Localizing concurrent sound sources with binaural microphones: A simulation study

The human auditory system can localize multiple sound sources using time, intensity, and frequency cues in the sound received by the two ears. Being able to spatially segregate the sources helps perception in a challenging condition when multiple sounds coexist. This study used model simulations to explore an algorithm for localizing multiple sources in azimuth with binaural (i.e., two) microphones. The algorithm relies on the "sparseness" property of daily signals in the time-frequency domain, and sound coming from different locations carrying unique spatial features will form clusters. Based on an interaural normalization procedure, the model generated spiral patterns for sound sources in the frontal hemifield. The model itself was created using broadband noise for better accuracy, because speech typically has sporadic energy at high frequencies. The model at an arbitrary frequency can be used to predict locations of speech and music that occurred alone or concurrently, and a classification algorithm was applied to measure the localization error. Under anechoic conditions, averaged errors in azimuth increased from 4.5° to 19° with RMS errors ranging from 6.4° to 26.7° as model frequency increased from 300 to 3000 Hz. The low-frequency model performance using short speech sound was notably better than the generalized cross-correlation model. Two types of room reverberations were then introduced to simulate difficult listening conditions. Model performance under reverberation was more resilient at low frequencies than at high frequencies. Overall, our study presented a spiral model for rapidly predicting horizontal locations of concurrent sound that is suitable for real-world scenarios.

Perioperative intravenous contrast administration and the incidence of acute kidney injury after major gastrointestinal surgery: prospective, multicentre cohort study

BACKGROUND

This study aimed to determine the impact of preoperative exposure to intravenous contrast for CT and the risk of developing postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery.

METHODS

This prospective, multicentre cohort study included adults undergoing gastrointestinal resection, stoma reversal or liver resection. Both elective and emergency procedures were included. Preoperative exposure to intravenous contrast was defined as exposure to contrast administered for the purposes of CT up to 7 days before surgery. The primary endpoint was the rate of AKI within 7 days. Propensity score-matched models were adjusted for patient, disease and operative variables. In a sensitivity analysis, a propensity score-matched model explored the association between preoperative exposure to contrast and AKI in the first 48 h after surgery.

RESULTS

A total of 5378 patients were included across 173 centres. Overall, 1249 patients (23·2 per cent) received intravenous contrast. The overall rate of AKI within 7 days of surgery was 13·4 per cent (718 of 5378). In the propensity score-matched model, preoperative exposure to contrast was not associated with AKI within 7 days (odds ratio (OR) 0·95, 95 per cent c.i. 0·73 to 1·21; P = 0·669). The sensitivity analysis showed no association between preoperative contrast administration and AKI within 48 h after operation (OR 1·09, 0·84 to 1·41; P = 0·498).

CONCLUSION

There was no association between preoperative intravenous contrast administered for CT up to 7 days before surgery and postoperative AKI. Risk of contrast-induced nephropathy should not be used as a reason to avoid contrast-enhanced CT.

Successful long-term outcome of liver transplantation in late-onset lysosomal acid lipase deficiency

Late-onset LAL deficiency, previously referred to as cholesteryl ester storage disorder, is a rare lysosomal storage disorder characterized by accumulation of cholesteryl esters. It has a heterogeneous clinical phenotype including abdominal pain, poor growth, hyperlipidemia with vascular complications and hepatosplenomegaly. End-stage liver disease may occur, but there are few reports of successful LT. There are also concerns that systemic manifestations of the disease might persist post-LT. We report a case with excellent outcome eight yr following LT. The subject was noted to have asymptomatic hepatosplenomegaly during an intercurrent illness, and LAL deficiency was confirmed with compound heterozygosity in the LIPA. Despite dietary fat restriction, he developed signs of progressive liver disease and subsequently developed hepatopulmonary syndrome. He underwent cadaveric LT at the age of nine and a half yr and recovered with prompt resolution of hepatopulmonary syndrome. Eight yr post-transplant he has normal growth, normal lipid profile, and liver and renal function tests. Liver histology showed no evidence of disease recurrence at this stage. LT in this subject resulted in an excellent functional correction of late-onset LAL deficiency.

Relation between drug-induced central nervous system effects and plasma levels of diazepam in man

Pharmacodynamic effects and plasma levels of diazepam were studied in healthy male volunteers at different dose levels. Responses to diazepam were quantified, using instruments which measured body sway (statometry) and psychomotor performance (stressalyser tests). High dose-related correlations were obtained between drug-induced changes in test parameters and drug plasma levels, both with regard to stimulant and depressive effects. Techniques were devised for evaluating and comparing the efficacy and usefulness of different types of tests, taking into account critical thresholds, slopes and error estimates, correcting for changes in predrug levels and control (nondrug) trials.

Segregation of Beaufort Sea beluga whales during the open-water season

Population segregation by habitat use occurs because energy requirements and survival strategies vary with age, sex, size, and reproductive stage. From late summer to early fall in 1993, 1995, and 1997, relative length (age), sex, and reproductive status of satellite-tagged beluga whales ( Delphinapterus leucas (Pallas, 1776)) in the eastern Beaufort Sea were tested for habitat segregation. We used (i) resource selection function models to evaluate how belugas used areas of varying sea ice concentration and shelf habitat and (ii) distance analysis to measure the selection of areas varying in distance to mainland and island coastlines. Resource selection functions and distance analysis established that habitat selection differed with length, sex, and reproductive status of whales: (i) females with calves and smaller males selected open-water habitats near the mainland; (ii) large males selected closed sea ice cover in and near the Arctic Archipelago; and (iii) smaller males and two females with calves (not newborn) selected habitat near the ice edge. The segregation of habitat use according to sex, age, and reproductive status relates to the different resources required at different life stages and may represent characteristics of beluga social structure. We discuss our results in the context of two common sexual segregation hypotheses and conclude that summer habitat segregation of belugas reflects differences in foraging ecology, risk of predation, and reproduction.

A comparison of different biogeographical classifications of Europe, Great Britain and Spain

Various biogeographical and bioclimatic classifications of a number of regions, countries and continents have been created to meet different objectives. A policy maker might ask the question 'why is there no single accepted classification and how do the different classifications compare with one another?' In order to answer these two questions three classifications created by different methods for Great Britain and two for Spain are compared using the Kappa statistic. All of the classifications were created from data on cellular grids with a set window size. Further non-statistical comparisons are made with other classifications. The biogeographic classifications studied in this paper produced three different types of zone: those that were always identified whatever the method; those that were broadly similar but where the boundaries differed; and those that were unique to a particular classification. These different types of zone are likely to exist for any comparison between classifications of a particular region. The extent of the geographic window from which data were obtained had a major effect on the classification of grid cells at the edges of the window. For example, the few grid cells in the south of England, with characteristics of continental Europe, are not detected if data from Great Britain alone are used for the classification. We conclude that the data window should always be larger than the area for which the classification is being made. The objective Kappa statistic, although useful, was not capable of discerning similarities and dissimilarities that appear obvious to the subjective human eye. Although the details of the classifications differed there were broad similarities between the classifications and these differences reflect important divisions along major environmental axes that have been inferred by earlier biogeographers. As the divisions are real there is a sound basis for their use in future land use or environmental policy.

Phase II trial of topotecan and cisplatin in persistent or recurrent squamous and nonsquamous carcinomas of the cervix

OBJECTIVE

Cisplatin is a standard treatment in advanced, recurrent cervical cancer. Because topotecan is an established treatment in gynecologic malignancies such as ovarian cancer and exhibits nonoverlapping toxicity with cisplatin, a phase II trial was conducted to evaluate the tolerability and antitumor activity of a cisplatin/topotecan doublet in persistent or recurrent cervical cancer patients.

METHODS

Patients with bidimensionally measurable persistent or recurrent squamous cell and non squamous cell cervical cancer and adequate bone marrow were enrolled. Patients received 50 mg/m(2) of cisplatin intravenously over 1 h on Day 1 and 0.75 mg/m(2) of topotecan intravenously over 30 min on Days 1, 2, and 3 of 21-day cycles for six cycles or until disease progression. Tumor response and regimen toxicity were assessed using established Gynecologic Oncology Group criteria.

RESULTS

Thirty-two of 35 enrolled patients were evaluable for toxicity and tumor response. All but 2 evaluable patients had received previous radiotherapy. No patient received prior chemotherapy. The cisplatin/topotecan doublet was well tolerated, with 77 and 78% of courses given without interruption or delay and at full doses, respectively. As anticipated, the most common toxicity was hematologic, with grade 3/4 neutropenia and thrombocytopenia reported in 30 and 10% of cycles, respectively. The overall response rate was 28% (9/32), with 3 complete and 6 partial responses. The antitumor response in nonirradiated fields (30%) was similar to the response observed in previously irradiated fields (33%), suggesting good drug penetration. Median duration of response was 5 months (range, 2 to 15+ months). An additional 9 (28%) patients achieved stable disease. Median survival was 10 months, with 3 patients in lasting remission.

CONCLUSIONS

These results demonstrate that the cisplatin/topotecan combination is safe, well tolerated, and active in persistent or recurrent cervical cancer patients. A phase III, multicenter trial is under way (cisplatin/topotecan versus cisplatin) based on these favorable results to confirm the safety and efficacy profile in this patient population.

Inequalities in health: evaluation and effectiveness in practice

This paper details the findings from a project that assessed the contribution made by nurses, midwives and health visitors to targeting health and social need. This is an important theme within the Northern Ireland Regional Strategy entitled 'Health and well-being into the next millennium: a regional strategy for health and social well-being 1997-2002', which is concerned with addressing inequalities in health status and social well-being. In response to this initial survey, the paper also highlights the second phase of the project that was the development of an evaluation manual specifically designed to assist health-care practitioners in establishing evaluation frameworks and in applying evaluation techniques and methods. The paper describes four research case studies that are intended to illustrate the kinds of evaluation methods necessary to cover the stages of evaluation, needs assessment, structure, process and outcome, and to reflect the experience of applied evaluation as it occurs in practice as opposed to how it appears in textbooks.

Bone cement mixing. Theatre staff's views and opinions

Acrylic bone cement has not substantially changed since it was first introduced more than 30 years ago, however the method by which it is mixed has evolved greatly (Dunne 1996).

Tackling inequalities in health and social wellbeing: evidence of 'good practice' by nurses, midwives and health visitors

This paper details a project which assessed the contribution made by nurses, midwives and health visitors to Targeting Health and Social Need (THSN). Targeting Health and Social Need is an important theme within the Northern Ireland Regional Strategy entitled Health and Wellbeing into the Next Millennium: A Regional Strategy for Health and Social Wellbeing 1997-2002 which is concerned with addressing inequalities in health status and social wellbeing. While there is a considerable body of research and information on variations in health and social wellbeing there is a paucity of corresponding research on those interventions which may improve the health of disadvantaged groups. Health professionals are addressing such inequalities so it is appropriate that their efforts should be recorded and assessed. The project was conducted jointly by the departments of nursing at The Queen's University of Belfast and the University of Ulster, funded by the Department of Health and Social Services and had a timetable that covered three phases. Phase 1 entailed the distribution of a survey questionnaire to all nurses, including those professionals working with community and voluntary groups, to assess their contribution to THSN. The paper describes the results from the 392 questionnaires identified (a response rate of almost 40%) and the work in phase 2 of analysing the responses by selection criteria devised by the Project Advisory Board to allow further investigation. The resulting interventions were reduced to 22 and in an overview of each of these a number of characteristics kept recurring that could serve to define aspects of 'good practice'. These 22 case studies demonstrate the efforts made by nurses and health professionals to change behaviour, practice, the community and the environment. Also highlighted are the nursing competencies gained through working, the lessons learnt and the problems and difficulties encountered. The paper concludes that the use of qualitative research opens the door to measures of social position that reflect the ways in which people define themselves and the relationships that sustain them. Although there is still some way to go in understanding the different approaches to evaluation, an environment that fosters the monitoring and assessment of practice might be created in the future within the nursing community.

The role of nursing partnership interventions in improving the health of disadvantaged women

This paper describes a project which assessed the contribution that nursing professionals are making to improving the health of deprived women living in Northern Ireland. The study is set within the context of the Targeting Health and Social Need (THSN) Initiative an important theme within the Northern Ireland Regional Strategy entitled Health and Well-being into the Next Millennium - A Regional Strategy for Health and Social Well-being 1997-2002 which is concerned with addressing inequalities in health status and social well-being. The paper describes the results of a survey (n=1,000, response rate 39%) and the criteria used to select 22 interventions to provide evidence of 'effective practice' within THSN. The study highlights the work of previous reviews in the area and provides evidence concerning effective interventions in practice. Although the interventions described may be lacking in 'pure scientific' method and may not meet the rigorous inclusion criteria of systematic review methodologies, there is evidence to suggest that nurses are using well-designed more qualitative evaluation methods and demonstrating improvements in health and social need for women in the lowest socio-economic groups. In terms of equity the case studies show that community nursing may be a powerful vehicle for researching people previously neglected by the formal health care system. Health policies such as THSN can now articulate the methods needed for reform or change, setting directions and articulating the barriers to implementation and achievement.

Health professionals' perspectives on service delivery in two Northern Ireland communities

This research builds on the findings of an ethnographic study of health inequalities in two small, rural communities in Northern Ireland. Through further analysis of existing data, this second study aimed to explore health professionals' perspectives on issues of service delivery relevant to government policy on primary care. Anthropological fieldwork was conducted for two consecutive 4-month periods during 1995 and 1996 in one predominantly Catholic and one predominantly Protestant town. To preserve confidentiality, the locations have been given the pseudonyms, respectively, of Ballymacross and Hunterstown. Research tools included fieldwork journals and a fieldwork diary, meetings with key informants, tape-recorded interviews, group discussions, participant observation and use of secondary material such as census data, local newspapers and community health profiles. Interviews with 15 health workers revealed that there was not a coherent approach to achieving health gain, little collaborative enterprise and minimal interaction between the different professional groups. The National Health Service (NHS)-employed primary care professionals, more than local community workers, appeared to be demoralized, exhausted and suspicious of the business-orientated health service. In this respect, the primary care-led NHS appeared not to be working. It is concluded that a shared health agenda should be developed by NHS-employed primary care professionals and local community workers to create a health-inducing environment at community level. This needs to be complemented by the establishment of formal mechanisms for inter-agency working at local, professional and government levels.

Semicontinuous cardiac output monitoring using a neural network

OBJECTIVES

This study compared 2-mL bolus thermodilution cardiac output measurements with standard 10-mL bolus measurements.

DESIGN

Cardiac output was measured with the new 2-mL bolus technique and the 10-mL standard thermodilution technique in a perspective series. We describe a system that automatically cools and injects 2-mL boluses of saline into a standard pulmonary artery catheter. It uses a Peltier effect solid-state cooler and pneumatically driven syringe injector to measure cardiac output once per minute.

SETTING

Animal laboratory.

ANIMALS

Eight adult Duroc swine weighing between 38.0 and 57.5 kg.

INTERVENTIONS

Once each minute, 2 mL of cooled 5% dextrose was injected through the pulmonary catheter. Once every 8 mins, four sequential measurements of cardiac output were made using 10-mL injections.

MEASUREMENTS AND MAIN RESULTS

A total of 1249 paired waveforms were processed with both a conventional algorithm and with a neural network. For the conventional algorithm, the correlation coefficient was r2 = .92 and the SD of the difference was 1.30 L/min. For the neural network, the correlation coefficient was r2 = .94 and the SD of the difference was 0.88 L/min. Output filtering improved the results in both cases.

CONCLUSION

Neural networks accurately derive cardiac output from 2-mL bolus thermodilution injections, allowing cardiac output to be monitored automatically once per minute in many patients. The technique is convenient and uses standard low-cost catheters.

A closed rebreathing system for dose maintenance during Partial Liquid Ventilation

Partial Liquid Ventilation (PLV), a treatment for acute respiratory failure in which the lungs are filled, either partially or to functional residual capacity (FRC), with perfluorochemical (PFC) liquid while the patient is on mechanical gas ventilation, has progressed to clinical trials using the PFC perflubron (PFB). Because gas expired during PLV is laden with PFB vapor, PFB is lost via evaporation, which increases dose consumption and necessitates periodic redosing. A device has been developed to minimize evaporative loss by confining PFC vapor to a gas volume breathed by the patient, which is isolated from the ventilator. This closed rebreathing system works with the ventilator such that after the lung is filled with PFB, the patient is connected to the rebreathing system, with breathing still "driven" by the ventilator. The rebreathing system consists of two gas circuits, or compartments, separated by a flexible bag (in a box) partition. One compartment is in gas communication with the lung, while the second communicates with the ventilator. The O2 level on the patient side is matched to that on the ventilator side by sensing gas concentrations and by feedback control of O2 introduction. Similarly, air is introduced into the patient side under pressure-based feedback control to maintain a constant gas volume. On inspiration, the ventilator delivers the tidal volume (breath) into the box surrounding the bag, which, in turn, is transmitted through the bag to the lung. On expiration, the process is reversed. Unidirectional circulation of gas in the rebreathing circuit is achieved via check valves, and expired CO2 is removed by a barium hydroxide lime cartridge. Airway humidification is maintained by captive water vapor in the system and water vapor from the CO2 absorber. It is recommended that flow, pressure, O2, and CO2 levels be monitored at the patient "Y," i.e., the proximal end of the endotracheal tube. Performance data from both in-vitro experiments and in-vivo PLV experiments in pigs are presented. The authors conclude that with the closed rebreathing system, the dose can be safely maintained with fewer redosing procedures, and an approximately 90% savings in dose is achieved.

Clinical evaluation of tracheal pressure estimation from the endotracheal tube cuff pressure

OBJECTIVE

Air flow through an endotracheal tube causes a pressure drop across the tube. This pressure drop creates a difference between air pressure measured in the trachea and the pressure measured in the breathing circuit, which can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have developed a method of estimating tracheal pressure from the pressure in the endotracheal tube cuff and tested this system in clinical trials.

METHODS

Pressure measurement ports were placed between the Y piece of the ventilator circuit and the ETT connector, in the trachea at the carinal end of the ETT, and in the ETT cuff inflation line. Tracheal pressures and cuff pressures were found at end-inspiration and end-expiration (no flow states) and used to define a linear relationship between cuff pressure and tracheal pressure. Using the estimated tracheal pressure (Ptrach) and the measured pressure at the Y piece of the breathing circuit (PY), the pressure drop across the ETT was found as a function of flow through the tube. Tracheal pressure was then calculated from the flow-dependent pressure drop and PY. Tests of this system were performed in six patients in the operating room and six patients in the intensive care unit.

RESULTS

The flow-based tracheal pressure estimates were within 0.7 +/- 0.4 cm H2O of actual tracheal pressure (mean +/- SD). At peak inspiratory pressure the difference averaged 0.5 +/- 0.3 cm H2O. The difference between our estimate of tracheal pressure and actual tracheal pressure was always less than 1 cm H2O.

CONCLUSION

The flow-based tracheal pressure estimates were accurate during intermittent spontaneous breathing, but not during spontaneous breathing or with a poorly inflated cuff. The estimates were more immune to noise than the cuff-based estimates of tracheal pressure. The estimates of tracheal pressure measured from the ETT cuff should be accurate enough for clinical use in the operating room.

Evaluation in animals of a system to estimate tracheal pressure from the endotracheal tube cuff

OBJECTIVE

Flow through an endotracheal tube (ETT) causes a pressure loss across the tube. This loss results in a difference between pressure measured at the airway and pressure measured in the trachea. This difference can lead to errors when calculating pulmonary mechanics and when setting ventilators. We have tested a method of estimating tracheal pressure from the pressure in the ETT cuff.

METHODS

Pressure transducers were placed in the proximal ETT connector, in the trachea, and in the ETT cuff (through the inflation port). Instantaneous periods of zero flow, detected with a flow meter, were used to calculate the slope and offset of the line relating cuff pressure to tracheal pressure. The system was tested on the bench using a ventilator and lung simulator and in 2 dogs and 5 pigs. Tests were performed at various cuff pressures, trachea diameters, ETT sizes, respiratory rates, tidal volumes, and airway obstructions.

RESULTS

In bench tests, our estimate of tracheal pressure was within -4.0 +/- 2.6% of the actual tracheal pressure (mean +/- standard deviation [SD]). In animal tests, our estimation of tracheal pressure was within -0.6 +/- 5%. In all bench test measurements and in 40 of 42 animal measurements, the error was less than 1 cm H2O.

CONCLUSIONS

The cuff estimation technique gives real-time, continuous, noninvasive tracheal pressure measurements in intubated animals with cuffed ETTs.

The implementation of Project 2000 in the community: a new perspective on the community nurse's role

This paper considers some of the initiatives taken by community nurses in England in implementing Project 2000 placements. The data were obtained during an English National Board funded study in two phases. The first phase involved a series of exploratory interviews, a postal questionnaire survey, and semi-structured interviews with 15 managers. In phase two, one Project 2000 demonstration district was studied in depth by means of interviews complemented by small-scale questionnaire studies. Community nurses had confronted a number of difficulties in implementing Project 2000. Among the most serious of these were shortage of time, poor communication with the colleges of nursing and lack of preparation. As a consequence, community nurses took what they saw as independent approaches to students' placements. Many set their own aims and objectives for placements and produced written guidelines and teaching plans for students. Many also asserted the importance of their role in the assessment of students' practical work.

Burn wound management: an overview

1. Accidents resulting in a burn/scald 2. Holistic care for each patient is essential in minimising potential complications in the healing of the burn wound. 3. A family-centred and multidisciplinary approach helps to ensure all physical and psychological needs are met.

Quantitative relationship between phenylalanine ammonia-lyase levels and phenylpropanoid accumulation in transgenic tobacco identifies a rate-determining step in natural product synthesis

Phenylalanine ammonia-lyase (PAL) catalyzes the first step in phenylpropanoid synthesis. The role of PAL in pathway regulation was investigated by measurement of product accumulation as a function of enzyme activity in a collection of near-isogenic transgenic tobacco plants exhibiting a range of PAL levels from wild type to 0.2% of wild type. In leaf tissue, PAL level is the dominant factor regulating accumulation of the major product chlorogenic acid and overall flux into the pathway. In stems, PAL at wild-type levels contributes, together with downstream steps, in the regulation of lignin deposition and becomes the dominant, rate-determining step at levels 3- to 4-fold below wild type. The metabolic impact of elevated PAL levels was investigated in transgenic leaf callus that overexpressed PAL. Accumulation of the flavonoid rutin, the major product in wild-type callus, was not increased, but several other products accumulated to similarly high levels. These data indicate that PAL is a key step in the regulation of overall flux into the pathway and, hence, accumulation of major phenylpropanoid products, with the regulatory architecture of the pathway poised so that downstream steps control partitioning into different branch pathways.