Search PubMed⌕ Search

Biomedical subjects

W W Muir

Publications and source records attributed to W W Muir.

At least 145 records · Page 8Linked to original sources
PubMed1989

Epithelium- and mucosa-dependent relaxation and contraction of normal equine trachealis muscle in vitro.

Strips of trachealis muscle were dissected from the mid-cervical portion of the trachea from horses that were free of respiratory tract disease. The epithelium and mucosa were removed from one group of tissues and were left intact in a second group of tissues. Each tissue was suspended in a bath filled with Krebs-bicarbonate solution that was aerated with 5% CO2 in oxygen and maintained at 37 degrees C. Isometric tension was continuously recorded. The contractile response to square-wave electrical stimulations increased as frequency (3, 5, 10, 15, 20, 25, and 30 Hz), voltage (10, 15, 18, and 25 V), and pulse duration (0.2, 0.5, 1.0, 1.5, and 2.0 ms) increased in tissues with the epithelium and mucosa intact. A stimulus of 18 V, 20 Hz, and 0.5 ms induced maximal contraction. Atropine (10(-6) M) abolished the response to 18 V and 0.5 ms at all frequencies. The increase in active isometric tension was concentration dependent when acetylcholine (10(-9) to 10(-4) M) was added to the baths in 0.5-logarithmic increments. Tissues that were contracted in response to acetylcholine (10(-5) M) had a concentration-dependent decrease in active isometric tension when isoproterenol was added to the baths in 0.5-logarithmic increments (10(-9) to 10(-4) M). The contraction and relaxation curves were qualitatively similar, but quantitatively different in tissues with and without the epithelium and mucosa. Removing the epithelium and mucosa increased the contractile response to acetylcholine at bath concentrations of 3.1 x 10(-7) M and 10(-6) M. The presence of epithelium and mucosa enhanced the magnitude of isoproterenol-induced relaxations.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1989

Response of equine airway smooth muscle to acetylcholine and electrical stimulation in vitro.

Smooth muscle strips from the midcervical portion of the trachea and bronchial smooth muscle strips from third-generation airways of horses were placed in tissue baths, and isometric contractile force was measured. Active force was measured in response to electrical stimulation and exogenous acetylcholine. Square-wave electrical stimuli were applied at various voltages (10, 12, 15, 18, 20, 25 V), frequencies (3, 5, 10, 15, 20, 25, 30 Hz), and pulse durations (0.2, 0.5, 1.0, 1.5, 2.0 ms). Isometric contractile force increased as voltage, frequency, and pulse duration increased. Maximal contractile response to electrical stimulation was obtained at 18 V, 25 Hz, and 0.5 ms. Atropine (10(-6)M) or tetrodotoxin (3 x 10(-6)M) blocked the contraction, indicating that the contractile response was attributable to the release of neurotransmitter from cholinergic nerves. Cumulative concentration-response curves to acetylcholine (10(-9)M through 10(-4)M) were determined. Isometric contractile force increased as acetylcholine concentration increased. There was a significant (P less than 0.05) difference in the 50% effective dose for acetylcholine in tracheal smooth muscle and bronchial smooth muscle. The mean (+/- SD) contractile response to maximal electrical stimulus was 89% (+/- 7.4%) of that in response to 10(-4)M acetylcholine in tracheal smooth muscle and was 68% (+/- 10.4%) of the response to 10(-4)M acetylcholine in bronchial smooth muscle.

Acetylcholine↗
PubMed1989

Comparative study of continuous lumbar segmental epidural and subarachnoid analgesia in Holstein cows.

Eight adult Holstein cows were used to compare the effects of lumbar segmental epidural analgesia (SEA) and lumbar segmental subarachnoid analgesia (SSA). A modified 17-gauge Huber point (Tuohy) needle was used to place a catheter with stylet into either the epidural space at the thoracolumbar (T13-L1) intervertebral space or the subarachnoid space at the lumbosacral intervertebral junction. The catheters were advanced so that their tips lay at the anterior lumbar (L1-L2) epidural space or at the thoracolumbar (T13-L1) subarachnoid space. The position of the catheter was confirmed radiographically. A 5% solution of procaine HCl was used at mean doses of 300 mg (6 ml) to induce SEA and 84.4 +/- 12.9 mg (1.7 +/- 0.3 ml) to induce SSA. Onset of analgesia to superficial and deep muscular pinprick stimulation was significantly (P less than 0.05) faster in cows with SSA than in those with SEA (10.4 +/- 2.3 minutes vs 15.9 +/- 3.8 minutes). Maximal thoracolumbar analgesia extended from spinal cord segments T12 to L4 on one or both sides of the vertebral column during SEA and from T10 to L3 on one or both sides during SSA. Duration of analgesia lasted significantly (P less than 0.05) longer in cows with SEA than in those with SSA (76.2 +/- 16.2 minutes vs 53.7 +/- 14.3 minutes). The advantages and disadvantages of the SEA catheter technique are discussed.

Analgesia↗
PubMed1988

Increasing halothane concentration abolishes anesthesia-associated arrhythmias in cats and dogs.

Fifteen cats and 6 dogs developed ventricular arrhythmias during halothane anesthesia. Halothane was administered by precision vaporizer, using a semiclosed anesthetic system. Cardiac arrhythmias were diagnosed within 5 to 10 minutes after a surgical plane of anesthesia was achieved. Arrhythmias in 9 of 15 cats and 3 of 6 dogs were converted to sinus rhythm by increasing the inspired halothane concentration. Conversion to sinus rhythm occurred within 4 minutes. Cardiac arrhythmias were reestablished in 8 of 9 cats and 2 of 3 dogs, after decreasing the inspired halothane concentration to its original value. Increasing the inspired halothane concentration can convert anesthetic-associated ventricular arrhythmias to sinus rhythm in dogs and cats.

Anesthesia↗
PubMed1988

Innervation of crab-eating monkey trachealis muscle determined in vitro.

Strips of smooth muscle from the cervical tracheae of six adult male crab-eating monkeys (Macaca fascicularis) were studied in jacketed 25 ml organ baths filled with Krebs-bicarbonate solution maintained at 37 degrees C and gassed with 5% CO2 in oxygen. Isometric tissue tension increased in response to electrical field stimulation (18 V, 25 Hz, 0.5 msec), norepinephrine in the presence of propranolol, acetylcholine and histamine. Atropine abolished the contractile response to electrical stimulation. Tissues that were contracted with acetylcholine or pretreated with atropine then contracted with histamine relaxed when stimulated electrically. The relaxation was unaffected by propranolol but was abolished by tetrodotoxin. Isoproterenol relaxed tissues that were contracted with histamine, but failed to relax histamine-contracted tissues that had been pretreated with propranolol. Norepinephrine did not change isometric tension in untreated tissues or tissues pretreated with phentolamine. These results demonstrate the presence of excitatory and inhibitory nerves and noninnervated beta-adrenergic receptors in macaque trachealis. The excitatory nerves appear to be cholinergic. The inhibitory response to electrical stimulation is not mediated through muscarinic cholinergic or beta-adrenergic receptors. The inhibitory response to electrical field stimulation was likely mediated through nonadrenergic noncholinergic nerves.

Acetylcholine↗
PubMed1988

Simultaneous evaluation of left ventricular end-systolic pressure-volume ratio and time constant of isovolumic pressure decline in dogs exposed to equivalent MAC halothane and isoflurane.

The effects of 1.5, 2.0, and 2.5 MAC halothane (N = 8) and isoflurane (N = 6) upon systolic performance and isovolumic relaxation were evaluated in open chest dogs. Left ventricular internal volume was determined using piezoelectric crystals. Left ventricular end-systolic pressure-volume points were determined for a series of normal sinus beats during transient venae caval occlusions. The slope of the line formed by those points is a load-independent inotropic index (EES). Left ventricular pressure points during isovolumic relaxation were plotted for computing the time constant of isovolumic pressure decline (T). Both drugs dose-dependently decreased mean arterial blood pressure with no change in heart rate, end-diastolic pressure, or end-diastolic volume. Increasing halothane concentration decreased the values of EES, the maximum rate of rise of left ventricular pressure (dP/dtMAX), and systolic ejection fraction (SEF). Total systemic resistance was unchanged by halothane. Increasing isoflurane concentration decreased EES and dP/dtMAX. The EES was significantly larger (P less than 0.05) with 2.5 MAC isoflurane than 2.5 MAC halothane. The SEF was unchanged by increasing isoflurane. Total systemic vascular resistance was decreased by increasing isoflurane. Isovolumic relaxation was prolonged and became more load-dependent with increasing halothane concentration. Isoflurane did not alter T, but the load-dependency of T was increased by 2.5 MAC isoflurane. There were no differences in T or its load-dependency between drug groups. These results indicate that both anesthetics evoke load-independent negative inotropic effects. Systolic ejection fraction is maintained during isoflurane anesthesia by decreased systemic vascular resistance and less pronounced negative inotropic effects than equivalent MAC halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Sequelae of myelography in the horse.

The records of 131 horses undergoing general anaesthesia and positive contrast cervical myelography with metrizamide were examined to determine the effect of the procedure on the 'patient'. Three per cent of minimally ataxic and moderately ataxic horses had serious complications after myelography. Thirty-two per cent of severely ataxic horses died or were destroyed after general anaesthesia and myelography. Although general anaesthesia and myelography are essential components of a complete neurological evaluation of a horse, they impose a significant risk.

Anesthesia, General↗
PubMed1988

Cardiopulmonary and anesthetic effects of ketamine and its enantiomers in dogs.

Dogs were used to determine cardiopulmonary and chemical restraining effects of racemic ketamine and its enantiomers. Levorotatory ketamine induced the shortest duration of unconsciousness and recumbency when compared with effects of dextrorotatory and racemic ketamine. Administration of racemic ketamine or either of its enantiomers (30 mg/kg of body weight, IV) to dogs recovering from isoflurane anesthesia induced transient, but significant (P less than 0.05), decreases in arterial blood pressure, left ventricular contractility, cardiac output, and total peripheral vascular resistance. Arterial blood pressure and left ventricular contractility significantly (P less than 0.05) increased at later times after ketamine administration. Arterial pH and the PO2 values decreased after IV administration of racemic ketamine or its enantiomers. Significant differences in cardiopulmonary variables were not observed between groups given ketamine or its enantiomers.

Anesthesia↗
PubMed1988

Hemodynamic and respiratory responses in halothane-anesthetized horses exposed to positive end-expiratory pressure alone and with dobutamine.

The influence of positive end-expiratory pressure (PEEP) on the alveolar-arterial O2 tension difference [P(A-a)O2], physiologic right-to-left shunt fraction, physiologic dead space-to-tidal volume ratio, and hemodynamic variables was studied in halothane-anesthetized horses maintained in dorsal recumbency during controlled ventilation. Dobutamine was used to minimize the adverse cardiovascular consequences of PEEP. Six adult horses were anesthetized, using xylazine (2.2 mg/kg of body weight, IM), guaifenesin (50 mg/kg, IV), thiamylal Na (4.4 mg/kg, IV), and halothane (1.5 to 2% inspired) in 100% O2. Mechanical ventilation was controlled to maintain arterial eucapnia for at least 45 minutes during base-line measurements. Hemodynamic and respiratory variables were determined every 15 minutes during equilibration. Each horse was subjected to 4 randomized treatments: 5 cm of H2O PEEP, 10 cm of H2O PEEP, 5 cm of H2O PEEP plus dobutamine (1 microgram/kg/min), and 10 cm of H2O PEEP plus dobutamine (1 microgram/kg/min). Each treatment lasted 15 minutes and immediately followed its predecessor. Although the magnitude of PEEP was randomized with and without dobutamine, PEEP without dobutamine always preceded PEEP with dobutamine. Differences in hemodynamic or respiratory variables among base-line measurements, 5 cm of H2O PEEP, or 10 cm of H2O PEEP were not significant (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1988

Effects of phenobarbital on thiopental pharmacokinetics in greyhounds.

The effects of phenobarbital on the pharmacokinetics of thiopental (15 mg/kg IV) were investigated in 12 trained racing Greyhounds. Phenobarbital (16 mg/kg of body weight, PO, q 24 h), administered for 14 days, reduced the area under the curve of plasma concentration of thiopental vs time from 10,688 micrograms.min/ml to 3,224 micrograms.min/ml. Furthermore, the time to recovery from anesthesia (ie, return to standing position) decreased from 103 minutes to 35.7 minutes after phenobarbital. These effects were attributed to an increase in the metabolic clearance of thiopental, as a result of induction of liver enzyme activity by phenobarbital. These results suggested that hepatic metabolism, in addition to distribution, is a factor that must be considered when assessing the difference in drug disappearance rates between Greyhounds and other breeds of dogs.

Animals↗
PubMed1987

Arterial blood gas tensions in the horse during recovery from anesthesia.

The effects of body position and postoperative oxygen supplementation on arterial blood gas tensions (PaO2 and PaCO2) and pH were examined in clinically normal adult horses during recovery from halothane anesthesia. Hypoxemia developed during recovery from anesthesia in spite of adequate alveolar ventilation in horses without postanesthetic oxygen supplementation. Hypoxemia developed in horses positioned in left lateral or right lateral recumbency, and in horses that were rolled to the opposite side during the recovery period. Arterial blood gas tensions were not significantly (P greater than 0.05) different between horses insufflated with 100% oxygen at the rate of 10 L/min during recovery and horses that did not receive oxygen supplementation during the recovery period. Horses that received 100% oxygen at the rate of 50 L/min through a demand valve had arterial blood gas tensions similar to those in standing awake horses.

Adult↗
PubMed1987

Cardiovascular drugs. Their pharmacology and use in horses.

Knowledge of the dosage, rate and route of administration, and potential side effects of drugs used to treat cardiac disease in horses has been refined. The judicious use of these drugs can increase exercise capacity, improve health, and potentially prolong life. Currently, antiarrhythmics (quinidine, lidocaine), positive inotropies (digoxin), and diuretics (furosemide) are the primary agents used to treat cardiovascular disease in horses. The development of newer drugs (verapamil, milrinone, bumetanide) and their usefulness in therapy for horses with cardiovascular disease require further investigation.

Animals↗
PubMed1987

Stereospecific effects of disopyramide enantiomers following pretreatment of canine cardiac Purkinje fibers with verapamil and nisoldipine.

The effect of racemic disopyramide and its enantiomers on the action potential was studied in Tyrodes (4.0 mM KCL)-superfused canine cardiac Purkinje fibers. Nonstereodependent depression of action potential amplitude and phase 0 Vmax was observed in control fibers and following pretreatment with either nisoldipine or verapamil. Stereospecific effects of the enantiomers were prominent during repolarization phases of the action potential and could be modified by pretreatment with the calcium channel blocking agents. R(-) disopyramide decreased action potential duration at 90% repolarization and shortened the effective refractory period. S(+) disopyramide increased action potential duration at 90% repolarization and prolonged refractoriness. This disparate effect of the enantiomers was eliminated following pretreatment with verapamil. Stereospecific effects on repolarization persisted when fibers were pretreated with nisoldipine, a more selective calcium channel blocking agent that lacks effects on outward plateau current. The data suggest that the increase in action potential duration and refractoriness produced by disopyramide is mediated by a stereospecific inhibition of outward repolarizing current by the S(+) enantiomer.

Action Potentials↗
PubMed1987

Plasma lidocaine concentrations in conscious horses after cervicothoracic (stellate) ganglion block with 1% lidocaine HCl solution.

Arterial and/or central venous plasma concentrations of lidocaine were determined in 12 nonmedicated adult horses (422 +/- 59 kg of body weight, mean +/- SD) after injecting a 1% lidocaine HCl solution into the cervicothoracic ganglion (CTG). A mean dosage of 2.9 +/- 0.5 mg of lidocaine/kg of body weight was used to induce unilateral CTG blockade in 8 horses and 4.8 +/- 0.8 mg was used to induce bilateral CTG blockade in 4 horses. Blood samples were collected before and at 5, 15, 30, 45, 60, 75, 90, 105, and 120 minutes after injection. The plasma lidocaine concentrations were determined by use of gas chromatography (sensitivity less than 0.01 microgram/ml). Cervicothoracic sympathetic blockade was characterized by Horner's syndrome and by profuse sweating over the face, neck, and thoracic limbs. Mean maximal venous concentrations of lidocaine were 0.86 +/- 0.33 microgram/ml at 26.3 +/- 6.9 minutes after unilateral CTG blockade, and 1.14 +/- 0.25 micrograms/ml at 31.2 +/- 18.9 minutes after bilateral CTG blockade. The mean venous and arterial concentrations of lidocaine were not significantly different at 45 and 120 minutes after injection. Venous concentrations of lidocaine were consistently higher than were concentrations in simultaneously collected arterial blood samples in 2 horses in which the right CTG and brachial plexus were temporarily anesthetized after repeated administration of 100 ml of lidocaine into the right CTG.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Doxapram: cardiopulmonary effects in the horse.

The cardiopulmonary effects of 3 dosages of doxapram hydrochloride (0.275 mg/kg, 0.55 mg/kg, and 1.1 mg/kg, IV) were studied in 6 adult horses. Doxapram given IV significantly (P less than 0.05) decreased PaCO2 and increased respiratory rate, cardiac output arterial blood pressures (systolic, mean, and diastolic) arterial pH, and PaO2 at 1 minute after each dose was administered. Heart rate and mean and diastolic pulmonary arterial blood pressure were significantly (P less than 0.05) increased 1 minute after the 2 larger dosages of doxapram were given (0.55 mg/kg and 1.1 mg/kg, IV), but not after the smallest dosage was given. All measurements, except heart rate and cardiac output, had returned to base line by 5 minutes after each dosing. Heart rate remained significantly (P less than 0.05) increased 10 minutes after the 0.55 mg/kg dosage was given and 30 minutes after the 1.1 mg/kg dosage. Cardiac output remained significantly (P less than 0.05) increased at 10 minutes, 5 minutes, and 30 minutes after the 0.275, 0.55, and 1.1 mg/kg dosages, respectively, were given.

Animals↗
PubMed1986

Dobutamine-induced augmentation of cardiac output does not enhance respiratory gas exchange in anesthetized recumbent healthy horses.

The influence of pharmacologic enhancement of cardiac output on the alveolar-to-arterial oxygen tension (difference (P[A-a]O2), physiologic right-to-left shunt fraction (Qs/Qt), and physiologic dead space-to-tidal volume ratio (VD/VT) ws studied in halothane-anesthetized horses in left lateral, right lateral, and dorsal recumbencies. Adult horses were anesthetized, using xylazine (2.2 mg/kg, IM), guaifenesin (50 mg/kg, IV), thiamylal (4.4 mg/kg, IV), and halothane (1.5% to 2% inspired) in 100% O2. Mechanical ventilation was controlled to maintain arterial eucapnia (PaCO2) 35 to 45 mm of Hg) for a period lasting at least 1 hour. Dobutamine was administered at dosages of 1, 3, and 5 micrograms/kg/min, IV, on a randomized basis. The P(A-a)O2, Qs/Qt, and VD/VT were calculated during equilibration and after each dobutamine infusion was given. The P(A-a)O2 and Qs/Qt were significantly (P less than 0.05) greater and VD/VT tended to be greater in horses in dorsal recumbency, compared with those values in horses in left lateral or right lateral recumbency. Cardiac output was similar in all horses, regardless of body position (recumbency). The qualitative relationship between horses in the 3 recumbent positions were not altered by dobutamine. Cardiac output was significantly (P less than 0.05) increased by 3 or 5 micrograms of dobutamine/kg/min in all horses, whereas P(A-a)O2, Qs/Qt, and VD/VT were not significantly altered by dobutamine. The results of the present study failed to substantiate our clinical observations of decreased P(A-a)O2 and Qs/Qt in anesthetized compromised horses given dobutamine.

Anesthesia, General↗