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Biomedical subjects

W W Muir

Publications and source records attributed to W W Muir.

At least 127 records · Page 7Linked to original sources
PubMed1990

Atrial fibrillation in halothane- and isoflurane-anesthetized dogs.

Programmed electrical stimulation techniques were used to evaluate the effects of halothane and isoflurane on induction of atrial fibrillation in anesthetized dogs. Experiments were performed in 16 dogs anesthetized with alpha-chloralose. Critically timed premature stimuli were applied to the right atrial appendage and Bachmann bundle to determine the atrial fibrillation threshold, defined as the minimal current required to induce rapid, irregular atrial electrical activity of at least 8 seconds' duration. Atrial fibrillation thresholds were determined at baseline (0.0% inhalational anesthetic), 0.5 minimal alveolar concentration (MAC), and 1.0 MAC of halothane (n = 8) and isoflurane (n = 8). In the absence of inhalation anesthetic, it was significantly (P less than 0.01) easier to induce atrial fibrillation at the Bachmann bundle vs the right atrial appendage. Atrial fibrillation threshold at the Bachmann bundle was not affected by increasing concentrations of halothane, but was increased by 1.0 MAC of isoflurane (P less than 0.05). It was concluded that at 1.0 MAC isoflurane, but not halothane, has antifibrillatory effects in atrial tissue.

Anesthesia↗
PubMed1990

Cardiopulmonary effects of position in conscious cattle.

The cardiopulmonary effects of 4 positions (standing, right lateral, left lateral, and dorsal recumbency) were evaluated in conscious cattle in which no sedatives or anesthetic drugs were given. Each position was maintained for 30 minutes, during which time there were no significant changes in heart rate, respiratory rate, mean arterial blood pressure, arterial pH, PaCO2, arterial base excess, or venous blood gas values. Significant decreases in PaO2 developed when cattle were in lateral positions and dorsal recumbency. Cardiac index was unchanged in all positions, except in dorsal recumbency at 30 minutes, when it was significantly decreased.

Animals↗
PubMed1990

Hemolytic potential of guaifenesin in cattle.

The hemolytic effect on bovine red blood cells of 5%, 10%, and 15% guaifenesin solutions in 5% dextrose, 0.9% saline (NaCl), or distilled water was determined in vitro at 2 plasma concentrations (250 micrograms/ml, 500 micrograms/ml). A solution of 5% guaifenesin in a 5% dextrose solution or 5% guaifenesin in 0.9% saline produced minimal hemolysis in vitro. The amount of hemolysis of bovine red blood cells in vitro was related to the concentration of guaifenesin, diluent (5% dextrose, 0.9% NaCl, distilled water) and the plasma concentration of guaifenesin. In addition, plasma hemoglobin was determined in 4 adult dairy cows following the IV administration of 5% and 10% guaifenesin. These studies suggest that a solution of 5% guaifenesin in 5% dextrose is the most suitable solution for clinical use in cattle.

Animals↗
PubMed1990

Influence of tolazoline on caudal epidural administration of xylazine in cattle.

Eight adult female cattle (6 Holstein, 1 Jersey, 1 Brown Swiss) were used to determine the antagonistic effects of tolazoline, and alpha 2-adrenoceptor antagonist, on xylazine-induced (via caudal epidural administration) depression of CNS, respiratory, and cardiovascular activity and rumen motility. A 2% solution of xylazine HCl was injected into the epidural space at the first coccygeal interspace, using a dosage of 0.05 mg/kg of body weight, diluted to a 5-ml volume with sterile water, and administered at a rate of approximately 1 ml/30 s. Eight minutes after xylazine injection, either tolazoline (0.3 mg/kg) or saline solution (4 ml) was administered IV. All 8 cattle were treated, using both regimens in a random sequence; at least 1 week elapsed between treatments. Epidurally administered xylazine induced caudal analgesia (S3 to coccyx), as evaluated by no response to superficial and deep muscular pinprick, and induced sedation, cardiopulmonary depression, and inhibition of rumen motility, but all cattle remained standing. Tolazoline effectively reversed xylazine-induced rumen hypomotility, and partially antagonized xylazine-induced cardiopulmonary depression without affecting sedation and desirable local (S3 to coccyx) analgesic effects.

Animals↗
PubMed1990

Influence of 7% NaCl on the mechanical properties of the systemic circulation in the hypovolemic dog.

We examined the effects of hypertonic saline (7%) administration during hypovolemia in the anesthetized dog on the mechanical properties of the systemic circulation that constitute the major determinants of venous return. By using a right-heart bypass preparation in which venous return from the splanchnic and non-splanchnic vascular beds was isolated and drained into a common reservoir, venous resistance, venous compliance, and blood flow distribution measurements were made during control conditions and during a period of lowered systemic blood flow (30 min at a mean arterial pressure of 50 mm Hg). These measurements were repeated following hypertonic saline administration at the reduced and control levels of systemic blood flow. Hypertonic saline administration (8 ml/kg) produced an average increase in reservoir volume of 23 ml/kg and osmolality of 25.5 mOsm/kg. Changes in venous compliance, venous resistance, and blood flow distribution in response to hypertonic saline accounted for no more than 5% of the reservoir volume increase. Furthermore, plasma volume expansion estimated from hematocrit dilution suggests that hypertonic saline does not alter unstressed vascular volume. The most likely mechanism by which hypertonic saline enhances venous return is by plasma volume expansion and not by alterations of the mechanical properties of the systemic circulation.

Animals↗
PubMed1990

Caudal epidural analgesia induced by xylazine administration in cows.

Xylazine (0.05 mg/kg of body weight diluted to a 5-ml volume, using 0.9% NaCl) or 5 ml of 0.9% NaCl was administered epidurally into the first caudal intervertebral space (Co1-Co2) in 8 cows (mean +/- SD body weight, 583 +/- 150 kg). Cows were observed for responses to deep needle pricking of the caudal dermatomes (S3 to Co), sedation, and ataxia. Heart rate, respiratory rate, body temperature, rate of ruminal contractions, coccygeal arterial blood pressure, pHa, blood gas tension (PaO2, PaCO2), base excess, total solids concentration, and PCV were determined before and after xylazine administration. Epidurally administered xylazine induced sedation and selective (S3 to Co) analgesia for at least 2 hours. Mild ataxia of hind limbs was observed in 6 cows, but all cows remained standing. Heart rate, respiratory rate, rate of ruminal contractions, arterial blood pressure, PaO2, PCV, and total solids concentration were significantly (P less than 0.05) decreased, and PaCO2, base excess, and bicarbonate concentration were significantly (P less than 0.05) increased after xylazine administration. Epidurally administered 0.9% NaCl did not alter sensory perception to needle pricking and did not affect any of the physiologic variables determined. Although epidural administration of xylazine induced analgesia and sedation in healthy cows, it should be avoided for epidural analgesia in cattle with heart disease, lung disease, and/or gastrointestinal disease because of its potent cardiopulmonary and ruminal depressant effects.

Analgesia, Epidural↗
PubMed1990

Changes in coagulation and fibrinolysis in horses during exercise.

Changes in clotting time (CT) and fibrinolytic activity (FA) were evaluated in 6 mature, female horses during exercise. Two trials were performed on consecutive days, using a randomized crossover design. Each mare was assigned to either an exercise trial or a control trial on the first day, and to the alternate trial 24 hours later. Mares exercised for 20 minutes on a treadmill at an elevation of 2 degrees and a velocity of 5 m/s. Venous blood samples were collected immediately before exercise, at 4, 8, 12, 16 and 20 minutes during exercise, and 15 minutes after cessation of exercise. Blood was placed into plain glass tubes for determination of CT, and into chilled, citrated tubes for determination of FA, plasminogen/plasmin complex activity (PLG), one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), and antithrombin-III (AT-III) activity. There were significant differences (P less than 0.05) between the control and exercise groups for CT, FA, and PLG. During exercise, clotting time decreased from 21.5 +/- 1.6 minutes to 9.9 +/- 1.6 minutes (mean +/- SD; P less than 0.05), without significant changes in OSPT, APTT, or AT-III. Fibrinolytic activity and PLG increased (P less than 0.05) during exercise. Changes in CT, FA, and PLG were significant at 4 minutes of exercise, remained altered until the end of exercise, and returned to baseline values by 15 minutes of recovery. Clotting time, OSPT, APTT, FA, AT-III, and PLG did not change (P greater than 0.05) during control trials.

Animals↗
PubMed1990

Ventricular arrhythmogenic dose of epinephrine in dogs and cats anesthetized with tiletamine/zolazepam and halothane.

The ventricular arrhythmogenic dose of epinephrine (ADE) was determined in 6 dogs anesthetized with halothane alone or with halothane after injection of tiletamine/zolazepam (TZ). Respiratory rate and tidal volume were controlled and sodium bicarbonate was administered to maintain arterial pH and blood gas values within reference range. Heart rate and arterial blood pressure were recorded during determination of the ADE. The ADE (mean +/- SD) was no different during anesthesia with use of halothane alone (8.9 +/- 4.3) than it was when injections of TZ preceded administration of halothane (6.7 +/- 2.8). Tiletamine/zolazepam was also administered IV immediately after determination of the ADE during halothane-induced anesthesia. The TZ administered in this manner did not alter the ADE. Blood pressure and heart rate were significantly greater during infusion of epinephrine than immediately prior to infusion. The administration of TZ did not alter blood pressure response. The ADE was also determined in 6 cats anesthetized with halothane preceded by administration of TZ. The ADE (mean +/- SD) was 0.7 +/- 0.23 micrograms/kg, a value similar to that reported for cats during anesthesia with halothane alone.

Anesthesia, Inhalation↗
PubMed1989

Side effects of etomidate in dogs.

Intravenous administration of etomidate, a nonbarbiturate sedative hypnotic, induced excitement, myoclonus, pain on injection, vomiting, and apnea during induction of anesthesia in 20 experimental dogs and 70 hospitalized dogs. The dogs had excitement and purposeless muscle movements during recovery from anesthesia. The frequency and severity of the side effects were markedly attenuated or eliminated by the administration of diazepam, acepromazine, or morphine prior to etomidate administration.

Acepromazine↗
PubMed1989

Tourniquet-induced hypertension in a horse.

Arterial hypertension developed in a horse anesthetized for arthroscopy and lavage of an inflamed right carpal joint. Anesthesia was induced with xylazine HCl, butorphanol, guaifenesin, and thiamylal Na and was maintained with halothane in oxygen. Arterial hypertension and tachycardia developed within 15 minutes after a pneumatic tourniquet was placed 8 to 10 cm proximal to the right carpus and inflated to 800 mm of Hg. The surgical procedure was expedited, halothane was discontinued and anesthesia was maintained with guaifenesin to facilitate bandaging. Heart rate decreased from 72 to 42 beats/min after the tourniquet cuff was deflated. Mean arterial pressure decreased from 260 mm of Hg to 128 mm of Hg. Differential diagnosis for a rapidly increasing arterial pressure during halothane anesthesia include inadequate plane of anesthesia, signs of pain, hypercapnia, hypoxemia, and/or hyperthermia.

Anesthesia↗
PubMed1989

Brain hypoperfusion post-resuscitation.

Post-resuscitation brain hypoperfusion is an all too common problem following successful CPR in dogs and cats. The deterioration of neurologic status may occur, regardless of the clinician's ability to restore and maintain heart rate and rhythm, mucous membrane color, capillary refill time, and arterial blood pressure. New insight has been gained into the mechanisms responsible for post-resuscitation brain hypoperfusion, which has improved current treatment regimens and the development of new therapeutic modalities. Proper use of fluids (isotonic or hypertonic saline, oncotic solutions), diuretics, corticosteroids, and sedatives, combined with appropriate CPR techniques, can improve outcome. New drugs and therapeutic techniques offer exciting potential for the future limitation of this problem.

Animals↗
PubMed1989

Hemodynamic and electrophysiologic effects of disopyramide enantiomers in a canine blood superfusion model.

The use of disopyramide is often limited because of adverse hemodynamic or electrophysiologic side effects. We compared the S(+) and R(-) enantiomers of disopyramide to the clinically used racemic mixture in a canine blood superfusion model. Eighteen support animals (group I) provided extracorporeal blood superfusion of isolated canine cardiac Purkinje fibers. Following administration of 2 mg/kg disopyramide intravenously (i.v.) [S(+), R(-), or racemic] hemodynamic and electrocardiographic parameters were temporally assessed in the support animals while simultaneous cellular electrophysiologic effects were recorded from the blood-superfused Purkinje fibers. An additional 13 animals (group II) underwent extended hemodynamic and pharmacokinetic analysis without the external atrioventricular (AV) shunt required for blood superfusion. Mean peak serum concentrations of racemic disopyramide and its enantiomers were similar (2.7 to 3.1 mg/L), but clearance was stereo-specific [half-life (t1/2) of 1.99 h for S(+) vs. 2.79 h for R(-) disopyramide]. Left ventricular (LV) function was impaired following drug administration, irrespective of optical rotation (cardiac output decreased by 20.8%, LV dP/dtmax decreased by 22.4%). Depression of phase 0 Vmax of the Purkinje fiber action potential was also nonstereo-dependent. S(+) disopyramide prolonged the QTC interval by 11.5% and increased terminal action potential duration (APD75) and effective refractory period (ERP) by 21.2 and 19.0%, respectively. R(-) disopyramide slightly increased the QTC interval (+2.3%) but decreased APD75 and ERP by 8.9 and 6.8%, respectively. The effect of racemic disopyramide on repolarization indexes was intermediate to that of its enantiomers. These data support nonstereodependent depression of both myocardial contractility and sodium channel conductance by disopyramide. Changes in APD and refractoriness were dependent on stereochemical configuration.

Animals↗
PubMed1989

Effects of halothane and isoflurane on baroreflex sensitivity in horses.

Baroreflex sensitivity (BS) was used to quantitatively assess the effects of halothane and isoflurane on the heart rate/arterial pressure relationship during steady-state (10 minutes) and dynamic pressure changes in adult horses. Arterial pressure was decreased in response to nitroglycerin or sodium nitroprusside and increased in response to phenylephrine HCl. Mean (+/- SEM) BS in awake horses was 28.9 +/- 2.6 and 13.2 +/- 2.0 ms/mm of Hg during steady-state decreases and increases in systolic arterial pressure (SAP), respectively. Halothane and isoflurane either significantly (P less than 0.05) decreased or eliminated BS during steady-state decreases in SAP, with no significant differences detected between anesthetic agents. During steady-state decreases in SAP, significant (P less than 0.05) correlation between R-R interval and arterial pressure was not observed for 6 of 10 and 4 of 11 halothane and isoflurane anesthesia periods, respectively. Halothane significantly (P less than 0.05) decreased BS during steady-state increases in SAP to 7.9 +/- 0.6 and 6.5 +/- 1.1 ms/mm of Hg during low and high minimal alveolar concentration (MAC) multiples, respectively. Isoflurane decreased BS during steady-state increases in SAP to 9.6 +/- 1.5 and 6.6 +/- 1.1 ms/mm of Hg during low and high MAC anesthesia, respectively, with high MAC of isoflurane decreasing BS significantly (P less than 0.05), compared with awake and low MAC values. Plasma catecholamine (epinephrine and norepinephrine) concentrations increased significantly (P less than 0.05), compared with baseline values during steady-state vasodilator infusions in halothane- and isoflurane-anesthetized horses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Small-volume resuscitation with hypertonic saline solution in hypovolemic cats.

We evaluated the hemodynamic effects of IV and intraaortic (aortic root) administration of 7.5% NaCl solution on hemodynamics in anesthetized cats with severe hypovolemia. Hypovolemic shock was induced by exsanguinating cats to a mean arterial blood pressure of 50 mm of Hg, which was maintained for 30 minutes prior to treatment. Shed blood volume was 38.4 +/- 2.1 ml/kg of body weight. The cats were treated with a small volume (4 ml/kg) of 0.9% NaCl solution IV, 7.5% NaCl solution IV, or 7.5% NaCl solution administered into the aortic root. The IV administration of 0.9% NaCl solution did not improve hemodynamics. The IV administration of 7.5% NaCl solution induced rapid restoration of arterial blood pressure, aortic blood flow, and cardiac contractility. Total peripheral vascular resistance decreased. The administration of 7.5% NaCl solution into the aortic root induced a further deterioration in hemodynamics resulting in death in 3 cats and a marked improvement in hemodynamics similar to that observed after IV administration of 7.5% NaCl solution in 2 cats. The duration of the beneficial hemodynamic effects after IV or intra-aortic administration of 7.5% NaCl solution did not exceed 60 minutes. Results of these studies suggested that either the IV or intra-aortic administration of 7.5% NaCl solution in cats can induce beneficial hemodynamic effects that may be of value in the field resuscitation of hypovolemic patients.

Animals↗
PubMed1989

Hemodynamic effects of high-frequency oscillatory ventilation in halothane-anesthetized dogs.

Hemodynamic effects of spontaneous ventilation, intermittent positive-pressure ventilation (IPPV), and high-frequency oscillatory ventilation (HFOV) were compared in 6 dogs during halothane anesthesia. Anesthesia was induced with IV thiamylal Na and was maintained with halothane (end-tidal concentration, 1.09%). During placement of catheters, dogs breathed spontaneously through a conventional semiclosed anesthesia circuit. Data were collected, and dogs were mechanically ventilated, using IPPV or HFOV in random order. Ventilation was adjusted to maintain PaCO2 between 38 and 43 mm of Hg during IPPV and HFOV. Cardiac index, aortic blood pressure, and maximum rate of increase of left ventricular pressure were significantly (P less than 0.05) less during HFOV than during spontaneous ventilation, whereas right atrial and pulmonary artery pressure were significantly greater during HFOV than during spontaneous ventilation. During IPPV, only the maximum rate of increase of left ventricular pressure was significantly less than that during spontaneous ventilation.

Anesthesia↗
PubMed1989

Xylazine and tiletamine-zolazepam anesthesia in horses.

The cardiopulmonary and anesthetic effects of xylazine in combination with a 1:1 mixture of tiletamine and zolazepam were determined in 6 horses. Each horse was given xylazine IV or IM, as well as tiletamine-zolazepam IV on 4 randomized occasions. Anesthetics were administered at the rate of 1.1 mg of xylazine/kg of body weight, IV, 1.1 mg of tiletamine-zolazepam/kg, IV (treatment 1); 1.1 mg of xylazine/kg, IV, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 2); 1.1 mg of xylazine/kg, IV, 2.2 mg of tiletamine-zolazepam/kg, IV (treatment 3); and 2.2 mg of xylazine/kg, IM, 1.65 mg of tiletamine-zolazepam/kg, IV (treatment 4). Tiletamine-zolazepam doses were the sum of tiletamine plus zolazepam. Xylazine, when given IV, was given 5 minutes before tiletamine-zolazepam. Xylazine, when given IM, was given 10 minutes before tiletamine-zolazepam. Tiletamine-zolazepam induced recumbency in all horses. Duration of recumbency in group 1 was 31.9 +/- 7.2 (mean +/- 1 SD) minutes. Increasing the dosage of tiletamine-zolazepam (treatments 2 and 3) significantly (P less than 0.05) increased the duration of recumbency. Xylazine caused significant (P less than 0.05) decreases in heart rate and cardiac output and significant (P less than 0.05) increases in central venous pressure and mean pulmonary artery pressure 5 minutes after administration. Respiratory rate was decreased. Arterial blood pressures increased significantly (P less than 0.05) after xylazine was administered IV in treatments 1 and 3, but the increases were not significant in treatment 2. Xylazine administered IM caused significant (P less than 0.05) increases in central venous pressure and significant (P less than 0.05) decreases in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Intravenous↗
PubMed1989

Isoproterenol- and salbutamol-induced relaxation of acetylcholine- and histamine-induced contraction of equine trachealis muscle in vitro.

Strips of trachealis muscle were dissected from the midcervical portion of the trachea of horses that were free of respiratory tract disease, and the overlying epithelium and mucosa were removed. Muscle strips were suspended in tissue baths that were filled with Krebs-bicarbonate solution, aerated with 5% CO2 in oxygen and maintained at 37 C. Isometric tension was continuously recorded. The increase in active isometric tension was concentration dependent when acetylcholine (10(-9) to 10(-4) M) or histamine (10(-9) to 10(-4) M) was added to the tissue baths in 0.5-logarithmic increments. When the tissues were contracted with acetylcholine (3.1 x 10(-6) M) or histamine (10(-4) M), the decrease in active isometric tension was concentration dependent when isoproterenol (10(-9) to 10(-4) M) or salbutamol (10(-9) to 10(-4) M) was added to the tissue baths in 0.5-logarithmic increments. There was no difference between the response to isoproterenol and salbutamol when tissues from the same horses were compared whether the tissues were contracted in response to acetylcholine (3.1 x 10(-6) M) or histamine (10(-4) M). Relaxation was antagonized by 10(-6) M propranolol. The degree of relaxation obtained in these muscle strips was considerably less than that reported from other species' tracheal muscle strips that had the epithelium and mucosa intact. We concluded that equine tracheal smooth muscle contains beta-adrenoceptors that can be stimulated by either a mixed beta-1, beta-2 agonist or a selective beta-2 agonist.

Acetylcholine↗