Biomedical subjects

H W Woo

Publications and source records attributed to H W Woo.

5 recordsLinked to original sources

PubMed1992

Permeability of arachidonic acid metabolites through the round window membrane in chinchillas.

Our previous studies showed that samples of middle ear effusion contain high concentrations of arachidonic acid metabolites (AAMs); both prostaglandins (PGs) and leukotrienes (LTs). Since abnormal levels of AAMs in the perilymph seem to be associated with salicylate ototoxicity and the round window membrane (RWM) is the most likely route of entry from the middle ear to the inner ear, it would be important to know the permeability of AAMs through the RWM. Permeability of AAMs was determined by applying labeled and standard representatives AAMs on the RWM and counting radioactivity or measuring concentrations of AAMs in perilymph at different time intervals. Using chinchillas as experimental animals, samples of perilymph were obtained through a fenestration made at the helicotrema of the cochlea after 0.5, 1, 2, and 4, hours from placing tritiated or standard PGE2, 6-keto-PGF1 alpha, LTB4, LTC4 and 15-hydroxyeicosatetraenoic acid (HETE) over RWMs. Radioactivity in the perilymph was determined by a scintillation counter and concentrations of AAMs were measured by reverse phase high performance liquid chromatography (RP-HPLC) and radioimmunoassay. AAMs, which are twenty carbon fatty acids, were found to cross the RWM readily. Radioactivity and concentrations of AAMs in perilymph were detected in 30 minutes and peaked by one hour from the application of AAMs on the RWM. The results of this study suggest that AAMs such as PGs and LTs present in the middle ear fluid can cross the RWM readily and enter into the perilymphatic space of the cochlea. Sensorineural hearing loss observed in chronic otitis media could be mediated by PGs and LTs in the middle ear effusion crossing over to the inner ear through the RWM.

Adrenal Cortex Hormones↗

PubMed1987

A prototype system and reconstruction algorithms for electrical impedance technique in medical body imaging.

We have developed an impedance imaging system to reconstruct cross-sectional images of the body's electrical characteristics based on static tissue impedance. The hardware system consists of a data collection subsystem and the Intel 380 host microcomputer system with an Intel 80286 microprocessor, an Intel 80287 numeric data processor, and an Intel 80186 microprocessor-based display board. The system is capable of initiating a data collection from an array of current-sensing electrodes and reconstructing impedance images based on these data measurements. We have tested the data collection subsystem with physical phantom models, and we have found that the prototype system is capable of discriminating high resistivity regions in contrast with the low resistivity background. Our system is flexible in that each electrode's function (sensing currents, applying voltages, grounding body surfaces, and disconnected from the body) can be programmed individually so that a variety of electrode configurations for different projection techniques can be tested for optimal system performance. Various reconstruction algorithms have been developed and tested particularly for this imaging modality. Since a computer body model is needed for some impedance reconstruction algorithms, we have created two- and three-dimensional computer body models based on the finite element method approach, and verified our finite element modelling technique by building physical phantoms and comparing measured experimental results with simulation results predicted by the computer model. We have found that the sensitivity is a function of position, pixel size (image resolution) and background resistivity. We have also tried to compensate the low sensitivity of impedance changes in the central region.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗

PubMed1986

Advantages and applications of the centerline method for characterizing regional ventricular function.

We sought to identify theoretical advantages and applications of the centerline method for quantitative assessment of regional ventricular function. Motion was measured along 100 chords constructed perpendicular to a centerline drawn midway between the end-diastolic and end-systolic contours, and normalized for heart size. Abnormality was expressed in units of standard deviations from the mean motion in a normal reference population to indicate both the severity and significance of the wall motion abnormality. The mean abnormality averaged over 100 chords correlated highly with the area ejection fraction (r = .97). The centerline method uses a "sliding window" to measure motion where it is abnormal, because assessment of wall motion in predefined regions of the ventricular contour underestimates abnormality. From the 100 data points, the extent (% of contour) of regional abnormalities can also be determined. The severity of hypokinesis at the site of acute myocardial infarction correlated better with infarct size estimated from creatine kinase release (r = -.78) than did the ejection fraction or the circumferential extent of hypokinesis. Because the centerline method measures motion along locally determined vectors, and requires no apex, origin, coordinate system, or geometric reference figure, it can be applied to contours as dissimilar as the 60 degree left anterior oblique projection of the left ventricle and the 75 degree left anterior oblique projection of the right ventricle.

Computers↗

PubMed1985

Development and applications of an interactive digital filter design program.

We have implemented an interactive digital filter design program in the HP 1000 computer at the Department of Electrical Engineering of the University of Washington. This program allows users to design different types of filters interactively with both amplitude and phase responses displayed on graphic devices. The performance of each designed filter can be evaluated conveniently before the best one is chosen and implemented for any particular application. This program can design recursive filters, e.g. Butterworth, Chebyshev and elliptic, or nonrecursive filters with one out of six different windows, i.e. rectangular, triangular, Hann, Hamming, Blackman and Kaiser. The main outputs from this program are coefficients of a transfer function of an analog filter, a digital filter, or both. Therefore, the design of both analog and digital filters is facilitated by using this program. The program is very simple to use and does not require background in analog or digital filter principles in order to run it. The program is written in standard FORTRAN and is about 30 kbytes in size excluding the graphics display routines. Since it uses standard FORTRAN, it can be easily transported to minicomputer and microcomputer systems that have a FORTRAN compiler and minimal graphics capabilities. This program is available for distribution to interested institutions and laboratories.

Biometry↗

PubMed1983

Value of partial ejection fraction, volume increment, and regional wall motion in identifying patients with clinically significant coronary artery disease.

Recent studies suggest that the partial ejection fraction (EF) in early systole is a more sensitive index of left ventricular (LV) dysfunction than the holosystolic EF. We examined LV volume, partial EF, and volume increment at each of 12 time points in systole to determine which parameter best distinguishes normal subjects from patients with coronary artery disease (CAD). Contrast ventriculograms, obtained either in the right anterior oblique projection (60 frames/sec) or in the biplane projection (30 frames/sec), of 58 normal subjects and 68 patients with CAD were studied. The endocardial contour in each frame of a sinus beat was traced to derive a volume curve. At each twelfth of systole, LV volume was extrapolated from the curve and the partial EF was calculated. The increment in volume between successive time points was also calculated. Both partial EF and LV volume in patients with CAD became progressively more abnormal with time; peak abnormality occurred at end-systole. In a subgroup of patients with CAD who had normal holosystolic EF, both partial EF and volume were normal throughout systole. The increment in volume with each twelfth of systole in patients with CAD deviated less than 1 SD from normal throughout systole. Thus, maximum abnormality in partial EF and volume occurs at end-systole. Of the parameters of global LV function tested, holosystolic EF best distinguishes patients with CAD from normal subjects. However, regional wall motion measured in the area of interest is more sensitive to localized abnormality, the severity of which may be overestimated or underestimated by the EF due to hyperkinesis or hypokinesis in other regions of the left ventricle.

Cardiac Catheterization↗