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Biomedical subjects

L W Hall

Publications and source records attributed to L W Hall.

At least 37 records · Page 2Linked to original sources
PubMed1990

Use of the forced oscillating airflow technique to measure the resistance of the equine upper airway: effects of laryngoventriculectomy and laryngoplasty.

Investigations were carried out to determine whether measurements of total respiratory resistance (TRR) made in resting animals could detect changes due to laryngeal hemiplegia. Control values of TRR were obtained in eight ponies and in six of these the measurements were repeated after division of the left recurrent laryngeal nerve in the mid-cervical region; two were retained as controls. A further set of measurements were made before two of the operated animals were subjected to left laryngoventriculectomy (Hobday operation). A laryngoplasty ('tie-back' operation) was performed on another two animals. Measurements of TRR were made at three-monthly intervals on all eight ponies for the next two years. Endoscopic examination of the larynx was carried out at the time of the measurements. All ponies showed a marked, but regular, variation in TRR over the two-year observation period. Nerve section was shown to be associated with an increase in TRR in five ponies. The Hobday operation decreased TRR in one animal and had no marked effect in the second. The tie-back operation was associated with a decreased TRR in one pony and an increase in the second. Autopsies were carried out on all six operated ponies and measurements of TRR and lower respiratory resistance (LRR) were made immediately before the animals were killed. Evidence of regeneration of the recurrent laryngeal nerve was seen in one of the ponies which underwent the Hobday operation. Histological evidence of regeneration was found in another pony.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1989

A rapid, non-invasive method for measuring total respiratory impedance in the horse.

Total respiratory impedance was measured rapidly and noninvasively in conscious horses over the frequency range 3 to 40 Hz by the forced random noise method. The shape of curve of impedance versus frequency in horses was markedly different from that of humans. Respiratory resistance was readily found as the real part of impedence and both its absolute value and frequency dependence are useful indices of pulmonary function. It was difficult to obtain meaningful results in intubated animals with the method because of the mechanical properties of the endotracheal tube itself.

Airway Resistance↗
PubMed1988

Effects of nitrous oxide on respiration during halothane anaesthesia in the dog.

The pattern of ventilation was studied in eight greyhounds anaesthetized with halothane in 50% oxygen with nitrogen and in eight with the same concentration of halothane in 50% oxygen with nitrous oxide. There was a significant reduction in both inspiratory and expiratory times in the animals breathing nitrous oxide and an increase in the negative pressures developed in the obstructed airway during inspiration. Measurements during the addition of carbon dioxide to the inspired gases also suggested less respiratory depression in the nitrous oxide breathing group. It was concluded that nitrous oxide may counteract the respiratory depressant effects of halothane.

Anesthesia, Inhalation↗
PubMed1988

Influence of acute isocapnic hypoxia on bronchial calibre and "expiratory reserve" volume in dogs.

The effects of hypoxia on bronchial calibre were investigated in anaesthetized dogs using a computer-aided forced airflow oscillation technique which derived specific lower airways conductance (sGlaw) and "expiratory reserve volume" (ERV). Measurements were made with inspired oxygen concentrations varying from 40% to 10%. sGlaw tended to be slightly reduced (indicating bronchoconstriction) by decreasing the oxygen concentration from 40% to 15%, these changes being statistically significant after the administration of atropine. ERV was unaffected by changes in oxygen concentration from 40% to 15%, but was significantly reduced during ventilation with 10% oxygen. This effect was reversed by re-oxygenation and was not abolished by prior administration of atropine. It was concluded that both bronchoconstriction and changes in lung volume may be responsible for changes in airway resistance during hypoxia.

Airway Resistance↗
PubMed1988

Effects of xylazine and acepromazine on bronchomotor tone of anaesthetised ponies.

The effects of xylazine (an alpha 2-adrenoceptor agonist) and acepromazine (an alpha-adrenoceptor antagonist) on bronchomotor tone were investigated in seven anaesthetised, apnoeic ponies using a computer aided forced oscillation technique, which separates changes in bronchial calibre from changes in lung volume. Both agents produced bronchodilatation and a decrease in lung volume.

Acepromazine↗
PubMed1987

Propofol as an intravenous anaesthetic agent in dogs.

Studies in dogs with an emulsion formulation of the intravenous anaesthetic, propofol, showed that induction of anaesthesia was smooth and it was possible to maintain anaesthesia by intermittent injection. The mean dose for induction of anaesthesia in unpremedicated dogs was 5.95 mg/kg body-weight. When no premedication was administered anaesthesia was maintained by a total dose of approximately 0.806 mg/kg/minute. Premedication with between 0.02 and 0.04 mg/kg of acepromazine reduced the mean induction dose by about 30 per cent and the maintenance dose by more than 50 per cent. In 68 unpremedicated dogs given one dose, recovery was complete in a mean time of 18 minutes and after maintenance of anaesthesia by intermittent injection in 65 dogs the mean recovery time was 22 minutes from administration of the last dose. Premedication with acepromazine did not produce statistically significant increases in these recovery times. The quiet, rapid and complete recovery proved to be most valuable in cases where the animal had to be returned to the owners' care with the minimum of delay.

Acepromazine↗
PubMed1987

A clinical trial of three anaesthetic regimens for the castration of ponies.

After premedication with intravenous xylazine 30 ponies were anaesthetised for castration under field conditions with intravenous ketamine, thiopentone or methohexitone. The duration of anaesthesia was adequate for surgery and the times taken to stand were similar in each group. The recovery of the ponies after ketamine was quieter than after either of the barbiturates and this may be an advantage when skilled assistance is lacking. However, all the anaesthetics appeared to be suitable for performing minor surgery in the field.

Anesthesia, General↗
PubMed1987

Effect of halothane, enflurane and isoflurane on bronchomotor tone in anaesthetized ponies.

The effects of halothane, enflurane and isoflurane on bronchial calibre were investigated in five anaesthetized ponies using a computer-aided forced airflow oscillation technique to derive specific lower airways conductance (s.Glaw) and expiratory reserve volume (ERV). All the agents tended to increase s.Glaw (indicating bronchodilatation), but ERV was reduced by halothane and enflurane, and increased by isoflurane. It was concluded that the effects of these agents on bronchomotor tone were similar to those which occur in man. However, the reasons for the differences in their effects on ERV compared with those found in man remain to be determined.

Anesthesia, Inhalation↗
PubMed1986

A portable oxygen generator.

The use of a portable generator which liberates oxygen from hydrogen peroxide solutions has been investigated in veterinary anaesthesia to assess its potential as an alternative to conventional oxygen supplies both in emergency situations and in the event of failure of cylinder systems. The reliability of the supply appears to be good and the operation of the generator simple, making it suitable for a number of potential uses. It should compare favourably with oxygen concentrator devices used for similar purposes.

Anesthesia, Inhalation↗
PubMed1985

Effects of a demand valve on pulmonary ventilation in spontaneously breathing, anaesthetised horses.

The pressure flow characteristics of a demand valve which has been suggested to be suitable for use in anaesthetised horses were determined at a range of flow rates commonly encountered in equine anaesthesia. The resistance of the valve was found to be very much greater than the resistance of normal large animal anaesthetic apparatus or the equine lower respiratory tract. The effects of the valve on pulmonary ventilation were investigated in seven anaesthetised, intubated horses. Respiratory rate and dynamic compliance were unaffected by connection of the valve but mean tidal and minute volumes and peak flow rates were substantially reduced. The change in transpulmonary pressure over the respiratory cycle was doubled and indices of work of breathing increased by a factor of three. It was concluded that the resistance offered by the valve was too great for its use in spontaneously breathing horses to be recommended.

Anesthesia↗
PubMed1985

Clinical anaesthesia in the horse: comparison of enflurane and halothane.

Anaesthesia was induced in 24 horses with xylazine and ketamine and maintained with halothane (12 cases) or enflurane (12 cases) in oxygen. Pulse rate, arterial blood pressure, arterial blood gas values, respiratory rate and tidal volume were measured at regular intervals during anaesthesia. Serial venous blood samples were taken for assay of glucose, urea, haemoglobin, packed cell volume, gamma glutamyl transpeptidase, aspartate aminotransferase, alanine aminotransferase and creatine kinase. Operating conditions and the horses' behaviour in the recovery period were also recorded. In the case of the group of horses receiving enflurane, difficulty was experienced maintaining anaesthesia deep enough for surgery. This group also displayed greater respiratory depression. There were no significant differences between arterial blood pressure values, or any of the haematological or biochemical parameters recorded in each group. Recovery from anaesthesia was significantly faster in horses receiving enflurane but less smooth. It was concluded that, although enflurane appeared to be safe in the horse, the respiratory depression and the unpleasant recovery did not make it a desirable alternative to halothane.

Anesthesia, Inhalation↗
PubMed1985

Total intravenous anaesthesia in the horse with propofol.

The use of propofol, solubilised in a non-ionic emulsifying agent, for the induction and maintenance of anaesthesia in experimental ponies was assessed. Pilot studies revealed that premedication with xylazine (0.5 mg/kg bodyweight [bwt]) intravenously (iv) followed by propofol (2.0 mg/kg bwt) iv provided a satisfactory smooth induction. Two infusion rates (0.15 mg/kg bwt/min and 0.2 mg/kg bwt/min) were compared for maintenance of anaesthesia. An infusion rate of 0.2 mg/kg/min produced adequate anaesthesia in these ponies. Cardiovascular changes included a decrease in arterial pressure and cardiac output during maintenance. Respiratory depression was manifested by a decrease in rate and an increase in arterial carbon dioxide tension. Recovery after 1 h anaesthesia was rapid and smooth. In conclusion, induction and maintenance of anaesthesia with propofol in premedicated ponies proved a satisfactory technique.

Anesthesia, Intravenous↗
PubMed1985

Acute and sublethal effects of organotin compounds on aquatic biota: an interpretative literature evaluation.

The objectives of this review were to: (1) collect, synthesize, and interpret acute and sublethal organotin toxicity data in both freshwater and estuarine-marine ecosystems; (2) present environmental water column and sediment concentrations of organotin compounds in both freshwater and estuarine-marine systems to facilitate interpretation of toxicity data; and (3) identify deficiencies in available data to recommend areas of future research for assessing ecological effects of organotin compounds in aquatic systems. The following recommendations are suggested: (1) evaluation of the bioavailability of organotin compounds in aquatic systems; (2) assessment of the relationship between physicochemical characteristics of organotin compounds and subsequent toxicity effects on aquatic organisms; (3) determination of organotin effects on food chains; (4) evaluation of the specific mechanisms and modes of toxicity for organotin compounds with aquatic biotia; (5) evaluations of the adaptive responses of aquatic biota to organotins; (6) measurement of organotin concentrations in testing chambers throughout toxicity tests using peer-reviewed analytical techniques (nominal concentrations can provide misleading data); (7) assessment of long-term "low level" exposures of organotin compounds on histological, histochemical, behavioral, and physiological responses of aquatic biota; and (8) toxicity assessment of plasticizer organotin compounds to aquatic biota.

Amphibians↗