Possible mechanism for aligning microscopic flexible filaments predicted using "caterpillar" hydrodynamics.

We use the "caterpillar" model for accurately calculating the inhomogeneous hydrodynamic friction along a microscopic slender cylindrical filaments using Oseen level hydrodynamics. The methodology is applied to study the motion of a flexible filament in a circularly polarized field. Our results predict that in dilute solution alignment occurs along the axis of the field. For electric fields, the strengths and frequencies required are deduced. These are experimentally accessible. We therefore propose that this is a practical method for aligning filaments such as microtubules and functionalized carbon nanotubes.

Testicular microlithiasis an ultrasound dilemma: survey of opinions regarding significance and management amongst UK ultrasound practitioners.

OBJECTIVE: To establish whether there is a consensus regarding the significance of testicular microlithiasis and a strategy for managing patients with this condition, amongst ultrasound practitioners in the UK. METHODS: An electronic questionnaire was distributed to 1482 members of the British Medical Ultrasound Society (BMUS), requesting information from ultrasound practitioners involved in scrotal ultrasound about their interpretation of the risk associated with testicular microlithiasis and their departmental or personal recommendations for managing patients with this condition. RESULTS: Responses were obtained from 221 BMUS members. Analysis demonstrated a wide variation in the significance attributed to the discovery of testicular microlithiasis and the risk of subsequent development of testicular germ cell tumours. There was also great variation in strategies for management of patients with testicular microlithiasis, including the need for surveillance ultrasound, amongst ultrasound practitioners regardless of their job description. CONCLUSION: Lack of consensus shown by this study highlights significant differences across the UK in managing patients with testicular microlithiasis and validates the importance of guidance currently being formulated by the European Society of Urogenital Radiology. ADVANCES IN KNOWLEDGE: We believe that this is the first survey to be conducted amongst imaging specialists in the UK regarding testicular microlithiasis and demonstrates that there is currently no uniform practice in managing patients with this condition.

The natural history of gastro-oesophageal reflux symptoms in the community and its effects on survival: a longitudinal 10-year follow-up study.

BACKGROUND: Gastro-oesophageal reflux symptoms (GERS) are common in the community. However, few studies have examined their long-term natural history, or impact on survival. AIM: To examine these issues in individuals recruited into a community-based screening programme for Helicobacter pylori in 1994. METHODS: Data on mortality and cause of death at 10 years were obtained from the Office for National Statistics. Baseline demographic data, lifestyle factors, gastrointestinal symptoms and quality of life were recorded at study entry. The effect of all these factors on persistent and new-onset GERS, and 10-year mortality, were examined using univariate and multivariate analysis, with results expressed as odds ratios (ORs) or hazard ratios (HR) with 99% confidence intervals (CI). RESULTS: Of 3967 individuals providing complete GERS data at baseline and 10 years, 549 (13.8%) had GERS at baseline. Of these, 183 (33.3%) had persistent symptoms. Among 3418 individuals asymptomatic at baseline, approximately 0.8% per year developed new-onset GERS. No predictors of persistent GERS were identified. New-onset symptoms were associated with lower quality of life or presence of irritable bowel syndrome (IBS) at baseline, and higher body mass index (BMI) at 10 years. There were 8331 (99.1%) of 8407 subjects providing complete GERS data at baseline, 1289 (15.5%) of whom were symptomatic. Presence of GERS at baseline did not affect survival (HR: 0.84; 99% CI: 0.44-1.59). CONCLUSIONS: Gastro-oesophageal reflux symptoms persisted in one-third of individuals, whilst new-onset gastro-oesophageal reflux symptoms were associated with poor quality of life, irritable bowel syndrome and higher body mass index. Gastro-oesophageal reflux symptoms did not impact adversely on survival.

Accurate simulation dynamics of microscopic filaments using "caterpillar" Oseen hydrodynamics.

Microscopic semiflexible filaments suspended in a viscous fluid are widely encountered in biophysical problems. The classic example is the flagella used by microorganisms to generate propulsion. Simulating the dynamics of these filaments numerically is complicated because of the coupling between the motion of the filament and that of the surrounding fluid. An attractive idea is to simplify this coupling by modeling the fluid motion by using Stokeslets distributed at equal intervals along the model filament. We show that, with an appropriate choice of the hydrodynamic radii, one can recover accurate hydrodynamic behavior of a filament with a finite cross section without requiring an explicit surface. This is true, however, only if the hydrodynamic radii take specific values and that they differ in the parallel and perpendicular directions leading to a caterpillarlike hydrodynamic shape. Having demonstrated this, we use the model to compare with analytic theory of filament deformation and rotation in the small deformation limit. Generalization of the methodology, including application to simulations using the Rotne-Prager tensor, is discussed.

MILCH SHAKE: an efficient method for constraint dynamics applied to alkanes.

We describe a method to impose constraints in a molecular dynamics simulation. A technique developed to solve the special case of a linear topology (MILC SHAKE) is hybridized with the SHAKE algorithm. The methodology, which we term MILC-hybridized SHAKE (or MILCH SHAKE), applies to more complex topologies. Here we consider the important case of all atom models of alkanes. Exploiting the mass difference between carbon and hydrogen we show that for higher alkanes MILCH SHAKE can be an order of magnitude faster than SHAKE.

Fluctuation of gastrointestinal symptoms in the community: a 10-year longitudinal follow-up study.

BACKGROUND: There are few studies examining the stability of gastrointestinal symptoms during prolonged periods of follow-up. AIM: To examine this issue in individuals previously recruited into a community screening programme for Helicobacter pylori providing symptom data at study entry. METHODS: All traceable participants were sent dyspepsia and IBS questionnaires by post at 10 years. Symptom subgroups were assigned at baseline and 10-year follow-up. Individuals symptomatic at both time points who changed subgroup were compared with those symptomatic and remaining in the same subgroup. RESULTS: Three-thousand eight hundred and nineteen individuals provided data. At baseline, 2417 (63%) were asymptomatic or did not meet diagnostic criteria for a subgroup. Of these, 1648 (68%) remained asymptomatic at 10 years, whilst 769 (32%) reported symptoms. Of the 1402 individuals symptomatic at baseline, 404 (29%) remained in the same subgroup at 10 years, 603 (43%) changed subgroup and symptoms resolved or did not meet criteria for a subgroup in 395 (28%). Symptom stability was more likely in males [odds ratio (OR): 1.50; 99% confidence interval (CI): 0.97-2.31] and older subjects (OR per year: 1.09; 99% CI: 1.01-1.17). CONCLUSION: Of those subjects symptomatic at baseline, almost three-quarters remained symptomatic at 10 years, but over 40% changed symptom subgroup.

Study of the three-dimensional geometry of the central conducting airways in man using computed tomographic (CT) images.

Clinical research on the deposition of inhaled substances (e.g. inhaled medications, airborne contaminants, fumes) in the lungs necessitates anatomical models of the airways. Current conducting airway models lack three-dimensional (3D) reality as little information is available in the literature on the distribution of the airways in space. This is a limitation to the assessment or predictions of the particle deposition in relation to the subject's anatomy. Detailed information on the full topology and morphology of the airways is thus required to model the airway tree realistically. This paper presents the length, diameter, gravity, coronal and sagittal angles that together describe completely the airways in 3D space. The angle at which the airways branch out from their parent (branching angle) and the rotation angle between successive bifurcation planes are also included. These data are from the study of two sets of airways computed tomography (CT) images. One CT scan was performed on a human tracheobronchial tree cast and the other on a healthy male volunteer. The airways in the first nine generations of the cast and in the first six conducting generations of the volunteer were measured using a computer-based algorithm. The data contribute to the knowledge of the lung anatomy. In particular, the spatial structure of the airways is shown to be strongly defined by the central airways with clear angular lobar patterns. Such patterns tend to disappear with a mean gravity, coronal and sagittal angles of 90 degrees in each generation higher than 13-15. The mean branching angle per generation appears independent of the lobe to which the airways belong. Non-planar geometry at bifurcation is observed with the mean (+/- SD) bifurcation plane rotation angle of 79 +/- 410 (n = 229). This angle appears constant over the generations studied. The data are useful for improving the 3D realism of the conducting airway structure modelling as well as for studying aerosol deposition, flow and biological significance of non-planar airway trees using analytical and computational flow dynamics modelling.

Evaluation of the accuracy and precision of lung aerosol deposition measurements from single-photon emission computed tomography using simulation.

Single-photon emission computed tomography (SPECT) imaging is being increasingly used to assess inhaled aerosol deposition. This study uses simulation to evaluate the errors involved in such measurements and to compare them with those from conventional planar imaging. SPECT images of known theoretical distributions of radioaerosol in the lung have been simulated using lung models derived from magnetic resonance studies in human subjects. Total lung activity was evaluated from the simulated images. A spherical transform of the lung distributions was performed, and the absolute penetration index (PI) and a relative value expressed as a fraction of that in a simulated ventilation image were calculated. All parameters were compared with the true value used in the simulation, and the errors were assessed. An iterative method was used to correct for the partial volume effect, and its effectiveness in improving errors was evaluated. The errors were compared with those of planar imaging. The precision of measurements was significantly better for SPECT than planar imaging (2.8 vs 6.3% for total lung activity, 6 vs 20% for PI, and 3 vs 6% for relative PI). The method of correcting for the influence of the partial volume effect significantly improved the accuracy of PI evaluation without affecting precision. SPECT is capable of accurate and precise measurements of aerosol distribution in the lung, which are improved compared with those measured by conventional planar imaging. A technique for correcting the SPECT data for the influence of the partial volume effect has been described. Simulation is demonstrated as a valuable method of technique evaluation and comparison.

A system to reproduce human breathing patterns: its development and validation.

Studies of aerosol deposition in models of the human respiratory tract play a significant role in developing our understanding of drug delivery by inhalation and particle retention in the lungs during exposure to polluted environments. To use replica casts of human airways and compare the results with in vivo data, a device is required to simulate human breathing. The objective of this study was to simulate human breathing for nasal casts. Breathing through the nose is normally limited to about 50 L/min. Therefore, a system was built to simulate human breathing patterns as well as artificial ones up to this flow rate. The system consists of a reciprocating piston in a cylinder, which is displaced by a synchronous motor via a linear actuator. The desired signal to drive the motor is given in real time by purpose-written software. The rotation and position of the motor are controlled by an electronic position control unit. The validation of the system shows that it simulates breathing up to 50 L/min closely even for complex waveforms. At breathing rates above 50 L/min, a slight difference is apparent between the desired breathing pattern and the simulated one. The breathing simulator has been shown to be a reliable tool for reproducing a wide variety of breathing patterns.

Semi-automated tabulation of the 3D topology and morphology of branching networks using CT: application to the airway tree.

Detailed information on biological branching networks (optical nerves, airways or blood vessels) is often required to improve the analysis of 3D medical imaging data. A semi-automated algorithm has been developed to obtain the full 3D topology and dimensions (direction cosine, length, diameter, branching and gravity angles) of branching networks using their CT images. It has been tested using CT images of a simple Perspex branching network and applied to the CT images of a human cast of the airway tree. The morphology and topology of the computer derived network were compared with the manually measured dimensions. Good agreement was found. The airways dimensions also compared well with previous values quoted in literature. This algorithm can provide complete data set analysis much more quickly than manual measurements. Its use is limited by the CT resolution which means that very small branches are not visible. New data are presented on the branching angles of the airway tree.

Tracheal extubation of deeply anesthetized pediatric patients: a comparison of isoflurane and sevoflurane.

UNLABELLED: We studied the emergence characteristics of unpremedicated children tracheally extubated while deeply anesthetized ("deep extubation") with isoflurane or sevoflurane. Forty children were assigned to one of two groups, Group I or Group S. At the end of the operation, Group I patients were extubated while breathing 1.5 times the minimum alveolar anesthetic concentration (MAC) of isoflurane. Group S patients were tracheally extubated while breathing 1.5 times the MAC of sevoflurane. Recovery characteristics and complications were noted. Group S patients were arousable sooner than Group I patients (10.1 + 6.5 vs 16.3 + 9.9 min). Later arousal scores and times to discharge were the same. There were no serious complications in either group. Breath-holding was more common in Group I. We conclude that the overall incidence of airway problems and desaturation episodes was similar between groups. Emergency delirium was common in both groups (32% overall: 40% for Group I, 25% for Group S). IMPLICATIONS: Deep extubation of children can be safely performed with either isoflurane or sevoflurane. After deep tracheal extubation, airway problems occur but are easily managed. Return to an arousable state occurred more quickly with sevoflurane, although time to meeting discharge criteria was not different between the two groups. Emergence delirium occurs frequently with either technique.

Evaluation of the accuracy and precision of lung aerosol deposition measurements from planar radionuclide imaging using simulation.

Planar images of known, theoretical distributions of radioaerosol in the lung have been simulated using lung models derived from magnetic resonance studies on human subjects. Total lung activity was evaluated from the simulated images together with the absolute penetration index (PI) and a relative value expressed as a fraction of that in a simulated ventilation image. The accuracy and precision of these measurements were calculated by comparison with the true values used in the simulation. Total activity was assessed with systematic errors within 5% and precision within 6.5%. Measured PIs varied only slowly with true PI and inter-model variation masked changes between measurements on the different distributions. The relative PI reduced inter-model variation and provided significant differences between all the distributions. PI was significantly affected by misalignment of the lung region of interest. The conducting airways deposition fraction (CADF) used in the simulation correlated linearly with the fractional activity in a central lung region, allowing CADF to be estimated with a precision of 21%.

Paediatric preoperative teaching: effects at induction and postoperatively.

In a randomized controlled trial at Duke University and University of North Carolina Hospitals, 143 two to six year old children undergoing elective ambulatory surgery were randomized into a control group who received routine preoperative teaching or an intervention group who received an interactive teaching book. Changes in behaviour were measured by a Vernon behavioural questionnaire preoperatively and again two weeks postoperatively. A Global Mood Score was assessed in the preoperative holding area, at arrival into the operating room, and at the time of mask induction. The children in the control group were significantly more aggressive postoperatively than the intervention group (P < 0.05). Children who received the interactive teaching book exhibited higher levels of anxiety on the day of surgery, but fewer behavioural changes two weeks following surgery. Parents in the intervention group reported that preoperative teaching helped their child (87%) and themselves (83%).

Three-dimensional description of pulmonary deposition of inhaled aerosol using data from multimodality imaging.

UNLABELLED: Three-dimensional assessment of pulmonary deposition of inhaled aerosol may be performed using SPECT. The use of aligned anatomical images enables improved accuracy of quantification and anatomical localization of deposition. METHODS: Techniques of analyzing these data and their application to deposition studies of two nebulizer-generated aerosols (mass median diameter 1.5 and 6.5 microM respectively) in 12 normal subjects are described. The deposition data were transformed to a standard hemispherical shape and the mean distribution pattern for each aerosol evaluated. Deposition by airway generation was then calculated using a spatial model of airway morphology. The results were compared to those from planar image analysis. RESULTS: The hemispherical transform yielded considerably more qualitative information on deposition pattern. The central-to-peripheral concentration ratio between conducting and alveolated airways was 5.27 for the coarser aerosol and 2.43 for the fine. The two-dimensional spatial estimates of the ratio were 2.61 and 2.03 respectively. CONCLUSION: Analysis of multimodality imaging data considerably enhanced information on deposition compared to planar imaging. It provides new data on aerosol deposition which will be of value to physicians involved in drug inhalation therapy.

Assessment of deposition of inhaled aerosol in the respiratory tract of man using three-dimensional multimodality imaging and mathematical modeling.

Multimodality medical imaging enables measurement of the three-dimensional spatial distribution of a radiolabeled aerosol within the lung. Using a conceptual spatial morphological model these data may be transformed to provide information on deposition per airway generation. This methodology has been used to study the intrapulmonary deposition patterns of two formulations of a metered dose inhaler and two nebulizers in control subjects. The nebulizer study has also been stimulated using a computer model of deposition. The comparison between derived experimental results and those from computer modeling shows areas of agreement, although there are also areas of discrepancy. The new methodology has considerable potential value in the fields of inhalation therapy and deposition modeling, although more detailed validation is still required.

Modelling the effect of charge on selective deposition of particles in a diseased lung using aerosol boli.

The technique of using a charged bolus of aerosol to deliver a drug or other agent is advantageous since sites of interest within the lung can be selectively targeted. Ideally, the volume of the bolus should match that of the targeted region allowing the aerosol bolus particles to be confined to the selected area during the pause period after inhalation. Our existing computer model for predicting the deposition of charged aerosol particles has been developed to encompass aerosol boli, some diseased lung morphologies and drug dose administered per breathing cycle. Aerosol deposition in the targeted region is found to be enhanced by increasing particle charge, pause period and particle size. For particles in the size range 1-2.5 microm, aerosol deposition in the region affected by bronchoconstriction does not alter significantly with flow rate variation (range 250-1000 ml s(-1)) for a targeted charged bolus of matched volume. The technique may enable the optimal delivery of therapeutic or other agents to diseased or normal lungs.

Epidural morphine combined with epidural or intravenous butorphanol for postoperative analgesia in pediatric patients.

We performed a prospective, randomized, double-blinded study in 60 postoperative pediatric patients aged 6 wk to 7 yr to compare the efficacy of butorphanol given epidurally or intravenously in preventing the side effects of epidural morphine. Three groups of patients received 60 micrograms/kg epidural morphine; 20 patients also received epidural butorphanol 30 micrograms/kg, and 20 patients also received 30 micrograms/kg intravenous butorphanol. All patients were evaluated for analgesia, sedation, vomiting, urinary retention, pruritus, and respiratory depression for 24 h postoperatively. Although the overall incidence of side effects was not different in the three groups, the epidural butorphanol group had a significant decrease in severity of pruritus. Sedation was seen more frequently in the groups receiving butorphanol, but was most pronounced in the epidural butorphanol group. We conclude that butorphanol has little or no effect on the side effects of epidural morphine.

Epidural fentanyl infusion with patient-controlled epidural analgesia for postoperative analgesia in children.

The use of epidural fentanyl infusion with patient-controlled epidural analgesia (PCEA) is becoming popular for postoperative analgesia in adults. Its use has not been reported in the pediatric population. We report our initial experience with this technique in pediatric patients. The charts of all children who received epidural fentanyl infusions for postoperative analgesia between June 1991 and February 1992, were reviewed. Thirty-one patients, ages 6 to 17 years (mean +/- SD, 13.2 +/- 2.7) received epidural fentanyl infusion with PCEA for 36 operative procedures. Epidural catheters were either inserted in the lumbar (n = 14) or thoracic (n = 22) epidural space at a level based on the surgery. A fentanyl bolus of 1.38 +/- 0.43 micrograms/kg was delivered via epidural catheter just prior to the conclusion of surgery. A continuous infusion of fentanyl (0.56 +/- 0.18 micrograms/kg/h) with a PCEA bolus (0.53 +/- 0.17 micrograms/kg) available every 15 minutes was initiated in the recovery room and was utilized for 8 to 110 hours (59 +/- 27 hours). Pain and sedation were assessed by verbal descriptive scales, and side effects were noted. Alterations in dosing regimen were made for inadequate analgesia or side effects. Analgesia was assessed as excellent or good in 78% of the patients, 91% in the thoracic catheter group and 57% in the lumbar catheter group (P < .02). Patients with thoracic catheters were more likely to need their infusion and PCEA doses decreased, whereas those with lumbar catheters more often needed their doses increased (P < .05). No patient had respiratory depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaesthetic management of infants requiring endobronchial argon laser surgery.

Small infants with endobronchial lesions primarily due to traumatic suction catheter injuries are now undergoing argon laser surgery to remove obstructive tissue. Providing an anaesthetic for these infants can be challenging because of the small airways involved which must be shared by the anaesthetist and the surgeon. We have performed 30 argon laser endobronchial surgeries in nine infants. The lungs of the majority of patients were ventilated through a tracheostomy intraoperatively, while the surgeon passed the argon laser fibre through the suction port of a fibreoptic bronchoscope which was passed trans-nasally. Three infants were too small to allow passage of the fibreoptic bronchoscope past an artificial airway. In these patients surgery and ventilation were accomplished through a rigid bronchoscope. Three larger patients without tracheostomies were managed with a modified nasal airway for intraoperative ventilation in conjunction with the fibreoptic bronchoscope.