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Biomedical subjects

A C Tan

Publications and source records attributed to A C Tan.

45 records · Page 3Linked to original sources
PubMed1989

Reciprocal changes in atrial natriuretic peptide levels and plasma renin activity during treatment of pulmonary embolism.

We followed atrial natriuretic peptide (ANP) levels in 12 patients during anticoagulant treatment of pulmonary embolism. In each patient with this disorder ANP decreased during treatment. Concomitantly, plasma renin activity (PRA) markedly rose. The decrease in ANP was significantly related to the rise in PRA. No consistent changes in ANP or in PRA were observed in five patients with peripheral venous thrombosis receiving the same anticoagulant treatment. Plasma aldosterone levels did not change in either group.

Adult↗
PubMed1989

Influence of age, posture and intra-individual variation on plasma levels of atrial natriuretic peptide.

This paper describes some factors to which attention should be paid when atrial natriuretic peptide (ANP) values are to be interpreted. Changing from the supine to the sitting position decreased ANP levels, while no further decrease was observed when the upright position was assumed. On the other hand, plasma renin activity (PRA) increased only when changing from the sitting to the upright position. Returning to the supine position decreased PRA, while ANP did not change. Under these conditions plasma aldosterone levels did not differ in any of the four positions. No correlation was observed between the percentage changes of ANP, PRA and aldosterone. ANP values measured in 66 healthy subjects positively correlated with age (r = 0.59, P less than 0.01). To study intra-individual variation, ANP was sampled eight times within one hour. The mean, standard deviation and the coefficient of variation (CV) for each subject were calculated. The CV of 9 out of 15 subjects significantly exceeded the intra-assay coefficient of variation (7.0%), thereby indicating that ANP levels, like those of many other hormones, may exhibit endogenous fluctuations.

Adult↗
PubMed1988

A sensitive radioimmunoassay of atrial natriuretic peptide in human plasma; some guidelines for clinical applications.

We report the development of an in-house RIA for human alpha-ANP. The method requires the extraction of EDTA-plasma on C18-cartridges followed by radioimmunoassay of the eluates with an antibody raised in sheep against human-alpha-ANP coupled to Keyhole Limped Hemocyanin, and a monoiodotyrosyl-alpha-ANP tracer purified with HPLC before use. The assay is precise and sensitive: intra- and interassay coefficients of variation were 8.6% and 11.6%, respectively, and the lower limit of detection was 0.8 pg/tube (4.0 pg/ml plasma). Normal values were 26.0 +/- 15.5 (mean +/- sd) pg/ml plasma (n = 25). Change from supine to sitting position significantly lowered the ANP immunoreactivity. No episodic variations were observed. Our method was applied in a study comparing plasma ANP values in samples of normal persons and CHF-patients. Assay of ANP after extraction using four different antibodies showed significant correlations. HPLC analysis of both plasma of CHF patients and plasma of normal persons revealed the existence of two major immunoreactive components besides alpha-ANP which were not detected in a radioreceptor assay.

Atrial Natriuretic Factor↗
PubMed1987

A sensitive radioimmunoassay of atrial natriuretic peptide in human plasma, using a tracer with an immobilized glycouril agent.

A highly specific and sensitive radioimmunoassay (RIA) for alpha-human atrial natriuretic peptide (hANP[1-28]) in plasma was developed. The assay used a [125I]monoiodotyrosyl-hANP[1-28] tracer, prepared with an immobilized glycouril agent (Protag) and purified by high pressure liquid chromatography (HPLC), and a highly specific antiserum raised against hANP[1-28], coupled to keyhole limpet haemocyanin, in sheep. Plasma was extracted using C-18 Seppak cartridges. A good parallelism was found after dilution prior to extraction of plasma of patients with congestive heart failure (CHF) or of plasma of healthy subjects. Recovery of hANP[1-28] added to plasma was 96%. The limit of detection was 0.8 pg/tube, intra- and inter-assay variation were 9 and 12%, respectively. Mean plasma ANP values in 25 normal persons with a normal salt intake was 26.0 +/- 15.5 (+/- SD) pg/ml. Plasma levels of 18 subjects (7 normals, 11 CHF) were measured using four different antisera after the extraction step. High correlations were found between the values obtained with these four antisera.

Animals↗
PubMed1987

Plasma atrial natriuretic peptide (ANP) in late pregnancy and puerperium.

Plasma concentrations of atrial natriuretic peptide (ANP) were determined ante- and post-partum in 7 healthy primiparous women. ANP was measured at weekly intervals from the 35th week of pregnancy onwards and throughout the puerperium up to the sixth week post-partum. In all seven patients the mean of the ANP values during the first four days post-partum was higher than in late pregnancy. The mean ANP level from the 6th day up to the 42nd day showed a marked decrease compared with the first four days after birth, which, however, did not differ significantly from the mean plasma concentration in late pregnancy. In conclusion, ANP is markedly elevated during the first few days post-partum compared with plasma levels in the normal late pregnancy and the subsequent puerperium.

Adult↗
PubMed1987

Atrial natriuretic peptide--the influence of various physiological and sampling conditions.

A study of various physiological conditions, possibly influencing levels of atrial natriuretic peptide (ANP), is described. Atrial natriuretic peptide was determined by a radioimmunoassay, suitable for routine measurements, using 1 mL of human plasma. Atrial naturetic peptide was adsorbed onto Sep-pak C-18 cartridges, eluted with acidified ethanol and subsequently radioimmunoassayed. The detection limit was slightly less than 2 pg/tube (approximately 5 pg/mL plasma). Intra- and interassay coefficients of variation were 7 and 10%, respectively. Study of various sampling conditions revealed that blood sampling in EDTA-tubes kept on ice, and centrifuged within 1 h, gives the most reliable results. Reference values in 74 individuals ranged between 10 to 69 pg/mL (mean +/- SD = 30 +/- 11 pg/mL). We observed no difference in reference values when the blood sampling procedure was in the sitting (29 +/- 11 pg/mL, n = 43) or supine (31 +/- 12 pg/mL, n = 31) position. Venepuncture stress did not consistently change ANP-levels. No difference was observed in ANP between the follicular and the luteal phase of the menstrual cycle. ANP levels of 7 ambulant female subjects declined significantly during the study period from 7 a.m. to 3 p.m.

Adult↗
PubMedDate not supplied

Pseudo-shading technique in the two-dimensional domain: a post-processing algorithm for enhancing the Z-buffer of a three-dimensional binary image.

Three-dimensional (3D) medical graphics is becoming popular in clinical use on tomographic scanners. Research work in 3D reconstructive display of computerized tomography (CT) and magnetic resonance imaging (MRI) scans on conventional computers has produced many so-called pseudo-3D images. The quality of these images depends on the rendering algorithm, the coarseness of the digitized object, the number of grey levels and the image screen resolution. CT and MRI data are fundamentally voxel based and they produce images that are coarse because of the resolution of the data acquisition system. 3D images produced by the Z-buffer depth shading technique suffer loss of detail when complex objects with fine textural detail need to be displayed. Attempts have been made to improve the display of voxel objects, and existing techniques have shown the improvement possible using these post-processing algorithms. The improved rendering technique works on the Z-buffer image to generate a shaded image using a single light source in any direction. The effectiveness of the technique in generating a shaded image has been shown to be a useful means of presenting 3D information for clinical use.

Algorithms↗