Utilization of a multilayer polyacrylamide phantom for evaluation of hyperthermia applicators.

A muscle-stimulating material made of polyacrylamide gel (PAG) for testing various kinds of hyperthermia applicators was investigated. The permittivity and conductivity dispersion of PAG, as well as an internal wavelength and penetration depth, were in good agreement with those of actual muscle at frequencies between 500 MHz and 3 GHz. A single formula for PAG covering three ISM bands, most commonly used for hyperthermia, 433, 915 and 2450 MHz, is presented. The physical properties of the PAG phantom allow any desired form or shape to be moulded, including shapes conforming to the actual geometry of an interstitial or intracavitary applicator. Utilization of a multilayer phantom makes possible the generation of experimental three-dimensional specific absorption rate (SAR) distributions composed from several two-dimensional SAR images at different depths or radial distances from the applicator. Spatial resolution of 1 mm can be achieved. The two-dimensional SAR distributions at different depth values for commercial superficial applicator, an interstitial antenna and a new oesophageal applicator are presented.     

The relevance of a staging laparotomy for Hodgkin's disease in India.

A retrospective analysis of 328 cases of Hodgkin's Disease (HD) subjected to a staging laparotomy at the Tata Memorial Hospital, Bombay, India, from 1974 to 1986 was undertaken to assess its relevance to our setup. Eighty percent of the patients were from clinical stages (CS) I and II, 38% with lymphocyte predominance (LP), and 41% with mixed cellularity (MC) histologies. Staging laparotomy was positive in 60% cases overall, including 50% from CS IA and IIA, 68% from CS IB and IIB, and 53% and 67%, respectively, from LP and MC histologies. Splenic involvement was seen in 54% cases. Operative complications were encountered in 2% of cases and deaths in two cases only. In view of the high propensity for abdominal spread, only selected CS IA and IIA cases would merit a staging laparotomy within which, nearly 50% cases with a negative yield could be offered radical segmental irradiation alone for cure. The majority of our patients would, however, require combination therapy.     

Susceptibility of hamsters to caecal amoebiasis by oral infection

A method is described for successfully establishing caecal amoebiasis in hamsters which were not fed and which were pretreated with 1 ml of magnesium sulphate every 24 hours for three days and then given 12 x 10(5) trophozoites of the HM-1 axenic strain or 18 x 10(5) trophozoites of the HK-9 axenic strain of Entamoeba histolytica by the oral route. All the animals developed diarrhoea within 24 hours of infection. When the animals were killed on the fifth day after infection the caecum was swollen and fused. Large macroscopic ulcers full of pus could be seen in the caecum. None of the control animals showed any of the changes mentioned above.     

Perioperative Complications of the Agility Total Ankle Replacement in 50 Initial, Consecutive Cases

Although functional and clinical outcomes after total ankle arthroplasty have been promising, a steep learning curve has been recognized. In addition, the performance of concomitant hindfoot realignment procedures is controversial. The purpose of this study was to report on a single surgeon's experience with the first 50 total ankle arthroplasty procedures. We wanted to define the characteristics of the learning curve and whether the rate of complications was increased in patients who required complex reconstruction for preexistent foot and ankle deformities. This was a retrospective study of 50 cases with an average follow-up of 24.2 months. The patient population consisted of 18 men and 30 women with an average age of 57.6 years. Twenty-six percent of the cases had concomitant bony realignment procedures, while 20% had prior history of major hindfoot corrective procedures. There were 19 cases with intraoperative malleolar fractures, 12 cases that exhibited some degree of malalignment, and 6 cases of syndesmotic nonunion, and 8 ankles required early component revision. Minor wound complications that resolved with local wound care occurred in 9 cases, while 1 patient had a major wound complication requiring flap coverage. Each of these complications, other than wound complications, decreased with the surgeon's experience. Our results also indicate that the performance of major realignment procedures at the same time of implant arthroplasty is not associated with an increased incidence of complications. The results of this study suggest that total ankle arthroplasty is associated with a learning curve. Perioperative complications may potentially decrease with surgeon experience.     

When Is a Bispectral Index of 60 Too Low?: Rational Processed Electroencephalographic Targets Are Dependent on the Sedative-Opioid Ratio

Background: Opioids are commonly used in conjunction with sedative drugs to provide anesthesia. Previous studies have shown that opioids reduce the clinical requirements of sedatives needed to provide adequate anesthesia. Processed electroencephalographic parameters, such as the Bispectral Index (BIS; Aspect Medical Systems, Newton, MA) and Auditory Evoked Potential Index (AAI; Alaris Medical Systems, San Diego, CA), can be used intraoperatively to assess the depth of sedation. The aim of this study was to characterize how the addition of opioids sufficient to change the clinical level of sedation influenced the BIS and AAI.

Methods: Twenty-four adult volunteers received a target-controlled infusion of remifentanil (0-15 ng/ml) and inhaled sevoflurane (0-6 vol%) at various target concentration pairs. After reaching pseudo-steady state drug levels, the modified Observer's Assessment of Alertness/Sedation score, BIS, and AAI were measured at each target concentration pair. Response surface pharmacodynamic interaction models were built using the pooled data for each pharmacodynamic endpoint.

Results: Response surface models adequately characterized all pharmacodynamic endpoints. Despite the fact that sevoflurane-remifentanil interactions were strongly synergistic for clinical sedation, BIS and AAI were minimally affected by the addition of remifentanil to sevoflurane anesthetics.     

An optimal dynamic output feedback controller for a flexible spacecraft

The design of a low-order dynamic output feedback controller for a flexible spacecraft is carried out using modified linear quadratic Gaussian (LQG) theory. The necessary conditions for optimization are given. The linear equations governing a flexible spacecraft with a central rigid body and two sun-tracking solar panels are presented. The parameters of the Solar Electric Propulsion Spacecraft (SEPS) are selected for analysis and simulation. The optimal gains for the dynamic controller are estimated using an iterative algorithm. The sequential procedure which assures convergence is selected. The initial gains which stabilize the system are chosen on the basis of the principle of a PD controller. A third-order controller for pitch, roll and yaw axes of the 18th-order system, which includes sensor and actuator dynamics, is designed. Numerical simulations carried out to ascertain the performance of the controller show the performance to be satisfactory.     

Effect of sleep on interictal spikes and distribution of sleep spindles on electrocorticography in children with focal epilepsy.

OBJECTIVE: To determine how sleep with central spindles alters the spatial distribution of interictal spike frequency in children with intractable focal seizures, and whether such children have spindles arising from the medial temporal region in addition to the frontal-central region. METHODS: Seventeen children (age: 7 months-17 years) were studied using extraoperative electrocorticography (ECoG). RESULTS: Overall spike frequency across the subdural electrodes was greater during sleep with central spindles compared to wakefulness. In 13 children showing at least 1 spike/min in an electrode, the spatial distribution of spike frequency was similar during wakefulness and sleep; in addition, the spike frequency was greater in the seizure onset zones compared to the non-onset areas, regardless of wakefulness or sleep. Spindles were identified in the medial temporal region during sleep with central spindles in all 17 children. CONCLUSION: Overall spike frequency may be increased by sleep with spindles, but the spatial distribution of spike frequency appears similar during wakefulness and sleep in children with intractable focal seizures. SIGNIFICANCE: Both awake and sleep ECoG may be useful to predict seizure onset zones in children with intractable focal epilepsy. Medial temporal spindles are present in some children with focal epilepsy.