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Biomedical subjects

P Lees

Publications and source records attributed to P Lees.

At least 181 records · Page 10Linked to original sources
PubMed1976

Effects of azaperone on cardiovascular and respiratory functions in the horse.

1 The butyrophenone tranquilizer, azaperone, was administered intramuscularly, at dose levels of 0.4 and 0.8 mg/kg, to ponies and its effects on cardiovascular and respiratory functions assessed. 2 Arterial blood pH, CO2 tension (PaCO2) and O2 tension (PaO2) remained relatively constant throughout the course of action of azaperone. 3 Azaperone did not modify plasma protein concentration but venous blood packed cell volume and haemoglobin concentration were reduced by 5 to 10% for at least 4 hours. These changes were probably caused by uptake of erythrocytes into the splenic reservoir. 4 Small increases in heart rate occurred for up to 60 min after administration of the drug, and this was followed by a slight bradycardia in some ponies. 5 Azaperone reduced mean arterial blood pressure (MAP) for at least 4 h, by which time its ataractic action was generally no longer apparent. The hypotension was caused, during the early phase of action at least, by a reduction in peripheral resistance, since cardiac output was increased slightly 20 min after its administration. Possible mechanisms underlying the cardiovascular changes are discussed. 6 In spite of reductions in arterial blood O2 content and MAP produced by azaperone, it is likely that tissue oxygenation was adequate, since arterial blood lactate concentrations were not increased.

Animals↗
PubMed1976

The applied pharmacology of azaperone in ponies.

The butyrophenone tranquilliser, azaperone, was administered intramuscularly to ponies in five series of experiments, using a dose level of 0-4 mg/kg once and 0-8 mg/kg four times. An excellent or good sedative effect was usually obtained with both dose levels, but the response was more consistent with the higher dose. The onset of sedation was apparent within 10 min of administration, the maximal effect usually occurring between 20 and 60 min while sedation was no longer apparent after 2 to 6 h. Body temperature was reduced in all animals for at least 2 h and respiratory rate was increased in some ponies but not in others. A mild tachycardia occurred in the first hour after administering azaperone (0-8 mg/kg) and arterial blood pressure was reduced for at least 4 h. The hypothesis that azaperone reduced blood pressure by blocking alpha-adrenoceptors, thereby decreasing vasomotor tone, was tested by measuring the ability of azaperone (0-8 mg/kg) to antagonise the action of standard intravenous doses of adrenaline (1-5 mug/kg) on blood pressure, Azaperone partially antagonised the pressor action of adrenaline and in comparative studies the phenothiazine tranquilliser, acepromazine (0-1 mg/kg), also exerted a similar blocking effect.

Acepromazine↗
PubMed1976

The rate of rise of intraventricular pressure as an index of myocardial contractility in conscious and anaesthetised ponies.

Measurements of the rate of rise of left ventricular blood pressure (dP/dt) have been made in conscious and anaesthetised ponies. Concurrent measurements of heart rate, mean arterial pressure and left ventricular pressure were also made in order to assess their relationship to values of dP/dt. Thiopentone-halothane and thiopentone-ether anaesthesia reduced the maximal rate of rise of intraventricular pressure (dP/dt max) from conscious control levels. After correcting for variations in the loading conditions of the ventricle, the depressant effect of halothane was still apparent, but the action of ether was not. It was concluded that the negative inotropic effect of halothane in the pony was greater than that of ether, possibly because a compensatory sympathoadrenal stimulation occurred during ether but not during halothane anaesthesia.

Anesthesia, Inhalation↗
PubMed1975

Cardiac output in the conscious and anaesthetised horse.

Cardiac output in the horse was measured before and at predetermined times during 2-hour periods of thiopentone-halothane and thiopentone-diethyl ether anaesthesia. Left ventricular stroke volume was decreased to a similar extent during anaesthesia with each volatile agent, but a greater reduction in cardiac output occurred during halothane anaesthesia. This finding reflected the differing effects of halothane and ether on heart rate, a slight bradycardia occurring with the former agent while ether produced a small degree of tachycardia. The latter effect was attributed to enhanced sympathoadrenal activity. Changes in cardiac output and stroke volume were considered in relation to other factors, including arterial blood pH and tensions of oxygen and carbon dioxide. Positive correlations between some of these variables and cardiac function were established. With both volatile agents the reductions in stroke volume and cardiac output were related to the duration of anaesthesia, being greatest during the early stages. Possible reasons for the tendency of stroke volume and cardiac output to return towards control levels are discussed.

Anesthesia, Inhalation↗
PubMed1975

Influence of the neuroleptanalgesic combination of etorphine and acepromazine on the horse: blood gases and acid-base balance.

Respiratory function and acid-base variables were studied in Welsh Mountain ponies before and at predetermined times after the intravenous injection of Immobilon and Revivon.A marked depression of respiratory rate was accompanied by large reductions in arterial blood oxygen tension and saturation and the development of a mild respiratory acidosis following the injection of Immobilon. It was concluded that at least three factors contributed to the hypoxic hypoxia produced by Immobilon; the posture of lateral recumbency, the decrease in respiratory rate and the laboured character of the respiration. Arterial oxygen and carbon dioxide tensions returned towards control levels soon after administering Revivon. Mixed venous oxygen tensions were little affected by either Immobilon or Revivon, and mixed venous carbon dioxide tensions were increased to smaller degrees that those of arterial blood. Haemoglobin was increased initially by Immobilon, had returned to the control level by 30 min and fell below the control following the administration of Revivon.

Acepromazine↗