bluuebunny/crossref_metadata_2025 huggingface dataset:
Noninvasive ventilatory support does not facilitate recovery from acute respiratory failure in chronic obstructive pulmonary disease
Authors: Barbe F , Togores B , Rubi M , Pons S , Maimo A , Agusti AG
Published: June 2003

This investigation evaluates, in a prospective, randomized and controlled manner, whether noninvasive ventilatory support (NIVS) with bilevel positive airway pressure (BiPAP) facilitates recovery from acute respiratory failure (ARF) in patients with chronic obstructive pulmonary disease (COPD). Twenty four patients (mean age (+/-SEM) 68 +/- 2 yrs) with COPD (forced expiratory volume in one second (FEV1) at discharge 33 +/- 2% predicted), who attended the emergency room because of ARF (pH 7.33 +/- 0.01; arterial oxygen tension (Pa,O2) 6.0 +/- 0.2 kPa; arterial carbon dioxide tension (Pa,CO2) 7.9 +/- 0.3 kPa), were initially randomized. Four out of the 14 patients (29%) allocated to received NIVS did not tolerate it. Of the remaining 20 patients, 10 received NIVS with BiPAP in a conventional hospital ward during the first 3 days of hospitalization (two daytime sessions of 3 h duration each). All 20 subjects were treated with oxygen, bronchodilators and steroids. On the first and third hospitalization days, before and 30 min after withdrawing oxygen therapy and/or BiPAP ventilatory support, we measured peak expiratory flow, arterial blood gas values, ventilatory pattern, occlusion pressure (P0.1), and maximal inspiratory (MIP) and maximal expiratory (MEP) pressures. All patients were discharged without requiring tracheal intubation and mechanical ventilation. Hospitalization time was similar in both groups (11.3 +/- 1.3 vs 10.6 +/- 0.9 days, control vs BiPAP, respectively). Arterial oxygenation, respiratory acidosis and airflow obstruction improved significantly throughout hospitalization in both groups. By contrast, the ventilatory pattern, P0.1, MIP and MEP did not change. NIVS with BiPAP did not cause any significant difference between groups. We conclude that noninvasive ventilatory support with bilevel positive airway pressure does not facilitate recovery from acute respiratory failure in patients with chronic obstructive pulmonary disease. Furthermore, a substantial proportion of patients (29%) do not tolerate noninvasive ventilatory support under these circumstances. From these results, we cannot recommend the use of noninvasive ventilatory support with bilevel positive airway pressure in the routine management of chronic obstructive pulmonary disease patients recovering from acute respiratory failure.
Long-term nasal intermittent positive pressure ventilation (NIPPV) in sixteen consecutive patients with bronchiectasis: a retrospective study
Authors: Gacouin A , Desrues B , Lena H , Quinquenel ML , Dassonville J , Delaval P
Published: June 2003

Life expectancy and quality of life are poor in patients with chronic respiratory failure due to bronchiectasis. The indication for nocturnal nasal intermittent positive pressure ventilation (NIPPV) remains controversial in chronic obstructive lung disease. The purpose of the present study was to determine whether some of the objectives of home mechanical ventilation, i.e. improvement in blood gas values and reduced length of hospitalization, were fulfilled by NIPPV and oxygen plus medical treatment in patients with chronic respiratory failure due to bronchiectasis. Sixteen consecutive patients (12 females and four males; mean age 57 +/- 11 yrs) with chronic respiratory failure due to bronchiectasis, treated at home with nocturnal NIPPV in addition to oxygen therapy, were retrospectively studied in terms of blood gas values and duration of hospitalization before and after NIPPV. Details of the therapy received by each patient were recorded. Nine patients agreed to complete a questionnaire to determine their perception of the benefits of the treatment. NIPPV was performed using a volumetric respirator and was applied with a customized nasal mask modelled with silicone paste. NIPPV was used for a mean of 26 months (range 0.5-60 months). Eleven patients were alive 12 months after use of NIPPV. No significant improvement in blood gas values was noted on room air during NIPPV, but arterial carbon dioxide tension (Pa,CO2) stabilized after the period of worsening observed before initiation of NIPPV. Duration of hospitalization, the year before and the year after NIPPV, was 19 (3-40) and 16 (8-37) days, respectively (NS). For the 11 patients who were alive 2 yrs after the start of NIPPV, duration of hospitalization the year before NIPPV and between 12 and 24 months after NIPPV were 17 (4-40) and 7 (2-27) days, respectively (p < 0.05). Nine patients who had received NIPPV for at least 12 months at the time of the study reported an improvement in their quality of life. The results suggest that home ventilatory support by nasal intermittent positive pressure ventilation offers an acceptable alternative to tracheotomy, with less discomfort, in the management of severe respiratory failure due to bronchiectasis, in order to allow the patient to return home. These results should be confirmed by controlled studies.
An unattended device for sleep-related breathing disorders: validation study in suspected obstructive sleep apnoea syndrome
Authors: Zucconi M , Ferini-Strambi L , Castronovo V , Oldani A , Smirne S
Published: June 2003

Portable devices for the diagnosis of obstructive sleep apnoea (OSA) are considered to be an acceptable alternative to polysomnography (PSG), but their validation is essential. The aim of our study was to validate a device specifically designed for OSA diagnosis. Twenty nine suspected OSA patients were studied with simultaneous nocturnal PSG and an unattended recording device (MicroDigitrapper-S) (M-S). The device measured body position, snoring sound, oronasal flow, thoracic and abdominal effort, heart rate and percentage arterial oxygen saturation (Sa,O2%). We compared the apnoea plus hypopnoea index (AHI) and Sa,O2% results of PSG with that of the system's automatic analysis (M-SA). We also performed a semiautomatic analysis (M-SS) with visual editing of the raw data. Results at different AHI cut-off levels were analysed to obtain an indication of accuracy in diagnosis and severity. Both M-SA and M-SS showed a sensitivity and specificity of 100% at the cut-off level of AHI > 10. When increasing the cut-off levels, M-SA sensitivity decreased (55% for AHI > 40), while specificity remained high (95%). This was improved to a clinically acceptable level of agreement by M-SS analysis (sensitivity 91% and specificity 94%). In conclusion, the MicroDigitrapper-S device showed a good sensitivity and specificity for the diagnosis of OSA. However, the device could not predict the severity of OSA precisely enough. In severe cases (apnoea plus hypopnoea index > 40), semi-automatic scoring was necessary to obtain a more accurate detection of the severity of the disease.
Gas exchange, expiratory flow obstruction and the clinical spectrum of asthma
Authors: Wagner PD , Hedenstierna G , Rodriguez-Roisin R
Published: June 2003

More than any other chronic respiratory disease, asthma is characterized by functional and clinical variability: expiratory flow obstruction, dyspnoea and wheezing may be absent, mild, or severe. Moreover, pulmonary gas exchange often does not closely relate to measured airway obstruction. Accordingly, the correlation between arterial oxygen tension and airflow (Pa,O2) rate indices of obstruction is poor, both in a single patient over time, and within groups of clinically similar patients. Here, these concepts are extended by examining relationships between airflow obstruction and gas exchange across the clinical spectrum of asthma (from asymptomatic to acute severe). Six individual studies encompassing 86 patients are analysed together, focusing on: 1) airways obstruction; 2) arterial blood gas data; and 3) the distribution of alveolar ventilation/perfusion (V'A/Q') ratios, measured by the multiple inert gas elimination technique. V'A/Q' mismatching was greater than normal even when forced expiratory volume in one second (FEV1) was normal, but with increasing severity of airways obstruction there was essentially no further deterioration in gas exchange until FEV1 reached about 40% of predicted normal values. Then, with little further airways obstruction, gas exchange rapidly worsened, Pa,O2 falling to about 50 torr. This study emphasizes that what has been observed in individual patients and within clinically similar patient groups can be extended across the spectrum of asthma severity: airways obstruction and gas exchange are poorly correlated. Furthermore, these results suggest that spirometric data alone may not adequately define remission, nor clearly identify those patients liable to serious gas exchange deterioration.
Intrinsic PEEP and cardiopulmonary interaction in patients with COPD and acute ventilatory failure
Authors: Ranieri VM , Dambrosio M , Brienza N
Published: June 2003

Deviation of end-expiratory lung volume from the elastic equilibrium volume of the respiratory system is recognized as a cardinal feature in mechanically-ventilated patients with severe chronic obstructive pulmonary disease (COPD) and acute ventilatory failure (AVF). The presence of dynamic hyperinflation implies that alveolar pressure remains positive throughout expiration. At the end of the expiration, this positive pressure is named intrinsic positive end-expiratory pressure (PEEPi). Recent studies have suggested that, in COPD patients with expiratory flow limitation, the application of external PEEP during assisted mechanical ventilation, or the use of continuous positive airway pressure (CPAP) in spontaneously breathing patients, can counterbalance and reduce the inspiratory threshold load imposed by PEEPi, without causing further increase in lung volume and alveolar and intrathoracic pressures until a critical value of PEEP (Pcrit) is reached. Above this critical limit further hyperinflation is observed. A specific and characteristic role of PEEPi in compromising the heart function in COPD patients during AVF may be identified based on: 1) an increase in right ventricular impedance due to lung hyperinflation; 2) an increase in the venous return to the right ventricle and, consequently, a leftward shift of the septum caused by the large negative deflections in intrathoracic pressure due to the inspiratory threshold load; 3) a further increase in venous return to the right ventricle, with the eventual collapse of the vena cava caused by the expiratory recruitment of abdominal muscles; and 4) hypoxia and hypercapnia consequent to acute ventilatory failure, which may further increase right ventricular impedance and venous return to the right ventricle. All these phenomenon are directly correlated to the large negative intrathoracic pressure developed by the respiratory muscles to overcome the inspiratory threshold caused by intrinsic positive end-expiratory pressure (preload effect), and to the increase in lung volume (afterload effect). Application of positive end-expiratory pressure/continuous positive airway pressure in chronic obstructive pulmonary disease patients during acute ventilatory failure may, hence, unload the respiratory muscles as well as the heart.
The role of apoptosis in the pathogenesis and treatment of diseases
Authors: Solary E , Dubrez L , Eymin B
Published: June 2003

In adult multicellular organisms, homeostasis is determined in each cell lineage by a balance between cell death and cell growth. Dysregulation of cell death mechanisms is involved in the pathogenesis of an increasing number of diseases. Defective apoptosis can participate in malignant transformation, viral latency and autoimmune diseases. Excessive apoptotic cell death is involved in CD4+ T-cell depletion observed in acquired immune deficiency syndrome, in fulminant hepatitis associated with infection by hepatitis B and C viruses, in some neurodegenerative disorders and haematological diseases, in polycystic kidney disease and ischaemia. Three steps can be distinguished in the pathway that leads to cell death. The first step involves interactions between the extracellular and intracellular signals that decide whether a cell should live or die. When death is chosen, a common pathway that involves at least the Bcl-2- family of proteins and the interleukin-1 beta (IL-1 beta)-converting enzyme-related cysteine proteases confirms whether or not the cell should die. Finally, if death is allowed to occur, the apoptotic process itself is characterized by deoxyribonucleic acid (DNA) fragmentation, proteolysis and morphological changes that precede the engulfment of apoptotic cells by neighbouring cells and phagocytes. Several inducers and inhibitors of apoptosis acting on one or several of these three steps that characterize the apoptotic process have been identified in vitro. Their potential usefulness in improving the current therapeutic strategies and designing new strategies in several different diseases is discussed.
Improvement of tidal breathing pattern analysis in children with asthma by on-line automatic data processing
Authors: van der Ent CK , Brackel HJ , Mulder P , Bogaard JM
Published: June 2003

The time taken to achieve peak tidal expiratory flow as a proportion of total expiratory time (t PTEF/t E) during tidal breathing (TB) is used as a parameter of airway obstruction in children with asthma. Curve selection bias is one of the most important limitations to the method. This study evaluates three curve selection methods, including a computer program, which on-line selects and analyses TB curves (Masterscreen Paediatric; Jaeger, Germany). TB analysis was performed in 26 children (aged 4-7 yrs) with asthma, before and after methacholine provocation and after subsequent bronchodilatation. Levels and stability of TB parameters derived from computer-selected, unselected and unbiased eye-selected curves were compared. t PTEF/t E ratios of the computer-selected curves agreed well with the unbiased eye-selected curves (limits of agreement -4.8 and +5.8%), but were significantly different from the ratios of unselected curves. Computer-derived t PTEF/t E ratios had the highest level of stability: the reliability coefficient of baseline measurements was 0.96 for computer selection, 0.84 for eye selection and 0.87 for no selection (reliability index = 1 at maximal stability). Tidal volume, respiratory rate, inspiratory and expiratory time were also assessed accurately by the computer program. The mean t PTEF/t E ratio (computer selection) dropped after methacholine provocation (from 30 +/- 9 to 22 +/- 9% at provocative dose at which forced expiratory volume in one second had dropped > or = 20% from baseline (FEV1-PD20 level), p < 0.001) and was restored after bronchodilation (30 +/- 6%; p < 0.001). We conclude that on-line computer analysis is preferable to no selection and to by-eye selection. The use of the program avoids curve selection bias and enhances the applicability of tidal breathing analysis as a measure of airflow obstruction in young children.
Perindopril-associated pneumonitis
Authors: Benard A , Melloni B , Gosselin B , Bonnaud F , Wallaert B
Published: June 2003

We report two cases of perindopril-associated pneumonitis with typical drug-induced clinical features. In the first case, biopsies showed granulomatous sarcoid-like lesions; in the second, bronchial wall eosinophil infiltratf2p4was reported with increased blood eosinophil count. In these two cases, improvement was obtained by withdrawal of the drug and was completed with steroids. All other causes were ruled out. Angiotensin-converting enzyme inhibitor (ACEI)-induced pneumonitis is still rare but has to be recognized as a real side-effect.
Bronchiolitis obliterans in a patient with localized scleroderma treated with D-penicillamine
Authors: Boehler A , Vogt P , Speich R , Weder W , Russi EW
Published: June 2003

D-penicillamine-associated bronchiolitis obliterans (BO) is a rare but well-known pulmonary complication in patients with rheumatoid arthritis or progressive systemic sclerosis. It has been assumed that in most, if not all cases, BO is a complication of the underlying disease rather than a side-effect of treatment. We report the case of a 46 year old man with scleroderma localized to his lower legs (morphea), who received a daily dose of 750 mg D-penicillamine. During the treatment of 1 yr duration, he developed progressive shortness of breath due to a worsening obstructive ventilatory defect suggesting BO, which was confirmed by surgical lung biopsy (constrictive BO). Bronchial obstruction progressed over the next 5 yrs and did not respond to corticosteroids. The patient finally underwent a successful single left lung transplantation. The histological features of constrictive BO were confirmed in the explanted lung. This observation suggests that D-penicillamine may induce bronchiolitis obliterans in the absence of a systemic connective tissue disease.
Bronchiolitis obliterans organizing pneumonia associated with chlamydial infection
Authors: Diehl JL , Gisselbrecht M , Meyer G , Israel-Biet D , Sors H
Published: June 2003

A 70 year old man presented with symptoms and laboratory findings suggestive of chlamydial pneumonia. Despite adequate antibiotic therapy, his condition did not improve and transbronchial biopsies disclosed a typical feature of bronchiolitis obliterans organizing pneumonia (BOOP). After initiation of corticosteroid therapy, there were marked clinical and radiographic improvements. This report demonstrates that chlamydial infection may be associated with BOOP.
Learning Cell Biology as a Team: A Project-Based Approach to Upper-Division Cell Biology
Authors: Wright Robin , Boggs James
Published: May 2003

To help students develop successful strategies for learning how to learn and communicate complex information in cell biology, we developed a quarter-long cell biology class based on team projects. Each team researches a particular human disease and presents information about the cellular structure or process affected by the disease, the cellular and molecular biology of the disease, and recent research focused on understanding the cellular mechanisms of the disease process. To support effective teamwork and to help students develop collaboration skills useful for their future careers, we provide training in working in small groups. A final poster presentation, held in a public forum, summarizes what students have learned throughout the quarter. Although student satisfaction with the course is similar to that of standard lecture-based classes, a project-based class offers unique benefits to both the student and the instructor.
Cloning, Stem Cells, and the Current National Debate: Incorporating Ethics into a Large Introductory Biology Course
Authors: Fink Rachel D.
Published: May 2003

Discussing the ethical issues involved in topics such as cloning and stem cell research in a large introductory biology course is often difficult. Teachers may be wary of presenting material biased by personal beliefs, and students often feel inhibited speaking about moral issues in a large group. Yet, to ignore what is happening “out there” beyond the textbooks and lab work is to do a disservice to students. This essay describes a semester-long project in which upperclass students presented some of the most complex and controversial ideas imaginable to introductory students by staging a mock debate and acting as members of the then newly appointed President's Council on Bioethics. Because the upperclass students were presenting the ideas of real people who play an important role in shaping national policy, no student's personal beliefs were put on the line, and many ideas were articulated. The introductory audience could accept or reject what they were hearing and learn information important for making up their own minds on these issues. This project is presented as an example of how current events can be used to put basic cell biology into context and of how exciting it can be when students teach students.
Learning How Scientists Work: Experiential Research Projects to Promote Cell Biology Learning and Scientific Process Skills
Authors: DebBurman Shubhik K.
Published: May 2003

Facilitating not only the mastery of sophisticated subject matter, but also the development of process skills is an ongoing challenge in teaching any introductory undergraduate course. To accomplish this goal in a sophomore-level introductory cell biology course, I require students to work in groups and complete several mock experiential research projects that imitate the professional activities of the scientific community. I designed these projects as a way to promote process skill development within content-rich pedagogy and to connect text-based and laboratory-based learning with the world of contemporary research. First, students become familiar with one primary article from a leading peer-reviewed journal, which they discuss by means of PowerPoint-based journal clubs and journalism reports highlighting public relevance. Second, relying mostly on primary articles, they investigate the molecular basis of a disease, compose reviews for an in-house journal, and present seminars in a public symposium. Last, students author primary articles detailing investigative experiments conducted in the lab. This curriculum has been successful in both quarter-based and semester-based institutions. Student attitudes toward their learning were assessed quantitatively with course surveys. Students consistently reported that these projects significantly lowered barriers to primary literature, improved research-associated skills, strengthened traditional pedagogy, and helped accomplish course objectives. Such approaches are widely suited for instructors seeking to integrate process with content in their courses.
Analysis of Protein Localization and Secretory Pathway Function Using the YeastSaccharomyces cerevisiae
Authors: Vallen Elizabeth
Published: May 2003

The isolation and characterization of mutants has been crucial in understanding a number of processes in the field of cell biology. In this exercise, students examine the effects of mutations in the secretory pathway on protein localization. Yeast strains deficient for synthesis of histidinol dehydrogenase are transformed with a plasmid encoding a chimeric protein. The chimera contains a signal sequence fused to histidinol dehydrogenase. A strain with a defect in the translocation of secretory proteins into the endoplasmic reticulum (ER) accumulates sufficient histidinol dehydrogenase in the cytoplasm to grow on media lacking histidine. In contrast, yeast proficient for secretion, or yeast with secretion defects later in the pathway, are unable to grow on media lacking histidine. Student analysis of the experimental yeast transformants and appropriate controls allows investigation into the effects of conditional defects in the secretory pathway on both cell viability and protein localization. The exercise is usually performed in a manner that allows students to execute a number of techniques common in molecular biology laboratories, including plasmid minipreps, restriction digestions, and Southern blots. Student understanding and enjoyment of the exercise was assessed by laboratory reports, oral and written examinations, and questionnaires. After completion of these experiments, students can describe the utility of protein fusions, the roles of mutant analysis in cell biology, and the steps taken by proteins transiting the secretory pathway.
Repeatability of multimode Rayleigh‐wave dispersion studies
Authors: Beaty Kristen S. , Schmitt Douglas R.
Published: May 2003

Rayleigh‐wave dispersion is used to study the near‐surface elastic properties of a thick, lacustrine clay to approximately 10 m depth. Ten repeated sets of Rayleigh dispersion curves were obtained through late spring to early fall. A variety of methodologies were used to extract the dispersion curves, but a modified frequency–ray parameter (f − p) method most successfully yields dispersion curves for the first three Rayleigh modes. The Rayleigh‐wave velocities varied from 100 to ∼350 m/s with frequency over the band from 75 to 10 Hz. Over this band, these velocities did not measurably vary during the study period. The observed phase velocity curves were inverted with P‐wave and density values obtained from shallow coring to obtain the shear‐wave velocity structure at the site down to > 14 m. This case study highlights the robust, repeatable, nature of surface wave dispersion methods when care is taken in the acquisition of field data.
3D inversion of a scalar radio magnetotelluric field data set
Authors: Newman Gregory A. , Recher Stephan , Tezkan Bülent , Neubauer Fritz M.
Published: May 2003

A radio magnetotelluric (MT) field data set, acquired in scalar mode, over a buried waste site has been successfully analyzed using a 3D MT inversion scheme using nonlinear conjugate gradients. The results of this analysis demonstrate the utility of the scheme where more than 4800 data points collected on multiple measurement profiles have been inverted simultaneously. The resulting image clearly detects the buried waste; when receiver profiles cross pit boundaries, the image maps the lateral extent of the pit. However, the base of the pit is poorly resolved, and depends upon the starting model used to launch the inversion. Hence, critical information on whether contamination is leaching into a resistive gravel bed lining the base of the pit, as well as the deeper geological horizons consisting of brown coal, clay, and tertiary sands, is inconclusive. Nevertheless, by incorporating within the inversion process a priori information of the background media that is host to the waste, sharper images of the base of the pit are obtained, which are in good agreement with borehole data. The 3D analysis applied in this paper overcomes previous limitations in the radio magnetotelluric (RMT) method using 2D data analysis and inversion. With 3D analysis, it is unnecessary to make assumptions regarding geological strike, and near‐surface statics can be accommodated in both source polarizations. Our findings also indicate that 2D MT interpretation can overestimate the pit's depth extent. This may lead to the erroneous conclusion that the geological horizons beneath the pit have been contaminated.
Quantifying subresolution saturation scales from time‐lapse seismic data: A reservoir monitoring case study
Authors: Sengupta Madhumita , Mavko Gary , Mukerji Tapan
Published: May 2003

The goal of this paper is to interpret and analyze time‐lapse seismic data quantitatively to better understand subsurface fluid saturations and saturation scales. We present a case study of a time‐lapse seismic survey. Water and gas were injected into an oil‐producing reservoir, and repeat seismic surveys were collected to monitor the subsurface fluids over a period of 14 years. In this study, we show that the subresolution spatial distribution of fluids, not captured by traditional flow simulators can impact the seismic response. Although there is a good qualitative match between the fluid changes predicted by the flow simulator and the fluid changes interpreted from the seismic data, the simulator predicts smooth saturation profiles that do not quantitatively match the time‐lapse seismic changes. We find that downscaling smooth saturation outputs from the flow simulator to a more realistic patchy distribution is required to provide a good quantitative match with the near‐ and far‐offset time‐lapse data, even though the fine details in the saturation distribution are below seismic resolution. We downscaled the smooth saturations from the simulator by incorporating high spatial frequencies from well logs and constraining the saturations to the total mass balance predicted by the flow simulator. The computed seismic response of the downscaled saturation distributions matched the real time‐lapse seismic data much better than the saturation distributions taken directly from the simulator. This study demonstrates the feasibility of using seismic and well‐log data to constrain subblock saturation scales, unobtainable from flow simulation alone. This important result has the potential to significantly impact and enhance the applicability of seismic data in reservoir monitoring.
Time‐lapse tomography
Authors: Vesnaver Aldo L. , Accaino Flavio , Bohm Gualtiero , Madrussani Gianni , Pajchel Jan , Rossi Giuliana , Moro Giancarlo Dal
Published: May 2003

In time‐lapse analysis, we have to distinguish the seismic response changes due to oil and gas production at a reservoir over the years from several other causes, such as the recording signature and random noise. In this paper, we focus our attention on the velocity macromodel provided by seismic tomography, which is a basic tool for the data regularization, its depth or time migration, and a possible final subtraction among different vintages. We show first that we cannot use just a single velocity model for all data sets, because of seasonal variations of the overburden velocity (which is mainly due to seawater temperature in marine cases and to the water table depth in land cases). However, we can exploit the basic assumption of time‐lapse analysis for constraining reflection/refraction tomography, i.e., by imposing the constraint that the layer structure and the local velocities do not change outside the reservoir (and in the shallowest part) over time. We thus get coupled models that are physically consistent, with a better spatial coverage and higher information redundancy. The new method is illustrated by a marine case history from the North Sea.
Rapid spatially coupled AVO inversion in the Fourier domain
Authors: Buland Arild , Kolbjørnsen Odd , Omre Henning
Published: May 2003

Spatial coupling of the model parameters in an inversion problem provides lateral consistency and robust solutions. We have defined the inversion problem in a Bayesian framework, where the solution is represented by a posterior distribution obtained from a prior distribution and a likelihood model for the recorded data. The spatial coupling of the model parameters is imposed via the prior distribution by a spatial correlation function. In the Fourier domain, the spatially correlated model parameters can be decoupled, and the inversion problem can be solved independently for each frequency component. For a spatial model parameter represented on n grid nodes, the computing time for the inversion in the Fourier domain follows a linear function of the number of grid nodes, while the computing time for the fast Fourier transform follows an n log n function. We have developed a 3D linearized amplitude variation with offset (AVO) inversion method with spatially coupled model parameters, where the objective is to obtain posterior distributions for P‐wave velocity, S‐wave velocity, and density. The inversion algorithm has been tested on a 3D dataset from Sleipner field with 4 million grid nodes, each with three unknown model parameters. The computing time was less than 3 minutes on the inversion in the Fourier domain, while each 3D Fourier transform used about 30 s on a single 400‐MHz Mips R12000 CPU.
AVO polarization and hodograms: AVO strength and polarization product
Authors: Mahob Patrice Nsoga , Castagna John P.
Published: May 2003

An alternative approach to identifying amplitude‐variation‐with offset (AVO) anomalies is to consider the AVO polarization in the AVO intercept–AVO gradient (A‐B) plane. This method does not require deviations or separations from a background trend exhibited in traditional crossplots such as intercept‐gradient (A‐B) or near trace–far trace (N‐F). A benefit of the hodogram or polarization method is that the wavelet is taken into consideration. Crossplotted intercept and gradient are polarized along a “background trend” for nonanomalous events and at angles different from the “background trend” for anomalous events. This allows recognition of anomalous behavior otherwise buried in a background.

Attributes resulting from this methodology include (1) the polarization angle, (2) the polarization angle difference, (3) the AVO strength, (4) the polarization product, and (5) the linear‐correlation coefficient. These different attributes can then be used to enhance AVO interpretation. Synthetic modeling for a succession of gas and brine layers encased in shale units indicates that the method can potentially be an effective hydrocarbon indicator. Application of the method to a real seismic dataset shows polarization anomalies associated with hydrocarbons.
Tube‐wave suppression in single‐well seismic acquisition
Authors: Daley Thomas M. , Gritto Roland , Majer Ernest L. , West Phillip
Published: May 2003

Single‐well seismic imaging is significantly hampered by the presence of borehole tube waves. A tube‐wave suppressor has been tested using single‐well seismic equipment at the Lost Hills (California) oil field. The suppressor uses a gas‐filled bladder kept slightly above borehole fluid pressure. Field tests show a measurable reduction in tube‐wave energy as compared to body waves propagating in the surrounding reservoir rock. When using a high‐frequency (500–4000 Hz) piezoelectric source, the P‐wave–tube‐wave amplitude ratio was increased by 33 dB. When using a lower frequency (50–350 Hz) orbital vibrator source, the S‐wave–tube‐wave amplitude ratio was increased by 21 dB while the P‐wave–tube‐wave amplitude ratio was increased by 23 dB. These reductions in tube‐wave amplitudes significantly improve single‐well data quality.
Correlations between seismic parameters, EM parameters, and petrophysical/petrological properties for sandstone and carbonate at low water saturations
Authors: Koesoemadinata Adam P. , McMechan George A.
Published: May 2003

Empirical relations are found between measured petrophysical/petrologic, seismic, and electrical properties of sandstone and carbonate samples by least‐squares fitting at room pressure and ambient saturation. The measured parameters include porosity (φ), fluid permeability (k), clay content (C), grain density (ρg), bulk density (ρb), P‐wave velocity (Vp), electrical conductivity (σ), and dielectric constant (κ). The samples are from reservoir analog sites in the Ferron Sandstone in central Utah and the Ellenburger carbonate in central Texas. Crossplots and regression analysis are done separately for the sandstone and the carbonate samples.

For the sandstone samples, predictions with correlation coefficients (R2) greater than 0.75 include ρb from φ, ln k from φ and C, κ from ln k and φ, κ from ρb and C, and κ from ln k. Predictions with 0.65 < R2 < 0.75 include κ from Vp and ρb, κ from Vp and φ, Vp from ln k and C, κ from ln φ, and κ from ρb. In general, σ is difficult to predict, with the best R2(0.48) obtained in a prediction of σ from ln k.

Relationships for the carbonate samples are generally less reliable, which is attributed to a complex history of multiple phases of karsting and burial. The largest R2 values obtained are 0.67 for prediction of σ from κ, and 0.36 for prediction of σ from ρg. All the other R2 values are ≤0.19.

Both the sandstone and the carbonate data show σ‐φ; relations with negative coefficients, rather than positive as predicted by Archie's law, because of the very low water saturations. In the sandstone, the water connectivity is reduced with increasing grain surface area (with increasing φ and k), so σ decreases. In the carbonate, σ correlates with the degree of dolomitization, and the water content is too low to contribute to σ.
Using measured velocity to estimate gas hydrates concentration
Authors: Reister David B.
Published: May 2003

A new method for using measured P‐wave and S‐wave velocities to estimate gas hydrate concentration uses the Hashin‐Shtrikman (HS) lower bound to provide both an upper and lower bound for mixtures of water and hydrate in unconsolidated marine sediments. The method parameterizes the region between the upper and lower bounds by using two upper bounds: HS and Voigt. Well log measurements of resistivity and the Archie equation are used to calculate hydrate concentration, and quadratic functions that relate the hydrate parameters to the hydrate concentration are estimated. For this data set, neither resistivity nor velocity provide a good method for detecting values of hydrate concentration that are less than 20%.
The paradox of anisotropy in electromagnetic loop‐loop responses over a uniaxial half‐space
Authors: al‐Garni Mansour , Everett Mark E.
Published: May 2003

The electromagnetic loop‐loop response of a uniaxial conducting half‐space is derived. The solution is presented in terms of the Geonics EM34 apparent conductivity, which is based on an underlying isotropic half‐space model of earth conductivity. The uniaxial medium generates an apparent conductivity that depends on the angle that the line joining the transmitter and receiver loops makes with respect to the strike of the anisotropy. Furthermore, a “paradox of anisotropy” occurs in which apparent conductivity is higher in the resistive across‐strike direction and lower in the conductive along‐strike direction. The paradox is resolved once it is recognized that the receiver loop response is controlled by the conductivity in the direction of the local induced electric current flow. Accurate geological interpretation of electromagnetic loop‐loop data in fractured rock terrains depends on the ability of the geophysicist to recognize the counterintuitive effects of anisotropy.
The face‐current concept and its application to survey design in electrical exploration
Authors: Mendonça Carlos A.
Published: May 2003

This paper presents a new method to identify the regions over a 3D geoelectrical structure that produce major contributions to the electrical potential established in response to a dc source at the ground surface. The measured potential is represented by a sum of a known primary potential (due to a homogeneous half space) plus an unknown potential caused by conductivity inhomogeneities. Because the primary potential is continuous everywhere, the interfaces with a conductivity contrast act as sources or sinks of currents in order to maintain the continuity of the current density related to the primary flux. These disturbing face currents are responsible for the generation of the secondary potential, and mapping them over a given structure allows us to assess the regions where the secondary potential is generated. In general, the face currents vanish away from the source according to the decay of the primary electric field. For this reason, deeper investigations can be expected when using pole sources because its primary field decays with the inverse of the squared distance, instead of the cubed distance as for dipole sources. For thin sheets, the polarization decay with distance is one order higher than that for large 3D bodies, which makes the detection of a sheet yet more difficult. The quantification of the total face current over the structure for different positions along a profile helps one choose the proper electrode array and determine its optimum length. This is done in two steps: (1) identification of the offset where the dc source provides the highest polarization (face current) on the targeted structure, and (2) determination of the array length by locating the potential electrodes closest to the region with the highest polarization. This second criterion came from an analogy between the face‐current and artificial current sources, where it is intuitively seen that the resulting potential is highest close to the source. The proposed survey design technique is applied to three models commonly used in electrical exploration: a shallow conductive heterogeneity, a buried contact, and a thin conductive sheet.
Evaluation of permeable reactive barrier (PRB) integrity using electrical imaging methods
Authors: Slater Lee , Binley Andrew
Published: May 2003

The permeable reactive barrier (PRB) is a promising in‐situ technology for treatment of hydrocarbon‐contaminated groundwater. A PRB is typically composed of granular iron which degrades chlorinated organics into potentially nontoxic dehalogenated organic compounds and inorganic chloride. Geophysical methods may assist assessment of in‐situ barrier integrity and evaluation of long‐term barrier performance. The highly conductive granular iron makes the PRB an excellent target for conductivity imaging methods. In addition, electrochemical storage of charge at the iron–solution interface generates an impedance that decreases with frequency. The PRB is thus a potential induced polarization (IP) target. Surface and cross‐borehole electrical imaging (conductivity and IP) was conducted at a PRB installed at the U.S. Department of Energy's Kansas City plant. Poor signal strength (25% of measurements exceeding 8% reciprocal error) and insensitivity at depth, which results from current channeling in the highly conductive iron, limited surface imaging. Crosshole 2D and 3D electrical measurements were highly effective at defining an accurate, approximately 0.3‐m resolution, cross‐sectional image of the barrier in‐situ. Both the conductivity and IP images reveal the barrier geometry. Crosshole images obtained for seven panels along the barrier suggest variability in iron emplacement along the installation. On five panels the PRB structure is imaged as a conductive feature exceeding 1 S/m. However, on two panels the conductivity in the assumed vicinity of the PRB is less than 1 S/m. The images also suggest variability in the integrity of the contact between the PRB and bedrock. This noninvasive, in‐situ evaluation of barrier geometry using conductivity/IP has broad implications for the long‐term monitoring of PRB performance as a method of hydrocarbon removal.
Electromagnetic induction in a generalized 3D anisotropic earth, Part 2: The LIN preconditioner
Authors: Weiss Chester J. , Newman Gregory A.
Published: May 2003

A practical limitation in the use of generalized 3D forward modeling algorithms for inversion of electromagnetic data is the high computational cost of solving large, ill‐conditioned systems of linear equations arising from the discretization of the governing Maxwell equations. To address this problem, a new class of preconditioners has recently been proposed which is based on a Helmholtz decomposition of the electric field in the low induction number (LIN) regime. This paper further develops that idea and introduces a LIN preconditioner which can be applied to problems characterized by a fully generalized anisotropic medium. Included are sample calculations demonstrating a reduction by two orders of magnitude in the number of “quasi‐minimal residual” iterates and a speedup by a factor of approximately four in the solution time for one forward calculation. Also included are results previously unobtainable by standard Jacobi preconditioning for simulating multicomponent induction sonde response in a horizontal well within a crossbedded formation.
Enhancing the resolving power of least‐squares inversion with active constraint balancing
Authors: Yi Myeong‐Jong , Kim Jung‐Ho , Chung Seung‐Hwan
Published: May 2003

Most geophysical inverse problems are solved using least‐squares inversion schemes with damping or smoothness constraints to improve stability and convergence rate. Since the Lagrangian multiplier controls resolution and stability of the inverse problem, we always want to use the optimum multiplier, which is not easy to get and is usually obtained by experience or a time‐consuming optimization process.

We present a new regularization approach, in which the Lagrangian multiplier is set as a spatial variable at each parameterized block and automatically determined via the parameter resolution matrix and spread function analysis. For highly resolvable parameters, a small value of the Lagrangian multiplier is assigned, and vice versa. This approach, named “active constraint balancing” (ACB), tries to balance the constraints of the least‐squares inversion according to sensitivity for a given problem so that it enhances the resolution as well as the stability of the inversion process. We demonstrate the performance of the ACB by applying it to a two‐dimensional resistivity tomography problem, which results in a remarkable enhancement of the spatial resolution. Enhancement of the resolution is also verified in the application of resistivity tomography to a field data set acquired at a tunnel construction site.
A versatile algorithm for joint 3D inversion of gravity and magnetic data
Authors: Gallardo‐Delgado Luis A. , Pérez‐Flores Marco Antonio , Gómez‐Treviño Enrique
Published: May 2003

We describe the implementation of a versatile method for interpreting gravity and magnetic data in terms of 3D structures. The algorithm combines a number of features that have proven useful in other algorithms. To accommodate structures of arbitrary geometry, we define the subsurface using a large number of prisms, with the depths to the tops and bottoms as unknowns to be determined by optimization. Included in the optimization process are the three components of the magnetization vector and the density contrast, which is assumed to be a continuous function with depth. We use polynomial variations of the density contrast to simulate the natural increase of rock density with depth in deep sedimentary basins. The algorithm minimizes the quadratic norm of residuals combined with a regularization term. This term controls the roughness of the upper and lower topographies defined by the prisms. This results in simple shapes by penalizing the norms of the first and second horizontal derivatives of the prism depths and bottoms. Finally, with the use of quadratic programming, it is a simple matter to include a priori information about the model in the form of equality or inequality constraints. The method is first tested using a hypothetical model, and then it is used to estimate the geometry of the Ensenada basin by means of joint inversion of land and offshore gravity and land, offshore, and airborne magnetic data. The inversion helps constrain the structure of the basin and helps extend the interpretation of known surface faults to the offshore.
Removal of wavelet dispersion from ground‐penetrating radar data
Authors: Irving James D. , Knight Rosemary J.
Published: May 2003

Wavelet dispersion caused by frequency‐dependent attenuation is a common occurrence in ground‐penetrating radar (GPR) data, and is displayed in the radar image as a characteristic “blurriness” that increases with depth. Correcting for wavelet dispersion is an important step that should be performed before GPR data are used for either qualitative interpretation or the quantitative determination of subsurface electrical properties. Over the bandwidth of a GPR wavelet, the attenuation of electromagnetic waves in many geological materials is approximately linear with frequency. As a result, the change in shape of a radar pulse as it propagates through these materials can be well described using one parameter, Q*, related to the slope of the linear region. Assuming that all subsurface materials can be characterized by some Q* value, the problem of estimating and correcting for wavelet dispersion becomes one of determining Q* in the subsurface and deconvolving its effects using an inverse‐Q filter. We present a method for the estimation of subsurface Q* from reflection GPR data based on a technique developed for seismic attenuation tomography. Essentially, Q* is computed from the downshift in the dominant frequency of the GPR signal with time. Once Q* has been obtained, we propose a damped‐least‐squares inverse‐Q filtering scheme based on a causal, linear model for constant‐Q wave propagation as a means of removing wavelet dispersion. Tests on synthetic and field data indicate that these steps can be very effective at enhancing the resolution of the GPR image.