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Biomedical subjects

P Baxter

Publications and source records attributed to P Baxter.

At least 19 recordsLinked to original sources
PubMed2006

Investigation of tetrakis hydroxymethyl phosphonium chloride as an antioxidant for use in x-ray computed tomography polyacrylamide gel dosimetry.

Of the antioxidants used to scavenge oxygen in polymer gel dosimeters, tetrakis (hydroxymethyl) phosphonium chloride (THPC) has been shown to hold great promise due to its rapid oxygen scavenging abilities. In this study we (a) investigate the use of THPC as an antioxidant for polyacrylamide gel (PAGAT) dosimeters used in conjunction with x-ray computed tomography (CT) and (b) work to establish the reaction mechanisms of THPC with the polymer gel constituents. We establish the dose response reproducibility of PAGAT dosimeters when imaged with CT and show that PAGAT dosimeters exhibit highly reproducible dose responses for a range of irradiation times post gel manufacture (2-6 h) and CT imaging times post gel irradiation (1-5 days). The THPC concentration within the gel leading to a maximized dose response and minimized O(2) inhibition of polymerization is found to be approximately 4.5 mM. We further assess the stability of PAGAT dosimeters by investigating the reactions of THPC with the individual gel constituents. The importance of utilizing deionized water in polymer gel manufacture is noted. We show that, while THPC remains unreactive with acrylamide and bis-acrylamide under unirradiated conditions, THPC can react with gelatin to increase the cross-linking of the gelatin matrix in unirradiated dosimeters. THPC reactions with gelatin can lead to the lower observed dose sensitivity of PAGAT (approximately 0.36 +/- 0.04 H Gy(-1)) as compared to polyacrylamide gels manufactured under anoxic conditions (approximately 0.83 +/- 0.03 H Gy(-1)). The reactions of THPC which lead to O(2) scavenging, and potential reactions of THPC with other gel constituents, are proposed.

Acrylic Resins↗
PubMed2002

Stress in UK intensive care unit doctors.

BACKGROUND: Doctors have long been considered at risk of occupational stress. METHODS: A postal survey of all members of the Intensive Care Society using validated instruments. RESULTS: Eight-five per cent of members returned questionnaires and 70% were eligible for the study. Twenty-nine per cent were suffering General Health Questionnaire-12 (GHQ-12) identified distress and 12% Symptom Checklist-Depression (SCL-D) defined depression. There were no significant age or sex differences between staff suffering distress or depression and those who did not. Dissatisfaction with career correlated highly with both distress and depression (P<0.01). Twenty doctors (3%) were bothered by suicidal thoughts. The most stressful aspects of work were bed allocation, being over-stretched, effect of hours of work and stress on personal/family life, and compromising standards when resources are short. Logistic regression revealed mental health problems were predicted by five stressors: 'lack of recognition of one's own contribution by others'; 'too much responsibility at times'; 'effect of stress on personal/family life'; 'keeping up to date with knowledge'; and 'making the right decision alone'. CONCLUSIONS: Nearly one in three ICU doctors appeared distressed (GHQ), and one in 10 depressed (SCL-D); this is no greater than that reported in other specialities. Perceived stressors reveal some key areas of concern for the employer and the specialty.

Adult↗
PubMed2001

Routine intracranial pressure monitoring in acute coma.

BACKGROUND: Studies in traumatic encephalopathy first led to the insight that the damage seen was not just due to direct consequences of the primary injury. A significant, and potentially preventable, contribution to the overall morbidity arose from secondary hypoxic-ischaemic damage. Brain swelling accompanied by raised intracranial pressure (ICP) resulted in inadequate cerebral perfusion with well-oxygenated blood. Detection of raised ICP could be useful in alerting clinicians to the need to improve cerebral perfusion, with consequent reductions in brain injury. OBJECTIVES: To determine whether routine ICP monitoring in all acute cases of severe coma reduces the risk of all-cause mortality or severe disability at final follow up. SEARCH STRATEGY: We searched MEDLINE, EMBASE, The Injuries Group's specialised register and the reference lists of all relevant articles and review articles. In addition we searched the Index of Scientific and Technical Proceedings using "intracranial pressure" as keyword. SELECTION CRITERIA: All randomised controlled studies of real-time ICP monitoring by invasive or semi-invasive means in acute coma (traumatic or non-traumatic aetiology) versus no ICP monitoring (ie clinical assessment of ICP ) DATA COLLECTION AND ANALYSIS: Primary outcome measures were all-cause mortality and severe disability at the end of the follow up period. MAIN RESULTS: No studies meeting the selection criteria have been identified to date. REVIEWER'S CONCLUSIONS: There are no data from randomised controlled trials that can clarify the role of ICP monitoring in acute coma.

Acute Disease↗
PubMed2001

Tethering of the vertebral artery in the congenital arcuate foramen of the atlas vertebra: a possible cause of vertebral artery dissection in children.

Twelve children with vertebrobasilar artery stroke are reported (seven males, five females; aged 6 months to 15 years). Patient 1 showed an arcuate foramen in the posterior arch of the atlas, an anatomical variant occurring in 3 to 15% of the population. It was hypothesized that the presence of the arcuate foramen might cause tethering of the vertebral artery and lead to its dissection by repetitive trauma. Lateral plain films of the cervical spine in cases of posterior circulation stroke were taken. Eight of 11 patients showed aberrant arcuate foramina. Of the remaining three patients, one had normal cervical spine X-rays, one had an absent right posterior arch of the atlas following previous surgery for a cervical meningocele, and one patient had incomplete ossification of the vertebrae. Seven of the nine patients with arcuate foramina had vertebral angiograms. In all cases this showed the vertebral artery passing through the arcuate foramen before entering the brain and an appearance consistent with arterial dissection and occlusion at the same site below the foramen. Most documented cases of posterior circulation stroke in children follow trauma, which may be minimal or repetitive, with thrombotic occlusion of the artery at C1-C2 level. The association with an arcuate foramen and its possible causative role in the genesis of posterior circulation stroke in children has not been previously recognized. There may be a causal association between the presence of an arcuate foramen, tethering of the vertebral artery in the foramen, and dissection from repetitive trauma with movement of the neck.

Adolescent↗
PubMed2000

Familial thrombophilia associated with fibrinogen paris V: Dusart syndrome.

We report on a family with a history of venous thromboembolism associated with fibrinogen Paris V (fibrinogen Aalpha-Arg554-->Cys). Ten members experienced thrombotic events, including 4 with fatal pulmonary emboli. Pulmonary embolism was the presenting feature in 4. Those with the mutation and a history of thrombosis had somewhat higher fibrinogen concentrations than those with the mutation and no thrombosis (294 +/- 70 mg/dL vs 217 +/- 37 mg/dL, respectively). The Paris V mutation consistently caused a prolongation of the reptilase time, and fibrin clots containing the abnormal fibrinogen were more translucent than normal clots. Given the early onset of symptoms and the initial presentation with pulmonary embolism in some family members, it was justifiable to offer prophylactic anticoagulation with warfarin to carriers of the mutation. Fibrinogen Paris V has now been reported in 4 apparently unrelated families, indicating that it is a relatively common cause of dysfibrinogenemia-associated thrombosis.

Adolescent↗
PubMed2000

Detection of damage to the mitochondrial genome in the oncocytic cells of Warthin's tumour.

Warthin's tumour of the salivary glands is composed of oncocytic cells containing excessive numbers of mitochondria which show frequent structural abnormalities and reduced metabolic function. Recent evidence of a strong association between cigarette smoking and the occurrence of Warthin's tumour prompted this study, to look for evidence of damage to mitochondrial DNA (mtDNA) that could be the result of an increase in oxidative stress; two-colour fluorescence in situ hybridization (FISH) was developed to show the distribution of mitochondria with deleted mtDNA in paraffin wax-embedded material. Approximately 10% of mtDNA bears the 'common' 4977 bp deletion. Using the polymerase chain reaction (PCR), the 4977 bp deletion was further quantified, in Warthin's tumour and age-matched normal parotid control tissue. Whilst the deletion was present in all parotid tissue, its presence was significantly higher in oncocytic tumour cells. In a small number of controls, there was a trend towards higher concentrations of the deletion in smokers.

Adenolymphoma↗
PubMed1999

Congenital paraplegia following maternal hypotension.

Congenital paraplegia, with partial improvement over the first months of life, occurred in a female neonate born at 35 weeks' gestation, whose mother had suffered hypotension and hypoxaemia due to anaphylaxis 12 weeks earlier. Our patient subsequently had an acute encephalopathy during a respiratory illness with later developmental delay. We speculate that the baby's paraplegia resulted from spinal-cord ischaemia in utero. The aim of this report is to describe the spinal presentation.

Adult↗
PubMed1999

Epidemiology of pyridoxine dependent and pyridoxine responsive seizures in the UK.

OBJECTIVE: To study the epidemiology of pyridoxine dependent seizures and other forms of pyridoxine responsive seizures. DESIGN: Monthly notifications to the British Paediatric Surveillance Unit over two years. Questionnaire follow up. SETTING: UK and the Republic of Ireland. PATIENTS: Children aged 15 years or younger whose seizures respond to pyridoxine. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Numbers of children with definite, probable, and possible pyridoxine dependent seizures or other seizures responsive to pyridoxine. RESULTS: Point prevalence and birth incidence: 1/687 000 and 1/783 000, respectively (definite and probable cases); 1/317 000 and 1/157 000, respectively (all types of pyridoxine responsiveness). NOTIFICATIONS: Pyridoxine dependency: 14 definite, 9 probable, and 10 possible cases; neonatal seizures not meeting case definitions: 7; infantile spasms: 5. Eight of 18 families of definite/probable cases had 2 affected siblings. Just over a third had atypical presentations and just under a third had features and/or initial diagnoses of birth asphyxia and neonatal hypoxic ischaemic encephalopathy. CONCLUSIONS: Pyridoxine dependency is rare. Atypical presentations are relatively frequent. A trial of pyridoxine is justified in all cases of early onset intractable seizures or status epilepticus, whatever the suspected cause.

Adolescent↗
PubMed1999

The laryngeal mask airway in experimental pig anaesthesia.

The pig is used as a large animal model in many research projects. Standard practice for airway maintenance under general anaesthesia is using endotracheal (ET) intubation after intravenous induction to a near surgical plane. This is a technically demanding skill, requiring the assistance of an experienced technician. A technique is required which simplifies pig anaesthesia. This study examined the feasibility and potential advantages of using the laryngeal mask airway (LMA) in 10 pigs during laparotomy under spontaneous breathing anaesthesia. The results show that the LMA can be inserted rapidly, with minimal time for airway control by researchers relatively inexperienced in anaesthesia and is associated with few complications. By removing the need for intravenous induction, an entire step in the anaesthetic process is removed. The LMA designed for humans fits well in the pig hypopharynx; all pigs could be manually ventilated with no detectable gas leak. Although the pigs in this study were spontaneously breathing it is proposed that the LMA should be further investigated in studies of artificially ventilated pigs.

Adrenergic alpha-Agonists↗
PubMed1999

An assessment of the sensitivity of the Cedars-Sinai quantitative gated SPECT software to changes in the reconstruction of the short-axis slices.

OBJECTIVE: This study assessed whether variations in count density, reconstruction filtering parameters and the short-axis orientation selected for reconstructions of myocardial short-axis slices significantly influenced the left ventricular ejection fraction (LVEF) calculated from a gated myocardial perfusion SPECT study. METHODS: The Cedars-Sinai quantitative gated SPECT software package was used to estimate the LVEF from gated 99mTc-sestamibi and 201TI gated SPECT studies in 20 patients. Oblique slices were reconstructed 12 times for each study, independently varying the filter cutoff and the orientation of the short axis each time. RESULTS: There were no clinically significant changes in the LVEF over the range of cutoff frequencies or orientation for either the 201TI or 99mTc-sestamibi studies. There was excellent agreement between the LVEF calculated from the 201TI and 99mTc-sestamibi studies on the same patients using the default filter (mean difference = 0.25% points). CONCLUSIONS: The Cedars-Sinai quantitative gated SPECT software package for parallel-hole collimators can be used with confidence to obtain an LVEF, and is not sensitive to variations in count density, filtering parameters or short-axis orientation.

Algorithms↗
PubMed1998

Experimental study of electrolysis-induced hepatic necrosis.

BACKGROUND: One of the most promising but unexplored methods for treating patients with irresectable liver tumours is electrolysis. This study examined the effect of increasing 'current dose' on the volume of the lesion induced in normal rat liver. METHODS: A direct current generator, connected to platinum electrodes implanted in the rat liver, was used to examine the effect of (1) varying current doses from 1 to 5 coulombs and (2) electrode separation (2 or 20 mm), on the volume of liver necrosis. RESULTS: There was a significant correlation (P < 0.001) between the current dose and the volume of necrosis produced for each electrode separation. Placing the electrodes 2 mm apart resulted in smaller total volumes of necrosis than placing them 20 mm apart when anode lesions were significantly larger than cathode lesions (P< 0.05). Liver enzymes (aspartate aminotransferase, alanine aminotransferase) were significantly raised 1 day after treatment (P < 0.001) and predicted the total volume of hepatic necrosis (P < 0.001). CONCLUSION: Predictable and reproducible areas of liver necrosis are produced with electrolysis. If these results extrapolate to larger animal models, this technique has potential for patients with irresectable primary and secondary liver tumours.

Animals↗