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Biomedical subjects

P Davey

Publications and source records attributed to P Davey.

At least 19 recordsLinked to original sources
PubMed1995

Frameless stereotaxy for radiosurgical planning and follow-up.

In our centre, 111 patients have been treated with linear accelerator stereotactic radiosurgery. Angiographic, CT and MRI images are generated and the target coordinates calculated in 3 dimensions. For CT scanning, cross sections of perpendicular and oblique fiducial markers are seen. For follow-up CT scans done without the frame, a virtual frame is generated by means of a computer program that places fiducial markers on each CT scan cut, as if the patient had been wearing the OBT frame and the scan produced with the gantry parallel to the base of the frame. The position of the oblique marker may be calculated by knowing the thickness and position of each CT cut. Various natural fiducial markers (bony landmarks) are identified by coordinates in the scan with the patient wearing the real frame and in the scan with the virtual frame applied. A transformation matrix is utilized to establish the equivalence between the original CT scan with the real frame applied and subsequent scans without the real frame but with the virtual frame applied. In effect, the virtual frame is re-applied in exactly the same position as the real frame. Lesion measurements may then be duplicated and growth or regression accurately established. The uncertainty in this system of re-application resides in possible patient movement, CT scan slice thickness and inter-observer error in the identification of natural fiducial markers.

Brain Neoplasms↗
PubMed1992

Cost effectiveness of once-daily oral antimicrobial therapy.

Once daily dosing of oral antimicrobials achieves significantly better patient compliance than three or four times daily dosing, and limited data suggest that this is associated with greater efficacy. Comparison of once daily and twice daily dosing is less consistent, and most studies show only marginally better compliance with once daily dosing versus twice daily dosing. Detection of urinary antimicrobial activity provides a simple method for checking compliance with oral antimicrobials and deserves wider study. Counts of residual tablets have been shown to overestimate compliance. Intravenous formulations are always more expensive than equivalent oral formulations, and preparation and administration of intravenous drugs adds significant additional costs. Moreover, intravenous regimens are complex, and a number of studies have shown that serious errors occur in both preparation and administration of intravenous drugs. There is increasing evidence that serious infections can be adequately treated with oral drugs, and the excellent bioavailability of quinolones makes them particularly attractive for these indications. Clinicians require a method for checking absorption by patients with severe infection, and the Serum Bactericidal Test may provide a practical method for monitoring a wide variety of drugs.

Administration, Oral↗
PubMed1992

Measuring the cost-effectiveness of antibiotic prophylaxis in surgery.

Cost-effectiveness analysis is primarily a decision-making aid for budget holders. The first questions that must be answered are: Costs to whom? Effects on whom? Ideally cost-effectiveness analysis should address these questions separately from the perspective of the hospital, the community health services, the patient, and society in general. However, it may not always be practical to perform such a wide-ranging study. Moreover, if the decision maker is primarily concerned with the hospital budget, it is tempting to confine the detailed analysis to items that affect that budget. A good analysis should acknowledge these inevitable limitations and explicitly state whose perspective is being used. Even if a detailed study of community health services is not possible, the analysis should include some evidence about the likely impact of the program on others outside the immediate sphere of the budget holder. Two situations commonly arise in applying cost-effectiveness analysis to surgical prophylaxis: (a) The prophylaxis is more expensive than current practice and its costs must be justified, e.g., the use of a more expensive drug for a recognized indication or the introduction of prophylaxis for a new indication. (b) The prophylaxis is cheaper than current practice and must be shown to be as cost-effective, e.g., the use of a single-dose prophylaxis instead of multiple-dose regimens or the administration of an oral dose instead of an intravenous dose. We believe that cost-effectiveness analysis adds a useful extra dimension to the evaluation of surgical prophylaxis.

Anti-Bacterial Agents↗
PubMed1992

A comparison of the costs of ceftazidime therapy and gentamicin combinations in three UK hospitals.

This study compares the utilization costs of ceftazidime therapy with those of gentamicin in combination with other antibacterial drugs. The results show that the relatively high purchase cost of ceftazidime compared to combinations is more than counterbalanced by the additional materials used for drug administration and serum antibiotic assays, even when other drugs were combined with ceftazidime. The average drug and equipment costs were 230.13 pounds for ceftazidime regimens and 253.94 pounds for gentamicin regimens. It is also shown that ceftazidime therapy is associated with a reduction in personnel time compared to gentamicin regimens. The average times per patient for administration and assay were 1 h 43 min for ceftazidime and 4 h 57 min for gentamicin regimens. We conclude that ceftazidime regimens are cheaper than gentamicin regimens when all drug and equipment costs are quantified. Moreover, the use of ceftazidime will release staff time for other purposes.

Anti-Bacterial Agents↗
PubMed1992

Cost-effectiveness of single dose cefotaxime plus metronidazole compared with three doses each of cefuroxime plus metronidazole for the prevention of wound infection after colorectal surgery.

The cost-effectiveness of prophylaxis for colonic surgery with single dose cefotaxime plus metronidazole has been compared with that of three doses each of cefuroxime plus metronidazole, by analysing data from a previously published study supplemented with additional data on the hospital and community costs of wound infection after colonic surgery. The original trial included 942 patients having elective colonic surgery in 14 hospitals. The data on costs of wound infection were collected from a further 124 patients undergoing elective colonic surgery at Ninewells Hospital. All these patients received a three dose regimen of cefuroxime plus metronidazole. The Dundee patients received three injections of 0.75 g cefuroxime at 8-hourly intervals whereas the trial patients received a single dose of 1.5 g followed by two further doses of 0.75 g at 8-hourly intervals. The cefuroxime prophylaxis regimen used in the trial cost 24.16 pounds per patient more than the cefotaxime regimen. The components of the excess cost were drugs (15.18 pounds), equipment (6.14 pounds) and staff time (2.84 pounds). The median cost to the hospital of a wound infection was 978.04 pounds (95% CI 482.04 pounds to 1521.22 pounds). The components of the hospital cost of wound infection were: hotel costs 858 pounds (88%), dressing costs 83.02 pounds (8%) and drug costs (excluding prophylaxis) 37.02 pounds (4%). Only five patients received additional antibiotic treatment in the community, and only one required home visits from the District Nurse. Applying the difference in costs of prophylaxis as 21 pounds (costs of drugs plus equipment) and the cost per wound infection as 1000 pounds to the observed wound infection rate of 7% in the cefuroxime group, the wound infection rate in the cefotaxime group would have to be 2.1% higher for the two regimens to be equally cost-effective. The probability that such a difference in efficacy exists is 0.088. A model was developed to calculate the probability of equal cost-effectiveness over a range of costs of wound infection.

Anti-Infective Agents↗
PubMed1992

Ventilation in chronic heart failure: effects of physical training.

OBJECTIVE: To assess the effects of exercise training on ventilatory function in chronic heart failure. DESIGN: Observer blinded random allocation crossover training and detraining trial. SETTING: Assessment in hospital based clinical laboratory; training home based. PATIENTS: 22 patients with chronic heart failure (New York Heart Association (NYHA) class II or III) recruited from a tertiary referral centre. All finished the study. INTERVENTION: Bicycle ergometer exercise for 20 minutes a day, five days a week for eight weeks at 70%-80% of maximum heart rate. MAIN OUTCOME MEASURES: Exercise capacity on graded incremental exercise test, minute ventilation, oxygen consumption and carbon dioxide output. RESULTS: Peak work load increased from 96 W to 112 W and peak oxygen consumption from 14.1 ml/kg/min to 15.4 ml/kg/min (p < 0.01). At submaximal workloads carbon dioxide excretion (VCO2) and minute ventilation (Vi) decreased significantly (p < 0.05) though oxygen consumption was unchanged. The relation between Vi and carbon dioxide excretion changed: the slope of the Vi to VCO2 plot decreased from 38.6 to 35.3, indicating an improvement in overall ventilary efficiency. The instantaneous carbon dioxide ventilatory equivalent (Vi/VCO2) decreased at submaximal workloads, and reached a lower minimum value after training, indicating that optimum ventilatory performance improved. The exercise capacity of patients was related to the optimum ventilatory performance. It is suggested that this may in part be mediated through changes in skeletal muscles. CONCLUSION: Exercise training reduces the ventilatory abnormalities in chronic heart failure; thus some of these changes may be due to physical deconditioning.

Aged↗
PubMed1992

Controlled trial of physical training in chronic heart failure. Exercise performance, hemodynamics, ventilation, and autonomic function.

BACKGROUND: Many secondary abnormalities in chronic heart failure (CHF) may reflect physical deconditioning. There has been no prospective, controlled study of the effects of physical training on hemodynamics and autonomic function in CHF. METHODS AND RESULTS: In a controlled crossover trial of 8 weeks of exercise training, 17 men with stable moderate to severe CHF (age, 61.8 +/- 1.5 years; left ventricular ejection fraction, 19.6 +/- 2.3%), increased exercise tolerance (13.9 +/- 1.0 to 16.5 +/- 1.0 minutes, p less than 0.001), and peak oxygen uptake (13.2 +/- 0.9 to 15.6 +/- 1.0 ml/kg/min, p less than 0.01) significantly compared with controls. Training increased cardiac output at submaximal (5.9-6.7 l/min, p less than 0.05) and peak exercise (6.3-7.1 l/min, p less than 0.05), with a significant reduction in systemic vascular resistance. Training reduced minute ventilation and the slope relating minute ventilation to carbon dioxide production (-10.5%, p less than 0.05). Sympathovagal balance was altered by physical training when assessed by three methods: 1) RR variability (+19.2%, p less than 0.05); 2) autoregressive power spectral analysis of the resting ECG divided into low-frequency (-21.2%, p less than 0.01) and high-frequency (+51.3%, p less than 0.05) components; and 3) whole-body radiolabeled norepinephrine spillover (-16%, p less than 0.05). These measurements all showed a significant shift away from sympathetic toward enhanced vagal activity after training. CONCLUSIONS: Carefully selected patients with moderate to severe CHF can achieve significant, worthwhile improvements with exercise training. Physical deconditioning may be partly responsible for some of the associated abnormalities and exercise limitation of CHF, including abnormalities in autonomic balance.

Autonomic Nervous System↗
PubMed1991

Human and non-financial costs of hospital-acquired infection.

Measurement of morbidity from hospital-acquired infection should include the suffering of patients who are denied treatment, 'the opportunity cost of infection'. We believe that this perspective will also reveal other inefficiencies which may be easier to correct than hospital-acquired infection. Infection control should be seen as a component of quality control and not as an end in itself.

Cost-Benefit Analysis↗
PubMed1991

Current status of radiosurgery for arteriovenous malformations.

Cerebral arteriovenous malformations (AVM), regardless of the mode of discovery, have an annual risk of hemorrhage of approximately 4 percent. A progressive obliterative vasculitis culminating in the occlusion of an AVM may be induced by the administration of radiation doses of approximately 20 Gy given in a single fraction. The process takes about two years and occlusion occurs in approximately 80% of patients so treated. Such a dose may be accurately administered to AVMs up to 3 cm in diameter with very little radiation imparted to the adjacent brain by means of multiple highly collimated radially arranged cobalt sources (the Gamma Knife) or by means of a modified linear accelerator turned through an arc or arcs with the target AVM as the centre of rotation. The Gamma Knife and the modified linear accelerator have nearly equal accuracy. Recent experience with modified linear accelerators indicates efficacy equal to the Gamma Knife. Both devices are effective treatment for small AVMs but the cost of modifying a pre-existing linear accelerator is only a few percent of the acquisition and installation costs of the Gamma Knife.

Evaluation Studies as Topic↗
PubMed1991

Disposition of cerebral metastases from malignant melanoma: implications for radiosurgery.

Radiosurgery is becoming more generally available and indications for its use continue to be defined. Cerebral metastases from malignant melanoma are often treated with whole-brain irradiation, but with limited benefit. Innovative treatments, such as radiosurgery, make possible the delivery of doses of radiation that are higher than usual. To determine how many patients might be candidates for radiosurgery, a retrospective analysis of computed tomographic brain scans performed on 41 patients with cerebral metastases from malignant melanoma was undertaken. One-third of these patients were found to have cerebral metastases amenable to a radiosurgical approach, as illustrated radiation dose-volume histograms. Patient and tumor characteristics suggest that this series is represent with cerebral metastases from malignant melanoma. The implications of radiosurgery for normal tissue radiation tolerance and its effects on melanoma are discussed.

Adult↗
PubMed1990

Spontaneous phenotypic and karyotypic progression in the SV40 transfected cell line SVG during prolonged passage in vitro.

Transfection of primary cultures of human cells with origin of replication deficient SV40 DNA has been carried out by others to generate in vitro models of malignant transformation in vivo. The present work describes progressive alterations in karyotype and phenotype in one such transfected (neuroglial) cell line (SVG). After repeated passage, recognisable marker chromosomes evolved. These may be related to karyotypic anomalies found in human glial tumors. Accompanying the evolution in karyotype were changes in phenotype. Although presaging malignant transformation, these stopped short of actual tumorigenicity.

Animals↗
PubMed1990

Mast cells in the ovine lower respiratory tract: heterogeneity, morphology and density.

The lower respiratory tract (LRT) of 6 adult sheep was fixed in either isotonic formalin-acetic acid or neutral buffered formalin in order to study the heterogeneity, morphology and density of mast cells (MCs). Two subtypes of MCs were found, one histochemically similar to connective tissue MCs (formalin resistant) and the other similar to mucosal MCs as found in the intestine of the rat (formalin sensitive). Although both subtypes were present at all levels of the tract, formalin-sensitive MCs were significantly more abundant (p less than 0.01) at all levels, and their density increased distally from the trachea to the peripheral lung. The formalin-sensitive MCs were predominantly located in the alveolar septa and in the superficial lamina propria of airways and less frequently within the airway epithelium. The MCs in the ovine LRT were found to be morphologically heterogeneous at both the light-microscopic and electron-microscopic levels. These findings indicate that ovine respiratory tract MCs have similarity to human lung MCs, and therefore potential for use as a model for the study of human allergic disease of the respiratory system.

Animals↗
PubMed1989

Comparative study of clindamycin, imipenem, oxacillin and vancomycin in the infected granuloma pouch model.

In a rat granuloma pouch model, Staphylococcus aureus infection was treated with clindamycin, oxacillin or vancomycin and Bacteroides fragilis infection with clindamycin or imipenem. The model simulates a subcutaneous abscess and has the advantage of permitting frequent sampling of exudate for bacterial counts and antibiotic levels in the same animal. In staphylococcal infection all drugs reduced the bacterial counts in the infected pouch by 1-1.7 log, with a significant effect lasting for 3 h after the last injection. A 1.06-1.4 log reduction lasted for 24 h with clindamycin and oxacillin, but there was only an 0.3 log reduction at 24 h with vancomycin. The ratio of the drug concentration in the infected pouch to the MIC was highest with clindamycin (2.3) compared to oxacillin (1.6) and vancomycin (0.8). With Bact. fragilis infection the bacterial counts dropped 1.5 log at 3 h after the last injection with clindamycin and imipenem. At 24 h the counts were reduced 1.0 log with clindamycin and 0.5 log with imipenem. The ratios of pouch fluid concentration to MIC was 7.6 and 4.08 for imipenem and clindamycin, respectively, at 3 h, and 1.0 and 2.3 for imipenem and clindamycin at 24 h.

Animals↗
PubMed1989

Radiobiology: nil desperandum.

Recent developments in radiobiology have provided a clearer understanding of the limitations of conventional radiotherapy in cancer treatment and suggest alternative and potentially more effective means of using this form of therapy.

Humans↗
PubMed1988

Tolerance of Pseudomonas aeruginosa to killing by ciprofloxacin, gentamicin and imipenem in vitro and in vivo.

In the rat croton oil pouch model, treatment with ciprofloxacin, gentamicin or imipenem caused a sharp reduction in the numbers of Pseudomonas aeruginosa when applied 24 h after infection but treatment had little or no effect when delayed until 48 h after infection. Surviving bacteria from treated animals were fully susceptible on subculture in vitro. Between 24 h and 48 h after infection there was an increase in the concentration of magnesium and a decrease in the concentration of oxygen but no significant change in the pH of the pouch fluid. In-vitro, the MBC of gentamicin was increased four-fold by the addition of magnesium ions and eight-fold under anaerobic conditions whereas these variables had no significant effect upon the MBC of ciprofloxacin and imipenem. However, cells of P. aeruginosa incubated in batch culture for 4, 24 and 48 h became progressively more tolerant to killing by all three drugs. We conclude that the tolerance of P. aeruginosa in vivo was only partly explained by biochemical changes at the site of infection. The stationary growth phase was associated with progressive tolerance to killing by ciprofloxacin, gentamicin and imipenem both in vivo and in vitro.

Animals↗