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Biomedical subjects

B J West

Publications and source records attributed to B J West.

At least 37 records · Page 2Linked to original sources
PubMed1987

Applications of nonlinear dynamics to clinical cardiology.

(1) Nonlinear mechanisms may apply both to the understanding of SA-AV node interactions and to bifurcations leading to certain types of AV block. (2) The fractal His-Purkinje system serves as the structural substrate for the generation of the broadband, inverse power-law spectrum of the stable ventricular depolarization (QRS) waveform. (3) Fractal anatomy is also seen in multiple other systems: pulmonary, hepatobiliary, renal, etc. Fractal morphogenesis may reflect a type of critical phenomenon that results in the generation of these irregular, but self-similar structures. (4) Self-similar (fractal) scaling may underlie the 1/f-like spectra seen in multiple systems (e.g., interbeat interval variability, daily neutrophil fluctuations). This fractal scaling may provide a mechanism for the "constrained randomness" that appears to underlie physiological variability and adaptability. (5) Behavior consistent with subharmonic bifurcations is seen in cardiac electrophysiology (e.g., sick sinus syndrome) and hemodynamic perturbations (e.g., swinging heart phenomenon in pericardial tamponade). (6) Ventricular tachyarrhythmias associated with sudden cardiac death (e.g., torsades de pointes, ventricular fibrillation) appear to reflect relatively periodic, not chaotic (turbulent) processes resulting from disruption of the physiologic fractal depolarization sequence. (7) Spectral analysis of Holter monitor data may help in the detection of patients at high risk for sudden death.

Cardiovascular Diseases↗
PubMed1986

Analysis of demand conditions associated with reluctant speech.

An analysis of five demand conditions affecting the reluctant speech of a preschool child was conducted in the classroom. Results indicated that demand conditions that did not permit escape from academic demand tasks, ignored mute responses, prompted answers and enthusiastically praised verbal responses resulted in higher rates of speech. Further, replication of these procedures across escape conditions resulted in increased speech rates that approximated those of a non-mute peer in the same classroom. Follow-up data at 8 months indicated that in the classroom the subject spoke more often to more people using a greater number of words, subsequent to analysis and intervention. The classroom teacher also reported a marked improvement in speech rate and quality and considered the time spent in analysis worthwhile. The study provides a model for further analysis of conditions associated with reluctant speech.

Behavior Therapy↗
PubMed1986

The role of reinforcement in reactive self-monitoring.

The role of reinforcement in reactive self-monitoring was investigated. Subjects for this study were three mentally retarded adults employed in a sheltered workshop. Changes in productivity rates in a party hat assembly task across experimental conditions (reinforcements, self-monitoring, and self-monitoring plus reinforcement) were evaluated. Findings showed that while reinforcement alone increased productivity, it was to a lesser degree and with less consistency than when combined with self-monitoring. In addition, self-monitoring alone did not increase productivity. These results support the Rachlin and Nelson and Hayes hypotheses that reactive effects of self-monitoring are dependent upon environmental contingencies. The results also showed that self-monitoring increases the salience of reinforcement.

Adult↗
PubMed1986

Beyond the principle of similitude: renormalization in the bronchial tree.

The average dimensions (diameter, length, and volume) of the airways in the mammalian bronchial tree, long thought to be exponential functions of the generation number, are shown to be power laws in generation number modulated by a harmonic variation. These data are satisfactorily described by means of a functional scaling relation--renormalization group property--between successive generations for the average variable of interest. This type of scaling may provide a mechanism for the morphogenesis of complex but highly stable structures.

Animals↗
PubMed1985

Bronchial asymmetry and Fibonacci scaling.

The irregular branching pattern of the bronchial tree in multiple mammalian species is consistent with a process of morphogenetic self-similarity described by Fibonacci scaling.

Animals↗
PubMed1985

On a mechanism of cardiac electrical stability. The fractal hypothesis.

Electrical activation of the ventricles via the His-Purkinje system is represented on the body surface by a waveform with a broad range of frequency components. We speculate that this process is mediated by current flow through a fractal-like conduction network and therefore that the broadband spectrum of the depolarization waveform should be scaled as a power-law distribution. The prediction is confirmed by Fourier analysis of electrocardiographic data from healthy men. This observation suggests a new dynamical link between nonlinear (fractal) structure and nonlinear function in a stable physiologic system.

Adult↗
PubMed1984

Physician decision-making--evaluation of data used in a computerized ICU.

New instrumentation, techniques and computers have made such large amounts of information rapidly available to ICU clinicians that there is now a danger of information overload. To help with this problem at LDS Hospital, a computerized system was implemented in the Shock-Trauma ICU. This ICU is almost totally computerized with each patient's physiologic, laboratory, drug, demographic, fluid input/output and nutritional data integrated into the patient's computer record. In the ICU, physician decision-making takes place in two situations: during rounds and on-site. For this study, data usage in decision-making was evaluated in both of these environments. The items of data used in decision-making were tabulated into six categories: bedside monitor, laboratory, drugs, input/output and IV, blood gas laboratory, observations and other. Comparisons were made between the portion of the computerized database occupied by a category and its use in decision-making. Combined laboratory data (clinical, microbiology and blood gas) made up 38 to 41% of total patient data reviewed and occupied 16.3% of the database. Observations made up 21-22% of the data reviewed and occupied 6.8% of the database. Drugs, input/output and IV data usage ranged from 13% to 23%, but occupied 36% of the database. Bedside monitor data usage was 12.5% to 22% and occupied 32.5% of the database. The 'other' category, used 2.5% to 5% of the time, made up 8.4% of the database. These results indicate that patient data collection and storage must be evaluated and optimized. This evaluation, along with implementation of the computerized ICU Rounds Report developed for optimal data presentation, will help physicians to evaluate patient status and should facilitate effective decisions.

Diagnosis, Computer-Assisted↗
PubMed1982

Fractal dimensionality of Lévy processes.

We determine the fractal dimensionality D of the trajectories of a class of translationally invariant Markov processes. We also provide two simple operational measures to estimate D.

Journal Article↗
PubMed1980

Evaluating commercially available spirometers.

This study was designed to: (1) determine the performance characteristics of available spirometers; (2) assess the practically and applicability of the American Thoracic Society's (ATS) Snowbird Workshop recommendations on Standardization of Spirometry; and (3) determine whether spirometer testing could be done with room air. Nineteen spirometers were tested with 16 different forced vital capacity waveforms. Fourteen spirometers met the ATS forced vital capacity requirements. Three of these 14 spirometers had difficulties in determining the end of expiration. Fourteen of the devices tested met the requirements for forced expiratory volume in one second. Ten of 13 devices tested for maximal voluntary ventilation were satisfactory. The standards recommended by ATS were believed to be applicable and practical. The testing methods recommended by ATS need to be expanded to include more patient waveforms. Testing with room air is easier and simpler and, for most devices, just as effective as heated and humidified air. We conclude that most available spirometers can faithfully record forced spirograms and that if a spirometer meets the ATS requirements, it makes no difference on which device the spirogram is recorded.

Evaluation Studies as Topic↗
PubMedDate not supplied

Seasonality of birth and conception to teenagers in Texas.

We study the births to teenagers during the years 1964-2000 and analyze separately the three main racial/ethnic groups in Texas (White, Hispanic, and African American), as well as married and unmarried teens during the years 1994-2000. By using traditional statistical methods of analysis and a filter based on the multiresolution wavelet analysis, we draw inferences about the times of the year when adolescent females of different racial/ethnic and marital groups have the highest probability for pregnancy ending in live birth. Multiple factors influencing teen pregnancy are identified and associated with temporal features of social, cultural, educational, and familial processes. In particular, we detect links between unmarried teen conception times and school terms, and weekly birth patterns associated with scheduled c-sections that differ according to racial/ethnic groups.

Adolescent↗