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Biomedical subjects

S S Chan

Publications and source records attributed to S S Chan.

At least 37 records · Page 2Linked to original sources
PubMed1997

Biomechanics of knee ligament healing, repair and reconstruction.

Injuries of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) are common, accounting for 90% of all knee ligament injuries in young and active individuals. During the last decade, our research center has focused on MCL healing and ACL reconstruction. We have found that the MCL heals without intervention after an isolated injury, and that primary repair offers no apparent advantage. After a combined injury of the ACL and MCL, the ACL requires reconstruction, whereas primary repair again contributes little or nothing toward MCL healing. Midsubstance ACL injuries have limited healing ability. Hence, the treatment of choice for a torn ACL in a young, active patient is generally reconstruction with an autograft or allograft. However, the appropriate replacement graft and reconstruction technique to use are still debated. Current research efforts have been placed on investigating the magnitude and direction of in situ forces in the human ACL. We use a six-component universal force moment sensor combined with a six-degree-of-freedom (DOF) robotic manipulator to learn as well as to reproduce the six-DOF motion of the knee before and after ACL injury. This way, the in situ force in the ACL under an anterior posterior tibial load of 110 N was obtained. This methodology should make it possible to obtain the needed data to aid in better understanding of ACL reconstruction and possible development of improved clinical management.

Animals↗
PubMed1997

Motor power pharmacodynamics of subarachnoid hyperbaric 5% lidocaine in the sitting position.

BACKGROUND: Repetitive dynamometric measurement using a plantar flexion power device (PFPD) provides detailed data describing the onset and offset of motor block following spinal administration of lidocaine. The aim of this study was to evaluate administration of two doses of spinal lidocaine in the sitting position to determine whether our dynamometric model produces data consistent with our current understanding of the pharmacokinetics of subarachnoid, hyperbaric, 5% lidocaine. METHODS: Twenty male patients (54 to 80 yr) undergoing cystoscopy received spinal anaesthesia with either 75 mg (n = 10) or 100 mg of hyperbaric lidocaine 5%, in the sitting position, under standardised conditions. Plantar flexion muscle power was recorded during onset and offset of anaesthesia using a load cell interfaced with a computer (PFPD). RESULTS: Onset of paralysis following spinal block in the sitting position was rapid and complete with motor power declining exponentially to 5% of preoperative values by 8.5 min in all patients. There was no difference in decay or recovery of plantar flexion motor power data between dosage groups in the sitting position. Measurement using the PFPD shows that onset of motor paralysis is described by an exponential decay and that motor recovery occurs at a fixed rate. Extent of block to cold and pinprick was similar in both dosage groups in the sitting position (median T4). CONCLUSION: This study shows that in the sitting position, doses less than 75 mg of 5% hyperbaric lidocaine are required to significantly improve ambulatory times.

Aged↗
PubMed1996

Deleted in Colorectal Cancer (DCC) encodes a netrin receptor.

The guidance of developing axons in the nervous system is mediated partly by diffusible chemoattractants secreted by axonal target cells. Netrins are chemoattractants for commissural axons in the vertebrate spinal cord, but the mechanisms through which they produce their effects are unknown. We show that Deleted in Colorectal Cancer (DCC), a transmembrane protein of the immunoglobulin superfamily, is expressed on spinal commissural axons and possesses netrin-1-binding activity. Moreover, an antibody to DCC selectively blocks the netrin-1-dependent outgrowth of commissural axons in vitro. These results indicate that DCC is a receptor or a component of a receptor that mediates the effects of netrin-1 on commissural axons, and they complement genetic evidence for interactions between DCC and netrin homologs in C. elegans and Drosophila.

Amino Acid Sequence↗
PubMed1996

UNC-40, a C. elegans homolog of DCC (Deleted in Colorectal Cancer), is required in motile cells responding to UNC-6 netrin cues.

UNC-6 netrin, a laminin-related protein secreted from neuroglia and neurons along the ventral midline, orients migrating cells and pioneering growth cones on the nematode epidermis. UNC-5, a cell surface protein expressed on motile cells and pioneer axons, orients movements away from UNC-6 sources. UNC-40, a homolog of the cell surface proteins DCC (Deleted in Colorectal Cancer) and neogenin, is also expressed on motile cells and pioneer neurons. UNC-40 acts cell autonomously to orient movement toward UNC-6 sources. For cells coexpressing UNC-5, it helps orient movement away from UNC-6 sources. Finally, UNC-40 helps determine the dorsoventral position of cells undergoing purely longitudinal migrations. Together with the recent report that DCC is a netrin receptor in vertebrates, our results suggest that UNC-40 is a component of UNC-6 receptors on motile cells.

Amino Acid Sequence↗
PubMed1996

Pulsed-field electrophoresis in microlithographic arrays.

Transverse pulsed-field electrophoresis of DNA has been conducted in a silicon array engineered by optical lithography and the motion of individual molecules observed by fluorescence microscopy. In strong fields, the molecules can be maintained in highly stretched, linear conformations. When the field is switched through an obtuse angle, they head off in the new direction led by what was formerly their tail end. This backtracking gives rise to fractionation that is linear with molecular weight. A simple prescription exists for choosing the field parameters to obtain a particular range of separation. Since the molecular motions are much more uniform than those that occur in a gel, it is anticipated that the arrays will permit more efficient fractionation than traditional pulsed-field gel electrophoresis. Arrays suitably scaled down in size may be useful for pulsed-field sequencing.

DNA↗
PubMed1996

Risk factors for falls in the Chinese elderly population.

BACKGROUND: Besides being the major cause of hip fracture, falls also have important consequences in injuries and mortality, especially in the elderly population. This study investigated the occurrence of and the correlates of falls in a cohort of Hong Kong Chinese elderly aged 70 years and above. METHODS: The research was based on the baseline cross-sectional study of an age- and sex-stratified cohort consisting of 1,947 ambulatory subjects. The occurrence of falls was based on the previous 12 months. Logistic regression analysis was used to test the effect of each independent variable, adjusting for age and sex. Multivariate logistic regression analysis based on the backward elimination procedure was used for the final model. RESULTS: Previous white-collar employment, poor self-perceived health, dizziness, slow gait velocity, difficulties in activities of daily living, non-practice of "morning walk," body mass index in the range of 20-24, use of local skin preparation, and presence of cerebrovascular disease were independently associated with falls. Smokers were found to have an independent decreased risk of falls. Neither age nor sex was significantly associated with falls after adjusting for the other explanatory variables. CONCLUSIONS: The results from this population-based cross-sectional study form a basis for further prospective study on falls in the Chinese elderly population. Both intrinsic and extrinsic factors including circumstances and consequences of falls are important considerations in the strategy for the prevention of falls.

Accidental Falls↗
PubMed1996

Pharmacodynamics of subarachnoid hyperbaric 5% lignocaine.

Twenty male patients (55 to 85 yr) undergoing cystoscopy received spinal anaesthesia with either 75 mg (n = 10) or 100 mg of hyperbaric lignocaine 5% under standardised conditions. Plantar flexion muscle power was recorded during onset and offset of anaesthesia using a load cell interfaced with a computer (PFPD) and these data were compared with intermittent clinical assessments of spinal anaesthesia. Onset of paralysis was rapid and complete with motor power declining exponentially to 5% of preoperative values by 5 minutes in all patients. Extent of block to cold and pinprick was similar in both dosage groups (median T4), as was the rate of block onset. Block regression was complete by three hours in all patients and restitution of plantar flexion motor power was associated with normal thermosensibility at L1 and recovery of the patient's ability to walk and micturate. Recovery of plantar flexion motor power occurred at 95.5 +/- 7.38 min in patients given 75 mg compared with 129 +/- 9.5 min in those given 100 mg lignocaine (P < 0.05). The time between onset and full motor recovery in the 75 mg group (7.2 +/- 1.2 min) was less than the 100 mg lignocaine group (29 +/- 5.1 min) (P < 0.001). The larger dose of lignocaine did not confer any clinical advantage in block onset or intensity and made the onset of recovery less predictable. The Bromage grading, while clinically appropriate during anaesthesia onset, does not provide data relating to the density of block and the PFPD was therefore useful for describing the anaesthesia recovery phase.

Aged↗
PubMed1996

A preliminary study of C-reactive protein in the diagnosis and monitoring of Lyme disease.

Concentrations of C-reactive protein (CRP) in the serum of 14 patients suffering from Lyme disease were measured. 86% of these patients were found to have abnormally high concentrations of serum CRP (range 14-158 mg/L). The CRP concentration of a 60-year-old patient abated from 29 mg/L to 13 mg/L after treatment. Results suggest that serum CRP concentration can provide a valuable and accurate means for the clinical diagnosis and monitoring of Lyme disease.

C-Reactive Protein↗
PubMed1996

[Cell cycle and apoptosis].

The progression of cell cycle in embryonic cells from oceanic bionts to mammalians is initiated, promoted and terminated under the regulation of cell cycle gene products, named cyclins, and a p34 (cdc 2). Besides, oncogene (proto-oncogene) products such as p53 and pRB also directly regulate the progression of cell cycle. However, the p34 (cdc 2) which promotes the mitotic cell division also initiates the apoptosis of certain cells. Therefore, mutations of genes that regulate the normal progression of cell cycle would cause cells in the cell cycle undergoing either apoptosis or uncontrollable proliferation.

Animals↗
PubMed1995

Determinants of bone mass in the Chinese old-old population.

One hundred and eighty-eight elderly men and women were included in a study of bone mass at the neck of femur and its related factors. The study subjects were a subsample of a Hong Kong wide study of the elderly population aged 70 years and above. The study variables included age, sex, body measurements of height, weight, body mass index, dietary calcium intake, grip strength, 16 feet (5 m) gait speed, smoking, drinking, and years since menopause among women. The neck of femur bone mineral density among elderly men was about 1 standard deviation higher than that of women. Subjects aged 85 years and above had about 20% lower bone mineral density at the neck of femur when compared with those in the age group 70-74 years. Mean dietary calcium intake ranged between 300 and 430 mg/day and was not associated with bone mass. Multiple regression analysis showed that body weight, 16 feet gait speed, sex and alcohol consumption explained 46% of the total variance of femoral neck bone mineral density. Body weight was the most significant predictor of bone mineral density, with a partial correlation coefficient of 0.5. The maintenance of body weight within the acceptable weight range and promotion of physical fitness may be important measures in reducing bone loss in the elderly population.

Aged↗
PubMed1995

Effect of partial laceration on the structural properties of the canine FDP tendon: an in vitro study.

The appropriate management of partially lacerated digital flexor tendons in zone 2 is controversial. Tenorrhaphy has been advocated by some on the basis of improving tendon gliding function, whereas others have recommended foregoing tenorrhaphy because of the negative impact of repair on the tensile strength of the tendon. In light of this division, we undertook a study of the effect of varying degrees of partial laceration on the structural properties of the canine flexor digitorum profundus tendon. Lacerations up to 90% of the tendon cross-sectional area were surgically fashioned. We conclude that the structural properties of the tendon are increasingly adversely affected as laceration size increases. However, based on previous estimates of in vivo forces, even tendons with up to 60% cross-sectional area involvement may be strong enough to withstand an early active mobilization regimen. Further, we conclude that neither calipers nor naked-eye estimates provide a reliable means of assessing the extent of tendon laceration.

Animals↗
PubMed1994

Determinants of serum 1,25-dihydroxyvitamin D concentration in healthy premenopausal subjects.

Concentrations of serum phosphate and parathyroid hormone (PTH) are well known regulators of the production of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and acidosis is known to affect the serum concentration of 1,25-(OH)2D. However, the factors that play a role in the regulation of serum 1,25-(OH)2D concentration in healthy subjects have not been fully evaluated. The associations of ionised calcium, pH, serum concentration of phosphate, PTH, 25-hydroxyvitamin D (25-OHD) and serum 1,25-(OH)2D were examined in 296 healthy premenopausal women (age range 17-40 years). Calculation of partial correlation coefficients showed that serum 1,25-(OH)2D was significantly correlated with phosphate (r = -0.148, P < 0.01), pH (r = 0.221, P < 0.001) and PTH (r = 0.136. P < 0.01). Ionised calcium was not related to serum 1,25-(OH)2D. When the results were stratified according to quartiles based on serum 1,25-(OH)2D concentration, significant trends (by analysis of variance) were seen in phosphate, pH, age, albumin and 25-OHD. Stepwise multiple regression analysis showed that phosphate and pH were the major contributors of serum 1,25-(OH)2D levels. There was a small contribution from PTH and 25-OHD. The results suggest that in young healthy premenopausal women plasma phosphate and pH may be important determinants of serum 1,25-(OH)2D concentration.

Adolescent↗
PubMed1994

Determinants of bone mass in Chinese women aged 21-40 years. II. Pattern of dietary calcium intake and association with bone mineral density.

A study on the determinants of bone mass in young women is being carried out among 287 young Chinese women aged 21-40 years. The baseline cross-sectional data show that the mean dietary calcium intake, estimated from the quantitative food frequency method, was 448 mg/day (standard deviation = 219). About 50% of the calcium source was from vegetables and 22% from dairy products. Among women aged 21-30 years, those with a dietary calcium intake of at least 600 mg/day had a 4%-7% higher mean bone mineral density at the spine and femur when compared with those with a mean intake below 300 mg/day. In women aged 31-40 years, subjects belonging to the highest quartile of calcium density (> or = 35 mg/420 kJ) had a 3%-8% higher mean bone mineral density at the spine and femur when compared with those in the lowest quartile (< 20.8 mg/420 kJ). Favorable calcium intake is beneficial in this population of young women with habitual low dietary calcium intake.

Adult↗
PubMed1993

Thermodynamics and premelting conformational changes of phased (dA)5 tracts.

Using synthetic 45 bp long DNAs of known sequences, we have studied (i) the unusual structure that the phased A-tracts have at temperatures below 37 degrees C, (ii) the thermodynamics of the loss of that aberrant structure well below the duplex melting temperature, and (iii) the conformational changes that occur with temperature. Using temperature-dependent circular dichroism, we detect a low-temperature structural transition in a 45-mer duplex with four segments of phased (dA)5 tracks separated by five segments of five randomized G-C pairs, but none in the corresponding isomeric random sequence 45-mer duplex. Differential scanning calorimetry measurements reveal the enthalpy of this preglobal melting transition to be 3.5 kcal/mol.AT pair or 4.4 kcal/mol.AA step. The integrated enthalpy change for this helix-to-helix intramolecular event only is about 16% of the global duplex-to-single-strands melting enthalpy and is relatively broad compared to the global melting event (about 30 vs 15 degrees C for the full width at half maxima). Electric birefringence decay measurements show that the phased 45 bp duplex has a rotational time constant of 100 ns at 5 degrees C which increases to 220 ns above 40 degrees C. Simple modeling of the dynamics within the junction model for bending yields that the bend per A-tract is 42 degrees at 5 degrees C, decreasing to 0 degrees above 40 degrees C. We suggest that this sequence-dependent structure which "melts" at physiological temperatures may be relevant to DNA topology and function.

Adenine Nucleotides↗
PubMed1993

A longitudinal study of the determinants of bone mass in Chinese women aged 21 to 40. I. Baseline association of anthropometric measurements with bone mineral density.

The bone mineral density of the lumbar spine (L2 to L4) and neck of the femur of 293 Chinese women aged 21 to 40 years was measured using a dual x-ray densitometer. The participants were recruited from subjects registered with the University Family Medicine Clinic in Hong Kong. Our cross-sectional data showed that maximal bone mass occurs in the early 30s. Both the spine and hip bone masses were observed to decline at a rate of around 1% per annum from the early 30s onward. Body weight, lean body mass, and body fatness were significantly associated with the mineral density of the spinal and femoral bones after or around the attainment of peak bone mass, while no correlation of these data was observed in the younger age group (20 to 28 years). Other factors may play a more important role than body mass in influencing bone mineral density before attainment of peak bone mass.

Absorptiometry, Photon↗
PubMed1991

Microalgae as bioabsorbents for treating mixture of electroplating and sewage effluent.

The effectiveness of copper and nickel uptake by microalgae grown in the mixture of electroplating effluent and sewage was studied. The results showed that a high percentage of copper removal (68.1%-88.2%) was achieved by Chlorella pyrenoidosa (strain No. 26) reared in the mixture of 90% electroplating effluent and 10% raw sewage during the first 3 days despite the fact that cell growth was inhibited. Similar results were also obtained by using Chlorella HKBC-C3, another species collected from one of the heavy metal polluted sites in Hong Kong, isolated and cultured in the Biology Department. There was no significant difference (P greater than 0.05) in the removal of copper and nickel from the effluent between these 2 algal species. However, it was noted that removal of nickel from the mixture by the two species were comparatively lower (less than 20%) than the removal of copper (greater than 68%).

Absorption↗
PubMed1990

Physical studies of DNA premelting equilibria in duplexes with and without homo dA.dT tracts: correlations with DNA bending.

We have employed a variety of physical methods to study the equilibrium melting and temperature-dependent conformational dynamics of dA.dT tracts in fractionated synthetic DNA polymers and in well-defined fragments of kinetoplast DNA (kDNA). Using circular dichroism (CD), we have detected a temperature-dependent, "premelting" event in poly(dA).poly(dT) which exhibits a midpoint near 37 degrees C. Significantly, we also detect this CD "premelting" behavior in a fragment of kDNA. By contrast, we do not observe this "premelting" behavior in the temperature-dependent CD spectra of poly[d(AT)].poly[d(AT)], poly(dG).poly(dC), poly[d(GC)].poly[d(GC)], or calf thymus DNA. Thus, poly(dA).poly(dT) and kDNA exhibit a common CD-detected "premelting" event which is absent in the other duplex systems studied in this work. Furthermore, we find that the anomalous electrophoretic retardation of the kDNA fragments we have investigated disappears at temperatures above approximately 37 degrees C. We also observe that the rotational dynamics of poly(dA).poly(dT) and kDNA as assessed by singlet depletion anisotropy decay (SDAD) and electric birefringence decay (EBD) also display a discontinuity near 37 degrees C, which is not observed for the other duplex systems studied. Thus, in the aggregate, our static and dynamic measurements suggest that the homo dA.dT sequence element [common to both poly(dA).poly(dT) and kDNA] is capable of a temperature-dependent equilibrium between at least two helical states in a temperature range well below that required to induce global melting of the host duplex. We suggest that this "preglobal" melting event may correspond to the thermally induced "disruption" of "bent" DNA.

Animals↗