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Biomedical subjects

J J Bailey

Publications and source records attributed to J J Bailey.

At least 19 recordsLinked to original sources
PubMed1992

A kinetic model of CD4+ lymphocytes with the human immunodeficiency virus (HIV).

This report describes a kinetic model of in vitro cytopathology involving interactions of human immunodeficiency virus (HIV) with CD4+ helper T lymphocytes. The model uses nonlinearly coupled, ordinary differential equations to simulate the dynamics of infected and uninfected cells and free virions. It is assumed that resting cells are more readily infected than activated cells, but once infected, only activated cells produce more virus. Resting cells can be activated by some appropriate stimulus (e.g. phytohemagglutinin, soluble antigen). The model predicts that the initial inoculum of virus is taken up by resting cells and without stimulation the system comes to a steady state of two populations, namely infected and uninfected cells. Stimulation of this system produces two additional populations, namely infected and uninfected activated cells which, along with the previous populations, exhibit cyclic behavior of growth, viral expression/release, and death. Additional stimuli enhance or diminish the cyclic behavior depending upon their occurrence in time. These simulations suggest a similar dynamics in human HIV infection and may explain a major factor responsible for the widely varying depletion rate of (CD4+) helper T cells in AIDS patients.

CD4-Positive T-Lymphocytes↗
PubMed1991

A filter to suppress ECG baseline wander and preserve ST-segment accuracy in a real-time environment.

Accurate monitoring of the ST-segment displacements in real-time environments can be distorted by the nonlinear phase response of a baseline filter such as the single-pole, high-pass (0.5 Hz) filter that is standard in the industry today. The authors have previously constructed a four-pole null phase (1.0 Hz) filter that is nearly ideal in suppressing baseline wander while preserving ST-segment accuracy; however, this foreward/backward filter requires capture of a large ECG segment before filtering, thereby producing a delay that is unacceptable in a real-time environment. As a practical compromise, a two-pole, phase-compensated (1.0 Hz) filter was constructed while introducing a small time delay (160 ms). It performs much better than the "standard filter" and almost as well as the "ideal" filter in several tests, namely (1) suppression of baseline wander in a series of ECGs, (2) suppression of artificial baseline, (3) response to a triangular impulse wave (American Heart Association test), and (4) J-point displacement in several ECGs.

Cardiomegaly↗
PubMed1989

Progress on the CSE diagnostic study. Application of McNemar's test revisited.

The authors describe an extension of McNemar's test that can be used to compare diagnostic performance when multiple statements are obtained from computer analysis or visual interpretation of the ECG. If two or more diagnostic statements are made, by definition only one can be correct for the cases in the CSE pilot database, which were selected for single, clinically well documented, abnormalities. If one statement stood out from others as being made with the highest degree of certainty, that was accepted as the single interpretation, right or wrong. However, when two or more statements were made with the same degree of certainty and only one statement was correct, then in the previous application of McNemar's test that interpretation was given credit for being correct. In the extension of the method presented in this article, such an interpretation is given partial credit for the one correct statement and partial discredit for any incorrect statement, thereby reporting the results more properly in the sensitivity and specificity statistics for the different diagnostic categories.

Algorithms↗
PubMed1989

Nonparametric comparison of entire ROC curves for computerized ECG left ventricular hypertrophy algorithms using data from the Framingham Heart Study.

A computer program may be capable of several different statements for left ventricular hypertrophy (eg, possible LVH, probable LVH, consistent with LVH), but such statements resulting from discretized levels of sensitivity/specificity would represent only isolated points on a receiver-operating characteristic (ROC) curve, which is a plot of all levels of sensitivity versus specificity. Even if two algorithms use the same discrete scales, their performances may not readily be compared. The authors present a comparison methodology for ROC curves using ROC area as a nonparametric measure of the ability of the algorithm to separate the two populations; the ROC area ranges from 0.5 (no ability) to 1.0 (perfect separation) and is unbiased if the normal versus abnormal populations have no common values for the measurement. The methodology compares the performance of ECG algorithms on the same population of cases by testing for significant differences of ROC areas and incorporating correlation of the algorithms in a nonparametric way. To illustrate this methodology, they use ECG and echocardiographic data from the Framingham Heart Study.

Algorithms↗
PubMed1989

Suppression of baseline wander in the ECG using a bilinearly transformed, null-phase filter.

The purpose of this study was to design and test a bilinearly transformed, null-phase (BLT/NP) filter for removing baseline wander and to compare it with the cubic spline for performance. For this purpose, the ECG data were filtered to remove high-frequency noise and low-frequency baseline wander to form a set of "clean" ECGs. Artificial low-frequency noise mimicking typical baseline wander was constructed from sine and cosine waves at 0.20 and 0.45 Hz and with amplitudes of 400 and 300 microV, respectively, and added to the "clean" ECGs to form the "test" ECGs. The BLT/NP filter and the cubic spline method each were applied to a "test" ECG to form a "restored" ECG. The measure of performance was the root mean square difference (RMSD) between the "restored" ECG and the initial "clean" ECG. RMSD values showed that on the average the BLT/NP filter performed as well as the cubic spline method and has the advantage that accurate determination of the QRS onset is not required.

Algorithms↗
PubMed1987

Studies of Trypanosoma cruzi clones in inbred mice. III. Histopathological and electrocardiographical responses to chronic infection.

Histopathological and electrocardiographical (ECG) changes occur in the heart of C3H/HeN and C57BL/6 mice infected for 1 year with Trypanosoma cruzi clones Sylvio-X10/4 (X10/4), Miranda/78 (M/78), or Miranda/80 (M/80). Heart parasitism and a variable degree of inflammation occurred following infection with clones X10/4 or M/78 but not with M/80. Clone X10/4 caused more extensive myocardial inflammation and fibrosis than clone M/78. Myocardial fibrosis was more extensive in C3H than in C57 mice infected with clone X10/4. The normal ECG pattern of C3H mice is distinctly different from C57 mice. The PR intervals of mice infected with clone X10/4 greater than M/78 greater than M/80 approximately equal to controls. ECG abnormalities occurred more frequently in mice infected with clone X10/4 than in controls or mice infected with either M/78 or M/80 regardless of strain or sex and were generally more severe in C57 than in C3H infected with X10/4. First degree atrioventricular block occurred more frequently in C3H mice infected with clone X10/4 or M/78 and C57 mice infected with X10/4 than in all other groups. Complete atrioventricular dissociation occurred frequently in C57 mice infected with X10/4 and rarely in other mice. These results demonstrate that the myocardial response of mice to T. cruzi infection, both histological and electrophysiological, is modulated by both the mouse strain and the parasite isolate used.

Animals↗
PubMed1987

The emerging prominence of computer electrocardiography in large population-based surveys.

The year 1987 marks the centennial of electrocardiography. As Beamish reminds us, it was the first and foremost technical aid to the cardiologist. During the history of cardiovascular epidemiology, which dates back roughly forty years, electrocardiography has played a central role as a relatively specific marker for coronary and hypertensive heart disease. The lack of sensitivity of electrocardiography and the advent of new technologies such as ultrasonography for assessment of such heart disease in cardiology and cardiovascular epidemiology has raised questions as to whether electrocardiography might be replaced in the next century. Recent developments in computer electrocardiography have rendered suggestions of the decreased importance of electrocardiography premature. Use of computer analysis of electrocardiograms in epidemiologic studies, which dates back less than three decades, has renewed interest in and expanded the role of electrocardiography in cardiology in general and cardiovascular epidemiology in particular. The computer analysis of electrocardiograms has allowed the processing and analysis of large numbers of electrocardiograms in a rapid, efficient, systematic and consistent manner. This has led to new, more sensitive criteria for detection of left ventricular hypertrophy as a discrete variable. In addition, the numerous waveform amplitude and duration measurements by computer have allowed the development of mathematical models to express the likelihood of coronary heart disease (myocardial infarction) and degree of left ventricular hypertrophy (estimates of left ventricular mass) on continuous scales. These developments have contributed substantially to the potential of electrocardiography (and particularly computer electrocardiography) in future studies and clinical applications.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiomegaly↗
PubMed1987

Electrocardiographic changes with advancing age. A cross-sectional study of the association of age with QRS axis, duration and voltage.

In order to examine the electrocardiographic (ECG) changes which occur with advancing age we defined an apparently healthy reference population derived from prospectively followed subjects of the Framingham Heart Study. Healthy subjects were clinically free of hypertension, coronary artery disease, congestive heart failure and valve disease and were not taking antihypertensive or other cardiac medications. ECG tracings were analyzed by the IBM Bonner (V2) program. Mean values and correlations with age for PR duration, QRS duration and axis, S wave voltage V1 and R wave voltage V5 are presented. With advancing age in men there is a narrowing of QRS, a leftward QRS axis shift, and a loss of S V1 and R V5 amplitude. In women only a leftward QRS axis shift is associated with advancing age. These changes should be considered in defining normal age- and sex-specific reference values. These findings underscore theoretical limitations of commonly-used criteria for the ECG diagnosis of conditions such as left ventricular hypertrophy.

Adult↗
PubMed1979

A comparison of simultaneous measurements of systolic function in the baboon by electromagnetic flowmeter and high frame rate ECG-gated blood pool scintigraphy.

Left ventricular (LV) systolic timing and relative volume variations were simultaneously measured by electromagnetic flowmeter (EMF) and high frame rate ECG-gated blood pool scintigraphy in five baboons. No significant differences (p greater than 0.1, paired t test) were observed in the time (from R wave) to peak aortic flow (maximum LV ejection rate), time to cessation of aortic flow (end-systole) or in the duration of aortic flow (LV ejection time). A small (approximately 15 msec) but significant systematic difference (p less than 0.02) was noted in the time to onset of aortic flow. The shape of each scintigraphic time-activity curve during systole was compared to an equivalent curve synthesized from 10 EMF flow profiles obtained in the same baboon. Comparison of these paired curves over systolic ejection yielded an average correlation or r = 0.95 (range 0.90--0.99). The ratio of peak flow to stroke volume determined from these data did not differ significantly (p greater than 0.05). In the baboon, quantitative high temporal resolution ECG-gated scintigraphy appears to reflect closely the detailed timing and relative magnitude variation of LV volume during the entire period of systolic ejection. We conclude that the assumptions underlying the scintigraphic method are valid in the baboon during the ejection interval.

Animals↗