Search PubMed⌕ Search

Biomedical subjects

K K Chan

Publications and source records attributed to K K Chan.

At least 163 records · Page 9Linked to original sources
PubMed1987

Microcomputer-based programs for calculating mean and variance residence time by the method of prospective areas.

A published package of microcomputer-based pharmacokinetic programs has been expanded to include programs to calculate mean and variance above the residence time (MRT and VRT) using the method of prospective areas. Three programs, one for plasma concentration time data, one for urinary excretion data, and one for in-vitro dissolution data, are available. All programs were tested with the data obtained from original articles or from simulated theoretical data. These programs were written in a modular fashion in such a way that they form an integrated software package. In conjunction with the programs previously developed, the user can choose/select how extensively the data are to be analyzed without reentry of data. This is particularly important since proper pharmacokinetic data analysis can only be made by using different calculations with different assumptions. Graphic display and linear regression subroutines are included in each module to simplify operation for the user. The modular design also facilitates modifications, upkeep, and accommodation to new methods of calculation.

Computers↗
PubMed1987

White matter damage following acute head injury.

The study of a series of brains from patients who had a severe head injury and died within 72 h without a lucid interval showed that there was a step-wise progression in the development of retraction balls. At 2 h after injury sinusoidal enlargement of the axons was evident. This progressed over 16 h when the lesions appeared as retraction balls which were fully developed at 72 h. There was a similar increase of staining with an immunoperoxidase method for glial fibrillary acid protein (GFAP) initially around blood vessels spreading diffusely into the white matter. The number of reactive astrocytes also increased. In a control case where the corpus callosum was torn at post-mortem there were sinusoidally distended and torn axons in the absence of GFAP staining. It is proposed that there are three components to a head injury. First, mechanical injury as seen in the control case; second, the development of retraction balls which are an active process probably representing damaged axons which cannot undergo repair where the sinusoidal swellings develop into retraction balls and third, an astrocytic reaction. The sinusoidal change, when present on its own, may not be separable from post-mortem trauma. However, when it is associated with an astrocytic response it should be correlated with coma in the same way as retraction balls.

Axons↗
PubMed1987

Prognostic factors in borderline and invasive ovarian tumors of the common epithelial type.

Present reports show that surgical factors, response to therapy and histological criteria are important for predicting the prognosis of patients with common epithelial types of ovarian tumors. Newer techniques such as morphometry, DNA cytometry, immunological and immunopathological techniques may help to define prognostic factors even more accurately. As a result, these recently developed methods may enhance the value of well-established classical predictors of the outcome in case of borderline or invasive ovarian tumour.

Carcinoma↗
PubMed1987

Path model of multidimensional compliance with cancer therapy.

Patients newly diagnosed with hematologic malignancies were followed for a 6-month treatment period to assess compliance with three regimen requirements for cancer therapy: anti-neoplastic medication self-administered intermittently, supportive medication self-administered daily, and monthly clinic appointments. The effect on compliance of three intervention "packages" (some combination of education, shaping of pill-taking behavior, and home restructuring) and the extent that patient satisfaction, knowledge, and uncertainty about illness-related events mediated the effects of the interventions were also examined. Blood levels of the drugs and self-report measures indicated that compliance with daily pill taking was higher for each intervention group compared to a control group. Similar results were obtained for compliance with clinic appointments. No improvement in intermittent self-medication was found. Although each intervention package increased patient knowledge and satisfaction, path analyses demonstrated that knowledge did not affect any aspect of compliance, whereas satisfaction was associated with increased appointment keeping only. Daily pill taking was influenced directly by the behavioral components of the interventions. Uncertainty did not influence compliance but was associated with depression, which was negatively correlated with intermittent self-medication.

Administration, Oral↗
PubMed1987

Serial urinary cyclic guanosine monophosphate measurements in the assessment of response to treatment in epithelial ovarian cancer.

Serial measurements of urinary cyclic guanosine monophosphate (cGMP) were performed in 47 patients with epithelial ovarian cancer. In 30 patients, the pre-chemotherapy cGMP level was above the range for normal controls (marker positive); the remainder were within the normal range. Marker positive patients demonstrated a 96% correlation of disease regression with a fall in marker level and a 75% correlation of disease progression with a rise in marker level. The corresponding correlations in the marker negative group were 41% and 39%. Marker positive patients also demonstrated a rise in marker before clinical recognition of disease progression in six of 11 instances whereas only one of nine instances in marker negative patients showed such a rise. Patients with evidence of static disease had normal and stable marker levels.

Chlorambucil↗
PubMed1987

Relation of alveolar size to forced vital capacity in professional divers.

Eight cases have been studied in which both lung function and histological morphometric data was available on divers' lungs. A correlation was found between the increase in forced vital capacity measured at routine annual medical examination and the morphometric measurement of alveoli by mean cord length. The results suggest that reduction of forced expiratory volume in one second may be due to narrowing of small airways by distention of the alveoli.

Adult↗
PubMed1987

Complicated colobomatous microphthalmia in the microphthalmic (mi/mi) mouse.

A study of the development of the eye in the cinnamon mouse, homozygous for the gene for microphthalmia (mi), has shown that the microphthalmia is due to failure of secondary vitreous formation associated with a coloboma. The retina is dystrophic but there is a residual population of large ganglion cells and the optic nerve also contains ganglion cells. All these ganglion cells have cytoplasm similar to the retinal ganglion cells in the normal controls. It is postulated that they communicate with axons in the optic nerve. In addition, the outer epithelial layer of the eye cup, which normally becomes pigmented, forms retinal tissue in the homozygous mouse and this is also true of the dorsal part of the eyestalk near the eye.

Animals↗
PubMed1986

Identification of new metabolites of phosphoramide and nor-nitrogen mustards and cyclophosphamide in rat urine using ion cluster techniques.

The metabolism of nor-nitrogen (NNM) and phosphoramide mustards (PM) and cyclophosphamide (CP) was investigated in the Sprague-Dawley rat using chemical ionization mass spectrometry and ion cluster techniques. Following administrations of a 1:1 mixture of the non-labeled and the corresponding side-chain deuterium-labeled compounds to separate rats, the urinary extracts were screened for cluster ions which were characteristic of the administered compounds and their derived metabolites, and on this basis, tentative identifications of known and new metabolites were accomplished. Combining derivatization, deuterium labeling on strategic locations, gas chromatography/mass spectrometry, and chemical synthesis in some cases, 3-(2-chloroethyl)-1,3-oxazolidin-2-one was identified as a major metabolite for NNM, PM and CP and 3-(2-chloroethyl)-4-hydroxy-1,3-oxazolidin-2-one was identified as a major metabolite for NNM and PM, but a minor metabolite for CP. A new dechlorinated metabolite for CP, 3-(2-hydroxyethyl)-1,3-oxazolidin-2-one, was also identified.

Amides↗
PubMed1986

Simultaneous first- and zero-order absorption of carbamazepine tablets in humans.

The absorption kinetics of carbamazepine (5H-dibenz[b,f]azepine-5-carboxamide) in healthy adult volunteers was investigated following a single 400-mg (2 X 200-mg) oral dose of commercially available conventional tablets (Tegretol). Wagner-Nelson plots of the data from all subjects (n = 10) showed that the fraction remaining to be absorbed declined in a biphasic manner, suggesting a mixed order of absorption. A model assuming the absorption of carbamazepine by simultaneous first-order and zero-order rates was used to describe the overall absorption process. Model parameters (and their mean +/- SD values) were: alpha, the fraction of the dose absorbed at a first-order rate (0.646 +/- 0.070); Ka, the first-order absorption rate constant (0.45 +/- 0.13 h-1); and tdur, the duration of the zero-order absorption component (36.0 +/- 4.4 h). If complete absorption can be assumed, then the corresponding average zero-order rate was 4.0 mg X h-1. The results indicate that 35% of the available dose is absorbed at a zero-order rate. These data suggest a prolonged constant rate of absorption due to continued delivery during its transit in the intestine. In addition, an assessment of the mean absorption time, based on the parameters from the model described above, compared closely (7.95 versus 8.44 h) with the mean absorption time estimated from an analysis of the fraction remaining to be absorbed versus time plot using a noncompartmental approach.

Adult↗
PubMed1986

A new motor-driven surgical probe and its in vitro comparison with the Cavitron Ultrasonic Surgical Aspirator.

The Cavitron Ultrasonic Surgical Aspirator (CUSA) has been applied in neurosurgery for several years, but its mode of action is not yet clear and its efficiency at removing soft tissue has not been quantified. We describe here how we have measured the rate of removing soft tissue per unit time, taking ox-liver tissue as the test material. A motor-driven vibrator/aspirator has been developed in our laboratory. It has permitted us to examine the effect of varying independently frequency, amplitude of the vibration, and suction pressure on the removal rate. The results of this investigation show that beyond a certain tip acceleration amplitude (about 100 g) the removal rate does not increase significantly. Also the removal rate is more or less independent of vibration amplitude within the range between 300 micron and 1 mm. Our in vitro experiments with the new probe show that a tip acceleration of about 100 g is enough to remove ox-liver tissue and then the rate of removal is comparable to that obtained with the CUSA operating at maximum vibration amplitude. Analysis of the particle size of the debris collected from CUSA and from our motor-driven device shows that the particle size distribution is similar over the range of 0.5 micron less than d less than 250 micron.

Animals↗
PubMed1986

Random urinary cyclic 3',5' guanosine monophosphate in epithelial ovarian cancer: relation to other prognostic variables and to survival.

Random urinary cyclic guanosine monophosphate (cyclic GMP) has been measured in a control group of 83 women and in 92 women with histologically proven epithelial ovarian cancer. Forty-eight cancer patients (53%) had levels greater than the mean +2SD of the control population. There was no correlation between urinary cyclic GMP and tumour histology, degree of differentiation or stage. Patients with gross residual disease after laparotomy had higher postoperative levels. This degree of sensitivity in addition to poor specificity for ovarian cancer renders this marker unsuitable for screening purposes. While residual disease state after surgery was found to be the best single predictor of survival, an elevated urinary cyclic GMP level before chemotherapy was found to be an independent adverse prognostic variable.

Adolescent↗
PubMed1986

Management of postconization cervical stenosis by laser vaporization.

In 18 patients with symptomatic cervical stenosis after conization, laser vaporization of the stenotic segment was performed. Total relief of symptoms was achieved in 12 patients and partial relief in four. In seven cases there was no evidence of stenosis at follow-up, and in a further nine cases the degree of stenosis was less. In seven cases it was possible to visualize the squamocolumnar junction at follow-up. This had not been possible in any cases before the procedure. Vaporization using the carbon dioxide laser provides a useful conservative management technique for postconization stenosis.

Adult↗
PubMed1985

Assessment of drug absorption after oral administration.

Simulated data using a linear two-compartment body model (2CBM) with drugs having different absorption characteristics and dosage forms with different dissolution rates were used to evaluate the inherent problems of pharmacokinetic data analysis (flip-flop phenomenon and vanishing exponential terms). When absorption from solution is slow or release from the solid dosage form is rate limiting, the characteristic nose of the 2CBM was lost and a one-compartment model prevailed. After the 2CBM disposition kinetic parameters were obtained from solution data, absorption kinetics were evaluated by the Loo-Riegelman method. The data were also evaluated by the statistical moments method. The statistical moments method consistently demonstrated superiority in regard to providing reliable results and ease in calculation. The information provided can be particularly useful for in vivo-in vitro correlation.

Administration, Oral↗
PubMed1985

Kinetics of hydrochlorothiazide absorption in humans.

The kinetics of absorption of hydrochlorothiazide was studied in four adult male volunteers. Plasma levels were monitored for 48 h after a 100-mg dose. Food, electrolyte, and water intake were regulated as far as possible. The plasma level data were fitted to a two-compartment open model with either first-order or zero-order absorption, using the pharmacokinetic computer program AUTOAN. A better fit of the data, both graphically and statistically, was obtained with zero-order absorption kinetics. Additional confirmation of absorption kinetics was obtained by treating the plasma level results by the Loo-Riegelman method. Cartesian graphs of the amount absorbed verus time afforded linear plots, which indicate a zero-order process.

Administration, Oral↗