Search PubMed⌕ Search

Biomedical subjects

C C Chen

Publications and source records attributed to C C Chen.

At least 469 records · Page 26Linked to original sources
PubMed1993

Loading and filtration characteristics of filtering facepieces.

Most filtering facepieces used today are made of electret material (material with significant electrical charges on the filter fibers). Because of the addition of this electrical removal force, the filtration efficiency can be significantly increased without increasing the air pressure drop inside the respirator; pressure drop is closely related to physiological load. However, the removal by electrical forces is reduced in time, as aerosols deposit on the filter fibers. We have studied the contribution of this electrical removal and its change in time as a function of aerosol loading. To prove the change in aerosol penetration is due to the reduction of electrical force, the electrical charges were removed from new facepieces by the application of appropriate chemicals. The dust-mist filtering facepieces tested have similar fiber diameters and packing densities, as determined by scanning electron microscopy and pressure drop data. At a face velocity of 10 cm/s (corresponding to 100 L/min through a complete filtering facepiece) and an aerosol size of 0.16 microns, electrical force removal accounts for 69% of the total filtration for the respirator found to have the best filter quality but only 25% for the respirator (from a different manufacturer) found to have the worst filter quality. Our experimental data show that the removal efficiency of these facepieces is reduced in time by as much as this amount. However, under normal wear conditions, the total aerosol particle load is not as high as shown and the filtering facepieces are likely to be discarded before the fiber charges (i.e., the electrostatic attractions) are significantly diminished.

Aerosols↗
PubMed1993

Plasma concentrations of immunoreactive inhibin and gonadotropins following removal of ovarian follicles in the domestic hen.

In the domestic hen, the preovulatory follicles are arranged in a hierarchy. The largest (F1) follicle ovulates first, the second largest (F2) follicle ovulates approximately 26 h later, and so on. The nature of this regulation is not known. Inhibin has been implicated in the feedback regulation of FSH in mammals, and bioactive as well as immunoreactive inhibin has been demonstrated in chickens. The present experiments were conducted with two aims: 1) to determine the plasma level of immunoreactive inhibin in response to removal of various numbers of preovulatory follicles and 2) to assess the gonadotropin response to such follicle removal. In experiment 1, the F1 (n = 4), F1 + F2 (n = 5), F1 + F2 + F3 (n = 5), and F1 + F2 + F3 + F4 (n = 4) follicles were removed surgically. Sham-operated animals served as controls. Blood samples were taken at time 0 (prior to surgery) and at 6, 24, and 48 h after surgery. In experiment 2, animals were sham-operated (n = 5) or the F1-F4 (n = 4) or F1-F4 plus small yellow follicles (SYF; n = 5) were removed. Blood samples were removed at time 0 and at 3, 6, and 24 h and at daily intervals until Day 10 after surgery. In both experiments, plasma immunoreactive inhibin was significantly lowered (p < 0.001) and plasma FSH was acutely increased (p < 0.05) by follicle removal. Plasma LH was decreased at some time points after follicle removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Bone mineral density in patients with noninsulin-dependent diabetes mellitus by dual photon absorptiometry.

Bone mineral density (BMD) in 38 male patients with noninsulin-dependent diabetes mellitus (NIDDM) was measured by dual photon absorptiometry (DPA) using a M & SE OsteoTech 300 scanner. The BMD of the second to fourth lumbar vertebrae was measured and the mean density was presented as g cm-2. The patients were distinguished according to the following three criteria: (1) blood sugar control was good or poor; (2) the duration of diabetes was long or short; (3) renal function was evaluated by effective renal plasma flow (ERPF) as good or poor. The results showed about half the cases of NIDDM had lower BMD. The patients with poor blood sugar control, longer disease duration and poor renal function had lower BMD. However, the difference between any two groups distinguished by the three criteria is not significant. We think that the causes of osteoporosis in patients with NIDDM may not be explained by only a single factor.

Absorptiometry, Photon↗
PubMed1993

Effects of dicentrine on haemodynamic, plasma lipid, lipoprotein level and vascular reactivity in hyperlipidaemic rats.

1. The effects of dicentrine on haemodynamic, plasma lipid, lipoprotein level and vascular reactivity were investigated in Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats, fed a high fat-high cholesterol diet. 2. In high fat-high cholesterol (HF-HC) diet fed WKY and SH rats, oral administration of dicentrine (5 and 10 mg kg-1, twice a day) for 4 weeks caused significant reductions in total plasma cholesterol (CE) by reducing the low density lipoprotein (LDL) fraction, and reductions in total plasma triglyceride (TG) by reducing the very low density lipoprotein (VLDL) fraction. 3. Dicentrine therapy was associated with increased high density lipoprotein (HDL)-cholesterol levels; thus the ratio of total plasma cholesterol to HDL-cholesterol was improved. 4. In HF-HC diet fed conscious WKY and SH rats, oral administration of dicentrine (5 and 10 mg kg-1, twice a day) also evoked dose-related decreases in mean arterial pressure (MAP) which were of greater magnitude in SH rats. Neither dose of dicentrine caused a significant change in heart rate (HR). 5. The aortic arches from SH rats fed the HF-HC diet for 8 weeks were significantly more affected by the atherosclerotic lesions than the abdominal aortae and renal arteries of WKY and SH rats. Oral administration of dicentrine (5 and 10 mg kg-1) for 4 weeks did not diminish the atherosclerotic lesion areas in WKY and SH rats. 6. In aortae of the hyperlipidaemic rats, significantly attenuated EC50 values and augmented maximal responses for phenylephrine-induced contraction were obtained. Endothelium-dependent relaxation to acetylcholine was abolished, while endothelium-independent relaxation to nitroprusside was well preserved. Dicentrine therapy caused significantly augmented EC50 values and attenuated maximal responses for phenylephrine-induced contraction in hyperlipidaemic rats. However, dicentrine neither prevented the impaired relaxation to acetylcholine, nor affected the relaxation to nitroprusside during atherosclerosis progression.7. It is concluded that dicentrine decreases MAP, plasma CE, LDL-CE, plasma TG, VLDL-TG,vascular hyperreactivity to phenylephrine and increases HDL-CE levels. Dicentrine may thus hold potential for the reduction of two of the major risk factors, hypertension and hyperlipidaemia, for cardiovascular disease.

Animals↗
PubMed1993

Adrenal androgens and cortisol in major depression.

Nine depressed subjects and nine comparison subjects completed a study of abnormalities in adrenal androgen and cortisol metabolism. Serum levels of cortisol and dehydroepiandrosterone (DHA) at 8:00 a.m. and 4:00 p.m. revealed hypercortisolemia and loss of diurnal DHA variation but not cortisol variation in the depressed group. These findings suggest that in depression, adrenal androgens, in contrast to cortisol, are partially regulated by mechanisms independent of ACTH.

Adrenocorticotropic Hormone↗
PubMed1993

Post-embedding in situ hybridization for localization of viral nucleic acid in ultra-thin sections.

We developed an in situ hybridization technique for localization of plant virus RNA in ultra-thin sections of virus-infected, Lowicryl HM20- or osmium-fixed, Araldite-embedded plant leaf tissues. A digoxigenin-labeled in vitro transcript corresponding to 173 nucleotides at the 3' end of bamboo mosaic virus (BaMV) RNA was used as a riboprobe and the hybrids were detected by incubation with sheep antidigoxigenin antibody followed by gold-labeled rabbit anti-sheep IgG. Pre-treatment of ultra-thin sections with an etching agent was the critical step in enhancing hybridization signals on Lowicryl-embedded thin sections. Etching combined with K-metaperiodate treatment increased the accessibility of nucleic acids to riboprobes in osmicated Araldite-embedded sections. BaMV RNA was specifically detected within chloroplasts, mitochondria, and nuclei of infected cells. BaMV virions and BaMV-specific electron-dense crystalline bodies were also labeled. The labeling intensity on Lowicryl-embedded samples, in general, was much higher than that on osmicated Araldite-embedded samples. However, our procedure offers the advantage that it permits labeling of viral nucleic acids in tissues already processed for routine EM and should be applicable for in situ labeling of any cellular nucleic acids.

Blotting, Northern↗
PubMed1993

Magnetic resonance imaging of cerebral hemiatrophy.

Twenty-one cases of cerebral hemiatrophy were studied using 1.0 T magnetic resonance imaging (MRI). In addition to showing the generalized decrease in volume of the cerebral hemisphere, three patterns of cerebral hemiatrophy were noted: pattern I, diffuse cortical and subcortical atrophy (six cases):pattern II, diffuse cortical atrophy associated with expanded porencephalic cysts (10 cases); pattern III, old infarction with necrosis in the territory of the middle cerebral artery (five cases). Pattern I and pattern II were believed to have resulted from hypoxic-ischemic encephalopathy with subcortical leukomalacia (SCL). In all 21 cases, MRI also showed Wallerian degeneration, hyperintensive signals in the posterior limb of the internal capsule on the T2-weighted images, and unilateral atrophy of the cerebral peduncle as far as the pyramid of the medulla oblongata. Structural changes such as thickness of the calvarium, dilatation of the ipsilateral side of the frontal and ethmoid sinus, and reduced size of the middle cranial fossa, were found in 13 cases. Thus, MRI is a useful method of examination in the diagnosis of cerebral hemiatrophy as it has the ability to highlight changes in the cerebral hemisphere, basal ganglion, thalamus and brainstem as well as highlighting bony structural changes.

Adolescent↗
PubMed1993

Urinary diversion in hypospadias repair.

A one-stage urethroplasty with preputial tubularized flap was carried out in 83 hypospadias proximal to the midshaft under two different modes of urinary diversion. In 62 cases using the first mode, the urine was diverted with a French 5 indwelling catheter for five to seven days and then allowed to void through an F10-12 silicon stent in the neourethra. In 21 cases using the second mode, the urine was diverted with an F8 indwelling catheter with multiple side holes for 10 to 14 days before starting spontaneous voiding. With the first mode of diversion, 23 urethrocutaneous fistulas and two nearly total disruptions of the urethroplasty developed to give rise to a failure rate of 40.3% (25/62). Two urethrocutaneous fistulas developed with the second mode to render a failure rate of 9.5% (2/21). A longer period of intravesical drainage of the urine along with gentle autoirrigation of the neourethra appears to be essential in providing a better chance for successful hypospadias repair.

Cutaneous Fistula↗
PubMed1993

Abnormalities on ventilation/perfusion lung scans induced by bronchoalveolar lavage.

Studies were performed before and at varying times after lavage in 10 normal volunteers to assess whether bronchoalveolar lavage results in significant abnormalities on ventilation/perfusion lung scans and chest x-rays. Abnormal lung scans were obtained in six subjects, interpretable as intermediate (three scans), low (one scan) and very low (two scans) probability for pulmonary emboli. Defects varied from multisegmental to subsegmental in size, while chest x-rays were normal in all but one. Both the extent and frequency of defects tended to decrease with time; 24 hr after bronchoalveolar lavage only one of four subjects had a minimally abnormal scan. It is recommended that ventilation/perfusion lung scanning be delayed at least 24 hr following bronchoalveolar lavage to avoid problems in interpretation of defects which may merely be the result of the lavage.

Adult↗
PubMed1993

Hemolytic disease of the newborn caused by maternal anti-Dib: a case report in Taiwan.

Possibly the first case of hemolytic disease caused by anti-Dib in a Chinese infant is reported. The infant developed jaundice soon after birth; based on study, the jaundice has been diagnosed as a result of maternal anti-Dib which was most likely induced by previous pregnancies. The phenotype of the mother's red cells was Di (a+b-). The frequency of the Dia antigen among Chinese in Taiwan is 3.2%. In Orientals, hemolytic disease of the newborn caused by maternal anti-Dib is likely to be more severe than that caused by anti-Dia.

Blood Group Antigens↗
PubMed1993

Definition of reference frames on human skeleton.

In our modeling study of the human cardiovascular system, some forms of subject motion or posture, e.g., those experienced or assumed by a fighter pilot, can not be neglected in considering the overall system dynamics. This investigation aims at establishing a set of reference frames on the human skeleton which are based on the observations and measurements taken on four skeleton systems. These frames are coupled together at the articulation positions to form a base of operation of 3-D translation and rotation. The coupling at a specified reference position was verified against the proportional measurements taken from X-ray films, CAT scan films, atlases and two human cadavers. A program was written to perform the forementioned transformations on the frames coupled at the reference position such that any posture can be achieved as long as the necessary angular anthropometric measurements are provided. If a set of angular profiles at all involved joints are given, the human motion can be mathematically animated to a certain degree of accuracy appropriate for specified computer simulation studies. Under this definition, any major segment of our cardiovascular system model can be specified in terms of spatial position and orientation. [table: see text]

Anthropometry↗
PubMed1993

A mobile real-time bioengineering front end system.

In the study of physiological system dynamics, a mobile Front End System is needed in faithfully monitoring and recording physiological signals at various experimental sites. Local real-time mode operation is required at the site of the experiment such that the significant dynamic response or event from the subject can be easily captured and displayed as the experiment progresses. An additional requirement is the interfacing with the campus computer network such that numerous network computing resources can be employed in further processing of the captured data. The system is configured by using general-purpose components such as a 50MHz PC-486, a DAS-HRES data acquisition board and some other necessary peripheral devices. An algorithm has been developed for the continuous manipulation of two queues to maintain the real-time task scheduling. Traces can be played back in forward or reverse mode at varied speed after the recording has been made. As desired, any trace segment can be picked up in the play back mode from the huge data files. The system is incorporated in a live subject bioinstrumentation laboratory and has the capability of monitoring signals from four simultaneously experimental setups. The signal types involved are membrane potentials, ECG, EMG, blood pressure, and respiratory flows and gas concentrations.

Algorithms↗
PubMed1993

[Sézary syndrome].

Sézary syndrome is a form of leukemia-lymphoma characterized clinically by erythroderma, pruritus, adenopathy, and circulating atypical cells with cerebriform nuclei. Histologically, atypical lymphocytes in the dermis and Pautrier's microabscesses are often present in skin biopsy specimens. We herein report a typical case of Sézary syndrome showing T-suppressor-cell characteristics, and related literatures are reviewed.

Aged↗
PubMed1992

Molecular thermodynamic model to predict the alpha-helical secondary structure of polypeptide chains in solution.

The native state of a protein molecule in aqueous solutions represents one of the lowest states of Gibbs energy [Anfinsen, C.B. (1973) Science 181, 223-230]. Much progress has been made about the rules of protein folding [King, J. (1989) Chem. Eng. News 67, 32-54] and the dominant forces in protein folding [Dill, K.A. (1990) Biochemistry 29, 7133-7155]. However, the quantitative contributions of different Gibbs energy terms to protein stability remains a controversial issue [Moult, J., & Unger, R. (1991) Biochemistry 30, 3816-3824]. A molecular thermodynamic model has been proposed for the Gibbs energy of folding a residue in aqueous homopolypeptides from a random-coiled state to either the alpha-helix state or the beta-sheet state [Chen, C.-C., Zhu, Y., King, J.A., & Evans, L.B. (1992) Biopolymers 32, 1375-1392]. In this work, we present a generalization of the molecular thermodynamic model for the Gibbs energy of folding natural and synthetic heteropolypeptides from random-coiled conformations into alpha-helical conformations. The generalized model incorporates the intrinsic folding potential due to residue-solvent interactions, the cooperative folding effect due to residue-residue interactions, and the location and length of alpha-helices. The utility of the model was demonstrated by examining the stability of alpha-helical conformations of a number of natural polypeptides including C-peptide (residues 1-13) and S-peptide (residues 1-20) of RNase A (bovine pancreatic ribonuclease A), the P alpha fragment in BPTI (bovine pancreatic trypsin inhibitor), and synthetic polypeptides (the copolymers of different amino acid residues) including alanine-based peptides (16 or 17 residues long) in water. The computed Gibbs energies correspond well with the experimental data on helicity. The results also accounted for the effects of amino acid substitution and temperature on the stability of alpha-helical conformations of the test polypeptides.

Amino Acid Sequence↗
PubMed1992

Possible mechanism of immunosuppressive effect of scoparone (6,7-dimethoxycoumarin).

The possible mechanism of the immunosuppressive effect of scoparone (6,7-dimethoxycoumarin) was investigated. Human peripheral blood mononuclear cells (10(6) cells/ml) were stimulated with 0.25% phytohemagglutinin (PHA) and the proliferative response was determined from the uptake of tritiated thymidine. Scoparone (10(-6) to 3 x 10(-4) M) reduced the proliferative response in a dose-dependent manner. The proliferative response of mononuclear cells to mixed lymphocyte reaction was also reduced by scoparone (10(-5) to 10(-4) M). Interleukin-1, interleukin-2 production and interleukin-2 receptor expression were all reduced in the presence of scoparone. Scoparone (10 and 30 microM) significantly reduced the suppression elicited by the diabetogenic drug, alloxan (10 mM). The suppressive activity of scoparone was significantly reduced by quinacrine (a phospholipase A2 inhibitor), indomethacin (a cyclooxygenase inhibitor) and nordihydroguaiaretic acid (a lipoxygenase inhibitor). The levels of prostaglandin E2, prostaglandin F2 alpha, leukotriene B4 and 2,3-dinor-thromboxane B2 in culture medium of PHA-stimulated mononuclear cells, measured with an enzyme immunoassay, were elevated by scoparone treatment. We compared the effect of scoparone on the mononuclear cell response to genistein, a specific inhibitor of protein tyrosine kinase and demonstrated the non-additivity and cross-desensitization of the two compounds. Our results suggest that the immunosuppressive effect of scoparone may be exerted in part through inhibition of protein tyrosine kinase and release of arachidonic acid metabolites.

Alloxan↗
PubMed1992

Inhibition of beta-lactamase by clavulanate. Trapped intermediates in cryocrystallographic studies.

Crystallographic studies of the complex between beta-lactamase and clavulanate reveal a structure of two acyl-enzymes with covalent bonds at the active site Ser70, representing two different stages of inhibitor degradation alternately occupying the active site. Models that are consistent with biochemical data are derived from the electron density map and refined at 2.2 A resolution: cis enamine, in which the carboxylate group of the clavulanate molecule makes a salt bridge with Lys234 of beta-lactamase; decarboxylated trans enamine, which is oriented away from Lys234. For both acyl-enzymes, the carbonyl oxygen atom of the ester group occupies the oxyanion hole in a manner similar to that found in inhibitor binding to serine proteases. Whereas the oxygen atom in the trans product is optimally positioned in the oxyanion hole, that of the cis product clashes with the main-chain nitrogen atom of Ser70 and the beta-carbon atom of the adjacent Ala69. In contrast to cis to trans isomerization in solution that relieves the steric strain inherent in a cis double bond, at the enzyme-inhibitor interface two additional factors play an important role. The salt bridge enhances the stability of the cis product, while the steric strain introduced by the short contacts with the protein reduces its stability.

Binding Sites↗