Biomedical subjects

A K Wood

Publications and source records attributed to A K Wood.

At least 19 recordsLinked to original sources

PubMed2001

Prolonged general anesthesia in MR studies of rats.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR) imaging of laboratory animals may require general anesthesia to minimize body movements over many hours. The anesthetization technique should allow physiologic parameters to remain as close to normal as possible, permit fast recovery, allow safe, repeated use, and avoid attachment of ferrous metal components to the animal. The purpose of this study was to evaluate an anesthetization technique that was developed to meet each of these qualifications. MATERIALS AND METHODS: In 15 rats (280-483-g body weight), general anesthesia was induced (with intramuscular ketamine hydrochloride, xylazine hydrochloride, acepromazine maleate, and atropine), a tail vein catheter was inserted, and preimaging surgical procedures were performed. A face mask was applied, the animal was positioned in a dorsal recumbent position on an acrylic board, and an isothermal heating pad was placed on the ventral aspect of the abdominal wall. The rat, on the board, was then inserted into a trough that contained a custom-built, linearly polarized birdcage head coil and placed in the bore of a 4.7-T horizontal-bore magnet. The face mask was connected to a non-rebreathing gaseous anesthetic system, and anesthesia was maintained with 1.5-2.0 L/min oxygen and 0.25%-1.50% isoflurane. Oxygen saturation, heart rate, and rectal temperature were continuously monitored. RESULTS: The duration of intramuscular anesthesia was 110 minutes +/- 12, and the duration of gaseous anesthesia was 106 minutes +/- 43. The monitoring equipment permitted display of vital signs. CONCLUSION: The method appeared safe, was easy to perform, maintained a stable physiologic state for the parameters monitored, and could be used for repeated anesthesia in the same animal.

Anesthesia, General↗

PubMed2001

Airway protection following simulated gastro-oesophageal reflux in sedated and sleeping neonatal piglets during active sleep.

1. In infants, promethazine has been implicated in the pathogenesis of sleep apnoea, apparent life threatening events (ALTE) and the Sudden Infant Death syndrome (SIDS). The aim of the present study was to investigate, in a neonatal animal, the effects of a commonly used promethazine-containing medication on airway protective mechanisms and cardiorespiratory reflexes following simulated gastro-oesophageal reflux (GER) to different levels in the oesophagus and pharynx. 2. Physiological and radiographic recordings were made in 21 naturally sleeping (controls) and 21 sedated (1.5 mg/kg, p.o., promethazine) piglets. On 3 consecutive days physiological recordings were made in all piglets during active sleep. Gastro-oesophageal reflux was simulated by the injection of boluses of 0.5 mL HCl, pH 2 or 3, or NaCl (0.9%) at 37 degrees C into the pharynx, upper or lower oesophagus. 3. In healthy neonatal piglets, minimal sedation with promethazine, which did not affect behaviour during wakefulness, revealed previously unreported findings during active sleep. 4. The most significant effects were observed following simulated GER to the pharynx, with no effect observed in the lower oesophagus. In sedated piglets, compared with naturally sleeping piglets, there was a significant reduction in swallowing (P < 0.01), delayed radiological clearance of fluid (P < 0.05), a reduction in breathing rate, oxygen saturation and heart rate and an increase in apnoea. 5. These findings are consistent with a low dose of promethazine producing a significant attenuation of airway protective mechanisms and, thus, stimulation of the laryngeal chemoreflex. The results suggest a mechanism for the association observed between promethazine use and the occurrence of ALTE and SIDS. The results support continued caution and suggest the need for greater regulation of promethazine-containing medications in infants.

Animals↗

PubMed2001

Doppler sonographic measurements of arterial blood flow and their repeatability in the equine foot during weight bearing and non-weight bearing.

In six normal adult horses, pulsed-wave Doppler sonographic inspections were made of the left and right lateral palmar proper digital artery (LPPDA) of each thoracic limb. Using a two-period, crossover design with repeated measures, each LPPDA was inspected on four occasions throughout the day over a 7 hour period and, on each occasion, with the limb weight bearing and non-weight bearing. In comparison with the observations made during weight bearing, there were significant increases (P<0.001) in blood-flow velocities when the limb was non-weight bearing. There was no relationship between blood velocities and the time of day, the order in which the inspections were made, resting heart rate, age of the horse, or hoof angle. In both weight bearing and nonweight bearing, the Doppler waveform demonstrated a systolic peak followed by at least two diastolic peaks and an end diastolic plateau. Horses that moved least during sonographic inspections had the lowest co-efficients variation.

Animals↗

PubMed2001

Use of quantitative analysis of sonographic brightness for detection of early healing of tendon injury in horses.

OBJECTIVES: To determine whether quantitative analysis of sonographic brightness could be used to detect healing of an induced injury of the superficial digital flexor tendon in horses and whether rate of healing was influenced by equine recombinant growth hormone. ANIMALS: 8 clinically normal Standardbreds. PROCEDURES: A localized injury was created in the left and right superficial digital flexor tendons of each horse by injection of 2,000 units of collagenase. After injury, 4 horses received equine recombinant growth hormone, a possible promoter of tendon healing. Sonographic images (7.5 MHz) of the flexor tendons and ligaments of the metacarpal region were recorded on videotape prior to injury and weekly for 7 weeks after injury. Images were digitized, and sonographic brightness of tendons and ligaments was calculated. RESULTS: Collagenase-induced injury was sonographically similar to naturally occurring injury. After injury, sonographic brightness of the tendon decreased; after 3 weeks, brightness progressively increased, although by 7 weeks brightness had not returned to preinjury value. Equine recombinant growth hormone had no significant effect on the rate of tendon healing, as evaluated sonographically or at necropsy. CONCLUSIONS AND CLINICAL RELEVANCE: As healing developed, alterations in sonographic brightness of injured tendons coincided with real changes in tendon structure. Quantitative sonographic brightness could be used to accurately monitor healing of equine tendon and ligament injuries and investigate the efficacy of various treatment regimens.

Animals↗

PubMed2001

Postprandial arterial vasodilation in the equine distal thoracic limb.

The effects of feeding on blood flow to the equine foot are poorly understood. In a temperature-controlled room, duplex Doppler ultrasonographic observations were made pre- and postprandially of the lateral proper palmar digital artery of 5 horses, randomly assigned to twice and 4 times daily feeding in an unbalanced 2 period crossover design. Arterial diameter and blood velocity were measured over 4 h and additional observations made of heart rate, blood pressure, total plasma protein, packed cell volume, plasma glucose and insulin. There was no effect of the feeding regimen on any variable. Postprandially, there were significant increases in arterial diameter, blood velocity, total plasma protein, plasma glucose and insulin; the other variables were unchanged. It appeared that the normal postprandial response was an increase in blood flow to the foot. The value of ultrasonography for noninvasive investigation of the peripheral vasculature of the conscious horse was established; and in the future it may have a role in the diagnosis of vascular diseases of the foot.

Animal Feed↗

PubMed2000

Ultrasonography of the equine neonatal kidney.

Ultrasonography is important in the clinical examination of the foal. The ultrasonographic appearance and size of the neonatal kidneys were defined and an imaging protocol established in 6 normal Thoroughbred foals (mean age +/- s.d. 5.0 +/- 3.2 days). Characteristically, in both the heart-shaped right kidney and bean-shaped left kidney, the renal cortex was more echogenic than the medulla. The terminal recesses, renal crest and pelvis were identified, as was the ureter, which contained anechoic urine in its lumen. The renal, interlobar and arcuate vessels were seen. For the right kidney, the ultrasonographic probe was placed at the 14-17th intercostal spaces and paralumbar fossa. For the left kidney, the probe was at the 16th or 17th intercostal spaces and paralumbar fossa. Perirenal structures, including the caudate lobe of the liver, the dorsal extremity of the spleen, the adrenals, the aorta and caudal vena cava were also identified. An understanding of the ultrasonographic appearance of the normal neonatal kidney, accompanied by a routine imaging protocol to ensure that all regions of each kidney are examined, permit a more informed interpretation of renal images in the first few days postpartum.

Animals↗

PubMed1999

Speciation of inorganic arsenic and selenium in leachates from landfills in relation to water quality assessment.

Speciation of arsenic and selenium was carried out on water samples taken from rivers used as water intake points in the vicinity of landfill areas used for land-based waste disposal system. Leachates from these landfill areas may contaminate the river water through underground seepage or overflowing, especially after a heavy downpour. Preconcentration of the chemical species was done using a mixture of ammonium pyrrolidinethiocarbamate-chloroform (APDTC-CHCl3). Because only the reduced forms of both arsenic and selenium species could be extracted by the preconcentrating mixture, suitable reducing agents such as 25% sodium thiosulfate for As(III) and 6M HCl for Se(IV) were used throughout the studies. Care was taken to exclude the interfering elements such as the alkali and alkali earth metals from the inorganic arsenic and selenium species by introducing 12% EDTA solution as the masking agent. The extracted mixture was irradiated in a thermal neutron flux of 4 x 10(12)/cm/s from a TRIGA Mk.II reactor at the Malaysia Institute of Nuclear Technology Research (MINT). Gamma rays of 559 keV and 297 keV from 76As and 75Se, respectively, were used in the quantitative determination of the inorganic species. Mixed standards of As(III) and Se(IV) used in the percentage efficiency procedure were prepared from salts of Analar grade. The water quality evaluation was viewed from the ratio of the inorganic species present.

Arsenic↗

PubMed1999

Effects of promethazine on porcine gastroduodenal function: a sonographic study.

This sonographic study was aimed at examining the effect of sedation with promethazine (1.5 mg x kg(-1)), on gastroduodenal function in neonatal piglets. On 3 consecutive days, observations of gastroduodenal motility during the first 3 postprandial h were made in 13 animals (3 to 5 days old; 7 sleeping naturally and 6 sedated 2 h prior to feeding). Promethazine significantly reduced both the closures per min of the terminal part of the pyloric antrum and pyloric canal and the percentage of gastric contractions that were followed by closure of the terminal pyloric antrum and canal. Such actions of promethazine on motility of the gastroduodenal junction could lead to a delay in gastric emptying of ingesta with a consequent increased risk of reflux of gastric contents into the esophagus. Because gastroesophageal reflux has been associated with the pathogenesis of sudden infant death syndrome (SIDS), care should be taken if promethazine is to be used as a sedative in neonates.

Animals↗

PubMed1999

Sonographic observations of the peripheral vasculature of the equine thoracic limb.

Investigations of the equine peripheral vascular system have been constrained by the lack of a non-invasive method of examining the arteries and veins of the limbs of the conscious horse. Precise correlations were established between the gross anatomical features of the peripheral vessels and their B-mode sonographic appearance in each thoracic limb of 35 horses. A sonographic imaging protocol was established. Additional Doppler sonographic recordings defined the arterial waveforms and demonstrated that blood flow to the foot could be evaluated in the lateral proper digital artery, distal to the level of the coronary band. Valves (with 2-4 cusps) were identified in the lumina of the medial and lateral palmar common digital veins and those of the medial and lateral palmar proper digital veins. Spontaneous echo contrast, a smoke-like haze of echoic blood, was seen in the lateral and medial palmar common digital veins, the distal deep palmar venous arch and communicating branches, and the palmar proper digital veins, and occasionally seen in the distal deep palmar arterial arch and distal proper palmar digital arteries. The value of duplex sonography (B-mode and Doppler) for anatomical and physiological studies of the peripheral vasculature of the horse was clearly established. Such data could be applied to the investigation of diseases affecting the peripheral circulation.

Animals↗

PubMed1999

Sedation with promethazine profoundly affects spontaneous airway protection in sleeping neonatal piglets.

1. Phenothiazine use in infants has been implicated in apparent life-threatening events, sleep apnoea and Sudden Infant Death Syndrome. 2. The aim of this study was to investigate the cumulative effects of a commonly used antihistamine medication containing promethazine on airway protective mechanisms and cardiorespiratory responses in 42 healthy neonatal piglets (21 naturally sleeping, 21 sedated sleeping). 3. Sedated piglets were given 1.5 mg/kg, p.o., promethazine 2 h prior to each recording session. Control animals slept naturally with no sedative given. On three consecutive days in all piglets, physiological recordings were made during sleep; on at least one of these days, simultaneous physiological and radiological observations were made. 4. Following sedation, sleep time and time in active sleep were increased significantly (P < 0.01). The spontaneous occurrence of swallowing, arousal, body movement, gastrooesophageal reflux and apnoea was compared between naturally and sedated sleeping piglets. Sedation with promethazine significantly decreased the spontaneous occurrence of swallowing (P < 0.05) and arousal (P < 0.05) and increased the occurrence of both central (P < 0.05) and obstructive sleep apnoea (P < 0.0001). 5. By the third day, a cumulative effect of promethazine was seen; the rate of swallowing and body movement significantly decreased (P < 0.01). 6. In summary, a low dose of promethazine profoundly altered sleep characteristics, airway protective mechanisms and cardiorespiratory responses in normal healthy sleeping piglets. Continued use of promethazine over several days may attenuate airway protective mechanisms to a potentially life-threatening degree. Our findings support continued caution in the use of promethazine-containing medications for the sedation of infants.

Animals↗

PubMed1998

Ultrasound-induced temperature increase in guinea-pig fetal brain in utero: third-trimester gestation.

Temperature increase was measured at various depths in the brain of living fetal guinea pigs during in utero exposure to unscanned pulsed ultrasound at ISPTA 2.8 W/cm2. Mean temperature increases of 4.9 degrees C close to parietal bone and 1.2 degrees C in the midbrain were recorded after 2-min exposures. When exposures were repeated on the same sites in each fetus after death, the corresponding mean temperature increases were 4.9 degrees C and 1.3 degrees C, respectively. Cerebral blood perfusion had little cooling effect on ultrasound-induced heating in the guinea pig fetus of 57-61 days gestational age.

Animals↗

PubMed1998

In vivo heating of the guinea-pig fetal brain by pulsed ultrasound and estimates of thermal index.

Temperature was measured in the brain in live near-term fetal guinea pigs (62-66 d gestational age), during in utero exposure to a fixed beam of pulsed ultrasound at intensity ISPTA 2.82 W/cm2. Mean temperature increases of 4.3 degrees C close to parietal bone and 1.1 degrees C in the mid-brain were recorded after 2-min exposures. These values were lower (12%) than those obtained for ultrasound-induced heating near the bone in dead fetuses insonated in utero. A significant cooling effect of vascular perfusion was observed only when guinea pig fetuses reached late gestation, near term, when the cerebral vessels were well developed. The estimated value for the thermal index (TIB), as used in AIUM/NEMA output display standard, underestimated the measured temperature increase at the bone-brain interface. The ratio of measured temperature to the TIB is 1.3. A modification of the cranial thermal index provided a more reasonable, conservative, estimate of the temperature increase at a biologically significant point of interest at the brain-bone interface.

Animals↗

PubMed1998

Sonographic observations of the gastroduodenal junction in neonatal piglets.

Knowledge of the function of the gastroduodenal junction is important, as changes in its motility are associated with gastrointestinal disorders. Sonographic observations were made of the stomach and duodenum of 19 neonatal piglets, 2-6 d of age. Contractions of the stomach and duodenum were identified clearly; the overall rate of gastric contractions was about 4 min-1. The percentage of contractions in which there was a closure of the terminal pyloric antrum and pyloric canal varied, being 57.2% +/- 4.6% in the first postprandial hour and 43.1% +/- 3.0% in the third. Antegrade flow of digesta principally occurred preceding a closure of the pyloric antrum and canal. During contractions of the pyloric antrum, the torus pyloricus moved caudally to fill the lumen of the pyloric canal. Our sonographic method provided a noninvasive technique for studying the form and function of gastroduodenal motility in the neonate, suitable for investigating factors that alter gastric emptying.

Animals↗

PubMed1997

Magnetic resonance imaging observations of blood-brain-barrier permeability in an animal model of brain injury.

RATIONALE AND OBJECTIVES: Knowledge of the in vivo relaxivity of paramagnetic contrast agents is important in the accurate measurement of the permeability of the blood-brain barrier (BBB). This study was aimed at developing an animal model for the magnetic resonance (MR) imaging investigation of injuries to the BBB. METHODS: MR imaging (1.9 T) was performed in 18 rats with acute, stable injuries to the brain caused by freezing. After injection of gadodiamide (0.05-0.20 mmol/kg), estimates were made of BBB permeability, leakage space, and relaxivity (also measured in saline). RESULTS: The BBB was always disrupted at the injured site (permeability = 0.038 min-1 +/- 0.0006). The central area of necrosis and the periphery of edema showed substantial differences in leakage space and relaxivity. The relaxivity of gadodiamide was much greater at the injured site than in saline. CONCLUSION: The in vivo relaxivity at a site of pathologic change in the brain may be substantially greater than that measured in aquo.

Animals↗

PubMed1997

Use of Doppler ultrasonography to evaluate renal arterial blood flow in horses.

OBJECTIVE: To obtain Doppler ultrasonographic images of renal arteries in horses and to establish reference range values for systolic and diastolic renal arterial blood flow and resistive indices. Also to determine whether Doppler ultrasonography could be used in horses to detect changes in renal blood flow after IV administration of furosemide. ANIMALS: 11 clinically normal adult horses. PROCEDURES: Pulsed-wave Doppler examinations were performed on arcuate arteries of 5 sedated horses. Continuous-wave Doppler examinations were performed on pyelorenal arteries in 7 nonsedated horses and were repeated in 6 horses after furosemide administration. Peak-systolic velocity (SV) and end-diastolic velocity (EDV) were measured and the resistive indices (RI) were calculated. RESULTS: Using pulse-wave Doppler ultrasonography in sedated horses, arcuate arteries were determined to have a SV of 0.406 +/- 0.116 m/s (mean +/- SD), EDV of 0.184 +/- 0.057 m/s, and RI of 0.549 +/- 0.044. Using continuous-wave Doppler ultrasonography in nonsedated horses, pyelorenal arteries were determined to have SV of 1.047 +/- 0.009 m/s, EDV of 0.510 +/- 0.006 m/s, and RI of 0.512 +/- 0.004. Doppler waveforms from the arcuate and pyelorenal arteries had a low resistance flow pattern, characterized by a systolic peak followed by a continuous antegrade diastolic flow. After furosemide administration, the pyelorenal arterial velocities increased, but the RI remained unchanged. CONCLUSIONS: Doppler ultrasonography may be used to record renal blood flow in horses and to detect changes following furosemide administration. CLINICAL RELEVANCE: Doppler ultrasonographic images may assist in the diagnosis of renal diseases that affect either blood flow or Doppler waveform.

Animals↗

PubMed1996

Students' learning of clinical sonography: use of computer-assisted instruction and practical class.

RATIONALE AND OBJECTIVES: The application of information technology to teaching radiology will profoundly change the way learning is mediated to students. In this project, the integration of veterinary medical students' knowledge of sonography was promoted by a computer-assisted instruction program and a subsequent practical class. METHODS: The computer-assisted instruction program emphasized the physical principles of clinical sonography and contained simulations and user-active experiments. In the practical class, the students used an actual sonographic machine for the first time and made images of a tissue-equivalent phantom. Students' responses to questionnaires were analyzed. RESULTS: On completing the overall project, 96% of the students said that they now understood sonographic concepts very or reasonably well, and 98% had become very or moderately interested in clinical sonography. CONCLUSIONS: The teaching and learning initiatives enhanced an integrated approach to learning, stimulated student interest and curiosity, improved understanding of sonographic principles, and contributed to an increased confidence and skill in using sonographic equipment.

Attitude↗

PubMed1996

Sonographic observations of the gastroduodenal junction of dogs.

OBJECTIVES: To determine the sonographic dimensions and an imaging protocol for the pyloric region of the normal canine stomach, and whether sonography could be used to demonstrate antroduodenal motility. ANIMALS: 20 clinically normal, mixed-breed dogs (mean +/- SD, 15.1 +/- 7.1 kg). PROCEDURE: In vitro sonographic observations of the gastroduodenal junction were made after each had been mounted on an acrylic rack placed in an organ bath. The in vivo studies were performed in anesthetized dogs. RESULTS: The wall of the pyloric antrum was 4 to 5 mm thick, that of the pylorus was 3 to 4 mm thick, and that of the cranial part of the duodenum was 2 to 3 mm thick. The pyloric canal had a length of 16 to 17 mm and overall in vivo diameter of 22 mm, and the muscular part of its wall was 2 to 3 mm thick. In vivo sonographic images were best made with the dog in dorsal recumbency, tilted 30 degrees to the right-the feasibility study clearly demonstrated the form and function of antroduodenal motility, including gastric and duodenal peristalsis, opening and closing of the pyloric canal, and duodenogastric reflux of fluid and gas. CONCLUSIONS AND CLINICAL RELEVANCE: The use of a routine imaging protocol, accompanied by mensuration of the gastroduodenal junction, will permit an opinion to be given as to whether the structure and function of the region are normal or whether pathologic change exists.

Aging↗

PubMed1995

Physiological studies of gastro-oesophageal reflux and airway protective responses in the young animal and human infant.

1. The mechanisms that underlie the Sudden Infant Death Syndrome (SIDS) must explain its two unique features; age at death and death during apparent sleep. 2. The occurrence of gastro-oesophageal reflux (GOR) during active sleep in infants presenting with apparent life threatening episodes (ALTE) and their similar age distribution to SIDS infants, suggested that reflux could be a cause of asphyxia. 3. Sleep related GOR was found to be a physiological and not a pathological event in normal, healthy term infants. 4. In healthy term infants, those infants that were formula-fed (who have a higher incidence of SIDS) had significantly longer oesophageal clearance times for acid reflux and significantly more active sleep compared with breast fed infants. 5. In very preterm infants (who are at increased risk for SIDS), both the frequency and duration of reflux during active sleep was significantly less at term equivalent age compared with healthy term infants, suggesting additional factors must operate to promote an ALTE. 6. One mechanism which may explain the pathogenesis of GOR could be that the reflux reaches the level of the pharynx and this, in turn, stimulates laryngeal receptors to produce apnoea. 7. Simulated reflux to the level of the pharynx in the sleeping piglet evoked airway protective responses, namely swallow, arousal and occasionally expectoration, but neither apnoea nor oxygen desaturation. 8. In the same piglets treated with pentobarbitone sodium, swallowing was impaired and arousal depressed. Simulated reflux to the pharynx produced significant apnoea and oxygen desaturation and death in two of five piglets.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗