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Biomedical subjects

A I Webb

Publications and source records attributed to A I Webb.

At least 19 recordsLinked to original sources
PubMed1994

Pharmacokinetics and pharmacodynamics of acepromazine in horses.

A specific, sensitive, reverse-phase high-performance liquid chromatographic assay for acepromazine, with analytic sensitivity as low as 5 ng/ml of plasma, and electrochemical detection with an oxidation potential of 0.7 V, was used to study the pharmacokinetics of acepromazine given at a dosage of 0.15 mg/kg of body weight in horses. The relation between effect and pharmacokinetics of the drug was examined. The effects studied included those on blood pressure, pulse, PCV, measures of respiration function, and sedation. Intravenously administered doses led to a biphasic concentration decay pattern with an alpha-phase distribution half-life of < 3 minutes. The beta-phase half-life was in the range of 50 to 150 minutes. The CNS effects peaked at 20 minutes after administration, and the hemodynamic effects peaked at 100 minutes. In all horses, the most sensitive variable was the PCV, which decreased by up to 20% (P < 0.0001). Systolic, diastolic, and mean blood pressures decreased (P < 0.0001); heart rate was unchanged (P > 0.05). Neither blood gas tensions nor blood pH changed noticeably (P > 0.05). In all horses studied, acepromazine had a significant (P < 0.0001) sedative effect, as observed by posture and alertness. None of the observed pharmacodynamic effects correlated well with plasma acepromazine concentration. These effects persisted beyond the time of detectable acepromazine concentration, indicating that they might be caused by active metabolites, or that their timing could result from complex pharmacokinetic compartment influences.

Acepromazine↗
PubMed1989

Pulmonary vascular reactivity of the newborn pony foal.

Adult ponies develop pulmonary hypertension at altitude (Bisgard, Orr and Will 1975), but the neonatal response to acute hypoxaemia is unknown. Seven foals aged five days were instrumented with a systemic and a Swan-Ganz pulmonary artery catheter while anesthetised and intubated. Cardiac index, pulmonary (PAP) and systemic (SAP) vascular pressures were measured as the foals breathed gas mixtures with FI02 of 8 to 94 per cent. Because foramen ovale or ductus arteriosus shunts might have altered thermodilution cardiac index measurements in the stressed foals, the ratio, PAP/SAP was calculated to define relative circulatory reactivity. Three foals, two of which were full siblings, had very marked elevation of PAP/SAP from 0.6 to 1.41 at low inspired oxygen tensions. Four different foals attained maximal PAP/SAP of only 0.2 to 0.92 at similarly low oxygen tensions (P less than 0.0001). Thus, pulmonary vascular reactivity to ventilatory hypoxaemia varied greatly in pony foals of the same age. The exaggerated reactivity in related foals suggested that, as in cattle, a genetic predisposition to develop reactive pulmonary hypertension under hypoxaemic stress may exist.

Animals↗
PubMed1989

Plasma and erythrocyte cholinesterase values for the common long-nosed armadillo, Dasypus novemcinctus.

Plasma and erythrocyte cholinesterase activities were determined for 40 free-living and 12 captive common long-nosed armadillos (Dasypus novemcinctus) in order to establish normal values for monitoring pesticide exposure. Plasma cholinesterase activity ranged from 105 to 549 U/liter with no sexual or seasonal differences. Plasma values from captive animals were significantly lower than those from wild armadillos. Erythrocyte cholinesterase activity ranged from 2,915 to 15,126 U/liter with no differences detected between captive and wild animals or between sexes. However, erythrocyte cholinesterase values varied seasonally. Erythrocyte and plasma cholinesterase activities were not significantly correlated. Packed cell volume ranged from 24 to 51% and did not vary significantly between captive and wild samples, between sexes or among seasons. However, both whole blood and erythrocyte cholinesterase activities showed significant negative correlations with packed cell volume. Controlled experiments are needed to find the factors responsible for the statistically significant difference between plasma cholinesterase activities of captive and wild armadillos. The seasonal variation in erythrocyte cholinesterase activity and the negative correlation between erythrocyte cholinesterase activity and packed cell volume can be explained by an hypothesis that relates the variation in erythrocyte cholinesterase activity to variation in erythrocyte turnover rate. Future work should involve experiments to test this hypothesis.

Animals↗
PubMed1988

Use of halothane to maintain anesthesia induced with etorphine in juvenile African elephants.

Sixteen 3- to 5-year-old African elephants were anesthetized one or more times for a total of 27 diagnostic and surgical procedures. Xylazine (0.1 +/- 0.04 mg/kg of body weight, mean +/- SD) and ketamine (0.6 +/- 0.13 mg/kg) administered IM induced good chemical restraint in standing juvenile elephants during a 45-minute transport period before administration of general anesthesia. After IM or IV administration of etorphine (1.9 +/- 0.56 micrograms/kg), the mean time to lateral recumbency was 20 +/- 6.6 and 3 +/- 0.0 minutes, respectively. The mean heart rate, systolic blood pressure, and respiration rate during all procedures was 50 +/- 12 beats/min, 106 +/- 19 mm of Hg, and 10 +/- 3 breaths/min, respectively. Cardiac arrhythmias were detected during 2 procedures. One elephant with hypotension responded to a decrease in the concentration of halothane and IV infusion of dobutamine HCl. Alterations in systolic blood pressure, ear flapping, and trunk muscle tone were useful for monitoring depth of anesthesia. Results indicated that halothane in oxygen was effective for maintenance of surgical anesthesia in juvenile African elephants after induction with etorphine.

Anesthesia↗
PubMed1987

Effect of anticholinergic preanesthetic medicaments on the requirements of halothane for anesthesia in the cat.

To study the effects of anticholinergics on anesthetic requirements, minimal alveolar concentrations (MAC) for halothane in the cat were measured before and after IM administration of an anticholinergic (atropine sulfate [0.045 mg/kg], glycopyrrolate [0.011 mg/kg], or scopolamine hydrobromide [0.02 mg/kg]) or a physiologic saline control. The study was performed in 8 adult cats, using a randomized-block experimental design. There was no significant difference between the mean MAC obtained before and after administration of any of the test drugs or vs the control values. The mean MAC of halothane in cats was 0.985% atmosphere.

Anesthesia, Inhalation↗
PubMed1986

Effect of acepromazine on the anesthetic requirement of halothane in the dog.

Five adult dogs were used to determine whether acepromazine maleate (ACP), administered IM, decreases the maintenance requirement of halothane and to measure any decrease for the ACP dosages of 0.02, 0.04, 0.06, 0.08, 0.10, and 0.20 mg/kg. The value minimal alveolar concentration, a measure of anesthetic potency, was used as the measure of anesthetic requirement of halothane before and after ACP was administered. All dogs were randomly exposed to each dosage of ACP, as well as to control of 0.2 ml of sterile water. At all dosages of ACP, the decrease in the minimal alveolar concentration of halothane was significant (P less than or equal to 0.05) when compared with that of the control. The decreases at the 0.04 and 0.20 mg/kg dosages were significantly (P less than or equal to 0.05) greater than those at the 0.02 and 0.06 mg/kg dosages. Halothane requirements at all other ACP dosages (0.08 and 0.10 mg/kg) were not significantly different from each other or from those at any of the other dosages. The percentage of decrease in anesthetic requirement after ACP was administered varied from 34% to 46%, with a mean decrease of 40%. The largest decrease was recorded at the dosage of 0.04 mg/kg.

Acepromazine↗
PubMed1985

Culture of retinal pigment epithelium from chorio-retinal biopsies.

The recently devised methods for surgical sampling of chorio-retinal tissue permits morphological evaluation of retina in various diseases. In the present report it is demonstrated, that the retinal pigment epithelium in such samples can be isolated as a viable cell population, and that the cell mass can be increased sufficiently in culture to permit biochemical as well as morphological studies. This procedure thereby expands the diagnostic potential of the sample tissue.

Animals↗
PubMed1985

Retinal pigment epithelial dysfunction in early ovine ceroid lipofuscinosis: electrophysiologic and pathologic correlates.

Retinal degeneration is a major finding in the human and ovine ceroid lipofuscinosis. Sequential electroretinographic (ERG) studies in a young, asymptomatic, affected lamb are presented here, which demonstrate a progressive loss of the scotopic b-wave and unrecordable c-waves under halothane anesthesia. Even at this initial stage of disease, lesions were evident in the form of dystrophic retinal pigment epithelial (RPE) villi, and loss of photoreceptor cells and rod outer segments. Cone inner segments were enlarged and scanning electron microscopy emphasized these abnormalities. All cells in tapetal and nontapetal areas contained fluorescent inclusions with similar emission spectra (maximum = 539 nm). By transmission electron microscopy, storage bodies consisted of 'finger-print' profiles and were most prominent in bipolar cells. The pathological features of the retina correlate well with the observed ERG changes, reaffirming the sheep as a useful model to delineate early events in ceroid lipofuscinosis.

Animals↗
PubMed1985

Preliminary studies on the measurement of conjunctival oxygen tension in the foal.

The capability of a transconjunctival oxygen monitoring system to provide an accurate and reliable means of observing arterial oxygenation trends was evaluated in 12 horse and pony foals between 5 and 20 days of age. Ten of the foals were anesthetized with isoflurane in oxygen and nitrous oxide, and 2 foals were conscious. Inspired oxygen concentration was manipulated by differing proportions of oxygen and nitrous oxide in the fresh gas supplied to the breathing circuit. With arterial oxygen tension values ranging from less than 20 to greater than 400 mm of Hg, all foals had significant positive correlations between arterial and conjunctival oxygen tensions (P less than 0.001). Although the system seemed accurate and reliable, monitoring oxygenation in awake and mobile foals may require a ring conformer made to fit the foal's eye.

Animals↗
PubMed1984

Developments in management of the newborn foal in respiratory distress 1: Evaluation.

Developments in evaluation of newborn foals with respiratory distress are discussed. Major causes of respiratory distress are outlined and discussed in terms of the similar respiratory signs exhibited by foals with this clinical syndrome. History, physical examination, clinical pathology, chest radiography and blood gas analyses are discussed as important elements of the evaluation of the condition of these foals. Foals with respiratory disease are grouped into three major categories on the basis of clinical signs and arterial blood gas profiles. The evaluation of foals with respiratory distress is designed not only to reach an accurate diagnosis of the aetiology but also to define the foal's need for respiratory support.

Animals↗
PubMed1984

Developments in management of the newborn foal in respiratory distress 2: Treatment.

New developments in therapy for foals in respiratory distress are discussed. Therapy is based on preservation of the foal's life by maintenance of a patent airway, resuscitation with fluids and warmth, provision of humidified oxygen to raise the fractional concentration of inspired oxygen sufficient to avoid hypoxia and provision of ventilatory support when hypercapnia becomes critical. Ventilatory support described includes assisted and controlled ventilation, positive end expiratory pressure, continuous positive airway pressure and intermittent mandatory ventilation. The aims of these techniques are discussed together with their associated indications, disadvantages and complications. Secondary therapy includes coupage, airway hygiene, drug therapy and stress management. Knowledge of equine neonatology is limited in comparison with human neonatology. More information in basic physiology and pharmacology relating to equine neonatology is needed and the efficacy of various modes of therapy must be evaluated.

Animals↗
PubMed1983

Fatal interaction between thiamylal sodium and a proprietary antidiarrheal preparation in the dog.

A drug interaction involving thiamylal sodium and a proprietary antidiarrheal preparation caused fatal ventricular fibrillation in a dog. Trials involving 4 dogs were conducted to recreate the interaction, and 1 of the 4 dogs died after ventricular fibrillation developed. The nature of the interaction was hypothesized to be mediated through the anticholinergic drug diphemanil methylsulfate, producing an autonomic imbalance.

Anesthetics↗
PubMed1983

Postural influence on systemic blood pressure, gas exchange, and acid/base status in the term-pregnant bitch during general anesthesia.

Effects of positioning on certain physiologic parameters were done in 7 term-pregnant bitches during general anesthesia. Five positions (right and left lateral recumbency, right and left 10 degrees to 15 degrees tilt toward lateral recumbency, and dorsal recumbency) were examined. Anesthesia was induced with thiamylal sodium and was maintained with halothane and nitrous oxide in oxygen. Direct arterial blood pressure, arterial blood gases, pH, base excess, heart rate, respiratory rate, and a lead II ECG were recorded from the bitches during each position. Effects of positioning for each bitch during general anesthesia were reexamined after the bitch weaned its pups; therefore, each bitch served as its own control. Maternal posture had no significant (P less than 0.05) effect on any measured parameters in bitches before or after parturition. Pregnancy had a significant (P less than 0.05) effect on every parameter, except heart rate. Pregnant bitches had a lower systolic blood pressure, lower Pao2, lower PCV, higher PaCO2, higher respiratory rate, and a more severe acidosis than did the bitches after parturition. Seemingly, supine hypotension did not occur in anesthetized term pregnant bitches (9 to 16 kg). Tilting the bitch 10 degrees to 15 degrees toward right or left lateral recumbency or true lateral recumbency was not preferable to dorsal recumbency for doing cesarean sections using general anesthesia.

Acid-Base Equilibrium↗