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Biomedical subjects

L G Olson

Publications and source records attributed to L G Olson.

At least 19 recordsLinked to original sources
PubMed2002

A new method for incorporating weighted temporal and spatial smoothing in the inverse problem of electrocardiography.

In this paper, we present a method for incorporating temporal smoothing (TS) into the estimate of epicardial potentials from body surface potential data. Our algorithm employs a different spatial smoothing parameter, chosen by the composite residual error and smoothing operator criteria, at each time step in the sequence. The total spatial smoothing term is then simply partitioned between temporal and spatial smoothing. The algorithm appears to be quite robust with regard to this partitioning. The new method was evaluated in the setting of additive Gaussian noise, but otherwise realistic conditions of body geometry and reference epicardial potentials. In examining the match between estimated and measured electrograms, or the match between estimated isopotential maps and measured isopotential maps, the estimates constructed using the new TS algorithm produced consistently smaller relative errors than those constructed using a quasi-static (QS) algorithm or those constructed by postprocessing the QS estimate with a moving average filter.

Algorithms↗
PubMed2001

Characterization of silane-modified immobilized gold colloids as a substrate for surface-enhanced Raman spectroscopy.

Immobilized gold colloid particles coated with a C-18 alkylsilane layer have been characterized as a substrate for surface-enhanced Raman scattering (SERS) studies of adsorption onto hydrophobic surfaces. Atomic force microscopy images, optical extinction spectra, and SERS measurements are reported as a function of accumulation of gold colloid on glass. As the metal particles become increasingly aggregated on the surface, the SERS enhancement increases until the plasmon resonance shifts to wavelengths longer than the excitation laser. The gold colloid substrates are stable and exhibit reproducible SERS enhancement. When octadecyltrimethoxysilane is self-assembled over the gold, the metal surface is protected from exposure to solution-phase species, as evidenced by the inhibition of chemisorption of a disulfide reagent to the overcoated gold surface. The results show that interactions with gold can be blocked by a silane layer so as not to significantly influence physisorption of molecules at the C-18/solution interface. The SERS enhancement from these C-18-overcoated gold substrates is reproducible for different films prepared from the same colloidal suspension; the substrates are also stable with time and upon exposure to laser irradiation.

Journal Article↗
PubMed2001

Parameter choice methods and temporal filtering for the generalized eigensystem method applied to the inverse problem of electrocardiography.

We have previously proposed the generalized eigensystem (GES) method as a modal expansion method for estimating electrical potentials on the heart outer surface from measurements of electrical potentials on the body surface. In this paper, we present an alternative formulation of GES more like that of classical Tikhonov regularization where a single continuous parameter needs to be chosen. We then compare this formulation of GES with zero order Tikhonov regularization on data collected from a swine experiment with the swine heart paced from six different sites. Although the inverse problems are solved at each time instant independently, we also incorporate temporal information by moving average filtering the estimates, and this is more effective for the GES methods than for Tikhonov.

Animals↗
PubMed2000

The effect of a Structured Question Grid on the validity and perceived fairness of a medical long case assessment.

PROBLEM: A perception that the reliability of our oral assessments of clinical competence was vitiated by lack of consistency in questioning. DESIGN: Parallel group controlled trial of a Structured Question Grid for use in clinical assessments. The Structured Question Grid required assessors to see the patient personally in advance of the student and to write down for each case the points they wished to examine. The Structured Question Grid limited assessors to two questions on each point, one designated a pass question and one at a higher level. Three basic science and three clinical reasoning issues were required, so that a total of 12 questions was allowed. SETTING: Small (70 students/year) undergraduate medical school with an integrated, problem-based curriculum. SUBJECTS: Sixty-seven students in the fourth year of a 5-year course were assessed, each seeing one patient and being examined by a pair of assessors. Assessor pairs were allocated to use the Structured Question Grid or to assess according to their usual practice. RESULTS: After the assessment but before being informed of the result the students completed a questionnaire on their experience and gave their performance a score between 0 and 100. The questions asked were based on focus group discussions with a previous student cohort, and concerned principally the perceived fairness and subjective validity of the assessment. The assessors independently completed a similar questionnaire, gave the student's performance a score between 0 and 100, and assigned an overall pass/fail grade. CONCLUSIONS: No difference was detected between students' or assessors' views of the fairness of the assessment for assessors who had used the Structured Question Grid compared to those who had not. Students whose assessors used the Structured Question Grid considered the assessment less representative of their ability. No difference was detected in the chance of students being assessed as failing or on the likelihood of a discrepancy between students' and assessors' ratings of students as passing or failing.

Clinical Competence↗
PubMed2000

Fusion of body surface potential and body surface Laplacian signals for electrocardiographic imaging.

Various approaches to the solution to the inverse problem of electrocardiography have been proposed over the years. Recently, the use of inverse algorithms using measured body surface Laplacians has been proposed, and in various studies this technique has been shown to outperform the traditional use of body surface potentials in certain model problems. In this paper, we compare the use of body surface potentials and body surface Laplacians on two model problems with different assumed cardiac sources. For the spherical cap model problems with an anterior source, the epicardial estimates using body surface potentials had smaller average relative errors than when body surface Laplacians were used. For the spherical cap model problems with a posterior source, the epicardial estimates using body surface potential or body surface Laplacian sensors generally produced similar relative errors. For the radial dipole model, the epicardial estimates using body surface Laplacians had smaller errors than when body surface potentials were used. We introduce a fusion algorithm that combines the different types of signals and generally produces a good estimate for both model problems.

Algorithms↗
PubMed1999

Prediction of sleep-disordered breathing by unattended overnight oximetry.

Between January 1994 and July 1997, 793 patients suspected of having sleep-disordered breathing had unattended overnight oximetry in their homes followed by laboratory polysomnography. From the oximetry data we extracted cumulative percentage time at SaO2 < 90% (CT90) and a saturation variability index (delta Index, the sum of the differences between successive readings divided by the number of readings - 1). CT90 was weakly correlated with polysomnographic apnea/hypopnea index (AHI). (Spearman rho = 0.36, P < 0.0001) and with delta Index (rho = 0.71, P < 0.0001). delta Index was more closely correlated with AHI (rho = 0.59, P < 0.0001). In a multivariate model, only delta Index was significantly related to AHI, the relationship being AHI = 18.8 delta Index + 7.7. The 95% CI for the coefficient were 16.2, 21.4, and for the constant were 5.8, 9.7. The sensitivity of a delta Index cut-off of 0.4 for the detection of AHI > or = 15 was 88%, for detection of AHI > or = 20 was 90% and for the detection of AHI > or = 25 was 91%. The specificity of delta Index > or = 0.4 for AHI > or = 15 was 40%. In 113 further patients, oximetry was performed simultaneously with laboratory polysomnography. Under these circumstances delta Index was more closely correlated with AHI (rho = 0.74, P < 0.0001), as was CT90 (rho = 0.58, P < 0.0001). Sensitivity of delta Index > or = 0.4 for detection of AHI > or = 15 was not improved at 88%, but specificity was better at 70%. We concluded that oximetry using a saturation variability index is sensitive but nonspecific for the detection of obstructive sleep apnea, and that few false negative but a significant proportion of false positive results arise from night-to-night variability.

Circadian Rhythm↗
PubMed1999

The ability of a long-case assessment in one discipline to predict students' performances on long-case assessments in other disciplines.

PURPOSE: To determine whether medical students' performances in a long-case assessment in one of four disciplines (internal medicine, pediatrics, reproductive medicine, or surgery) could predict later performances in long-case assessments in the other disciplines. METHOD: In their fourth of five years at the University of Newcastle, at the end of 12-week rotations in internal medicine, pediatrics, surgery, and reproductive medicine, students undertake long-case assessments. Each long-case assessment involves a real patient and a vive voce examination, and each is scored by two assessors. The author reviewed these scores, which could range from 5 to 20, for the years 1992 to 1997. RESULTS: Over the six years, 391 students completed 1,564 cases. In 249 cases, the students scored better than 11 on their first long-case assessments; of those, 16 (6.5%) went on to fail one of the three subsequent assessments. Of the 142 students who scored 10 or less on their first assessments, 25 (17.6%) went on to fail one of the subsequent three, and 9 (6.3%) went on to fail two more assessments. Of the 24 students who scored 10 or less on the first two assessments, 9 (37.5%) went on to fail one of the next two. There were statistically significant correlations among scores in all disciplines. CONCLUSIONS: Performance in any one of the four disciplines was a good predictor of performance in any other discipline. Except for borderline students, one case was almost as good a predictor as three, and for borderline or weak students two cases were nearly as good as three.

Clinical Clerkship↗
PubMed1998

Correlations among Epworth Sleepiness Scale scores, multiple sleep latency tests and psychological symptoms.

The aim of this study was to identify factors other than objective sleep tendency associated with scores on the Epworth Sleepiness Scale (ESS). There were 225 subjects, of whom 40% had obstructive sleep apnoea (OSA), 16% had simple snoring, and 4.9% had snoring with sleep disruption (upper airway resistance syndrome); 9.3% had narcolepsy and 7.5% had hypersomnolence without REM sleep abnormalities; 12% had chronic fatigue syndrome; 7.5% had periodic limb movement disorder and 3% had diurnal rhythm disorders. ESS, the results of overnight polysomnography and multiple sleep latency test (MSLT) and SCL-90 as a measure of psychological symptoms were recorded. The ESS score and the mean sleep latency (MSL) were correlated (Spearman rho = -0.30, P < 0.0001). The MSL was correlated with total sleep time (TST) and with sleep efficiency but not with apnoea/hypopnoea index. There was no association between the MSL and any aspect of SCL-90 scores, except a borderline significant association with the somatisation subscale. The ESS was correlated with TST but not with sleep efficiency or apnoea/hypopnoea index. The ESS was correlated with all subscales of the SCL-90 except psychoticism. An ESS > or = 10 had poor sensitivity and specificity as a predictor of MSL < 10 min or MSL < 5 min. We conclude that the MSLT and the ESS are not interchangeable. The ESS was influenced by psychological factors by which the MSL was not affected. The ESS cannot be used to demonstrate or exclude sleepiness as it is measured by MSLT.

Adult↗
PubMed1997

Generalized eigensystem techniques for the inverse problem of electrocardiography applied to a realistic heart-torso geometry.

We have previously proposed two novel solutions to the inverse problem of electrocardiography, the generalized eigensystem technique (GES) and the modified generalized eigensystem technique (tGES), and have compared these techniques with other numerical techniques using both homogeneous and inhomogeneous eccentric spheres model problems. In those studies we found our generalized eigensystem approaches generally gave superior performance over both truncated singular value decomposition (SVD) and zero-order Tikhonov regularization (TIK). In this paper we extend the comparison to the case of a realistic heart-torso geometry. With this model, the GES and tGES approaches again provide smaller relative errors between the true potentials and the numerically derived potentials than the other methods studied. In addition, the isopotential maps recovered using GES and tGES appear to be more accurate than the maps recovered using either SVD and TIK.

Animals↗
PubMed1997

A systematic evaluation of mechanisms in chronic cough.

We tested the hypothesis that hyperresponsiveness of the upper airway (UAHR) is present in patients with chronic cough of diverse etiology. We determined the frequency of bronchial hyperresponsiveness (BHR), hyperresponsiveness of the upper airway, sputum eosinophilia, pulmonary aspiration, and psychological symptoms in adults with chronic cough. Consecutive adults (n = 30) presenting to a tertiary referral clinic with chronic cough were compared with a group of 20 asymptomatic adults. Measurements included histamine provocation testing with measurement of flow volume curves to determine inspiratory and expiratory airflow obstruction; hypertonic saline induced sputum for analysis of eosinophils, mast cells and lipid-laden macrophages; and a validated psychological symptom questionnaire. Symptomatic rhinitis and gastroesophageal reflux were common causes of chronic cough. BHR occurred in seven patients (23%) and in no control subjects (p < 0.05). UAHR occurred in 40% of patients with cough and in four (20%) control subjects (p > 0.05). Eosinophils were present in the sputum of more patients with cough than control subjects (50% versus 19%; p < 0.05). High degrees of eosinophilia were present in six patients with cough, including three without BHR. No subject had significant lipid-laden macrophages. There was greater somatization in patients with chronic cough; ten subjects scored in the clinically significant range (p < 0.05). Abnormalities in one or more of these tests were 7.67-fold (95% CI 1.83-34.52) more likely to occur in cough patients than control subjects. We conclude that chronic cough is a nonspecific symptom that is associated with several apparently unrelated mechanisms. These include UAHR, somatization, BHR, and eosinophilic bronchitis. UAHR cannot be implicated as a single unifying mechanism. These findings emphasize the need to systematically evaluate several different causes of cough in patients who present with chronic cough.

Adult↗
PubMed1997

Higher order regularization techniques for inverse electrocardiography.

We have previously presented the generalized eigensystem (GES) approach as an alternative to truncated singular value decomposition and zero order Tikhonov regularization methods for the ill-conditioned inverse problem of electrocardiography. In this paper we extend our comparison of GES with Tikhonov regularization utilizing higher order regularizers applied to a realistic heart/torso geometry with measured epicardial and body surface potentials. Utilizing higher order regularizers the results from Tikhonov regularization more closely match those of the GES techniques.

Animals↗
PubMed1996

Emerging issues in sleep-disordered breathing.

Community studies of problems with breathing during sleep suggest that sleep-disordered breathing is a better general term than sleep apnoea. Male sex, increasing age and increasing neck size are the main factors differentiating people with from those without sleep-disordered breathing. The contribution of sleep-disordered breathing to morbidity has not been established. Future research should address the possible cardiovascular associations of sleep-disordered breathing, its impact on sleepiness in the community, and the cost-effectiveness of treatment.

Australia↗
PubMed1996

Nasal inflammation and chronic ear disease in Australian Aboriginal children.

OBJECTIVE: Chronic middle ear disease is common in Aboriginal children, and may be linked to nasal inflammation and Eustachian tube dysfunction. The pattern of nasal inflammation is unknown. The study reported here was performed to define the role of allergy and infection in causing nasal inflammation in Aboriginal children with chronic middle ear disease. METHODOLOGY: Thirty-one Aboriginal children aged between 3 and 7 years underwent clinical assessment, audiometry and allergy skin tests. Nasal swabs for bacterial culture and cytology were performed during the winter and again in spring to identify any seasonal variation. A randomized trial of nasal beclomethasone for 8 weeks was conducted in children with abnormal tympanometry to identify the effect of therapy upon nasal cytology. RESULTS: Twenty-six of the 31 children had abnormal tympanograms. Average hearing levels were reduced in nine children. Pathogenic organisms were isolated from most children: Streptococcus pneumoniae (82%), Haemophilus influenzae (79%), Moraxella catarrhalis (39%) and Staphylococcus aureus (29%). Eight of the 31 children (26%) were atopic. Nasal cytology disclosed a marked neutrophil infiltrate (80% of cells) during the winter, which fell significantly in spring to 52% of cells. Only two subjects had nasal eosinophilia of >10%. There was no effect of beclomethasone on nasal cytology. CONCLUSIONS: Chronic ear disease in Aboriginal children is associated with nasal inflammation, neutrophil infiltration and the presence of bacteria. These features suggest respiratory infection as the main cause of chronic nasal inflammation in Aboriginal children with middle ear disease. There is a seasonal variation in the severity of the nasal infiltrate, consistent with increased infections during winter. Despite a high prevalence of atopy, allergic nasal disease was uncommon.

Anti-Inflammatory Agents↗
PubMed1996

A community survey of insomnia in Newcastle.

This study aimed to estimate the prevalence of sleeping difficulty in an urban community and the frequency with which those with sleep difficulty seek medical care and use prescribed medication for sleep. Randomly selected persons aged over 16 years were invited to participate in a telephone survey. A total of 628 individuals was approached and 535 (85 per cent) were interviewed. Older subjects, women and those not in paid employment were overrepresented in the sample. Difficulty sleeping often or always was reported by 17 per cent of men and 25 per cent of women. Of subjects with difficulty in sleeping, 31 per cent had sought medical care. There was no difference between men and women in this regard. Use of prescription medication was reported by 20 per cent of men and 29 per cent of women with sleep difficulty.

Adolescent↗
PubMed1996

Vector expansion techniques for the inverse problem of electrocardiography: application to a realistic heart-torso geometry.

We have previously compared four numerical techniques utilizing both a homogeneous and inhomogeneous eccentric sphere model problem. In those studies we found that the Generalized Eigensystem approach generally gave superior performance over both truncated singular value decomposition and zero order Tikhonov regularization. In this paper we extend the comparison to the case of a realistic heart-torso geometry. With this model, the generalized eigensystem approach again provides superior performance as measured by both relative error and correlation coefficient.

Animals↗
PubMed1995

Using quality-control analysis of peak expiratory flow recordings to guide therapy for asthma.

OBJECTIVE: To compare the action points in published asthma management plans with those derived from quality-control analysis of peak expiratory flow recordings. DESIGN: Longitudinal observational study. SETTING: An ambulatory asthma education and management program in a tertiary care hospital. PATIENTS: 35 adults with asthma and exacerbation of asthma. MEASUREMENTS: Peak expiratory flow diaries and symptom recordings. RESULTS: Asthma action points from published asthma management guidelines had poor operating characteristics. The success rate was 35% when the action point was a peak expiratory flow rate less than 60% of the patient's best peak flow. The success rate improved to 88% when the action point was a peak expiratory flow rate less than 80% of the patient's best peak flow. Published action points had a high failure rate. Peak flow decreased to below the published action points during a stable period of asthma in 7% to 51% of patients studied. Action points defined using quality-control analysis did significantly better. A peak flow value less than 3 standard deviations below the patient's mean peak flow detected 84% of exacerbations and had a low failure rate (19%). Other quality-control tests had sensitivities of 91% and 71%. Quality-control action points could detect exacerbations up to 4.5 days earlier than conventional methods. CONCLUSIONS: Individualized action points can be derived for patients with asthma by applying quality-control analysis to peak flow recordings. These action points are more sensitive in detecting exacerbations of asthma and have fewer false-positive results. Action plans developed in this manner should be more useful for the early detection of deteriorating asthma.

Adrenal Cortex Hormones↗