 cm. To corroborate the echocardiographic findings, echocardiographic, cineangiographic, and postmortem studies were conducted on a 2nd group of 3 pigs. Aortic root, diastolic lumenal dimensions, and wall thickness were compared and the results never differed more than 2 mm. Echograms can conveniently be acquired from restrained, mature swine, and they provide useful, reliable structural and hemodynamic information, without the hazards or expense of invasive techniques.

Animals↗
PubMed1978

Evaluation of xylazine, guaifenesin, and ketamine hydrochloride for restraint in horses.

A combination of intramuscular xylazine plus intravenous guaifenesin and ketamine hydrochloride was evaluated as a method for chemical restraint and casting of the adult horse. This drug combination provided safe and rapid induction of the horse and uneventful recovery from lateral recumbency. Cardiopulmonary function remained within base-line values for the adult horse, although cardiac output, arterial blood pressure, and arterial partial pressure of oxygen were decreased from base-line values. Xylazine, guaifenesin, and ketamine hydrochloride provided safe induction to general anesthesia with the inhalation anesthetics halothane or enflurane. Respiratory rate was significantly lower and arterial carbon dioxide higher during maintenance anesthesia with enflurane than with halothane. Recovery from general anesthesia was more rapid after enflurane than after halothane anesthesia.

Anesthesia, Inhalation↗
PubMed1978

Cardiopulmonary effects of narcotic agonists and a partial agonist in horses.

The cardiopulmonary effects of the narcotic agonists morphine, meperidine, oxymorphone, and methadone and of the partial agonist pentazocine were examined in the pain-free adult horse. The drugs produced dysphoric followed by euphoric effects. Increases in heart rate, arterial blood pressure, and cardiac output were observed in all horses with all drugs. Arterial blood pressure remained increased even after heart rate and cardiac output had returned to base-line values. Respiratory rate generally remained unchanged or increased shortly after drug administration and then decreased insignificantly (P less than 0.05) below base-line values at later times. Arterial pH and blood gas values (Paco2, Pao2) did not change.

Animals↗
PubMed1978

Effects of furosemide on plasma volume and extracellular fluid volume in horses.

The effects of IV administered furosemide upon plasma volume (PV) and extracellular fluid volume were determined in horses at rest and after exercise. Serum sodium, potassium, chloride, and osmolality determinations were made. Furosemide caused a significant (P less than 0.05) decrease in PV and serum potassium concentrations in resting horses only. Furosemide's effects upon PV and electrolytes were evident longer than its hemodynamic effects.

Animals↗
PubMed1978

Plasma volume and extracellular fluid volume in horses at rest and following exercise.

Plasma volume and extracellular fluid volume were determined in horses at rest and immediately after a standardized exercise test. Exercising during training demonstrated no detectable effect on plasma or extracellular fluid volume determinations when compared with resting values. An explanation of this finding and an argument for the proper analysis of plasma and extravascular fluid volumes are presented.

Animals↗
PubMed1977

Electrocardiographic interpretation of thiobarbiturate-induced dysrhthymias in dogs.

The cardiac dysrhythmia occuring most commonly during intravenous administration of thiamylal sodium is ventricular bigeminy (ventricular premature depolarization coupled to the preceding sinus beat). Electrocardiographic tracings obtained during thiamylal-induced dyshythmias must be interpreted accurately if an accurate prognosis is to be give. Ventricular bigeminy seemed to originate in the ventricle, distal to the bundle of His. When ventricular premature depolarization was late in diastole, occuring simultaneiously with the next sinus-conducted impulse, a fusion beat resulted. The resultant ventricular bigeminy appeared as: (1) alternating ventricular premature dipolarizations, (2) an electrical alternans, and (3) alternating preexcitation syndrome. This dysrhythmia was associated with palpable alternating strong and weak frmoral arterial pulse. The likelihood that ventricular dysrhythmias will be caused by thiamylal is closely related to dose, concentration, and rate of administration. In a 23-month period, clinical occurrence of ventricular bigeminy during induction of anesthesia with thiamylal was approximately 4%.

Anesthesia, Intravenous↗
PubMed1977

Evaluation of xylazine and ketamine hydrochloride for anesthesia in horses.

The cardiopulmonary effects resulting from the combination of xylazine and ketamine hydrochloride were evaluated in the adult horse. Xylazine (1.1 mg mg/kg) administered intravenously prior to or simultaneously with ketamine hydrochloride (2.2 mg/kg; intravenous) provided excellent analgesia and light anesthesia in all horses. Cardiac output, arterial blood pressure, pulmonary arterial pressure, central venous pressure, and pulmonary arterial wedge pressure remained within normal limits for the adult horse. Evidence of respiratory acidosis developed with time during the anesthetic period. Induction and recovery from anesthesia appeared smooth and excitement-free. In the horse, larger dosages of ketamine hydrochloride (6.6 mg/kg) following sedation with xylazine (1.1 mg/kg; intravenous) were accompanied by muscular tremor and rigidity, mydriasis, oculogyric movements, sweating, hypertension, tachycardia, and increased rectal temperature during recovery from anesthesia. Providing there is good sedation from xylazine, the combination of xylazine and ketamine hydrochloride as a short-term intravenous anesthetic technique in the horse appears safe and acceptable providing reasonably stable cardiopulmonary function. If the sedative properties of xylazine are not apparent or if excessive dosages of ketamine hydrochloride are used, the drug combination results in serious side effects precluding its use for anesthesia in the horse.

Analgesia↗
PubMed1977

Effect of xylazine on indices of myocardial contractility in the dog.

Changes in cardiac contractility were assessed by 2 indices of myocardial contractile performance (dP/dt/Kp max, V max). Both indices demonstrated an initial positive inotropic response to intravenous administration of xylazine (1.1 mg/kg). This positive inotropic effect was followed by a return to or significant decrease from base-line recordings in these contractile indices at faster heart rates or later times following xylazine administration. In addition, an increase in heart rate in control dogs was accompanied by a rise in both dP/dt/Kp max and V max, confirming earlier evidence of the Bowditch staircase effect in the intact dog ventricle.

Animals↗
PubMed1977

Thiobarbiturate-induced dysrhythmias: the role of heart rate and autonomic imbalance.

Constantly coupled ventricular bigeminy in dogs can be elicited by intravenous boluses of thiamylal sodium. Properties of the bigeminal rhythm are similar to those produced by halothane or cyclopropane inhalation anesthetic-epinephrine-induced dysrhythmias. The mechanism responsible for the initiation of ventricular bigeminy, and perhaps most dysrhythmias in the dog during thiobarbiturate anesthesia, appears to be an imbalance between parasympathetic and sympathetic efferent activity. Moderate increases in arterial blood pressure and atrial rate augment the tendency for dysrhythmia production. Atropine was effective in abolishing ventricular bigeminy in most cases through overdrive suppression. Propranolol appeared to abolish ventricular bigeminal rhythms by suppression of sympathetic efferent activity without causing noticeable changes in arterial blood pressure.

Animals↗
PubMed1976

Hot film coronary artery velocity measurements in horses.

Coronary velocity measurements have been carried out in anaesthetized, open-chest horses using a constant-temperature, hot-film anemometer system. L-shaped needle probes inserted by direct vessel puncture have been used to measure velocity profiles in the left common, left anterior descending (LAD), and left circumflex coronary arteries. The flow conditions were characterized by peak Reynolds numbers from approximately 200 to 1500 and values of the unsteadiness parameter from 3 to 10. These measurements indicate that in the left common coronary artery the profile is in general skewed towards the outer wall as would be expected for fully viscous flow in a curved tube. In the left anterior descending and left circumflex coronary arteries just distal to the bifurcation, the skewing was found in general to be away from the flow divider. However, in regions of the LAD and left circumflex 5-6 diameters downstream of the bifurcation, the peak systolic and diastolic profiles were indicative of a more fully developed, Poiseuille type flow with only slight skewing observed. The results of this study indicate that the flow in the coronary system, though in general laminar and disturbance free, is extremely varied in character and may exhibit large amplitude, low frequency flow oscillations. Furthermore, for these vessels which all lie on the surface of the myocardium, large systolic flows were observed to be present, even though the major portion of the volume flow was reserved for the diastolic period.

Animals↗
PubMed1976

Estimation of cardiac output in the horse by thermodilution techniques.

An evaluation and comparison of thermodilution technique with dye dilution technique was made in the computation of cardiac output in 39 conscious adult horses (av body wt, 450 kg). Estimation of cardiac output by thermodilution was found to compare favorably with values obtained from dye dilution when a volume of 30 to 40 ml at a temperature of 0 C was used. Difficulties in obtaining accurate thermodilution curves in the horse seem predominantly associated with errors in mixing and observation.

Animals↗
PubMed1976

Systolic time intervals for left and right ventricles of swine.

Because swine are used often in cardiovascular research, and because systolic time intervals (durations of preejection and ejection) are useful in evaluating the ventricular function in health and disease and the effects of drugs on ventricular function, systolic time intervals for left and right ventricles were obtained from 12 healthy anesthetized shoats. Catheter-tip micromamonmeters were placed just distal to the semilunar valves, and pressure pulses from these positions in the ascending aorta and pulmonary trunk were simultaneously recorded with an electrocardiograph at paper speed of 200 mm/second on a photographic oscillograph. Equations of regression relating preejection period (PEP) and ejection time (ET) for the left ventricle (L) to heart rate (HR) are as follows: PEPL = 53 + 0.56 HR ETL = 329 -- 0.94 HR Systolic time intervals for the right ventricle did not relate to heart rate.

Animals↗
PubMed1976

Acute hemodynamic effects of furosemide administered intravenously in the horse.

Intravenous administration of furosemide in the horse resulted in an immediate and significant decrease in right atrial pressure, pulmonary arterial pressure, pulmonary arterial wedge pressure, cardiac output, and stroke volume (P less than 0.05). There was a significant increase in total systemic vascular resistance and heart rate (P less than 0.05). There were no significant alterations in mean arterial pressure. Coincidental with these hemodynamic changes were increased urine production and associated increase in packed cell volume and total serum protein. All variables except cardiac output, stroke volume, packed cell volume, and total solids returned to base line levels within 105 minutes after furosemide was injected. It is suggested that the effects of intravnously administered furosemide in the horse are transitory and dependent upon the decrease in plasma volume from diuresis.

Animals↗