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Biomedical subjects

L W Hall

Publications and source records attributed to L W Hall.

At least 19 recordsLinked to original sources
PubMed1992

Effect of inhalation anaesthetics on total respiratory resistance in conscious ponies.

Total respiratory resistance was measured rapidly and non-invasively in 6 conscious ponies before and after they inhaled approximately 25% of the minimal anaesthetic concentration (0.25 MAC) of either enflurane, halothane, or isoflurane, over a 10 min period. The forced random noise (FRN) method was used to measure the impedance over the frequency range of 5 to 40 Hz and its real part, the resistance, was extracted from these impedance measurements. At the concentrations used, halothane appeared to have no effect on the total respiratory resistance; enflurane and isoflurane seemed to increase it but the changes were not statistically significant.

Airway Resistance↗
PubMed1992

Environmental concentrations and aquatic toxicity data on diflubenzuron (dimilin).

The insecticide diflubenzuron (DFB) is commonly used in various mid-Atlantic states for suppression of gypsy moths in hardwood forests. DFB is potentially toxic to nontarget biota because it can enter aquatic systems through aerial application or runoff after precipitation events. Based on this concern, the objectives of this study were to: (1) compile, review, and synthesize literature on the fate, persistence, and environmental concentrations of DFB in both freshwater and saltwater environments; (2) compile, review, and synthesize acute and chronic aquatic toxicity data on DFB effects on freshwater and saltwater organisms; (3) assess possible risk to aquatic biota associated with the use of this insecticide in one specific area (Maryland); and (4) recommend future research based on the data gaps identified from this study. DFB has low solubility in water and exists as a technical grade (TG) and wettable powder (WP) formulation. The toxicity of both formulations is similar at concentrations less than 10 micrograms/l. Organic matter is a major factor influencing the adsorption and degradation of DFB in freshwater, saltwater, and sediment. The half-life of this insecticide in freshwater is approximately 3 days at a pH of 10 and temperature of 36 degrees C. At lower pH conditions of 6 and at the same temperature, DFB is more persistent since half-life values of approximately 9 days have been reported. The half-life of DFB in soil is less than 14 days when the particle size was approximately 2 microns. The half-life is generally greater in cool, dry soil than in hot, wet soil. Aquatic vegetation acts as a sink for DFB by gradually adsorbing the chemical and releasing it over a period of time. Freshwater organisms demonstrated a wide range of sensitivity to DFB. Sensitivity was dependent on body composition (i.e., exo- vs. endoskeleton), trophic level, and life stage. During acute exposures, aquatic invertebrates were more than 25,000 times as sensitive to DFB than fishes. The most acutely sensitive species tested was the Amphipod, Hyallela azteca (96-h LC50 = 1.84 micrograms/l). A mature Plecopteran, Skwala sp., was the most resistant invertebrate species tested in acute tests (96-h LC50 greater than 100,000 micrograms/l). In chronic tests, DFB concentrations of 1 microgram/l or greater were reported to eliminate populations of various Plecopteran (stoneflies) and Ephemeropteran (mayflies) species after 1 month of exposure. A 30-day LC50 of 0.1 micrograms/l DFB was also reported for the Tricopteran, Clistorinia magnifica.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Ambulatory electrocardiography in dogs.

Twenty-four hour ambulatory electrocardiographic recording using a Medilog tape recorder was attempted in 16 healthy pet dogs weighing between 18.4 and 34 kg, while they were living in familiar surroundings. Full 24-hour records were obtained from 10 of them and recordings of more than 10 hours duration from two others; and the findings in these recordings were similar. Maximum heart rates ranged between 110 and 300 beats/minute and the minimum rates ranged between 17 and 46 beats/minute. Intermittent ventricular premature complexes were recorded from these apparently healthy dogs and all but one dog demonstrated a sinus pause, longer than two seconds; the longest pause was 5.7 seconds. The pauses were associated with marked sinus arrhythmia and occurred in both brachycephalic and non-brachycephalic breeds.

Animals↗
PubMed1991

Electromyography of some respiratory muscles in the horse.

To investigate activity in respiratory muscles, insulated wire electrodes were used to record electromyographic activity in the costal diaphragm and in the intercostal, serratus ventralis, internal abdominal oblique, transversalis and rectus abdominis muscles in conscious horses and in the same animals when anaesthetised. Electromyographic activity was related to respiratory phases as recorded by a stethograph around the chest wall. The costal diaphragm showed tonic and inspiratory activity in both conscious and anaesthetised animals. The principal muscle actively involved in expiration was the transversalis muscle. Intercostal muscle activity, and any increased activity in the second part of either inspiration or expiration recorded in the conscious animal, was absent under anaesthesia. The very marked tonic activity found in the serratus ventralis muscle in standing horses disappeared during anaesthesia. It was concluded that any stabilisation of the chest wall contributed by activity in the serratus ventralis and intercostal muscles in conscious, standing horses is greatly reduced during anaesthesia.

Abdominal Muscles↗
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↗
PubMed1979

Radiographic evidence of impaired pulmonary function in laterally recumbent anaesthetised horses.

Studies in conscious and anaesthetised ponies demonstrated that starvation, anaesthesia and changes in body position influence the radiographic appearance of the lungs in the lateral and dorsoventral views. Radiographic appearances could not be closely correlated with blood gas values, but they suggested that the volume of the lowermost lung of the laterally recumbent animal is greatly reduced.

Anesthesia↗
PubMed1979

Oxygenation of pulmonary vein blood in conscious and anaesthetised ponies.

Catheters were implanted through the left atrium into large veins drawing blood from regions of the diaphragmatic lobes in five ponies. Measurement of oxygen and carbon dioxide tensions in blood samples drawn through these catheters showed that in laterally recumbent conscious and anaesthetised animals the function of the lowermost lung is progressively impaired while in the supine position the function of both lungs is adversely affected.

Anesthesia↗
PubMed1978

The effects of a simulated refinery effluent on the grass shrimp, Palaemonetes pugio.

Duplicate static bioassays were conducted using a simulated refinery effluent on the grass shrimp (Palaemonetes pugio, Hippolyte sp.) with the LC-50 values recorded at 4-, 8-, 24-, 48-, and 96-hr intervals. The stimulated refinery effluent contained phenol (0.10 mg/L), sulfide (0.17 mg/L), chromium (0.25 mg/L), ammonia (10 mg/L), No. 2 fuel oil (10 mg/L), and kaolinite (20 mg/L). This arbitrary reference mixture (ARM) contains approximately the concentration of compounds recommended by EPA for 1977. Of the six ARM components, No. 2 fuel oil was the most toxic followed in decreasing order by sulfide, ammonia, phenol, chromium, and kaolinite. Temperature was the most important environmental variable affecting short term toxicity of the ARM to the grass shrimp. Light intensity, photo-period, and salinity had no significant effect. There was no difference in sensitivity of grass shrimp collected from five locations along the gulf and eastern coasts of the United States. Similarly, there was no difference in the response of two grass shrimp genera, Palaemonetes and Hippolyte to the ARM and there was no differences among the three species of Palaemonetes tested. In comparing the sensitivities of the two genera of grass shrimp and the pinfish (Lagodon rhombroides) to the ARM, the grass shrimp were more sensitive.

Animals↗
PubMed1978

Temperature preference of the crayfish Orconectes obscurus.

Acclimation temperature influenced the acute preferred temperature of the crayfish Orconectes obscurus. This species preferred a higher temperature than its acclimation temperature for those acclimation temperatures ranging from 6 degrees to 26 degrees C. When acclimated to 30 degrees and 33 degrees C, the crayfish preferred a lower temperature than its acclimation temperature. The final temperature preferendum is estimated to be approximately 30 degrees C.

Acclimatization↗