Simulating ion beam extraction from a single aperture triode acceleration column: a comparison of the beam transport codes IGUN and PBGUNS with test stand data.

Ion beam extraction from two different ion sources with single aperture triode extraction columns was simulated with the particle beam transport codes PBGUNS and IGUN. For each ion source, the simulation results are compared to experimental data generated on well-equipped test stands. Both codes reproduced the qualitative behavior of the extracted ion beams to incremental and scaled changes to the extraction electrode geometry observed on the test stands. Numerical values of optimum beam currents and beam emittance generated by the simulations also agree well with test stand data.

The development of hypoxaemia during apnoea in children: a computational modelling investigation.

BACKGROUND: Hypoxaemia during apnoea develops earlier and progresses faster in children than in adults. Ethical and practical considerations prevent detailed investigation of the issue. METHODS: We used the Nottingham Physiology Simulator, an integrated, computational model of the respiratory and cardiovascular systems, to model four healthy virtual children (ages: 1 month, 1, 8 and 18 yr) and exposed them to apnoea after a variety of preoxygenation periods (0, 1 and 3 min) and with open and obstructed airways during apnoea. RESULTS: The rate of oxygen desaturation of haemoglobin from 90 to 40% was similar across the ages studied, being approximately 30% min(-1). The greatest difference between ages was found in the speed of early desaturation (i.e. between the onset of apnoea and the acceleration of haemoglobin desaturation); in the absence of preoxygenation and with an open airway, this time was 6.6 s in the 1-month-old and 33.6 s in the 8-yr-old. CONCLUSIONS: Preoxygenation had a substantial effect on the speed of early desaturation, but less effect on the time for SaO2 to decrease from 90 to 40%. Preoxygenation substantially delayed dangerous desaturation in all age groups, although the rapidity of denitrogenation in the very young (caused by the large ratio of minute ventilation to functional residual capacity) resulted in lengthy preoxygenation having little benefit over brief preoxygenation. Airway obstruction during apnoea accelerated every child's hypoxaemia through prevention of mass flow addition to oxygen stores and through intrathoracic depressurization. On average, haemoglobin desaturation from SaO2 90 to 40% was 33% min(-1) with an obstructed airway and 26% min(-1) with an open airway; all ages were similarly susceptible to this effect.

The effect of a mechanical glottis on peak expiratory flow rate and time to peak flow during a peak expiratory flow manoeuvre: a study in normal subjects and patients with motor neurone disease.

We have evaluated a mechanical glottis in healthy volunteers and in patients with bulbar motor neurone disease. In healthy volunteers, the mechanical glottis increased peak flow rate and decreased the time to peak flow during forced expiration, but cough produced even higher flow rates and shorter times to peak flow. In patients, the mechanical glottis increased peak flow rate and decreased the time to peak flow. The mechanical glottis also produced higher peak flow rates when compared to the cough manoeuvres, and the time to peak flow was also significantly shorter with the mechanical glottis. We have shown that the use of a mechanical glottis tends to convert the airflow profile of a peak expiratory flow manoeuvre into that of a cough in both healthy volunteers and patients with motor neurone disease. Its potential role as an aid to clearance of airway secretions in patients with impaired laryngeal function remains to be seen.

The X-ray attenuation characteristics and density of human calcaneal marrow do not change significantly during adulthood.

Changes in the material characteristics of bone marrow with aging can be a significant source of error in measurements of bone density when using X-ray and ultrasound imaging modalities. In the context of computed tomography, dual-energy computed techniques have been used to correct for changes in marrow composition. However, dual-energy quantitative computed tomography (DE-QCT) protocols, while increasing the accuracy of the measurement, reduce the precision and increase the radiation dose to the patient in comparison to single-energy quantitative computed tomography (SE-QCT) protocols. If the attenuation properties of the marrow for a particular bone can be shown to be relatively constant with age, it should be possible to use single-energy techniques without experiencing errors caused by unknown marrow composition. Marrow was extracted by centrifugation from 10 mm thick frontal sections of 34 adult cadaver calcanei (28 males, 6 females, ages 17-65 years). The density and energy-dependent linear X-ray attenuation coefficient of each marrow sample were determined. For purposes of comparing our results, we then computed an effective CT number at two GE CT/i scan voltages (80 and 120 kVp) for each specimen. The coefficients of variation for the density, CT number at 80 kVp and CT number at 120 kVp were each less than 1%, and the parameters did not change significantly with age (p > 0.2, r2 < 0.02, power > 0.8 where the minimum acceptable r2 = 0.216). We could demonstrate no significant gender-associated differences in these relationships. These data suggest that calcaneal bone marrow X-ray attenuation properties and marrow density are essentially constant from the third through sixth decades of life.

A pilot study of patient-led identification of the midline of the lumbar spine.

The midline of the lumbar spine is usually identified by palpation of the spinous processes. Placement of an epidural or spinal needle is more difficult when these bony landmarks are impalpable. This pilot study investigated the ability of 50 healthy volunteers to identify the midline of their own backs, using light touch or proprioception. The midline as identified in this manner was compared with the 'gold standard' as defined by the interspinous line. Sensation to light touch was the most accurate, with 90% of the volunteers able to identify the midline to within 6.5 mm. Proprioception using a finger to touch the midline was less accurate. This study was carried out on volunteers with palpable spinous processes but suggests that, in certain circumstances, a patient-led identification of the midline may be of value.

Investigating hypoxemia during apnea: validation of a set of physiological models.

UNLABELLED: The aim of our study was to validate the Nottingham Physiology Simulator (NPS) for examining pulmonary denitrogenation and apnea by reproducing the methodology and results of previous clinical studies. Only four studies provided sufficient detail in their description of their methodology to allow accurate reproduction by using the NPS or provided a sufficiently detailed description of their subjects to allow accurate modelling. The results of the NPS recreation of the studies were within 13% of the values found clinically in all cases and were within 2% in the majority of cases. The four studies included healthy and morbidly obese patients, conscious and anesthetized patients, and included examination of the effect of denitrogenation and apnea on plasma pH and on lung and arterial oxygen and carbon dioxide tensions at various lung volumes. IMPLICATIONS: We used mathematical, physiological models to recreate the methods and subjects of four clinical studies investigating oxygenation and low oxygen levels during cessation of breathing. Our aim was to validate the models, allowing theoretical investigations into this area. The blindly recreated results closely matched the clinical studies, validating the models.

Factors determining the onset and course of hypoxemia during apnea: an investigation using physiological modelling.

UNLABELLED: We used the Nottingham Physiology Simulator to examine the onset and course of hypoxemia during apnea after pulmonary denitrogenation. The following factors, as possible determinants of the hypoxemia profile, were varied to examine their effect: functional residual capacity, oxygen consumption, respiratory quotient, hemoglobin concentration, ventilatory minute volume, duration of denitrogenation, pulmonary venous admixture, and state of the airway (closed versus open). Airway obstruction significantly reduced the time to 50% oxyhemoglobin saturation (8 vs 11 min). Provision of 100% oxygen rather than air to the open, apneic patient model greatly prolonged time to 50% oxyhemoglobin saturation (66 vs 11 min). Hemoglobin concentration, venous admixture, and respiratory quotient had small, insignificant effects on the time to desaturation. Reduced functional residual capacity, short duration of denitrogenation, hypoventilation, and increased oxygen consumption significantly shortened the time to 50% oxyhemoglobin saturation during apnea. IMPLICATIONS: Reduction in oxygen levels during cessation of breathing is dangerous and common in anesthetic practice. We used validated, mathematical, physiological models to reveal the impact of physiological factors on the deterioration of oxygen levels. This study could not be performed on patients and reveals important information.

Entanglement of guide wires by vena cava filters during central venous catheter insertion: report of three cases and a review of the literature.

Since 1993, 14 cases of central line guide wires becoming entangled with vena cava filters have been reported. We present three additional cases and review the 14 cases in the literature. Obtaining a detailed patient history is important in identifying patients with a vena cava filter. A low threshold of suspicion is needed and immediate radiograph obtained. Entangled guide wires required fluoroscopic manipulation and or retrieval of the dislodged filter. Of all reported cases, only one sustained an arrhythmia. With no signs and symptoms, conservative management of the dislodged filter is a viable option.

The diagnosis and management of small (< or = 3 cm) renal neoplasms: a commentary.

Many renal cell carcinomas are discovered incidentally. This phenomenon is largely attributable to advances in renal imaging, particularly regarding CT, to the widespread use of cross-sectional imaging in the diagnosis of abdominal disease, and to growing experience with the detection and diagnosis of renal masses. Accompanying the apparent increasing prevalence of renal masses are several controversies that specifically concern small (< or = 3 cm) neoplasms, those that are of a size associated with relatively slow growth and a low risk of metastasis. Are some of these small neoplasms renal adenomas? What is their growth pattern, and of what significance is their enlargement? Are all small renal carcinomas truly "cancers"? And what are the implications for management of such lesions in an asymptomatic individual? These controversies are discussed in depth in the hope of stimulating further investigation of this complex problem.

Laparoscopic cholecystectomy: imaging of complications and normal postoperative CT appearance.

Six patients underwent imaging studies to evaluate complications related to laparoscopic cholecystectomy. In addition, computed tomography (CT) of the abdomen and pelvis was performed on six patients 3-5 days after uncomplicated laparoscopic cholecystectomy in order to further clarify the normal postoperative CT appearance in these patients. Complications included ureteral laceration with periureteric hematoma and ureteroperitoneal fistula, hepatic artery pseudoaneurysm, hepatic laceration, retained common bile duct stone, bile leak, and biloma of the abdominal wall. At 3-5 days following uncomplicated laparoscopic cholecystectomy, typical CT findings include fluid density in the gallbladder fossa, a very small amount of pelvic fluid, and small densities within the subcutaneous fat at the expected sites of trocar insertion.