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Biomedical subjects

C L Chan

Publications and source records attributed to C L Chan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Impact of a patient-centered, computer-based health information/support system.

BACKGROUND: Consumer health information systems potentially improve a patient's quality of life and activate patient self-care. OBJECTIVES: Test a computerized system (CHESS: Comprehensive Health Enhancement Support System), which, in this application, provided HIV-positive patients with information, decision support, and connections to experts and other patients. Would patients given in-home access to computers use the system, improve their quality of life, reduce health-risk behaviors, and use medical services more efficiently? RESEARCH DESIGN: Randomized controlled trial: CHESS computers in experimental subjects' homes in Madison or Milwaukee, Wisconsin, for 3 or 6 months; controls received no intervention. Subjects were compensated for self-report surveys completed before, during, and after CHESS installation. SUBJECTS: Of 204 HIV-positive patients recruited (90% male, 84% white, average education some college, and 65% experiencing HIV-related symptoms), 90% completed the study. MEASURES: Self-reports of quality of life and frequency and duration of use of medical services. RESULTS: CHESS was used daily with little difference between demographic subgroups. While CHESS was in the home, its users reported quality-of-life improvements: active life, negative emotions, cognitive function, social support, and participation in health care. They also reported spending less time during ambulatory care visits, making more phone calls to providers, and experiencing fewer and shorter hospitalizations. CONCLUSIONS: A computer-based personal health support system can improve a patient's quality of life and promote more efficient use of health care.

Adult↗
PubMed1999

Exploring the feasibility and effects of a high-fruit and -vegetable diet in healthy women.

Based on reports that fruits and vegetables may protect against breast cancer, this randomized intervention study tested the feasibility of increasing fruit and vegetable intake among healthy women to 9 daily servings through individual dietary counseling and group activities. Adherence to the dietary recommendations was monitored by 24-h food recalls, log sheets, and plasma carotenoid assessments. To explore possible cancer protective mechanisms of fruits and vegetables, we investigated the treatment effect on plasma phenol levels and on thiobarbituric acid-reactive substances measured as malondialdehyde equivalents, a possible marker of oxidative damage. At baseline, women in the intervention (n = 13) and control (n = 16) group reported an average daily consumption of 3.3 and 3.2 fruit and vegetable servings, respectively. After 3 and 6 months of intervention, intake in the intervention group had increased to 8.3 and 7.4 servings, whereas the control group reported an average of 4.2 and 4.1 daily servings. An increase of plasma carotenoid levels from 1249 microg/liter at baseline to 1854 and 1827 microg/liter after 3 and 6 months confirmed compliance with the dietary recommendations in the intervention group. Plasma carotenoid levels among controls changed slightly from 1165 to 1231 and 1291 microg/liter Whereas total phenol levels did not respond according to our hypothesis, malondialdehyde levels decreased slightly in the intervention group. These results suggest that motivated women can substantially increase their fruit and vegetable intake, which leads to a notable increase in plasma carotenoid levels.

Adult↗
PubMed1998

The first 2 case reports of frozen embryo donation twin pregnancies in Singapore: hormonal profiles and obstetrical outcome.

A 35 year old women with premature ovarian failure and another 30 year old women with gonadal dysgenesis were the recipients of donated supernumerous frozen embryos after successfully prepared with cyclic steroid replacement therapy as described previously. One patient received 4 and the second 2 frozen embryos, transferred transcervically on the 3rd day of progesterone administration. Both patients had viable twin pregnancies. The plasma beta hCG levels for both patients at 2 weeks post replacement (4 weeks gestation) were lower than the median values in our normal, uncomplicated singleton pregnancy for the same gestation. The level after 4 weeks post-replacement (6 weeks gestation) became comparable. Plasma progesterone profiles suggested a level of above 70 ng/ml would be enough to support the twin pregnancies. The first patient developed antepartum haemorrhage of unknown origin at 34 weeks of gestation preceding preterm premature rupture of membranes and subsequently had preterm labour. The second patient developed proteinuric hypertension at 33 weeks of gestation. Both ended in a lower segment cesarean section. Both sets of twins and their mothers were discharged well.

Adult↗
PubMed1997

Identification and diurnal studies of pineal and serum 5-methoxytryptamine in the rat and quail.

Picomole to femtomole per gland/ml levels of 5-methoxytryptamine (5MT) in the pineal gland and serum of the rat and quail were determined, in the absence of a monoamine oxidase inhibitor, by using the ultra-sensitive technique of capillary column gas chromatography/electron-capture negative ion chemical ionization mass spectrometry. Diurnal rhythms of pineal 5MT with high levels at mid-light and low levels at mid-dark were found in both species, while serum 5MT levels showed less or no diurnal variations. The definitive presence of 5MT in the pineal gland and blood circulation provides further evidence that it is potentially a neurohormone. Whether 5MT is implicated in the photoperiodic responses and/or other physiological functions of animals, however, remains to be investigated.

5-Methoxytryptamine↗
PubMed1997

Effects of neutral salts on RNA chain elongation and pausing by Escherichia coli RNA polymerase.

We examined the effects of neutral salts and the non-ionic solute 2-methyl,-2,4-pentanediol (MPD) on transcript elongation by Escherichia coli RNA polymerase and on pausing induced by the multipartite his leader pause signal. All solutes tested slowed the overall rate of elongation, with anions showing the dominant effects in the order: (most inhibitory) HPO4(2-) > OAc- > SO4(2-) > ClO4- > I- approximately NO3- > Br approximately Cl- approximately MPD (least inhibitory). Although the protein structure-stabilizing anions HPO4(2-), OAc-, and SO4(2-) also increased the pause half-life at the his leader pause site, the remaining solutes accelerated escape from pause site in the order: (greatest acceleration) NO3- > ClO4- > I- > Br- > Cl- > MPD (least acceleration). Cl(-)-induced acceleration of escape from the pause site also occurred on mutant templates altered for the 3'-proximal region, RNA 3' end, or downstream DNA. The effect was eliminated, however, by base substitutions that destabilize the pause RNA hairpin or that extend it toward the 3' end. This "perfect hairpin" itself reduced the pause half-life by a factor of 3. We suggest that the pause RNA hairpin stabilizes a paused conformation of the transcription complex through an interaction with an easily disordered region of RNA polymerase. Extending the stem of the pause hairpin may disrupt the interaction by altering the position of the hairpin in the transcription complex. Anions may either compete for the interaction directly or disorder the site of hairpin interaction by chaotropic effects. We suggest that the negative effect of structure-stabilizing anions like OAc- and SO4(2-) may reflect passage of RNA polymerase through significantly different conformations during rapid elongation, some of which may expose hydrophobic surface.

Anions↗
PubMed1997

Multiple interactions stabilize a single paused transcription intermediate in which hairpin to 3' end spacing distinguishes pause and termination pathways.

Transcription is delayed in the leader regions of the Escherichia coli trp and his operons by multipartite pause signals that consist of four components: a nascent RNA structure (the pause hairpin), the 10 or 11 nt 3'-proximal region between the pause hairpin and the RNA 3' end, the bases in the active site, and approximately 14 bp of duplex DNA downstream from the pause site. Results described in the accompanying paper suggest that the his pause hairpin slows nucleotide addition via interaction with an easily disordered surface on RNA polymerase. Here we report that the four pause signal components slow nucleotide addition in a single kinetic intermediate. Formation of the paused transcription complex, in contrast, involves synergistic effects of RNA and DNA sequences that select the wild-type pause site from among several adjacent possibilities. Extending the pause hairpin with one G x C base-pair reduces pausing, apparently by interfering with pause hairpin interaction; adding a second C x G base-pair that reduces the 3'-proximal RNA to 9 nt or less (within the 7 to 9 nt characteristic of rho-independent terminators) induces transcript release. We propose that escape from the pause is governed by a rate-limiting isomerization that may require substrate NTP binding to re-establish the active site geometry, whereas transcript release and termination ensue when the hairpin interaction is weakened and isomerization to an active conformation is blocked.

Bacterial Proteins↗
PubMed1997

The electron-dose distribution surrounding an 192Ir wire brachytherapy source investigated using EGS4 simulations and GafChromic film.

The steep dose gradient around 192Ir brachytherapy wire implants is predicted by the EGS4 (PRESTA version) Monte Carlo simulation. When considering radiation absorbing regions close to the wire source, the accurate dose distribution cannot be calculated by the GE Target II Sun Sparc treatment-planning system. Experiments using GafChromic film have been performed to prove the validity of the EGS4 user code when calculating the dose close to the wire source in a low energy range.

Brachytherapy↗
PubMed1997

Midline extraperitoneal approach for elective abdominal aortic aneurysm repair.

The incidence of abdominal aortic aneurysms (AAA) is rising and elective repair is becoming more commonplace. We describe a new, simple midline extraperitoneal approach for AAA repair. It is particularly suitable for patients who have an inflammatory AAA, abdominal adhesions or a horseshoe kidney. This approach provides excellent exposure to the whole aortoiliac system without the need for separate incisions, whilst retaining the potential advantages of the extraperitoneal approach.

Aortic Aneurysm, Abdominal↗
PubMed1997

The dose distribution close to an 192Ir wire source: EGS4 Monte Carlo calculations.

A Monte Carlo simulation using the PRESTA version of the EGS4 code has been employed as an investigative tool to calculate the absorbed dose in water close to 192Ir wire implants. It has been shown that a treatment planning system, such as GE Target II, using the Sievert integral and the Meisberger polynomial is only able to reproduce the Monte Carlo results at radial distance of 1 mm and farther away. The Sievert integral used with the Meisberger polynomial is proven to be in good agreement with the Monte Carlo generated data at distances between 1 mm and 1 cm.

Brachytherapy↗
PubMed1997

Chronic low-dose follicle-stimulating hormone compared with clomiphene/human menopausal gonadotropin for induction of ovulation.

Concurrent administration of clomiphene can reduce the amount of gonadotropins required for induction of ovulation. Recently, follicle-stimulating hormone (FSH) administered in a chronic, low-dose fashion has been reported to give satisfactory pregnancy rates. We compared the conventional clomiphene/human menopausal gonadotropin (hMG) with the chronic, low-dose FSH regimen for induction of ovulation in 87 patients over 110 cycles. The clomiphene/hMG regimen required half the amount of gonadotropin compared to the chronic FSH regimen to achieve follicular maturation. Despite the reduced amount of gonadotropin, the clomiphene/hMG regimen induced a mean fourfold higher level of estradiol production and was associated with significantly greater numbers of large and intermediate-sized follicles compared to the chronic FSH regimen. The proportion of clomiphene/hMG cases with multifollicular development and overstimulation was therefore high (30%). In contrast, the chronic FSH regimen, despite requiring larger amounts of gonadotropin and longer periods of treatment, resulted in unifollicular development, low rates of overstimulation and improved pregnancy rates. We conclude that although clomiphene can reduce the requirement for gonadotropins, the relative safety and effectiveness of the chronic low-dose FSH regimen makes it the method of choice for ovulation induction.

Adult↗
PubMed1996

Sigma domain structure: one down, one to go.

The recent publication of the 2.6 A crystal structure of a portion of sigma70 provides insight into the role of sigma during transcription initiation. This high resolution picture unveils novel questions.

Bacterial Proteins↗
PubMed1996

Analysis of 5-methoxytryptamine at the femtomole level in the rat and quail brain by gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry.

A sensitive method for the measurement of endogenous 5-methoxytryptamine in brain tissue has been developed using capillary column gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry. 5-Methoxytryptamine was first converted to N-[2H3]acetyl-5-methoxytryptamine by reaction with hexa-deuterated acetic anhydride, followed by reaction with pentafluoropropionic anhydride to yield the highly electron-capturing 3,3'-spirocyclic pentafluoro-propionyl indolenine derivative. Quantitative analysis was carried out by selected-ion monitoring of the [M-HF].- and [M-HF-DF].- ion intensity of the 3.3'-spirocyclic pentafluoropropionyl indolenine derivative, using 5-methoxy-[alpha, alpha, beta, beta-2H4]tryptamine as the internal standard. The presence of 5-methoxytryptamine in the brain tissue was demonstrated. In the absence of a monoamine oxidase inhibitor, the mean +/- S.D. levels of 5-methoxytryptamine in the rat and quail whole brain were found to be 30 +/- 6 and 347 +/- 52 pg/g, respectively. The possible physiological functions of 5-methoxytryptamine as a neuromodulator and/or neurotransmitter have to be considered.

5-Methoxytryptamine↗
PubMed1996

A structure/function analysis of Escherichia coli RNA polymerase.

Control of RNA polymerase is a common means of regulating gene expression. A detailed picture of both the structure and how the structural details of RNA polymerase encode function is a key to understanding the molecular strategies used to regulate RNA polymerase. We review here data which ascribes functions to some regions of the primary sequence of the subunits (alpha, beta beta' sigma) which make up E. coli RNA polymerase. We review both genetic and biochemical data which place regions of the primary sequence that are distant from one another in close proximity in the tertiary structure. Finally we discuss the implications of these findings on the quaternary structure of RNA polymerase.

DNA-Directed RNA Polymerases↗
PubMed1996

The first frozen embryo donation pregnancy for hypergonadotrophic hypogonadism in Singapore--hormonal profile and obstetric outcome.

This is the first report in South East Asia of a singleton frozen embryo donation pregnancy for hypergonadotrophic hypogonadism. The hormonal profile was compared with that of a control group of normal uncomplicated singleton pregnancies in Singapore. The plasma beta hCG levels were lower compared to those of our normal uncomplicated singleton pregnancies at 2 to 3 weeks after the embryo transfer but became comparable at 4 to 5 weeks after embryo transfer. The successful vaginal delivery and the obstetric complications developed in this case are discussed.

Adult↗