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Biomedical subjects

A Donner

Publications and source records attributed to A Donner.

At least 91 records · Page 5Linked to original sources
PubMed1995

[Laryngeal surgery with a 3-D technique. Early results with the jet-laryngoscope in superimposed high-frequency jet ventilation].

Surgery by three-dimensional (3D) endoscopy is being used routinely in abdominal surgery and, in special cases, in thoracic surgery; however, it has not been reported as being used in microlaryngeal surgery. METHODS. We inserted a 3-D endoscope into a jet laryngoscope and studied the pressure properties at the tip of the laryngoscope as well as intrapulmonary pressures while applying superimposed high-frequency jet ventilation. The studies were conducted initially using a lung simulator, and then in seven patients undergoing microlaryngeal surgery. RESULTS. Due to the rather large 3-D endoscope, the diameter of the jet laryngoscope was reduced by between 25.2% and 70.9%, depending on its size. The measurements on the lung simulator revealed that reduction of laryngoscope diameter leads to an increase in the following parameters: expiratory resistance, tidal volume, and peak inspiratory pressure. The mean FiO2 was 0.74 +/- 0.1; the mean paO2 was 169.2 +/- 80.4 mmHg; and the mean paCO2 was 40.9 +/- 2.4 mmHg. The mean airway pressure was 19 +/- 5.3 mmHg prior to insertion of the endoscope and 12.3 +/- 6.9 mmHg after insertion. The mean positive end-expiratory pressure values increased from 2 +/- 0.6 to 3.6 +/- 2.3 mmHg. Reduction of the working pressure resulted in restoration of the initial inspiratory pressures and tidal volumes. CONCLUSIONS. In the clinical application of 3-D endoscopy via a jet laryngoscope, it was possible to achieve sufficient ventilation, inspection of the surgical field, and performance of the surgical procedure. A CO2 laser was used without changing the ventilation regime. Although technical alterations would be desirable for its application to microlaryngeal surgery, it is presently possible to safely use the 3-D endoscope via the jet laryngoscope for microlaryngeal surgery, presenting the surgeon with new possibilities in voice-improving microsurgery of the larynx.

Aged↗
PubMed1995

[Preliminary experiences with superimpoposed high-frequence jet ventilation in intensive care].

The study aimed to evaluate whether superimposed high-frequency jet ventilation (SHFJV) is a useful tool in intensive care medicine to ventilate patients with pulmonary insufficiency. METHODS. SHFJV is the simultaneous application of low- and high-frequency jet ventilation performed using a specially designed ventilator. SHFJV versus conventional mechanical ventilation (CMV) was were applied in three groups of patients. Group 1 (Gr 1) included patients without pulmonary insufficiency; group 2 (Gr 2) patients had moderate and those in group 3 (Gr 3) had severe pulmonary insufficiency. RESULTS. In Gr 1 and Gr 2, SHFJV was associated with a significant decrease in mean airway pressure (mPAW 12.9 vs. 13.3 mm Hg, P < 0.05). In Gr 3 oxygenation was significantly better with SHFJV (mean paO2 140.1 vs. 109.9 mm Hg, P < 0.05; mean FiO2 0.66 vs. 0.86, P < 0.05). Other parameters, such as maximum airway pressure (Pmax) and mean Paw, were significantly lower with SHFJV than CMV (mean Pmax 29.6 vs. 40.1 mm Hg, mean Paw 18 vs. 21.9 mm Hg, P < 0.05). Intrapulmonary shunt fractions showed a significant decrease with SHFJV (24.6 vs. 34.4, P < 0.05). CONCLUSIONS. Significant differences were observed primarily in Gr 3 patients, indicating that patients with severe pulmonary insufficiency may benefit from SHFJV. SHFJV may thus represent an alternative mode of ventilation in critically ill patients.

Adolescent↗
PubMed1995

[Flow pattern of respiratory gases in superimposed high-frequency jet ventilation (SHFJV) with the jet laryngoscope].

High-frequency ventilation techniques have been applied for a number of years for laryngeal surgery in order to ventilate patients without endotracheal tubes or catheters. A further development of high-frequency jet ventilation (HFJV) is the technique of superimposed HFJV (SHFJV), which was achieved by combining low- and high-frequency jet streams. Although good clinical results were observed, which have been published in the past, the clinical details of development of SHFJV have not been previously published. METHODS. In order to understand and study the mechanism of superimposition of a high-frequency jet stream, extensive experiments on a lung simulator at defined measuring points, which represented the operating field in microlaryngeal surgery and the trachea, were conducted prior to the clinical application of SHFJV. RESULTS. The measurements demonstrated that superposition of the two jet streams led to greater velocity during inspiration, and therefore produced an increase in tidal volume and entrainment of inspiratory gas. This demonstrates that it is possible to apply a HFJV technique in patients even with an open system. During expiration, the velocity of the low-frequency gas stream is decreased by the opposing flow of the high-frequency jet stream, leading to the buildup of positive end-expiratory pressure. The pulsations of the high-frequency jet stream induce continuous alveolar ventilation. The positioning of the jet nozzles in the jet laryngoscopy has the result that the velocities are already decreased at the tip of the laryngoscope and decrease further with distance from the nozzles. This prevents possible damage to the laryngeal mucosa.

Air Pressure↗
PubMed1995

[Superimposed high-frequency jet ventilation (SHFJV) in the administration of NO. Technical basis and early clinical results with ARDS].

The mortality of patients with acute respiratory distress syndrome (ARDS) is still above 50% despite continuous progress in intensive care medicine. Recent therapy regimens such as the extra corporeal life support (ECLS), permissive hypercarbia, high-frequency ventilation techniques and inhaled nitric oxide (NO) are being applied. All of the above techniques are aimed at different parts of the problems caused by ARDS. This study was designed to evaluate the possible additive benefits of superimposed high-frequency jet ventilation (SHFJV) and inhaled NO. METHODS. In experiments on a lung simulator it was demonstrated that it is possible to administer exact amounts of NO using a computer-controlled system with a feedback loop (Pulmonox) using the SHFJV. Applying the therapeutic reference point of 20 ppm of NO, the deviation was +/- 3 ppm at this setting. CASE REPORT. After successfully concluding our experiments, this combined therapy concept was applied in a patient with terminal ARDS. Under CMV, paO2 was 69.4 mm Hg and the oxygen saturation 88.3% with a F1O2 of 1.0. Significant improvement was observed within 30 min after starting SHFJV with inhaled NO (paO2 282.9 mm Hg; oxygen saturation 99.5%). There were no differences observed in hemodynamic parameters between CMV and SHFJV. Although the pulmonary status of the patient improved, the patient died due to therapy-resistant hemodynamic failure. CONCLUSION. It will take further studies to judge whether the success of this new ventilation strategy is reproducible and if the improvement of the oxygenation is more pronounced when adding inhaled NO to SHFJV than when each technique is applied separately.

Anesthetics, Inhalation↗
PubMed1995

[Behavior of cerebral blood flow velocity in conventional ventilation and superimposed high frequency jet ventilation].

OBJECTIVE: Patients with increased intracranial pressure or vasospasm after subarachnoidal haemorrhage with decreased cerebral perfusion present a special problem on developing respiratory insufficiency, since kinetic therapy or extracorporal life support are contraindicated. Superimposed High Frequency Jet Ventilation (SHFJV) has been shown to be of benefit in ventilating patients with pulmonary insufficiency. The aim of this study was to evaluate if SHFJV could be safely applied in patients with critical cerebral blood flow; if so, SHFJV might be beneficial when pulmonary insufficiency occurs concomitantly. METHODS: The study was performed in 14 patients (3 with pulmonary insufficiency) applying first moderate hyperventilation (paCO2 31 to 36 mmHg) followed by increased hyperventilation (paCO2 27 to 30 mmHg) with CMV and SHFJV and measuring intracranial pressure (ICP), cerebral perfusion pressure (CPP) and blood flow velocity (BFV) of the middle cerebral artery. BFV of the middle cerebral artery which correlates closely to the cerebral blood flow, was measured continuously with transcranial Doppler ultrasound. RESULTS: CMV: Increased hyperventilation leads to a statistically significant increase in paO2 (121.3 to 147.2 mmHg, p < 0.05), SaO2 (98.5% to 99.2%, p < 0.05) and decrease in BFV (systole 115.9 to 89.6 cm/s, diastole 44.6 to 31.8 cm/s, p < 0.05). Heart rate, mean arterial blood pressure, ICP and ventilation parameters did not show any statistically significant differences. SHFJV: During SHFJV the parameters demonstrated similar patterns as during CMV. However, none of the changes were statistically significant (paO2 111.9 to 125.9 mmHg, SaO2 97.9 to 98.8, BFV systole 106 to 95 cm/s, diastole 52.7 to 42.4 cm/s, n.s.). After calculating the mean BFV according to the Markwalder formula to a standard paCO2 of 40 mmHg CMV and SHFJV were compared to one another. No statistical difference was seen between the two different ventilation techniques. CONCLUSION: In patients with increased ICP, pulmonary complications such as pneumonia or ARDS are frequently observed. Since there are indications that SHFJV is of benefit in pulmonary insufficiency, the study was conducted to demonstrate that SHFJV can be safely applied in patients with increased ICP.

Adolescent↗
PubMed1995

[Ventilation during tracheotomy in extensive, 90% laryngeal stenosis using superimposed high frequency jet ventilation via the jet laryngoscope].

In a 35-year old male patient with laryngeal carcinoma an acute respiratory insufficiency with early hypoxaemia developed due to massive laryngeal stenosis. An endotracheal intubation was not possible since the available lumen was too small. Tracheotomy using local anaesthesia was not possible since spontaneous respiration with a Venturi mask applying 100% oxygen was not sufficient and the patient was becoming restless and agitated due to the hypoxaemia. Transcutaneous jet ventilation was considered to be too risky since the needle would have to pass highly vascularised tumour tissue and the detection of such a small rest lumen would have been quite difficult. Ventilating the patient using a percutaneous catheter would have been very risky as well since, due to the massive stenosis, a sufficient expiration would not be likely and therefore was considered to carry a high risk of barotrauma. The patient was ventilated under general anaesthesia via a specially designed endoscopy tube with integrated jet nozzles applying superimposed high frequency jet ventilation above the stenosis. Since it was possible to achieve sufficient ventilation during the inspection of the larynx the jet laryngoscope was left in place and the supporting apparatus was covered with sterile drapes. The tracheotomy was performed using the superimposed high frequency jet ventilation. Throughout the procedure oxygenation and ventilation were adequate. The laryngectomy performed several days later revealed a cauliflower type protrusion into the tracheal lumen and a 5 cm long stenosis of the larynx with a lumen of 3 mm.

Adult↗
PubMed1995

Optimal intravenous dosing strategies for sedatives and analgesics in the intensive care unit.

Achieving and maintaining adequate levels of analgesia and sedation in critically ill patients is a fundamental part of ICU care. Understanding the clinical pharmacology of commonly used sedative agents (e.g., midazolam, lorazepam, and propofol) and opioids (e.g., fentanyl and morphine) enables clinicians to best dose these drugs to the desired clinical effect while minimizing the risk of excessive sedation and cardiopulmonary depression. This has significant safety and cost implications for patient care in the ICU. Simulations of plasma concentrations of these medications when administered to ICU patients provide useful insight into the clinical pharmacology of these agents. A number of points should be made with regards to the interpretation of these predicted plasma concentrations, however. First, it is important to remember that PK parameters for most of these agents, with the exception of midazolam and propofol, were derived from bolus or short-term infusions administered to healthy patients, and that the PK parameters for lorazepam, fentanyl, and morphine when administered as long-term infusions to critically ill patients may vary dramatically from these initial estimates. Specifically, their volumes of distribution and elimination half-lives may prove to be significantly larger and longer, respectively, when administered to patients in the ICU. This pharmacokinetic variability may result in even longer emergence times than predicted herein following discontinuation of continuous infusions of these agents. Until similar studies in ICU patients are performed for lorazepam, fentanyl, and morphine, the clinical pharmacology of these agents in ICU patients remains uncertain. Additionally, midazolam and morphine both have active metabolites that can accumulate in critically ill patients receiving long-term infusions. These metabolites add significantly to the sedative effects of the primary compound. Other drugs with sedative effects given concurrently with any of these agents (i.e., psychotropic agents, epidural opioids, etc.) may also contribute to the sedative effects of these drugs. These studies do not account for the development of tolerance (which can occur with both benzodiazepines and opioids) or changing kinetic profiles within an individual patient over time (i.e., due to changes in volume of distribution, protein binding, or clearance). Finally, there is a high degree of interpatient variability among critically ill patients, and medication dosing must be tailored to individual patients' needs (i.e., one dose does not fit all patients). Given the uncertainty of resulting plasma concentrations with long-term administration of these medications, the best ways to achieve and maintain optimal levels of sedation and analgesia while minimizing the risk of oversedation and side effects are to (1) initiate sedation in an incremental fashion until the desired level of sedation is achieved, then periodically (i.e., once a day) titrate the infusion rate of sedative-hypnotics and opioids downward until the patient begins to emerge from the sedative effects of these drugs; and finally gradually increase the infusion rate until the desired level of sedation is once again achieved; and (2) consider the use of a sedation scale to standardize the level of sedation to be maintained (see Table 3). The use of such a scale enables physicians to communicate to nursing staff the specific level of sedation to be achieved and maintained in an individual patient (i.e., titrate the midazolam infusion between 0 to 5 mg/hr to maintain a sedation score of 2-3; call MD for inadequate sedation, respiratory depression, or hypotension). Achieving optimal sedation and analgesia of patients in the ICU requires not only that the choice of medication(s) be appropriate for the clinical setting but also that there are specific clinical endpoints for the agents used (i.e., light versus deep sedation, continuous versus intermittent sedation, sedation with

Benzodiazepines↗
PubMed1994

Evaluation of a palliative care service: problems and pitfalls.

OBJECTIVE: To evaluate a palliative care home support team based on an inpatient unit. DESIGN: Randomised controlled trial with waiting list. Patients in the study group received the service immediately, those in the control group received it after one month. Main comparison point was at one month. SETTING: A city of 300,000 people with a publicly funded home care service and about 200 general practitioners, most of whom provide home care. MAIN OUTCOME MEASURES: Pain and nausea levels were measured at entry to trial and at one month, as were quality of life for patients and care givers' health. RESULTS: Because of early deaths, problems with recruitment, and a low compliance rate for completion of questionnaires, the required sample size was not attained. CONCLUSION: In designing evaluations of palliative care services, investigators should be prepared to deal with the following issues: attrition due to early death, opposition to randomisation by patients and referral sources, ethical problems raised by randomisation of dying patients, the appropriate timing of comparison points, and difficulties of collecting data from sick or exhausted patients and care givers. Investigators may choose to evaluate a service from various perspectives using different methods: controlled trials, qualitative studies, surveys, and audits. Randomised trials may prove to be impracticable for evaluation of palliative care.

Canada↗
PubMed1994

Methods for comparing event rates in intervention studies when the unit of allocation is a cluster.

The aim of many research investigations is to compare the proportion of individuals in each of several groups that have a certain characteristic. The unit of allocation for such investigations is often an intact social unit, as in randomizing families, medical practices, schools, or entire communities, to different intervention groups. Standard statistical methods are not appropriate for these designs, since they do not take into account the dependencies among individuals within the same cluster. The authors review the strengths and weaknesses of several approaches for dealing with this problem, using data from a school-based smoking cessation trial. A principal conclusion is that the choice of method should depend on whether or not random allocation is used in the assignment of interventions.

Chi-Square Distribution↗
PubMed1994

A comparison of methods for testing homogeneity of proportions in teratologic studies.

We consider teratologic studies in which the aim is to compare the survival rate of animals in a treatment group to the corresponding rate in a control group. The design of such studies often involves the allocation of intact litters of animals to treatment, invalidating the application of standard statistical methods. We review the strengths and weaknesses of several approaches for dealing with this problem including methodology recently developed for the analysis of clustered binary data. A simulation study is conducted in which litter sizes are generated from a distribution having specified mean and degree of imbalance. It is recommended on the basis of this study and on theoretical considerations that the choice of method should depend on whether the comparison of interest is experimental or observational. For experimental comparisons, involving the random assignment of litters to different treatment groups, methods based on the adjustment of standard chi-square statistics are recommended unless the number of litters in each group is very large.

Animals↗
PubMed1994

[Jet ventilation superimposed on a special jet laryngoscope for endoluminal stent insertion in the tracheobronchial system].

BACKGROUND: Stenotic processes of the tracheobronchial system may lead to dyspnoea that can become lift-threatening. To restore sufficient function of the blocked airway, a silicone stent can be inserted. The anaesthesia techniques used for this intervention so far have been complicated. The object of this study was to determine whether the super-imposed high-frequency jet ventilation (SHFJV) via the jet laryngoscope originally designed for microlaryngeal surgery can be utilized for endoluminal stent insertion. METHODS: In 12 patients with acute respiratory insufficiency (ASA 3-5) due to stenosis of the tracheobronchial system, an endoluminal silicone stent was inserted through the jet laryngoscope while the patient was ventilated using SHFJV: RESULTS: A significant rise in paO2 readings prior to the jet ventilation and subsequent measurements was observed. The CO2 elimination was good (average paCO2 31.5 +/- 7.5-53.1 +/- 14 mmHg). Variably high paCO2 readings during stent insertion were related to the respective surgical phases. At the end of the surgical manipulation, all patients had sufficient spontaneous ventilation. CONCLUSIONS: First clinical applications of the jet laryngoscope combined with superimposed jet ventilation for stent insertion demonstrated satisfactory results. Not only were the patients ventilated throughout the procedure, but CO2 elimination was also satisfactory. Superimposed jet ventilation provides a sufficient tidal volume with low ventilation pressures, and therefore oxygenation and CO2 elimination are unproblematic. SHFJV enables the anaesthetist to ventilate the patient nearly continuously with minimal phases of apnoea. The only apnoea phases, as with any other method, occur during surgical manipulation while inserting the stent and thus blocking the airway. We believe that the jet laryngoscope with SHFJV presents a distinct advantage for both anaesthetist and surgeon when inserting stents in the tracheobronchial system.

Acute Disease↗
PubMed1994

[Anesthesia in acute respiratory tract obstructions caused by high degree laryngeal and tracheobronchial stenoses].

UNLABELLED: Stenotic process of the laryngeal and/or tracheobronchial system may lead to dyspnoea which can become life threatening. OBJECTIVE: The object of our study was to determine whether sufficient gas exchange can be ensured in patients with a massive stenosis of the respiratory tract applying the Superimposed High-Frequency-Jet-Ventilation (SHFJV) via the jet laryngoscope. Further, it was to be determined whether SHFJV can be applied for insertion of endoluminal stents into the tracheo-bronchial system. METHOD: SHFJV was applied using the Bronchotron-ventilator (capable of generating simultaneous low frequency and high frequency jets) and the laryngoscope, basically a modified endoscopy tube permitting simultaneous application of two jet modes. SHFJV was performed in 14 patients (including 4 children) suffering from massive laryngeal stenosis and in further 12 patients with stenosis of the tracheo-bronchial system. In all patients total intravenous anaesthesia was performed. RESULTS: In the patients with laryngeal stenosis the average paO2 was 117.5 +/- 43 mmHg, and the mean paCO2 47.3 +/- 11.6 mmHg. In the patients with stenosis of the tracheo-bronchial system the mean paO2 was 125 +/- 77 mmHg and the average paCO2 53.3 +/- 18 mmHg. CONCLUSIONS: The SHFJV technique presents the possibility to ventilate the patients continuously for surgical procedures even with massive stenosis of the respiratory tract. The application of SHFJV via the jet laryngoscope not only enables the anaesthesist to ventilate this group of patients but also helps the surgeon and therefore results in more safety for the patient.

Adult↗
PubMed1994

[Ventilation in laryngeal laser-surgical interventions using superimposed high frequency jet ventilation (SHFJV)--a further revision of jet ventilation technique for laryngeal interventions].

In laser surgery of the larynx the surgeon and the anaesthesist have to compete for the limited space available. The surgeon requiring good visibility and an undisturbed operating area whereas the anesthetist has to ensure sufficient ventilation of the patient. Further, complications of anaesthesia and laser must be avoided. These requirements are met by using the jet-tube (jet-laryngoscope) with two integrated nozzles applying simultaneously low- and high-frequency jet-ventilation giving the surgeon total access to the area operated on, and at the same time enables safe ventilation of the patient. Of 334 operations with the tubeless ventilation technique 76 cases were laser surgical interventions. In 6 patients stenoses were enlarged. The average duration of the jet-ventilation was 25 +/- 10 minutes. The maximum duration of a laser surgical intervention was 140 minutes. The age distribution of the patients was 18 months to 82 years. In all patients pulmonary gas exchange was satisfactory. We believe that the advantage of the tubeless jet-ventilation is: optimal visibility and surgical freedom for the surgeon, no time limitation, even in very severe stenoses. Since no volatile anaesthetics or any type of endotracheal tube are applied there is no danger of interaction with the laser when using the SHFJV via the jet-laryngoscope. Application of the tubeless jet-ventilation technique is however limited if patients suffer from severe pulmonary obstruction; likewise highly obese patients and patients in whom massive bleeding occurs are not amenable to tubeless jet-ventilation.

Adult↗
PubMed1994

[Tubeless superimposed high frequency jet ventilation in high grade laryngeal stenoses].

UNLABELLED: Massive stenosis of the larynx may present a potentially life-threatening situation for the patient, requiring immediate measures to ensure a patient's airway. The aim of this prospective study was to evaluate potential benefits of Superimposed High Frequency Jet Ventilation (SHFJV) in patients requiring microlaryngeal surgery due to massive stenosis of the larynx. PATIENTS AND METHODS: 23 patients (age range 1.5 to 90 years) with laryngeal stenosis grade 2 and 3 according to the Cotton scale were ventilated using SHFJV. The duration of the SHFJV was 12 to 116 minutes. SHFJV was performed using a Bronchotron Respirator via a jet-laryngoscope. RESULTS: Arterial blood gases demonstrated paO2 between 71 and 295 mmHg and paCO2 of 28 to 81 mmHg. The mean FiO2 applied was 61.75 +/- 19.26. The airway pressure was measured at the tip of the jet-laryngoscope and was between 6 and 15 mmHg, and PEEP was 1 to 5 mmHg. In 13 patients a CO2 laser was utilised during surgery. DISCUSSION: In all patients SHFJV was performed without problems. Since the ventilation is delivered above any possible stenosis the danger of barotrauma is minimised. The surgeon obtains optimal visibility of the larynx and is not obstructed in the surgical procedure. SHFJV enables both the surgeon and the anesthetist to perform their respective duties and therefore increases the safety of the patient in the management of such a difficult problem as massive stenosis of the larynx.

Adolescent↗
PubMed1994

[3-D endoscopy for laryngeal interventions in tubeless superimposed high frequency jet ventilation. A clinical trial].

UNLABELLED: Surgery by 3-dimensional (3D) endoscopy is being used routinely in abdominal surgery and, in special cases, in thoracic surgery; however, it has not been reported to be used in laryngeal surgery. METHODS: We inserted a 3-D endoscope into a jet laryngoscope and studied the pressure properties at the tip of the jet laryngoscope as well as the intrapulmonary pressures while applying SHFJV. The studies were conducted initially using a lung simulator, and then in 6 patients undergoing endoscopic laryngeal surgery. RESULTS: Due to the rather large 3-D endoscope the diameter of the jet laryngoscope was reduced between 25.2% and 70.9% depending on the size of the jet laryngoscope. The measurements on the lung simulator revealed that the reduction of the diameter of the jet laryngoscope leads to an increase in the following parameters: expiratory resistance, tidal volume, and peak inspiratory pressure. The mean FiO2 was 0.74 +/- 0.1; the mean airway pressure was 19 +/- 5.3 mmHg prior to the insertion of the endoscope and 12.3 +/- 6.9 mmHg after the insertion. The mean PEEP values increased from 2 +/- 0.6 to 3.6 +/- 2.3 mmHg. Reduction of the working pressure resulted in regaining the initial inspiratory pressures and tidal volumes. CONCLUSIONS: In the clinical application of 3-D endoscopy via a jet laryngoscope it was possible to achieve sufficient ventilation, inspection of the surgical field and performance of the surgical procedure. A CO2 laser was used without changing the ventilation regime.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Biochemical characterization of binding of multiple HIV-1 Rev monomeric proteins to the Rev responsive element.

Recombinant HIV-1 Rev protein was overexpressed in Escherichia coli using translational coupling to the beta-glucuronidase gene and demonstrated to interact with high affinity and specificity with the Rev responsive element (RRE). A complex Rev-dependent binding pattern was observed using the gel shift assay which could be simplified to one or two primary bands in the presence of stoichiometric concentrations of RRE. Competition of these bands with a series of homopolymer RNA species demonstrated that Rev is essentially a poly-G binding protein, although poly-I was also shown to compete for specific RRE binding. The stoichiometry of the Rev-dependent gel shift complexes was determined using 125I-labeled Rev. The stable, lowest mobility complex was determined to possess a ratio of between 7 and 8 Rev molecules per RRE containing RNA fragment while the two fastest migrating complexes contained ratios of one and two Rev molecules per RRE, respectively. Using the Hill equation as a model for cooperative interactions, a Hill coefficient of n(app) = 2 was obtained from fitting of direct nitrocellulose filter binding assays, reflecting cooperatively bound Rev molecules on the RRE under equilibrium binding conditions. An increase in ionic strength from 0.0 to 0.3 M NaCl reduced cooperative Rev binding to the RRE, but specificity of Rev for the RRE relative to antisense RNA was increased 100,000-fold. At molar ratios of Rev to RRE above 2, Rev dissociated from the RRE with a T1/2 of approximately 20-25 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1992

Small sample performance of tests of homogeneity of odds ratios in K 2 x 2 tables.

In this note we study, by simulation, small sample performance in terms of size of ten procedures for testing the homogeneity of odds ratios in K 2 x 2 contingency tables. These ten statistics are derived for 'large-stratum' settings. Our study concerns the behaviour of these statistics for 'small-stratum' settings.

Chi-Square Distribution↗