Postanaesthetic cerebral necrosis in five horses.
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Anesthesia, General↗
Biomedical subjects
L W Hall
Publications and source records attributed to L W Hall.
Ecological risks of diazinon from agricultural use in the Sacramento-San Joaquin River Basins, California.
A probabilistic risk assessment was conducted to evaluate the likelihood and ecological significance of potential toxic effects of diazinon in the Sacramento-San Joaquin system. Diazinon, an organophosphorus insecticide, is used in the Sacramento-San Joaquin River Basin as a dormant spray on almonds and other tree crops, as well as for other agricultural and urban applications. Diazinon and other pesticides have been detected in the Sacramento and San Joaquin Rivers and their tributaries. Diazinon exposure was characterized based on monitoring programs conducted in 1991-94. Diazinon effects were characterized using laboratory toxicity data for 63 species, supplemented by results from field mesocosm and microcosm studies. The assessment addressed the possibility that reductions in invertebrate populations could lead to impacts on species of fish that feed on those invertebrates. The risk assessment concluded that fish in these rivers are not at risk from the direct effects of diazinon in the water. Invertebrates are at greater risk, especially in agriculturally dominated streams and drainage channels during January and February. Cladocerans--including Daphnia magna and Ceriodaphnia dubia, two common bioassay species--are especially sensitive to diazinon and other organophosphates and are likely to be subject to acute toxic effects in some locations at some times. Any ecological damage that may occur, however, is brief and limited to cladocerans. None of the fish species of concern depend on cladocerans as critical components of their diet. Invertebrates that are not affected by observed concentrations of diazinon (copepods, mysids, amphipods, rotifers, and insects) are preferred foods for fish in the Sacramento-San Joaquin system.
Animals↗
Malignant hyperpyrexic syndrome.
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Animals↗
An ecological risk assessment for the use of Irgarol 1051 as an algaecide for antifoulant paints.
Irgarol 1051 is an algaecide used in copper-based antifoulant paints for controlling fouling organisms on the hulls of recreational and commercial watercraft. Paints containing this algaecide have been used in Europe since the mid-1980s. In 1998, the first antifouling paints containing Irgarol 1051 were registered for use in the U. S. To examine the risk that Irgarol may pose to aquatic ecosystems, a probabilistic ecological risk assessment was conducted using distributions of exposure and toxicity data. Exposure data for this assessment were derived from 11 monitoring studies (146 stations) conducted in marinas, estuaries, and coastal waters from 1992 to 1997 in six European countries. A comparison of 90th percentile concentrations pooled by station types across all regions showed that concentrations in marinas (316 ng/l) were higher than in estuaries and coastal waters (41 and 19 ng/l, respectively). A 90th percentile of 133 ng/l was reported for all pooled stations. Temporal trends showed that Irgarol concentrations typically peaked in early summer after launching of small boats with much lower concentrations occurring during the spring, fall, and winter. Toxicity data used for this risk assessment were derived primarily from unpublished studies submitted to regulatory agencies. Because Irgarol is a photosynthesis-inhibiting herbicide, it is much more toxic to plants than animals. Toxicity values for animals (fish and invertebrates) were much greater than concentrations of Irgarol reported in the environment. Therefore, a conservative approach using a distribution of only plant toxicity data (EC50s for plant growth) was used to derive a 10th percentile of 136 ng/l. This plant toxicity benchmark of 136 ng/l was used for risk characterization. Results from probabilistic analysis showed that ecological risk from Irgarol exposure was low in estuaries, coastal areas, and various open-type marinas. However, 10% or more of the plant species in enclosed marinas with low flushing rates may be exposed to Irgarol concentrations that would reduce photosynthesis activity and growth during the summer. Ecological risk to these sensitive plant species in enclosed marinas will likely be moderated because of the reversibility of Irgarol's inhibition of photosynthesis and the rapid recovery potential of plant communities. The ecological significance of marinas that generally contain numerous stressors such as trace metals, tributyltin, petroleum hydrocarbons, high nutrient concentrations, and low dissolved oxygen concentrations is a management issue that needs to be addressed.
Biomass↗
Nature and site of action of endogenous nitric oxide in vasculature of isolated pig lungs.
The site of action of endogenous and exogenous nitric oxide (NO) in isolated pig lungs was investigated by using arterial, double, and venous occlusions, which allowed precapillary, postcapillary, and venous segments to be partitioned into arterial, precapillary, postcapillary, and venous segments. NG-nitro-L-arginine (L-NNA; 10(-5) M) increased resistance in the arterial (35 +/- 6.6%. P = 0.003), precapillary (39.3 +/- 5.1%, P = 0.001), and venous (18.3 +/- 4.8%, P = 0.01) segments, respectively. Sodium nitroprusside (10(-5) M) NO (80 parts/million) reversed the effects of L-NNA. Total pulmonary vascular resistance fell with increasing flow, due to a fall in precapillary resistance and dynamic resistance, and was significantly lower than mean total resistance. L-NNA increased the resistances but did not alter the pattern of the pressure-flow relationships. It is concluded that, in isolated pig lungs, the effect of endogenous NO seems to be dependent on flow in the arterial segment and independent of flow in the precapillary segment, but variation of its release does not appear to be fundamental to accommodation to changes in steady flow.
Animals↗
Medetomidine, alpha 2 adrenoceptors and small animal practice.
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Adrenergic alpha-Agonists↗
The influence of salinity on the toxicity of various classes of chemicals to aquatic biota.
The objective of this study was to review all available aquatic toxicity literature regarding the effects of salinity on the toxicity of various classes of inorganic and organic chemicals. Toxicity data for studies in which toxicity was assessed at various salinities were organized by chemical classes and trophic groups. Seventy percent of the studies were conducted with either crustaceans or fish. The other 30% were with mollusks, annelids, zooplankton, bacteria, phytoplankton, or fungi. Results from 173 data entries showed that negative correlations (toxicity increasing with decreasing salinity) were reported most frequently (55%), followed by no correlations (27%) and positive correlations (18%). The toxicity of most metals such as cadmium, chromium, copper, mercury, nickel, and zinc was reported to increase with decreasing salinity. This finding is likely related to the greater bioavailability of the free metal ion (toxic form) at lower salinity conditions. There was generally no consistent trend for the toxicity of most organic chemicals with salinity. The one exception to this was reported with organophosphate insecticides, the toxicity of which appeared to increase with increasing salinity. Physiological characteristics of the various test species were important in determining the toxicity of the various classes of chemicals at a range of salinities. Results from various studies showed that euryhaline species were more resistant to toxic conditions at isosmotic salinities due to minimization of osmotic stress. Specific examples showed that fish were more resistant to toxic chemicals at middle salinities when compared with either lower or higher extremes. Life history and ecology of test species were important factors to consider when interpreting salinity/contaminant interaction data.
Animals↗
Effect of inhibitors of nitric oxide release and action on vascular tone in isolated lungs of pig, sheep, dog and man.
1. The actions of inhibitors of the release or action of nitric oxide (NO) on pulmonary vascular resistance (PVR) were investigated in lungs isolated from pig, sheep, dog and man. 2. In pig, sheep and human lungs perfused with Krebs-dextran solution, both N omega-nitro-L-arginine methyl ester (L-NAME; 10(-5) M) and Methylene Blue (10(-4) M) increased basal PVR. This increase was reversed by sodium nitroprusside (10(-5) M). In pig lungs N omega-monomethyl-L-arginine (10(-4) M) increased PVR by 154%. This increase was partially reversed by L-arginine (10(-3) M). L-NAME had no effect in dog lungs. 3. Pulmonary artery pressure-flow (PPA/Q) relationships were studied over a wide range of flows. In pigs, sheep and human lungs perfused with Krebs-dextran solution, L-NAME increased the PPA/Q slope. This increase was reversed by sodium nitroprusside. In dog lungs L-NAME had no effect. 4. In blood-perfused lungs, the respective responses to L-NAME were similar to those observed with saline. Acute hypoxia in pig and dog lungs increased intercept pressure. Addition of L-NAME during hypoxia increased the PPA/Q slope in both species. 5. In the human, there was no difference in the absolute increase of PVR or PPA/Q slope elicited by L-NAME between hypertensive and control lungs. 6. We conclude that NO is continuously released in the pulmonary vascular bed of pig, sheep and humans under normoxic conditions. In dog lungs inhibition of NO synthesis increases PVR only under hypoxic conditions. In human lungs with pulmonary hypertension, NO is still released under basal conditions.
Adolescent↗
Succinylcholine and vecuronium blockade of the diaphragm, laryngeal and limb muscles in the anaesthetized goat.
The purpose of the study was to compare the response of the cricoarytenoideus dorsalis muscle (CD) to neuromuscular blocking drugs with those of the thyroarytenoideus (TA), diaphragm (DI) and ulnaris lateralis (UL) muscles. Evoked electromyographic response to indirect supramaximal stimulation at 1 Hz was monitored in ten adult goats under thiopentone-halothane anaesthesia. The onset time and duration of neuromuscular blockade after intravenous administration of 500 micrograms.kg-1 of succinylcholine or 4 micrograms.kg-1 of vecuronium were determined. Times to 100% paralysis in CD, TA, DI and UL after succinylcholine were (mean +/- SD) 39 +/- 11, 39 +/- 11, 42 +/- 8 and 57 +/- 8 seconds, respectively; the corresponding times for vecuronium were 5.6 +/- 2.3, 4.6 +/- 1.7, 6.0 +/- 1.9 and 9.6 +/- 1.7 min. The order of recovery to 25% spontaneous EMG activity was TA, CD, DI and UL after succinylcholine (durations: 9.7 +/- 3.6, 11.0 +/- 3.0, 15.3 +/- 1.3 and 22.0 +/- 1.2 min, respectively) but DI, CD, TA and UL after vecuronium (durations: 31.9 +/- 18.6, 35.2 +/- 19.5, 47.1 +/- 19.9 and 71.7 +/- 16.1 minutes, respectively). Thus, as in the diaphragm and thyroarytenoideus muscles, onset time and duration of succinylcholine or vecuronium blockade were shorter in the abductor muscle of the glottis, cricoarytenoideus dorsalis, than in the limb muscle.
Action Potentials↗
Effect of medetomidine on the pharmacokinetics of propofol in dogs.
Pharmacokinetic variables of propofol were investigated in 6 mixed-breed dogs, and the effect of medetomidine (10 micrograms/kg of body weight) on these kinetics was investigated using a two-way crossover design. On 2 occasions, dogs received either a bolus dose of propofol sufficient to allow endotracheal intubation, followed by an infusion of propofol (0.4 mg/kg/min) for 120 minutes, or medetomidine (10 micrograms/kg, IM), 15 minutes prior to induction of anesthesia as described, followed by infusion of propofol (0.2 mg/kg/min). Dogs given medetomidine received atipamezole (50 micrograms/kg, IM) at the end of the 120-minute propofol infusion. Blood propofol concentration was measured, using high-performance liquid chromatography with fluorescence detection. Mean elimination half-life, blood clearance, mean residence time, and mean volume of distribution at steady state, were 486.2 minutes, 34.4 ml/kg/min, 301.8 minutes, and 6.04 L/kg, respectively, in the absence of medetomidine, and 136.9 minutes, 36.2 ml/kg/min, 215.1 minutes, and 3.38 L/kg, respectively, in the presence of medetomidine. Mean time to walking without ataxia was 174 minutes in the nonpremedicated dogs (with a median blood propofol concentration of 2.2 micrograms/ml) and was 160 minutes in the premedicated dogs in which median blood propofol concentration was 1.03 microgram/ml.
Adrenergic alpha-Agonists↗
Muscle fibre diameter and sensitivity to neuromuscular blocking drugs.
In order to investigate the relationship between muscle fibre composition or size and muscle sensitivity to neuromuscular blocking drugs, data on the fibre composition and size of the ulnaris lateralis, thyroarytenoideus, cricoarytenoideus dorsalis and diaphragm muscles of the goat were related to the rate of recovery of these muscles from suxamethonium or vecuronium block. Muscle sensitivity (time to spontaneous 25% recovery of evoked EMG response after 100% block) correlated well with fibre size, the association being significant for the diameter of type I (r > or = 0.94; P < or = 0.016) and types I and II fibres taken together (r > or = 0.95; P < or = 0.013), but not for type II fibre diameter (r < or = 0.83; P > or = 0.084), for both suxamethonium and vecuronium. There was no association between the composition of types I or II fibres in these muscles and sensitivity (r < or = 0.37; P > or = 0.546). This suggests that muscle sensitivity to both depolarizing and non-depolarizing drugs increases with fibre size, and may account partly for the unequal sensitivities of different muscles.
Action Potentials↗
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↗
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↗
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↗
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↗
Propofol and excitatory sequelae in dogs.
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Anesthesia, Intravenous↗
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↗