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Biomedical subjects

S Snowden

Publications and source records attributed to S Snowden.

At least 19 recordsLinked to original sources
PubMed2003

A mathematical model of CO2 variation in the ventilated neonate.

A mathematical model of the variation of partial pressure of carbon dioxide in the arterial blood of a ventilated neonate is developed. The model comprises alveolar, arterial, pulmonary, venous and tissue compartments, with gas exchange in the lung determined by inspiration and expiration terms. Gas exchange is modelled through diffusion and convective transfer. Carbon dioxide is produced in the tissue by a metabolic term. Shunting is modelled by allowing blood flow to bypass the pulmonary compartment in which diffusion takes place. The model predicts changes in the carbon dioxide partial pressures that occur following abrupt changes in the ventilation settings, and show broad agreement with actual data obtained from novel sensing technology.

Carbon Dioxide↗
PubMed2002

Temperature rise during reamed tibial nailing.

The current study determined the temperature rise during reamed tibial intramedullary nailing in vivo. Eighteen adult patients were studied. The tibial medullary canal diameter ranged from 8 to 11 mm and was reamed to at least 1.5 mm above the required nail diameter with AO reamers. Reaming of the medullary cavity ranged from 9 to 12 mm before nail insertion. Intraoperative monitoring of the heat produced during reaming of the medullary cavity was done by inserting two platinum resistance thermometer probes into the cortical bone at the short isthmic segment of the tibial shaft. The probes were connected to a data logger, and temperature readings were taken every 5 seconds during each reaming procedure. The mean tibial temperature before initiation of reaming was 35.6 degrees C (standard deviation, +/- 0.5 degrees), and peak temperatures recorded were from 36.1 degrees C to 51.6 degrees C. A direct correlation was observed between temperature elevation and amount of reaming. With reaming above 10 mm, tibias with a canal diameter of 8 mm showed a statistically higher temperature rise compared with tibias with a canal diameter of 9, 10, or 11 mm. No patients had intraoperative or postoperative complications related to skin or bone thermal necrosis, and bony healing progressed uneventfully. The small amount of reaming required to insert a nail into a normal 9-, 10-, or 11- mm tibial canal does not seem to produce a clinical problem. Reaming smaller canals (8 mm) to a larger size may induce a significant heating effect.

Adolescent↗
PubMed2002

Friction burns within the tibia during reaming. Are they affected by the use of a tourniquet?

We have carried out a prospective, randomised trial to measure the rise of temperature during reaming of the tibia before intramedullary nailing. We studied 34 patients with a mean age of 35.1 years (18 to 63) and mean injury severity score of 10 (9 to 13). The patients were randomised into two groups: group 1 included 18 patients whose procedure was undertaken without a tourniquet and group 2, 16 patients in whom a tourniquet was used. The temperature in the bone was measured directly by two thermocouples inserted into the cortical bone near the isthmus of the tibial diaphysis. Reaming was carried out to at least 1.5 mm above the required diameter of the nail. Blood loss was assessed by recording the preoperative and postoperative haemoglobin (Hb) level. The minimum clinical follow-up was six months. In group 1 (no tourniquet), the mean Hb dropped 2.8 g/dl from 14.3 +/- 1.02 g/dl to 11.5 +/- 1.04 g/dl (p = 0.0001), whereas with the tourniquet, the mean decrease was 1.3 g/dl from 14 +/- 1 g/dl to 12.7 +/- 1.3 g/dl (p = 0.007). This difference was not statistically significant. The mean initial tibial temperature was 35.6 degrees C (SD 0.6) and rose with reaming to levels between 36.3 degrees C and 51.6 degrees C. The highest temperatures were obtained with the largest reamers (11 and 12 mm, p = 0.0001) and the most rapid rise with the smallest diameters of medullary canal (8 or 9 mm). The rise of temperature was transient (20 s). We were unable to identify any effect of the use of a tourniquet on the temperature achieved. Reamed intramedullary tibial nailing induces a transient elevation of temperature which is directly related to the amount of reaming.

Adolescent↗
PubMed2001

European randomised trial of dual versus triple tacrolimus-based regimens for control of acute rejection in renal allograft recipients.

Two large multicentre studies have shown superiority of tacrolimus-based immunosuppressive regimens compared with standard cyclosporine-based therapy in renal transplantation. In these studies, tacrolimus was used in a triple drug regimen of tacrolimus, corticosteroids, and azathioprine. The present study aimed to determine whether a tacrolimus-based dual regimen achieves a similar efficacy and safety profile compared with conventional triple therapy. In this prospective, open, multicentre trial, 249 patients were randomised to receive either dual therapy (n = 125) of oral tacrolimus (initial daily dose of 0.2 mg/kg) and oral prednisone or additionally, as a triple therapy (n = 124), oral azathioprine. The primary endpoint was the incidence of acute rejection at month 3. In addition, all patients were included into a follow-up evaluation at 1 year after transplantation. Both treatment groups had similar baseline characteristics. At month 3, patient survival was 97.6 % (dual) and 96.7 % (triple); graft survival was 92.7 % (dual) and 91.7 % (triple). The incidence of treated acute rejection confirmed by biopsy was 27.4 % (dual) and 24.8 % (triple); difference 2.6 %, 95 % CI [-9.4 %-12.9 %], P = 0.755. The incidence of corticosteroid-resistant rejection (biopsy-confirmed) was 9.7 % (dual) and 10.7 % (triple). The overall adverse events profile was similar; leukopenia (1.6 % vs 11.6 %, P = 0.002) was more frequent with triple therapy. Between months 4 and 12, six (dual) and eight (triple) patients had a rejection. At month 12, patient survival was 95.6 % (dual) and 93.6 % (triple); graft survival was 91.8 % (dual) and 90.7 % (triple). Tacrolimus proved to be efficacious and safe with both dual and triple low-dose regimens. The addition of azathioprine to a tacrolimus/corticosteroid-based therapy did not result in an increased efficacy.

Acute Disease↗
PubMed2001

A digital system for recording the electrical activity of the uterus.

The ability to identify true pre-term labour would be of considerable clinical benefit as electrical signals from the uterus, recorded using surface electrodes, may discriminate between labouring and non-labouring states in human pregnancy. A digital recording system for recording the electrical activity of the uterus has been developed and is described in this paper. A pilot study in which entire recordings in 21 women were subjected to power spectral analysis suggests that the relative power in two frequency bands (0.2-0.45 Hz and 0.8-3 Hz) changes as pregnancy progresses into early labour.

Adult↗
PubMed2001

General practitioner participants in a telemedicine trial: comparisons with their peers.

A study was conducted to determine whether general practitioners (GPs) participating in a telemedicine trial were self-selected enthusiasts for information technology compared with GPs in general. We compared two experimental groups of GPs in London and Wales (n = 126) who had volunteered to participate in a telemedicine trial and two randomly selected groups of GPs from the same areas (total n = 300) who acted as controls. A postal questionnaire was used and achieved a 79% response rate. There were no significant differences in the demographic characteristics of the experimental and control groups in London and Wales, except that the London telemedicine GPs (mean age 41.9 years) were significantly younger than the London controls (mean age 46.6 years). The control GPs were similar to the telemedicine GPs in terms of frequency of computer use and their responses to statements about their attitudes to computers. In the combined telemedicine and control groups, 85% and 77% respectively said that they enjoyed using computers. Telemedicine GPs used computers more frequently for administrative purposes but they shared the same attitudes towards information technology as GPs in general. In all situations where GPs could exercise personal choice, the control and experimental groups were similar.

Adult↗
PubMed2000

Ruptured abdominal aortic aneurysm: a novel method of outcome prediction using neural network technology.

BACKGROUND: reported survival following emergency surgery for ruptured abdominal aortic aneurysm (RAAA) varies widely between institutions. This is largely attributable to differences in case mix. The aim of this study was to identify and evaluate a set of prognostic variables that would accurately predict outcome for individual patients from perioperative indices. METHODS: perioperative factors associated with subsequent mortality at our institution were identified by retrospective review of 102 consecutive operations for RAAA over a 7-year period (January 1990 to January 1997). Logistic regression analysis was used to select the most significant variables associated with subsequent mortality. These were used to construct, train, and validate a neural network designed to predict survival from surgery in individual cases on a prospective basis. RESULTS: the 30-day mortality rate was 53%. Multivariate analysis identified four highly significant independent predictors of mortality; preoperative hypotension, intraperitoneal rupture, preoperative coagulopathy, and preoperative cardiac arrest. Using these inputs, the neural network correctly predicted outcome in 82.5% of individual cases. CONCLUSION: a neural network based on just four perioperative variables can accurately predict outcome of RAAA. Prognostic variables should be reported in studies as a measure of the effect of case mix on survival data. Neural networks have potential to aid decision-making relating to outcome for individual cases.

Aged↗
PubMed1999

Neural networks in the diagnosis of malignant ovarian tumours.

OBJECTIVE: To assess the role of neural networks in predicting the likelihood of malignancy in women presenting with ovarian tumours. DESIGN: Retrospective case study. SETTING: University Department of Obstetrics and Gynaecology, St James's Hospital, Leeds. METHODS: Information from 217 cases with histologically proven benign, borderline or malignant tumours was extracted for study. Four variables (age, ultrasound findings with and without colour Doppler imaging and CA125) were entered in the neural network classifier. The neural network results were compared with logistic regression analysis. RESULTS: When used in the neural network the variables of age, CA125 and ultrasound score produced the best result with a sensitivity of 95% and a corresponding specificity of 78% in predicting malignancy. Logistic regression gave a sensitivity or 82% for a specificity of 51%. CONCLUSION: The neural network is a good method of combining diagnostic variables and may be a useful predictor of malignancy in women presenting with ovarian tumours. A comparison of the performance of the neural network with conventional diagnostic methods would be warranted prior to use in clinical practice.

Adolescent↗
PubMed1997

The application of neural networks in predicting the outcome of in-vitro fertilization.

Infertility affects one in six couples at some time in their lives, with 48% of these couples requiring assisted conception techniques in order to achieve a pregnancy. Whilst the overall clinical pregnancy rate per embryo transfer is 23%, this varies widely between clinics. The Human Fertilisation and Embryology Authority has attempted to analyse the results of all units, with weighting of different factors affecting assisted conception, and the published data have invariably led to comparisons between units. However, statistical models need to be developed to eliminate bias for valid comparisons. Neural networks offer a novel approach to pattern recognition. In some instances neural networks can identify a wider range of associations than other statistical techniques due in part to their ability to recognize highly non-linear associations. It was hoped that a neural network approach may be able to predict success for individual couples about to undergo in-vitro fertilization (IVF) treatment. A neural network was constructed using the variables of age, number of eggs recovered, number of embryos transferred and whether there was embryo freezing. Overall the network managed to achieve an accuracy of 59%.

Adult↗
PubMed1996

5-year follow-up of patients successfully transplanted after immunoadsorption to remove anti-HLA antibodies.

The function of renal allografts in patients who had received pretransplant immunoadsorption in order to remove cytotoxic anti-HLA antibodies was studied. We reviewed 6 patients who received a graft which functioned beyond 3 months; the mean follow-up period was 76 (range 62-89) months. Two grafts have been lost from chronic rejection, at 12 and 62 months, respectively. The mean plasma creatinine levels at 1 and 5 years were 169 (range 143-211) mumol/l and 155 (range 92-235) mumol/l, respectively (1.91, range 1.62-2.39, mg/dl and 1.75, range 1.04-2.66 mg/dl, respectively). The major source of morbidity during long-term follow-up has been the occurrence of renal artery stenosis in 5 patient and renal vein stenosis in 1. In conclusion, the 5-year graft survival and function was good in patients who received immunoadsorption and whose grafts survived beyond the first 3 months after transplantation.

Aged↗
PubMed1995

Reduction of gangrene and amputations in diabetic renal transplant patients: the role of a special foot clinic.

This 4-year prospective study investigated the reasons for high levels of gangrene and major amputation in diabetic renal transplant patients and whether regular multidisciplinary foot care could reduce morbidity. All foot lesions were documented and investigated in 50 diabetic patients, mean age 49.2 +/- 11.0 (SD) years, duration of diabetes 25.3 +/- 9.0 years, time since renal transplantation 60.2 +/- 35.1 months, who attended a special foot clinic monthly for education, vascular and neurological assessment, podiatry and footwear. Foot lesions included: neuropathic ulcers, ischaemic ulcers, traumatic lesions, Charcot's arthropathy, pathological fracture. Treatment included antibiotics, podiatry, footwear, and angioplasty or distal bypass where appropriate. Only 13 patients were deemed ischaemic but peripheral neuropathy was a very common finding (mean VPT 24.8 +/- 12.9 V). Gangrene and major amputations showed a decrease on previous years and healing times for lesions were similar to those previously reported in diabetic patients without renal transplants. The majority of foot lesions, both in soft tissue and bone, were related to neuropathy and trauma and responded well to optimal foot care within the renal unit. Gangrene and major amputations were usually preventable.

Ambulatory Care Facilities↗
PubMed1994

To PEEP or not to PEEP?

It is well recognised that reducing positive end expiratory pressure (PEEP) leads to an increase in the tidal volume and minute volume in ventilated neonates. The magnitude of this effect is perhaps not commonly appreciated, however. Effectively, PEEP is four times as potent as peak inflation pressure (PIP) in bringing about changes in tidal volume. The influence of changes in PEEP and PIP on tidal volume and the relative magnitude of each are considered. Twenty one preterm infants were studied on 38 separate occasions. All were sedated, paralysed, and ventilated, 19 for hyaline membrane disease. A 1 cm H2O reduction in PEEP was twice as potent as a 2 cm H2O increase in PIP in achieving an increase in tidal volume (14 v 7%). Similarly, increasing PEEP by 1 cm H2O was twice as effective as a 2 cm H2O decrease in PIP in reducing tidal volume (13 v 6%). Small (0.5-1 cm H2O) changes in PEEP can often be used to improve ventilation and carbon dioxide elimination. Levels of PEEP of 4-5 cm H2O may, at times, impair gas exchange and contribute to overdistension.

Humans↗
PubMed1988

Non-insulin-dependent diabetes and renal replacement therapy.

Reports of renal replacement therapy in diabetes usually refer to patients with insulin-dependent diabetes mellitus (IDDM) only, and little is known about renal failure in non-insulin-dependent diabetics (NIDDM). A high proportion, 46/141 (32%), of the diabetics treated at our unit since 1974 had NIDDM. They were older at treatment (56 +/- 9 years, mean +/- SD) compared to the IDDM patients (39 +/- 10 years, p less than 0.001), and had a shorter duration of diabetes (13 +/- 8 years versus 23 +/- 8 years, p less than 0.001). Asians and Afro-Caribbeans accounted for 48% of the NIDDM patients (22/46) compared to only 7% of those having IDDM (6/95, p less than 0.0001). Non-diabetic renal disease accounted for the renal failure in 32% (15/46) of the NIDDM patients but only in 10.5% (10/95) of the IDDMs (p less than 0.001). Despite these differences the prevalence of other diabetic complications (retinopathy, neuropathy, and cardiovascular disease) was similar. Patient survival after transplantation was poorer in NIDDM than IDDM (23% and 57%, respectively, at 2 years). Survival on dialysis was equally poor in NIDDM and IDDM. Thus, NIDDM patients treated for renal failure are more commonly non-European and more often have non-diabetic renal disease. Yet other diabetic complications occur to the same extent in both IDDM and NIDDM patients with diabetic nephropathy.

Adult↗