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Biomedical subjects

D A Allen

Publications and source records attributed to D A Allen.

At least 19 recordsLinked to original sources
PubMed2006

Outcome and prognostic factors in non-ambulatory Hansen Type I intervertebral disc extrusions: 308 cases.

Thoracolumbar intervertebral disc disease is the most common cause of caudal paresis in dogs. Whilst the pathogenesis of the extrusion has been widely studied, treatment protocols and prognostic factors relating to outcome remain controversial. Recent studies have examined a multitude of factors relating to time to regain ambulation after decompressive surgery. Most intervertebral disc herniations occur in the thoracolumbar region, causing upper motor neuron signs in the rear limbs, which are thought to have a more favourable prognosis compared to the lower motor neuron signs created by herniation of an intervertebral disc in the caudal lumbar region. Due to the potential disruption of the lumbar intumescence, lower motor neuron signs have been reported as having a less favourable prognosis. The purpose of this study was to evaluate the intervertebral disc space as a prognostic factor relating to ambulatory outcome and time to ambulation after decompressive surgery. Hansen Type I intervertebral disc extrusions were studied in 308 non-ambulatory dogs. Preoperative and postoperative neurological status, corticosteroid use, signalment, intervertebral disc space, postoperative physical rehabilitation, previous hemilaminectomy surgery, disc fenestration, return to ambulation, and time to ambulation were reviewed.

Animals↗
PubMed2005

Comparison of radiographic arthritic changes associated with two variations of tibial plateau leveling osteotomy.

Osteoarthritis (OA) progresses in the canine cranial cruciate ligament (CCL) deficient stifle. Progression of OA is also documented in canine patients after various surgical repair techniques for this injury. We evaluated the radiographic arthritic changes in canine stifle joints that have sustained a CCL injury, and compared radiographic OA scores between Tibial Plateau Leveling Osteotomy (TPLO)surgery patients receiving a medial parapatellar exploratory arthrotomy for CCL remnant removal versus those receiving a limited caudal medial arthrotomy without removal of the CCL remnants. Medial/lateral and caudal/cranial stifle radiographs were obtained before surgery, immediately following TPLO surgery and at 7-38 months (mean 20.5) after surgery. Sixty-eight patients (72 stifles) were included in the study. The cases were divided into two groups. The patients in group 1 (n = 49 patients, 51 stifles) had a limited caudal medial arthrotomy, and patients in group 2 (n = 19 patients, 21 stifles) had a medial parapatellar open arthrotomy. A previously described radiographic osteoarthritis scoring system was used to quantify changes in both of the groups. The age, weight, OA scores, initial tibial plateau angle, final tibial plateau angle, and the change in angle were compared between the groups. The results showed that there was significantly less progression of OA in the group that had the limited caudal medial, arthrotomy, versus a medial parapatellar open arthrotomy. There was a significant advancement of the OA scores of patients that had TPLO surgery.

Animals↗
PubMed2001

Autistic disorder versus other pervasive developmental disorders in young children: same or different?

Eighteen preschool children diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders Third Edition Revised (DSM III-R) as having Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS) were compared to 176 children with DSM III-R Autistic Disorder (AD), and to 311 non-autistic children with developmental language disorders (DLD) (N = 201) or low IQ (N = 110). All children were partitioned into "high" and "low" cognitive subgroups at a nonverbal IQ of 80. Within cognitive subgroups, the 18 PDD-NOS children did not differ significantly from either the DLD or the AD children in verbal and adaptive skills and obtained scores intermediate between those of these groups. The PDD-NOS did not differ from the AD children in maladaptive behaviors. Both the PDD-NOS and AD children had many more of these behaviors than the non-autistic comparison groups. Children in the "high" and "low" cognitive subgroups of AD, but not of PDD-NOS, differed substantially on most measures, with the children with lower cognitive scores significantly more impaired on all measures. Similarity of PDD-NOS children to AD children in maladaptive behaviors and an intermediate position between autistic and non-autistic groups on virtually all measures explains the difficulty clinicians encounter in classifying children with PDD and raises questions about the specificity of these diagnostic subtypes of the autistic spectrum.

Autistic Disorder↗
PubMed2000

What is the best proton energy for accelerator-based BNCT using the 7Li(p,n)7Be reaction?

With a growing interest in the use of accelerator-based epithermal neutron sources for BNCT programs, in particular those based upon the 7Li(p,n)7Be reaction, there is a need to address the question of "what is the best proton energy to use?" This paper considers this question by using radiation transport calculations to investigate a range of proton energies from 2.15 to 3.5 MeV and a range of moderator sizes. This study has moved away completely from the use of empty therapy beam parameters and instead defines the beam quality and optimizes the moderator design using widely accepted in-phantom treatment planning figures of merit. It is concluded that up to a proton energy of about 2.8 MeV there is no observed variation in the achievable therapy beam quality, but a price is paid in terms of treatment time for not choosing the upper limit of this range. For higher proton energies, the beam quality falls, but with no improvement in treatment time for optimum configurations.

Beryllium↗
PubMed1999

Design for an accelerator-based orthogonal epithermal neutron beam for boron neutron capture therapy.

This paper is concerned with the proposed Birmingham accelerator-based epithermal neutron beam for boron neutron capture therapy (BNCT). In particular, the option of producing a therapy beam at an orthogonal direction to the incoming protons is considered. Monte Carlo radiation transport simulations, both with and without a head phantom, have shown that an orthogonal beam geometry is not only acceptable but is indeed beneficial, in terms of a lower mean neutron energy and an enhanced therapeutic ratio for the same useful neutron fluence in the therapy beam. Typical treatment times for various beam options have been calculated, and range from 20 to 48 min with a 5 mA beam of 2.8 MeV protons, if the maximum photon-equivalent dose delivered to healthy tissue is to be 12.6 Gy Eq. The effects of proton beam diameter upon the therapy beam parameters have also been considered.

Boron Neutron Capture Therapy↗
PubMed1999

Toward a final design for the Birmingham boron neutron capture therapy neutron beam.

This paper is concerned with the proposed Birmingham accelerator-based epithermal neutron beam for boron neutron capture therapy (BNCT). Details of the final moderator design, such as beam delimiter, shield, and beam exit surface shape are considered. Monte Carlo radiation transport simulations with a head and body phantom have shown that a simple flat moderator beam exit surface is preferable to the previously envisioned spherical design. Dose rates to individual body organs during treatment have been calculated using a standard MIRD phantom. We have shown that a simple polyethylene shield, doped with natural lithium, is sufficient to provide adequate protection to the rest of the body during head irradiations. The effect upon the head phantom dose distributions of the use of such a shield to delimit the therapy beam has been evaluated.

Boron Neutron Capture Therapy↗
PubMed1999

Inhibition of CFU-E colony formation in uremic patients with inflammatory disease: role of IFN-gamma and TNF-alpha.

BACKGROUND: There is evidence for the role of inflammatory cytokines in the inhibition of erythropoiesis in the anemia of chronic disease, but the extent to which they contribute to resistance to erythropoietin (EPO) in patients with chronic renal failure is not clear. The purpose of the present study was to assess the effect of sera from patients with end-stage renal failure with and without infection or inflammatory disease on CFU-E colony formation in vitro. METHODS: Bone marrow was obtained from uremic patients with inflammatory disease and from healthy controls. Standard colony assays were used to assess erythroid colony formation (CFU-E) in response to EPO in the presence or absence of 5% autologous serum. Normal bone marrow mononuclear cells were cultured with 5% v/v sera from three groups of patients: healthy volunteers, uremic controls, and uremic patients with inflammatory disease. RESULTS: There was no difference between normal and uremic bone marrow response to EPO. However, when uremic/inflammatory bone marrow was cultured with autologous serum the optimal response to EPO was significantly inhibited. Optimal CFU-E colony formation was suppressed significantly by sera from either uremic group when compared with cultures containing sera from controls. Treatment of parallel cultures with a combination of antibodies to interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) almost completely restored the response to EPO. Additionally, bone marrow from healthy controls incubated with uremic sera showed an increased production of interleukin-1 alpha (IL-1 alpha) and IFN-gamma, and TNF-alpha was present in uremic sera. CONCLUSIONS: CFU-E colony formation is inhibited by soluble factors present in the sera of uremic patients with or without inflammatory disease. These soluble factors stimulate the production of IFN-gamma and TNF-alpha, which directly inhibit erythropoiesis at a local level in the bone marrow.

Adult↗
PubMed1998

In-phantom neutron fluence measurements in the orthogonal Birmingham boron neutron capture therapy beam.

This paper presents the results of an experimental investigation into the performance of the Birmingham accelerator-based epithermal BNCT beam. In-phantom gold foil activation and boron trifluoride tube measurements have been used. The results have been compared with calculated response rates using Monte Carlo modeling of the entire neutron system from source to phantom and detector. The excellent agreement obtained gives us confidence in the validity of the simulations and our ability to predict accurately the neutronic performance of our BNCT facility.

Biophysical Phenomena↗
PubMed1997

Evaluation of a hypertonic saline-dextran solution for treatment of dogs with shock induced by gastric dilatation-volvulus.

OBJECTIVE: To test the hypothesis that small volumes of hypertonic saline-dextran (HSD) solution can be used to effectively resuscitate dogs in shock induced by gastric dilatation-volvulus (GDV), and, compared with administration of large volumes of lactated Ringer's solution (LRS), can be used to limit the overall volume of fluid needed for resuscitation. DESIGN: Prospective, clinical study. ANIMALS: 15 dogs with GDV-induced shock. PROCEDURE: Initially, HSD solution (5 ml/kg of body weight) or LRS (60 to 90 ml/kg) was administered. All dogs then received a maintenance administration (20 ml/kg/h) of LRS. Cardiorespiratory, blood gas, and serum biochemical analyses were performed over a 4-hour period after initiation of treatment. RESULTS: Systolic arterial and central venous pressures and plasma volume increased more rapidly in dogs in the HSD + LRS group. The cumulative dose of fluids administered to dogs in the HSD + LRS group was significantly less than that administered to dogs in the LRS group. Serum sodium and chloride concentrations and osmolality increased significantly in dogs in the HSD + LRS group, but not in dogs in the LRS group. Ventricular arrhythmias were detected in both groups of dogs, but did not appear to be induced by either form of fluid therapy. CLINICAL IMPLICATIONS: Administration of HSD rapidly restored cardiorespiratory function and induced resuscitation equivalent to administration of large volumes of LRS. Use of HSD solutions to treat dogs in GDV-induced shock may be more efficient than use of isotonic fluids. Administration of HSD solution was not associated with noticeable complications.

Animals↗
PubMed1996

Factors associated with perioperative mortality in dogs with surgically managed gastric dilatation-volvulus: 137 cases (1988-1993).

OBJECTIVE: To evaluate factors associated with perioperative mortality in dogs with gastric dilatation-volvulus and to determine the influence of treatment differences between university and private specialty practices on outcome. DESIGN: Retrospective analysis of medical records. ANIMALS: 137 dogs with gastric dilatation-volvulus. PROCEDURE: Signalment; frequency of preoperative and postoperative treatments and complications; intraoperative findings; surgical technique; and hematologic, serum biochemical, and electrocardiographic results were recorded, evaluated for association with mortality, and compared between institutions. RESULTS: Mortality did not differ between institutions, and overall mortality was 18% (24/137). Surgical techniques differed between institutions, but were not associated with mortality. Gastric necrosis was associated with significantly higher mortality (46%; 13/28). When partial gastrectomy or splenectomy was performed, mortality (35 and 32% or 8/23 and 10/31, respectively) was significantly increased. Splenectomy was performed in 11 of 23 dogs requiring partial gastrectomy, and when both procedures were performed, mortality (55%; 6/11) was significantly increased. Preoperative cardiac arrhythmias were associated with significantly higher mortality (38%; 6/16). Mortality in dogs > 10 years old was not significantly greater than that in younger dogs. CLINICAL IMPLICATIONS: Patient management differences between practices did not seem to influence survival in dogs with surgically managed gastric dilatation-volvulus. Signalment, including age, did not influence mortality. Gastric necrosis, gastric resection, splenectomy, and preoperative cardiac arrhythmias were associated with mortality > 30%.

Animals↗
PubMed1996

Evaluation of a hypertonic sodium chloride/dextran solution for treatment of traumatic shock in dogs.

OBJECTIVE: To compare the efficacy of 7% NaCl solution (hypertonic saline) in 6% dextran 70 solution (HSD) with that of lactated Ringer's solution (LRS) for treatment of dogs in traumatic shock. DESIGN: Prospective, randomized, clinical study. ANIMALS: 16 traumatized adult dogs with clinical signs of shock. PROCEDURE: Physical, hemodynamic, blood gas, and clinical chemistry measurements were performed prior to treatment. Initial treatment consisted of HSD (n = 8) or LRS (n = 8) administered as a bolus (5 ml/kg of body weight, IV) over a 3-minute period, followed by administration of additional LRS and other treatments to restore hemodynamic and physical criteria to within reference limits. Measurements were repeated for 3 hours after initial treatment. The volumes of LRS and HSD administered were recorded hourly. Degree of injury was scored by using a trauma severity index. RESULTS: Dogs responded similarly to the treatments, and all but 3 dogs survived to be discharged. The amount of fluid administered to dogs in the HSD group over the final 2 hours of the study was significantly less than that administered to the dogs in the LRS group. Serum sodium concentration and osmolality of the dogs in the HSD group were not significantly greater than those values in the LRS group. Bradyarrhythmias were observed in 2 dogs in the HSD group. CLINICAL IMPLICATIONS: Hypertonic sodium chloride/dextran solution is safe and effective for resuscitating dogs in traumatic shock. Seven percent NaCl in 6% dextran 70 may reduce the need for isotonic fluids in the hours after initial resuscitation.

Accidents, Traffic↗
PubMed1995

A design study for an accelerator-based epithermal neutron beam for BNCT.

An achievable design concept for a boron neutron capture therapy (BNCT) facility, based on a high-current, low-energy proton accelerator, is described. Neutrons are produced within a thick natural lithium target, under bombardment from protons with an initial energy between 2.5 and 3.0 MeV. The proton current will be up to 10 mA. After gamma-ray filtering, the neutrons are partially moderated to epithermal energies within a heavy-water moderator, poisoned with 6Li to remove thermal neutrons. Monte Carlo modelling has been used to predict system performance in terms of neutron fluence rate and neutron and gamma-ray dose at the patient position. The relationship between the system performance and key parameters, such as proton energy, moderator depth and 6Li concentration, has been investigated. With a proton current of 10 mA, the facility is capable of providing a therapy beam with a useful neutron fluence rate of 10(9) cm-2 s-1 and a neutron dose per unit fluence of less than 6 x 10(-13) Gy cm2, with a gamma-ray contamination of the therapy beam of about 10(-13) Gy cm2.

Biophysical Phenomena↗
PubMed1994

Pathogenic aspects of circulatory shock.

Shock has been described and defined by the inciting cause. This method of categorization does little to clarify common pathophysiologic changes known to occur regardless of the etiology. Each type of shock involves different stages that are determined by the inciting cause, its duration, severity of the initial result, susceptibility of the patient, and adequacy of treatment.

Animals↗
PubMed1994

Comparative effects of 7% NaCl in 6% dextran 70 and 0.9% NaCl on oxygen transport in endotoxemic dogs.

We compared the effects of 7% NaCl in 6% dextran 70 (HSD) and 0.9% NaCl (IS) resuscitation of endotoxic dogs on hemodynamic and cardiorespiratory parameters and the oxygen consumption-delivery relationship. Escherichia coli endotoxin (3 mg.kg-1, intravenously) was infused over 5 min into 13 paralyzed, chloralose-anesthetized, splenectomized dogs. Six additional dogs received a sham endotoxin infusion (saline) and served as controls. After 30 min, the endotoxic animals were resuscitated to 150% of their baseline cardiac output (CO) and maintained at this CO for 30 min using 7% NaCl in 6% dextran 70 (HSD at 1 ml.kg-1.min-1; n = 7) or 0.9% NaCl (IS at 4 ml.kg-1.min-1; n = 6). Oxygen consumption (VO2), measured by indirect calorimetry, hemodynamic parameters, and oxygen delivery (DO2), improved in similar temporal patterns in both groups during resuscitation and VO2 reached steady-state values. Oxygen delivery, VO2, mean arterial pressure, and cardiac output did not significantly differ between groups at the end of resuscitation, but VO2 increased significantly from baseline values only in the HSD group. The total volume of HSD administered averaged 10.0 +/- 0.2 ml.kg-1 which was significantly less than the volume of IS, which averaged 67.2 +/- 9.3 ml.kg-1. Incremental hemorrhages (2-5 ml.kg-1) were then performed in all dogs to determine the oxygen consumption-delivery relationship and the critical level of oxygen delivery (DO2Crit). The average DO2Crit values of the HSD, IS, and control groups were 9.42, 9.15, and 6.82 ml.min-1.kg-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Acute lung injury isolated to an in situ lung preparation causes sustained reflex cardiovascular depression in dogs.

We tested the hypothesis that acute lung injury (ALI) isolated to a perfused in situ left lung preparation results in sustained reflex cardiovascular depression. Phorbol myristate acetate (PMA), an agent that activates neutrophils, administered into the isolated lung preparation of chloralose-anesthetized dogs resulted in ALI, as assessed by wet-to-dry weight ratios and histopathology, and significant decreases in heart rate (43%), mean arterial pressure (27%), aortic blood flow (29%) and maximum rate of change in left ventricular pressure (30%). Significant reflex effects occurred by 20 min after PMA administration and were sustained for 40 min (n = 7). Hemodynamic variables recovered when the left lung was denervated 60 min after PMA administration. Indomethacin administered into the isolated circulation before PMA (n = 5) did not significantly influence the ALI or reflex effects. Systemic atropinization (n = 6) prevented only the bradycardia. Left lung denervation before ALI (n = 3) prevented all reflex effects. We conclude that PMA administration into an isolated in situ lung preparation results in ALI and sustained reflex cardiovascular depression that is most likely elicited by pulmonary C-fiber stimulation and mediated by withdrawal of sympathetic efferent nerve activity.

Animals↗
PubMed1993

Continuous pulmonary C-fiber stimulation produces sustained reflex cardiovascular depression.

We used an isolated perfused in situ left lung preparation to evaluate the hemodynamic response to specific pulmonary C-fiber stimulation with capsaicin in two groups of anesthetized dogs. In one group (n = 6), continuous administration of capsaicin at 5 micrograms.kg-1.min-1 into the isolated pulmonary circulation produced sustained (20 min) reflex decreases in mean arterial pressure, cardiac output, maximal left ventricular rate of pressure over time, and heart rate. These effects were abolished by vagotomy. In a second group (n = 5) of atropinized dogs, a mild hemorrhage was first performed in each dog during control conditions (capsaicin vehicle administration). The hemorrhage was performed by removing 10% of blood volume over 3 min and then replacing this blood 3 min later. After reinfusion and stabilization, the mild hemorrhage was repeated during continuous administration of capsaicin (6.0 +/- 1.0 microgram.kg-1.min-1) into the isolated pulmonary circulation. The decrease of mean arterial pressure in response to hemorrhage was significantly greater during capsaicin administration than during control conditions. Lung denervation prevented the effect of capsaicin administration on the response to hemorrhage. We concluded that continuous pulmonary C-fiber stimulation produces sustained cardiovascular depression and compromises the hemodynamic response to mild hemorrhage in dogs. This latter effect may represent a central alteration of baroreflex gain.

Animals↗
PubMed1993

Reflex cardiovascular effects of continuous prostacyclin administration into an isolated in situ lung in the dog.

Bolus administration of prostacyclin (PGI2), an inflammatory product produced by the arachidonic acid cyclooxygenase pathway, into the pulmonary circulation is known to stimulate pulmonary C-fibers and to produce transient reflex cardiovascular depression. We used an isolated perfused in situ left lung preparation to examine the reflex cardiovascular effects of continuous administration of PGI2 into the isolated pulmonary circulation of dogs. PGI2 was infused for 30 min (5 micrograms.kg-1 x min-1) into the innervated isolated left pulmonary circulation in six dogs and into the denervated isolated circulation in seven dogs. Mean arterial pressure and cardiac output were significantly decreased from baseline values during the final 20 min of PGI2 infusion. There were no significant changes in maximum rate of change of left ventricular pressure during systole and in heart rate. All variables returned to baseline levels within 15 min of discontinuation of PGI2 infusion. PGI2 infusion produced no significant measured hemodynamic changes in the denervated group. Control experiments demonstrated that the observed response was not affected by duration of the preparation, lung denervation, or infusion vehicle. These findings suggest that continuous infusion of PGI2 into the isolated pulmonary circulation produces sustained cardiovascular depression via a vagal reflex mechanism that is probably mediated by pulmonary C-fibers.

Animals↗