bluuebunny/crossref_metadata_2025 huggingface dataset:
Body composition and health-related quality of life in patients with obstructive airways disease
Authors: Shoup R , Dalsky G , Warner S , Davies M , Connors M , Khan M , Khan F , ZuWallack R
Published: April 2003

This study evaluated the effects of body weight and lean mass abnormalities on health-related quality of life (HRQL) in obstructive airways disease. Body weight, lean mass (using dual-energy X-ray absorptiometry), and HRQL (using the St George's Respiratory Questionnaire (SGRQ)) were measured in 50 patients. Low lean mass was defined as a lean mass index (lean mass/height2) below the fifth percentile of a control population. Dyspnoea was measured by the baseline dyspnoea index. The mean (SD) age was 69+/-9 yrs; the forced expiratory volume in one second (FEV1) was 39+/-19% of predicted. Patients had 2.4+/-4.1 kg less lean mass than predicted. Increased dyspnoea was the most influential predictor of poor HRQL. Compared to normal-weight patients, those who were underweight had significantly greater impairment in activity, impact, and total SGRQ scores, while those who were overweight had greater impairment in impact and total SGRQ scores. Low lean mass was associated with greater impairment in symptoms, activity and impact subscores and the total SGRQ score. When dyspnoea was added to the model as a covariate, neither weight nor lean mass remained significantly related to HRQL. Thus, although body weight and lean mass abnormalities influence health-related quality of life, their effects appear to be mediated through increased levels of dyspnoea.
Effects of psychotherapy in moderately severe COPD: a pilot study
Authors: Eiser N , West C , Evans S , Jeffers A , Quirk F
Published: April 2003

Anxiety is common in the "pink puffer" syndrome associated with chronic obstructive pulmonary disease (COPD). The degree of anxiety correlates well with perceived dyspnoea. This pilot study examines the effect of group psychotherapy on anxiety, exercise tolerance, dyspnoea and quality of life. Ten patients with moderately severe, stable COPD (mean forced expiratory volume in one second (FEV1)-1.15 L) had six 90 min sessions of cognitive and behavioural psychotherapy at weekly intervals. Patients completed the Hospital Anxiety and Depression Scale (HADS), Medical Research Council Questionnaire (MRCQ) and St George's Respiratory Questionnaires (SGRQ), 1 week before and after therapy. FEV1, forced vital capacity (FVC), slow vital capacity (SVC), blood gas tensions and 6 min walking distance (6MWD) were measured. Eight control patients attended weekly for lung function and 6MWD for 6 weeks, but had no psychotherapy. Mean baseline HADS score was significantly higher in the psychotherapy group (12) than in controls (7), but otherwise there were no differences in lung function, blood gas tensions, 6MWD, or the other questionnaire scores between groups. After treatment, the physiological and psychological parameters where unchanged in both groups with the exception of the mean 6MWD, which had improved in the psychotherapy group only, from 351 to 423 m (p<0.001), an increase of 24%. Three months after treatment, the 6MWD was still 16% above the baseline value (p=0.02). In conclusion, six sessions of cognitive and behavioural psychotherapy produced a sustained improvement in exercise tolerance in a group of 10 anxious patients with severe chronic obstructive pulmonary disease, without any change in anxiety scores on the Hospital Anxiety and Depression Scale. Further studies of more prolonged, intensive psychotherapy would establish whether better symptom and quality of life scores accompany more dramatic increases in exercise tolerance in "pink puffers".
A double-blind randomized trial of nicotine nasal spray as an aid in smoking cessation
Authors: Blondal T , Franzon M , Westin A
Published: April 2003

The objective of the study was to evaluate the therapeutic efficacy of nicotine nasal solution (NNS) for smoking cessation from the stopping day up to 3 months. We also followed the participants for 2 yrs after ceasing smoking to assess what happens after stopping using NNS. In a placebo-controlled, double-blind, 2 yr prospective study, 157 smokers were given either NNS, one dose containing 1 mg of nicotine per 100 microL (n=79), or placebo (n=78). Treatment was continued for up to 1 yr. One day after quitting smoking, the average number of daily doses was 11 in the group assigned NNS and 14 in the group assigned the placebo, and after 6 weeks, 14 and 6 doses, respectively, among abstinent participants still using spray. After 3 months, 65% of the abstainers in the nicotine group were still using the NNS. The abstinence rates were 51, 39 and 29% after 6 weeks, 3 and 6 months, respectively, as compared to 24, 19 and 18% in the placebo group (p=0.0003; p=0.003; p=0.050). The proportion abstinent at the 1 yr (25 vs 17%) and 2 yr follow-ups (19 vs 14%) was higher among those assigned to the nicotine than to the placebo group, but not significantly so for the numbers used in the study. In conclusion, the use of nicotine nasal spray significantly increased the abstinence rate during the first 6 months following the quitting day.
Published models and local data can bridge the gap between reference values of lung function for children and adults
Authors: Nysom K , Ulrik CS , Hesse B , Dirksen A
Published: April 2003

The aim of this study was to create reference equations for pulmonary function tests (PFTs) that span the age range from childhood to young adulthood. PFT results (forced vital capacity (FVC), forced expiratory volume in one second (FEV1), ratio of FEV1 to FVC (FEV1/FVC), total lung capacity (TLC), transfer factor) of 348 healthy 13-24 yr old Caucasian never-smokers from a local population study were compared with 13 selected sets of published reference equations. Predicted and observed PFT results differed significantly for 63 of 92 reference equations tested, and most equations accounted poorly for the increase in PFT variables which takes place during adolescence. We selected the equations with the best fit and adjusted their parameters, so that the level and variance of predicted values agreed with the local data. For subjects older than 18 yrs, we selected the European Community for Steel and Coal (ECSC) equations. For subjects younger than 18 yrs, we chose European summary equations for FVC, FEV1, and FEV1/FVC, and recent British equations for TLC and transfer factor. The customized reference equations are the best available (maximum likelihood) for analysing PFTs of patients tested in our laboratory. Our approach can be used whenever generally accepted reference equations are lacking and a local sample of normal subjects is available.
Measurement of the specific airway resistance by plethysmography in young children accompanied by an adult
Authors: Klug B , Bisgaard H
Published: April 2003

The purpose of this study was to evaluate a procedure for measurement of specific airway resistance (sRaw) by whole body plethysmography in young awake children accompanied by an adult. sRaw was measured by a single-step procedure, omitting the measurement of the thoracic gas volume. The frequency dependency of sRaw was investigated and the accuracy of simulating body temperature, atmospheric pressure and saturation with water vapour (BTPS) conditions by electronic compensation was assessed. One hundred and thirty one children with asthma were studied. In 57 children (mean (SD) age 5.6 (1.8) yrs) who performed measurements with and without an accompanying adult, the mean value of sRaw was 1.45 (0.36) and 1.44 (0.38) kPa x s, respectively, with a mean difference of 0.008 (0.152) kPa x s, and mean within-subject coefficients of variations (CV) of 8% and 10%, respectively. In 52 children (mean age 3.3 (0.8) yrs), for whom measurements made only in the presence of an accompanying adult, the CV was 8.5%. No measurements could be obtained in 22 children (17%) (mean age 2.8 (0.5) yrs). Measurements exhibited a significant frequency dependency, and electronic BTPS compensation substantially overestimated SRaw. In conclusion, the use of electronic compensation for simulating body temperature, atmospheric pressure and saturation with water vapour introduces a bias that affects the accuracy of the estimate of specific airway resistance. Nevertheless, plethysmographic measurements with and without an accompanying adult yielded comparable and equally repeatable estimates of specific airway resistance. The single-step plethysmographic procedure with an accompanying adult is a clinically useful method for evaluating airway function in children too young to perform plethysmographic measurements alone.
Pulmonary function in infants with neonatal chronic lung disease with or without hyaline membrane disease at birth
Authors: Merth IT , de Winter JP , Zonderland HM , Borsboom GJ , Quanjer PH
Published: April 2003

We studied whether neonatal chronic lung disease (NCLD), hyaline membrane disease (HMD) and differences in ventilatory support affected pulmonary function during the first year of life, in 65 infants born prematurely. The relationship between body weight and oxygen consumption (V'O2) was also analysed. The study comprised 14 infants without cardiorespiratory disease, 19 infants with HMD but without NCLD, 9 infants with NCLD without prior HMD, and 23 infants with NCLD following HMD. At 6 and 12 months corrected postnatal age, static respiratory system compliance (Crs) was measured by weighted spirometry and the functional residual capacity by closed circuit helium dilution (FRCHe) combined with assessment of ventilation distribution from the mixing index (MI). Ventilatory support during the first 5 days of therapy was quantified from peak inspiratory pressure (PIP), mean airway pressure (MAP) and fractional inspiratory concentration of oxygen (FI,O2). Infants with NCLD had a shorter duration of gestation and lower birth weight than those without NCLD (Wilcoxon, p=0.002 and p=0.001, respectively). Pulmonary function at 6 and 12 months corrected age was not different between NCLD infants with or without HMD at birth. Infants with NCLD had lower Crs and MI than those without NCLD (analysis of variance (ANOVA), p<0.011), but their FRCHe was not different. V'O2 adjusted for body weight was comparable in the four groups. PIP and FI,O2 were higher (Wilcoxon, p<0.01) in the NCLD infants than in those with HMD alone, but MAP was not different. Except for FI,O2, these indices were not different among the infants with NCLD. We conclude that birth weight is the major determinant of the development of neonatal chronic lung disease. At 6 and 12 months corrected age, the abnormal pulmonary function is not associated with prior hyaline membrane disease.
Breathing pattern and respiratory mechanics in patients with amyotrophic lateral sclerosis
Authors: Vitacca M , Clini E , Facchetti D , Pagani M , Poloni M , Porta R , Ambrosino N
Published: April 2003

The aim of this study was to evaluate the time course of breathing pattern and respiratory mechanics in patients with amyotrophic lateral sclerosis (ALS). A study was conducted on 25 out of 38 eligible ALS patients. Neurological status, arterial blood gases (ABGs), spirometry, breathing pattern (minute ventilation (V'E), tidal volume (VT), respiratory frequency (fR), duty cycle (duration of inspiration/duration of total breathing cycle (tI/ttot)), respiratory drive (P0.1)), respiratory mechanics (oesophageal pressure (Ppl), dynamic compliance (CL,dyn), pressure time product (PTP) and index (PTI), work of breathing (WOB)), and respiratory muscle (RM) strength as assessed by maximal oesophageal pressure (Ppl,max) were evaluated at presentation (to) in all patients and after 6 months (t6) in 11 patients. At to, the mean values of the degree of neurological impairment were 60+/-20 and 103+/-30 as assessed by the Norris scale and Medical Research Council (MRC) score, respectively. From the time of the first neurological symptom, survival time ranged 7-50 months. Diurnal ABGs were normal. A mild restrictive pattern was observed, a forced vital capacity (FVC) <70% of predicted being present in 45% of patients, only FVC % pred (r=0.59; p<0.05), forced expiratory volume in one second (FEV1) % pred (r=0.53; p<0.05) and survival (r=0.64; p<0.05) showing a significant correlation with the Norris scale. A Ppl,max <30 cmH2O was associated with a significantly greater mortality, Ppl,max being correlated with survival (r=0.79, p<0.05). At t6, fR, fR/VT, P0.1/Ppl,max, were significantly increased in comparison to to, while FVC % pred, vital capacity (VC) % pred, FEV1 % pred, VT and Ppl,max were significantly reduced. These results suggest a progressive deterioration in breathing pattern and in respiratory muscle strength with progression of disease.
Respiratory mechanics in patients with tense cirrhotic ascites
Authors: Duranti R , Laffi G , Misuri G , Riccardi D , Gorini M , Foschi M , Iandelli I , Mazzanti R , Mancini M , Scano G , Gentilini P
Published: April 2003

Lung volumes are decreased by tense ascites and increase after large volume paracentesis (LVP). The overall effect of ascites and LVP on the respiratory function is poorly understood. We studied eight cirrhotic patients with tense ascites before and after LVP. Inspiratory muscle force (maximal transdiaphragmatic pressure (Pdi,max), and the lowest pleural pressure (Pp1,min)) was assessed while the patients were seated. Rib cage and abdominal volume displacements, as well as pleural and gastric pressures were measured during quiet breathing while the patients were supine. Pdi,max and Ppl,min were normal and did not change after LVP (from 84.2+/-19.7 to 85.2+/-17.0 cmH2O and from 68.3+/-19.7 to 74+/-15.9 cmH2O, respectively). The abdominal contribution to the generation of tidal volume was greater than that of the rib cage (79 vs 21%), a pattern which did not change after LVP (73 and 27%). Before LVP, tidal swings both of pleural pressure (Ppl,sw) and transdiaphragmatic pressure (Pdi,sw) were large (15.3+/-4.3 and 18.5+/-3.9 cmH2O, respectively) and the load on inspiratory muscles was increased as a consequence of elevated dynamic elastance of the lung (El,dyn) (11.4+/-2.6 cmH2O x L(-1)) and ("intrinsic") positive end-expiratory pressure (PEEPi) (4.3+/-3.5 cmH2O). LVP reduced the load on the inspiratory muscles, as shown by the significant decrease in Ppl,sw (10.6+/-2.0 cmH2O), Pdi,sw (12.8+/-3.0 cmH2O), El,dyn (10.0+/-2.0 cmH2O x L(-1)) and PEEPi (1.1+/-1.3 cmH2O). The amount of fluid removed was closely related to changes in Ppl,sw and PEEPi. We conclude that the strength of the inspiratory muscles is normal or reduced in seated cirrhotic patients. In the supine position, tense ascites results in an increase in lung elastic load and development of positive end-expiratory pressure, with a consequent overload and increased activation of inspiratory muscles. Large volume paracentesis decreases overloading and activation, but does not change the strength of the inspiratory muscles.
A new device for in vivo measurement of nasal transepithelial potential difference in cystic fibrosis patients and normal subjects
Authors: Duperrex O , Berclaz PY , Bertrand D , Lacroix JS , Pochon N , Belli D , Rochat T
Published: April 2003

Measurement of transepithelial potential difference (PD) on the nasal mucosa has been proposed to test for defective ion transport in cystic fibrosis (CF), and its possible correction after gene therapy or other treatments. The "classical" method records nasal PD under the inferior turbinate, with the disadvantage that the tip of the electrode is not seen by the operator. We have developed a purpose-designed perfusion electrode for PD recording on the visible, medial/posterior aspect of the turbinate. We wanted to determine whether such PD recordings adequately discriminate between CF patients and normal subjects. Measurements of baseline PD and response to a standardized perfusion protocol were performed in 20 normal subjects and 12 CF patients. Solutions of amiloride, with or without low chloride buffer were applied for 3 min. Increased baseline PD and depolarization after amiloride discriminated CF patients from normal subjects. Only one CF patient overlapped with the normal range. Superfusion of low chloride buffer with amiloride and terbutaline caused repolarization in 18 out of 20 normal subjects (90%), consistent with physiological Cl- secretion process, but in none of the CF patients. We conclude that measurements of potential difference on the medial/posterior aspect of the turbinate can discriminate between cystic fibrosis patients and normal subjects. At this site, visual control of the measurement is possible, and the mucosa is easily accessible for subsequent cytological sampling or biopsy.
Glucocorticoid-resistant asthma: pathogenesis and clinical implications for management
Authors: Szefler SJ , Leung DY
Published: April 2003

At the present time, emphasis is placed on viewing asthma as a manifestation of chronic airway inflammation, possibly secondary to allergen hypersensitivity. Consequently, one aspect of management is to institute measures of environmental control to minimize the inflammatory response related to allergen stimulation, and to administer anti-inflammatory therapy to resolve inflammation and prevent progression of disease. Most patients respond very favourably to conventional therapy, as recommended in recent guidelines for asthma management. Some cases, however, remain very difficult to control despite high-dose inhaled glucocorticoids, even combined with oral glucocorticoid therapy. Management of these patients raises questions about the conditions that alter response to glucocorticoid therapy. The patient with difficult to control asthma not only presents a challenge to clinical management but raises new questions concerning our ability to control the progression of disease. Is difficult to control asthma secondary to overwhelming or ongoing allergen exposure? Do anti-inflammatory medications, specifically inhaled glucocorticoids, really control the progression of the disease? Are these patients destined to become severe asthmatics at birth due to the inherent characteristics of their airways, or is this indeed a consequence of progressive inflammation? This review will summarize present concepts of glucocorticoid-resistant asthma, current knowledge of the mechanisms of persistent inflammation, and the implications for management. The gaps in information will also be addressed in order to stimulate interest in further research that could lead to better understanding of the disease and potential windows for therapeutic intervention.
Pleurodesis: state of the art
Authors: Rodriguez-Panadero F , Antony VB
Published: April 2003

Pleurodesis aims to achieve a symphysis between parietal and visceral pleural surfaces, in order to prevent accumulation of fluid or air in the pleural space. Its major indications are malignant effusions and pneumothorax, and a re-expandable lung is essential for the success of the technique. Moreover, expectation of a reasonably long survival is important before attempting pleurodesis. A successful lung re-expansion is unlikely if the pleural pressure falls more than 20 cmH2O x L(-1) of fluid removed, because there is a central bronchial obstruction or the lung is trapped by tumour and/or fibrin. Pleural fluid pH (<7.20) is a good indicator of the presence of trapped lung; moreover, a successful pleurodesis is less likely when pH is low, and this parameter is also a good predictor for survival of the patients. Among the many sclerosing agents that have been used for pleurodesis, talc has achieved the best results, with an average success rate of approximately 90%. The cellular and biochemical mechanisms involved in pleurodesis may be specific to the agent used, however, they may all follow a common final pathway leading to activation of the pleural coagulation cascade, the appearance of fibrin networks, and the proliferation of fibroblasts. The details of these mechanisms are still unclear and need to be further elaborated.
Airway mucosa: secretory cells, mucus and mucin genes
Authors: Jeffery PK , Li D
Published: April 2003

The airway mucosa is lined by a continuous epithelium comprised of multiple cell phenotypes, several of which are secretory. Secretions produced by these cells mix with a variety of macromolecules, ions and water to form a respiratory tract fluid that protects the more distal airways and alveoli from injury and infection. The present article highlights the structure of the mucosa, particularly its secretory cells, gives a synopsis of the structure of mucus, and provides new information on the localization of mucin (MUC) genes that determine the peptide sequence of the protein backbone of the glycoproteins, which are a major component of mucus. Airway secretory cells comprise the mucous, serous, Clara and dense-core granulated cells of the surface epithelium, and the mucous and serous acinar cells of the submucosal glands. Several transitional phenotypes may be found, especially during irritation or disease. Respiratory tract mucins constitute a heterogeneous group of high molecular weight, polydisperse richly glycosylated molecules: both secreted and membrane-associated forms of mucin are found. Several mucin (MUC) genes encoding the protein core of mucin have been identified. We demonstrate the localization of MUC gene expression to a number of distinct cell types and their upregulation both in response to experimentally administered lipopolysaccharide and cystic fibrosis.
Pulmonary hyperinflation and ventilator-dependent patients
Authors: Rossi A , Ganassini A , Polese G , Grassi V
Published: April 2003

Pulmonary hyperinflation is a major medical problem in patients with advanced chronic obstructive pulmonary disease (COPD) or acute asthma. The apparent beneficial effects of pulmonary hyperinflation on lung mechanics, such as an increased airway patency and lung elastic recoil, are by far overwhelmed by the deleterious effects on the pressure generating capacity of the respiratory muscles. Moreover, the ventilatory workload can be remarkably increased: 1) by the displacement of the respiratory system toward the upper, flat portion of the pressure-volume curve; 2) by the need to expand the chest wall and not only the lungs; and 3) by the intrinsic positive end-expiratory pressure (PEEPi) systematically associated with dynamic hyperinflation. In mechanically ventilated patients, the mechanisms underlying pulmonary hyperinflation as well as its pathophysiological consequences do not differ from those described in spontaneously breathing patients. However, there are some specific issues that should be taken into account, namely the effect of the endotracheal tube and the mode and setting of the ventilator. In mechanically ventilated patients, pulmonary hyperinflation increases the risk of barotrauma and may hamper weaning due to the excessive burden of PEEPi, which can even lead to ineffective inspiratory efforts. Because of its harmful consequences, pulmonary hyperinflation must be treated aggressively by pharmacological therapy and, when needed, by ventilatory treatment. The setting of the ventilator must be predetermined to ensure the longest possible time for expiration, and positive end-expiratory pressure can be applied to prevent an excessive workload for the patient and ineffective inspiratory efforts.
Gastropleural fistula due to gastric lymphoma presenting as tension pneumothorax and empyema
Authors: Warburton CJ , Calverley PM
Published: April 2003

The formation of a gastropleural fistula is an uncommon complication of a number of conditions. The case of a patient with gastropleural fistula, as a complication of gastric lymphoma, is presented. The patient developed a tension pneumothorax and empyema. On cytological examination of the empyematous fluid, the presence of food debris aided diagnosis. The patient died 2 days after a total gastrectomy. The development of this complication in gastric lymphoma appears to have a particularly poor prognosis.
Clinical, radiographic and lung function features of diffuse congenital cystic adenomatoid malformation of the lung in an adult
Authors: Plit ML , Blott JA , Lakis N , Murray J , Plit M
Published: April 2003

Congenital cystic adenomatoid malformation of the bronchi with bilateral lung involvement has only previously been reported in one possible adult case. This report describes a young man with bilateral diffuse lung involvement, characteristic histological features, and a mixed restrictive/obstructive lung function pattern.
FDTD simulation of EM wave propagation in 3-D media
Authors: Wang Tsili , Tripp Alan C.
Published: April 2003

A finite‐difference, time‐domain solution to Maxwell’s equations has been developed for simulating electromagnetic wave propagation in 3-D media. The algorithm allows arbitrary electrical conductivity and permittivity variations within a model. The staggered grid technique of Yee is used to sample the fields. A new optimized second‐order difference scheme is designed to approximate the spatial derivatives. Like the conventional fourth‐order difference scheme, the optimized second‐order scheme needs four discrete values to calculate a single derivative. However, the optimized scheme is accurate over a wider wavenumber range. Compared to the fourth‐order scheme, the optimized scheme imposes stricter limitations on the time step sizes but allows coarser grids. The net effect is that the optimized scheme is more efficient in terms of computation time and memory requirement than the fourth‐order scheme. The temporal derivatives are approximated by second‐order central differences throughout. The Liao transmitting boundary conditions are used to truncate an open problem. A reflection coefficient analysis shows that this transmitting boundary condition works very well. However, it is subject to instability. A method that can be easily implemented is proposed to stabilize the boundary condition. The finite‐difference solution is compared to closed‐form solutions for conducting and nonconducting whole spaces and to an integral‐equation solution for a 3-D body in a homogeneous half‐space. In all cases, the finite‐difference solutions are in good agreement with the other solutions. Finally, the use of the algorithm is demonstrated with a 3-D model. Numerical results show that both the magnetic field response and electric field response can be useful for shallow‐depth and small‐scale investigations.
A numerical evaluation of electromagnetic methods in geothermal exploration
Authors: Pellerin Louise , Johnston Jeffrey M. , Hohmann Gerald W.
Published: April 2003

The size and low resistivity of the clay cap associated with a geothermal system create a target well suited for electromagnetic (EM) methods and also make electrical detection of the underlying geothermal reservoir a challenge. Using 3-D numerical models, we evaluate four EM techniques for use in geothermal exploration: magnetotellurics (MT), controlled‐source audio magnetotellurics (CSAMT), long‐offset time‐domain EM (LOTEM), and short‐offset time‐domain EM (TEM). Our results show that all of these techniques can delineate the clay cap, but none can be said to unequivocally detect the reservoir. We do find, however, that the EM anomaly from a deep, conductive reservoir overlain by a larger, more conductive clay cap is caused by the presence of the electric charge at conductivity boundaries rather than electromagnetic induction. This means that, for detection of the reservoir, methods such as MT, which rely on electric field measurements, are superior to those where only the magnetic field is measured. The anomaly produced by boundary charges at the reservoir is subtle and will be evident only if high‐quality data are collected at closely spaced measurement sites. LOTEM electric field measurements look promising and should be useful when efficient multidimensional tools are developed for LOTEM interpretation. Although CSAMT employs electric field measurements, this method is not recommended for reservoir detection because the anomaly caused by a deep reservoir is obscured by transmitter effects that cannot be isolated reliably. A combination of CSAMT and TEM measurements appears most appropriate for delineation of the clay cap.
An improved technique for reduction to the pole at low latitudes
Authors: Keating Pierre , Zerbo L.
Published: April 2003

Reduction to the pole at low latitudes based on a Wiener filtering approach has been improved by introducing a deterministic noise model. It is assumed that the noise power is a fixed fraction of the signal power. This allows the method to be fully automated. Further improvement is obtained by requiring the reduced‐to‐the‐pole field to map into the observed field when projected to the geomagnetic latitude of the observed field. This is done by iteratively minimizing the difference between the measured field and the reduced‐to‐the‐pole field projected to the geomagnetic latitude of the measured data. This results in a reduced‐to‐the‐pole magnetic map that, when projected to the geomagnetic latitude of the given data, closely matches the measured data. The final reduced‐to‐the‐pole field does not show any of the artifacts typical of reduction‐to‐the‐pole at low geomagnetic latitudes. The method is demonstrated on a data set from an aeromagnetic survey flown over north‐central Burkina Faso, West Africa.
Prestack migration velocity estimation using nonlinear methods
Authors: Jervis Michael , Sen Mrinal K. , Stoffa Paul L.
Published: April 2003

We describe here methods of estimating interval velocities based on two nonlinear optimization methods; very fast simulated annealing (VFSA) and a genetic algorithm (GA). The objective function is defined using prestack seismic data after depth migration. This inverse problem involves optimizing the lateral consistency of reflectors between adjacent migrated shot records. In effect, the normal moveout correction in velocity analysis is replaced by prestack depth migration. When the least‐squared difference between each pair of migrated shots is at a minimum, the true velocity model has been found. Our model is parameterized using cubic‐B splines distributed on a rectangular grid. The main advantages of using migrated data are that they do not require traveltime picking, knowledge of the source wavelet, and expensive computation of synthetic waveform data to assess the degree of data‐model fit. Nonlinear methods allow automated determination of the global minimum without relying on estimates of the gradient of the objective function, the starting model, or making assumptions about the nature of the objective function itself. For the velocity estimation problem, the VFSA converges 4 to 5 times faster than the GA for both a 2-D synthetic example and a structurally complex real data example from the Gulf of Mexico. Though computationally intensive, this problem requires few model parameters, and use of a fast traveltime code for Kirchhoff migration makes the algorithm tractable for real earth problems.
2-D resistivity inversion using spline parameterization and simulated annealing
Authors: Chunduru Raghu K. , Sen Mrinal K. , Stoffa Paul L.
Published: April 2003

Successful inversion of geophysical data depends on prior information, proper choice of inversion scheme, and on effective parameterization of the model space such that the model representation is appropriate and efficient. Inversion of resistivity data has long been recognized as a nonlinear or quasi‐linear problem. Traditionally, 2-D resistivity inversion has been performed by trial and error methods and with linear and iterative linear methods. The linear and iterative linear methods are limited because of the requirement of good prior knowledge of the subsurface. Unlike linear and iterative linear methods, most nonlinear inversion schemes do not depend strongly on the starting solution, but prior information helps to reduce the computational cost and to obtain geologically meaningful results. In the present study, we have applied a nonlinear optimization scheme called very fast simulated annealing (VFSA) in the inversion of 2-D dipole‐dipole resistivity data to image the subsurface. Unlike Metropolis simulated annealing (SA) in which each new model is drawn from a uniform distribution, VFSA draws a model from a Cauchy‐like distribution, which is also a function of a control parameter called temperature. The advantage of using such a scheme is that at high temperatures, the algorithm allows for searches far beyond the current position, while at low temperatures, it looks for improvement in the close vicinity of the current model. We have used the mean square error between the synthetics and original data as the error function to be minimized. The synthetic response for 2-D models was obtained by finite‐difference modeling, and cubic splines were used to parameterize the model space to get smooth images of the subsurface and to reduce computational cost. VFSA was used to estimate the conductivity at each spline node location. The inversion was applied to various synthetic data to study the influence of the starting solution and the location of the spline nodes. Finally, we applied it to real data collected over a disseminated sulfide zone at Safford, Arizona, and compared the results with those obtained from a linearized inversion and from a model based on geologic and well‐log data. The VFSA results are in good agreement with the previously published results.
Conductivity of two‐component systems
Authors: de Kuijper A. , Sandor R. K. J. , Hofman J. P. , de Waal J. A.
Published: April 2003

We present measurements and computer simulation results on the electrical conductivity of nonconducting grains embedded in a conductive brine host. The shapes of the grains ranged from prolate‐ellipsoidal (with an axis ratio of 5:1) through spherical to oblate‐ellipsoidal (with an axis ratio of 1:5). The conductivity was studied as a function of porosity and packing, and Archie’s cementation exponent was found to depend on porosity. We used spatially regular and random configurations with aligned and nonaligned packings. The experimental results agree well with the computer simulation data. This data set will enable extensive tests of models for calculating the anisotropic conductivity of two‐component systems.
Fast resistivity/IP inversion using a low‐contrast approximation
Authors: Beard Les P. , Hohmann Gerald W. , Tripp Alan C.
Published: April 2003

By computing only the diagonal terms of the volume integral equation forward solution of the 3-D DC resistivity problem, we have achieved a fast forward solution accurate at low to moderate resistivity contrasts. The speed and accuracy of the solution make it practical for use in 2-D or 3-D inversion algorithms. The low‐contrast approximation is particularly well‐suited to the smooth nature of minimum structure inversion, since complete forward solutions may be computationally expensive. By using this approximate 3-D solution as the forward model in an inversion algorithm, and by constraining the resistivities and polarizabilities along any row of cells in the strike direction to be held constant, we effect a fast 2-D resistivity inversion that contains end corrections. Because the low‐contrast solution is inaccurate for cells near the electrodes, we employ a full solution to compute the response of the near‐surface when the near‐surface environment is substantially different from the host rock. This response is stored and used in the iterative resistivity inversion in conjunction with the approximate solution. Once an adequate estimated resistivity model has been found, derivatives from this model are used with Seigel’s formula to compute the inverse solution to the linear polarizability problem in a single iteration.
Comparison of explosive and vibroseis source energy penetration during COCORP deep seismic reflection profiling in the Williston Basin
Authors: Steer David N. , Brown Larry D. , Knapp James H. , Baird David J.
Published: April 2003

Comparison of high‐fold (50) vibroseis recordings with coincident low‐fold (6) explosive source data from deep reflection surveys in the Williston Basin indicates that while vibroseis generated energy decays to ambient noise levels at 7–9 s two‐way traveltime (twtt) (20–30 km depth), energy from explosive sources remains above ambient levels to 35–60 s twtt (105–180 km depth). Moreover, single, moderately sized (30 kg) and well‐placed charges proved to be as effective as larger (90 kg) sources at penetrating to mantle traveltimes in this area. However, the explosive source energy proved highly variable, with source‐to‐ground coupling being a major limiting factor in shot efficacy. Stacked results from the vibroseis sources provide superior imagery of shallow and moderate crustal levels by virtue of greater redundancy and shot‐to‐shot uniformity; shot statics, low fold, and ray‐path distortion across the relatively large (24–30 km aperture) spreads used during the explosive recording have proven to be especially problematic in producing “conventional” seismic sections. In spite of these complications, the explosive source recording served its primary purpose in confirming Moho truncation and the presence of a dipping reflection fabric in the upper mantle along the western flank of the Trans‐Hudson orogen buried beneath the Williston Basin.
Natural recession of the eastern margin of the Leofnard salt in western Canada
Authors: Anderson Neil L. , Brown R. James , Cederwall Dale A.
Published: April 2003

The Lloydminster area (T35-65, R15W3M-10W4M) of east‐central Alberta and west‐central Saskatchewan, Canada, is dissected by the north‐northwest trending updip active dissolution margin, of the Devonian Leofnard Member rock salt. West of this margin, up to 150 m of rock salt is preserved; updip and to the east, the salt has mostly been leached from the rock record. The margin is up to 40 km wide and characterized by extreme local variations in net salt thickness. The dissolution of the Leofnard rock salt in the Lloydminster area has resulted in the entrapment of significant hydrocarbon accumulation. Stratigraphic traps, for example, have formed where reservoir facies were either preferentially deposited or preserved in salt‐dissolution lows. Structural traps, in contrast, have formed where reservoir facies are draped across residual salt or collapse features. It has been estimated that three trillion barrels of oil (mostly of high viscosity and unrecoverable) are entrapped along the eastern dissolution margin of the Leofnard rock salt in western Canada. A record of the westward progression of the dissolutional edge of the Leofnard salt is locked in the stratigraphic column. This progression is recorded as localized interval thickening in areas where dissolution and deposition were contemporaneous. The horizontal positioning of these interval thicks as a function of their geologic age provides a time record for the positioning of the salt edge. To further explain the process of salt dissolution in the Lloydminster area, we present a suite of contour maps, geologic cross‐sections, and seismic profiles. These data depict the present‐day distribution of the Leofnard salt in the Lloydminster study area. They support the theses that: (1) the dissolution margin of the Leofnard rock salt originated along the Elk Point outcrop to the east of the study area during the pre‐Cretaceous; and (2) the margin receded into the northeastern part of the Lloydminster study area during earliest Cretaceous or pre‐Cretaceous time and migrated progressively thereafter into its current position. From the perspective of the explorationist, such information is important because it identifies prospective play areas with high potential for the formation of salt‐related stratigraphic traps and/or structural traps.
Broadband receiver response from dual‐streamer data and applications in deep reflection seismology
Authors: Singh Satish C. , Hobbs R. W. , Snyder D. B.
Published: April 2003

A method to process dual‐streamer data with under and over configuration is presented. The method combines the results of dephase‐sum and dephase‐subtraction methods. In the dephase methods, the response of one streamer is time shifted so that the primary arrivals on both streamers are aligned, and these responses are then summed or subtracted. The method provides a broad spectral response from dual‐streamer data and increases the signal‐to‐noise ratio by a factor of 1.5. Testing was done on synthetic data and then applied to a real data set collected by the British Institutions Reflection Profiling Syndicate (BIRPS). Its application to a deep seismic reflection data set from the British Isles shows that the reflections from the lower crust contain frequencies up to 80 Hz, suggesting that some of the lower crustal reflectors may have sharp boundaries and could be 20–30 m thick.
Boundary conditions and the source term for one‐way acoustic depth extrapolation
Authors: Charara Marwan , Tarantola Albert
Published: April 2003

The one‐way acoustic wave equations can be derived, using eigenvalue decomposition of the two‐way wave equation in the Fourier domain, in such a manner that the source term and the free‐surface boundary condition are explicitly introduced. The proposed form of the one‐way wave equations is well adapted to seismic reflection modeling because it allows a pressure field recorded at the surface to be extrapolated directly in depth. A numerical example illustrates the appropriate implementation of the source term and the free‐surface boundary conditions. A comparison with a two‐way modeling shows a good agreement of the computed wave fields.
Theory of 2-D complex seismic trace analysis
Authors: Barnes Arthur E.
Published: April 2003

The ideas of 1-D complex seismic trace analysis extend readily to two dimensions. Two‐dimensional instantaneous amplitude and phase are scalars, and 2-D instantaneous frequency and bandwidth are vectors perpendicular to local wavefronts, each defined by a magnitude and a dip angle. The two independent measures of instantaneous dip correspond to instantaneous apparent phase velocity and group velocity. Instantaneous phase dips are aliased for steep reflection dips following the same rule that governs the aliasing of 2-D sinusoids in f-k space. Two‐dimensional frequency and bandwidth are appropriate for migrated data, whereas 1-D frequency and bandwidth are appropriate for unmigrated data. The 2-D Hilbert transform and 2-D complex trace attributes can be efficiently computed with little more effort than their 1-D counterparts. In three dimensions, amplitude and phase remain scalars, but frequency and bandwidth are 3-D vectors with magnitude, dip angle, and azimuth.
Horizontal acceleration corrections in airborne gravimetry
Authors: Swain Christopher J.
Published: April 2003

The stabilized platforms used in marine and airborne gravimeters behave like damped long‐period pendulums. When subjected to horizontal accelerations they tilt, resulting in gravimeter reading errors. The amount of tilt depends on the ratio of the period of the horizontal motion to that of the platform and is negligible if this ratio is less than about 0.1 (LaCoste, 1967). This condition can be achieved in straight and level flight using an auto pilot, provided the platform period is set to a sufficiently long period (Brozena and Peters, 1988). Course changes are sometimes unavoidable, however, resulting in lost data (Bell et al., 1991; Brozena, 1984). The aim of this paper is to show that such data loss is unnecessary since the tilt, and hence the gravimeter error, can be accurately modeled from the horizontal accelerations. Moreover the technique will improve data quality whenever long period horizontal accelerations occur. Measuring these accelerations is now straightforward with differential carrier phase GPS.
Potential pitfalls of crooked‐line seismic reflection surveys
Authors: Wu Jianjun
Published: April 2003

During the last few years, the Geological Survey of Canada has pioneered the application of seismic reflection profiling to mineral exploration, in close collaboration with Canadian mining companies and with the Lithoprobe project (e.g., Spencer et al., 1993; Milkereit et al., 1994). Because of the rugged terrain in crystalline rock environments (Dahle et al., 1985; Spencer et al., 1993), vibroseis seismic surveys are frequently conducted along existing roads, resulting in extremely crooked survey profiles. Crooked profiling geometry, coupled with the complex nature of the geological targets, pose special challenges for seismic data processing and interpretation. Many common‐midpoint seismic processing techniques are based on an implicit assumption of a straight‐line survey and are most effective with uniform fold and even offset distribution within common‐midpoint (CMP) gathers. However, with crooked‐line acquisition the CMP gathers are characterized by variable fold and uneven offset distribution. Based on experience with several seismic data sets from mining camps, I have identified two potential pitfalls that stem from acquisition along crooked profiles: (1) seismic transparent zones; and (2) coherent noise. To address these problems, I have critically re‐examined the basic aspects of the CMP processing techniques and have developed robust strategies for dealing with crooked profiles. In this paper, I present a field data example to demonstrate the artifacts and also discuss solutions to eliminate them. Although developed for seismic prospecting in mining camps, the methods presented here are applicable to seismic data acquired in any environment.
Pressure in a fluid‐filled borehole caused by a seismic source in stratified media
Authors: Peng Chengbin , Lee Jung M. , Toksöz M. Nafi
Published: April 2003

A method for numerically simulating hydrophone vertical seismic profiles (VSP) and crosswell data measured in a fluid‐filled borehole (either open or cased) embedded in stratified media is presented. The method makes use of both the borehole coupling theory and the global matrix formulation for computing synthetic seismograms in a stratified medium. The global matrix formulation is used to calculate the stress field at the borehole location. Borehole coupling theory is then employed to obtain the pressure in the borehole fluid. Comparisons with exact solutions for an open borehole in a homogeneous and unbounded formation show that this method is accurate for frequencies below 2 kHz. This method is used to model the Kent Cliffs hydrophone VSP data, where good agreement between the numerical simulations and the field measurements has been found, in both traveltimes and rms amplitudes of the direct P‐wave. Examples show that this method is efficient and accurate, and can be applied to model VSP and crosswell experiments using an array of hydrophones.