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Biomedical subjects

H S Lim

Publications and source records attributed to H S Lim.

At least 19 recordsLinked to original sources
PubMed2005

Spin waves in nickel nanorings of large aspect ratio.

The spin dynamics of high-aspect-ratio nickel nanorings in a longitudinal magnetic field have been investigated by Brillouin spectroscopy and the results are compared with a macroscopic theory and three-dimensional micromagnetic simulations. Good agreement is found between the measured and calculated magnetic field dependence of the spin wave frequency. Simulations show that as the field decreases from saturation, the rings switch from a "bamboo" to a novel "twisted bamboo" state at a certain critical field, and predict a corresponding dip in the dependence of the spin wave frequency on the magnetic field.

Journal Article↗
PubMed2005

Tissue inhibitor of metalloproteinse-1 is a marker of diastolic dysfunction using tissue doppler in patients with type 2 diabetes and hypertension.

BACKGROUND: Tissue inhibitor of metalloproteinase-1 (TIMP-1) is associated with increased fibrosis of the extracellular matrix (ECM). Myocardial stiffness is a feature of diastolic dysfunction. We assessed circulating TIMP-1 as a marker of diastolic dysfunction in patients with type 2 diabetes mellitus (DM) and hypertension, who were compared with healthy controls. METHODS: We recruited 54 patients (43 males; mean age 68 +/- 5 years) with treated type 2 DM (i.e. controlled glycaemia, hypertension, hyperlipidaemia), 35 (30 males; 69 +/- 8 years) treated nondiabetic hypertensives, and 31 healthy controls (18 males; 66 +/- 5 years). Circulating TIMP-1 was measured by ELISA. Using transthoracic echocardiography, the early (E) diastolic mitral inflow velocity was measured with pulse wave Doppler, and the early mitral annular velocity (e'), a recognized index of diastolic relaxation, was measured with tissue Doppler. The E/A ratio was also calculated and isovolumic relaxation time measured. RESULTS: Mean e' levels differed significantly between controls, diabetics and hypertensives (P < 0.0001). Circulating TIMP-1 was significantly different between patients and controls (P = 0.006), but there was no statistically significant difference between the DM and hypertension group. In both groups, only e' was negatively correlated with TIMP-1 levels, with a stronger correlation among the hypertensive patients (Spearman r = -0.544, P = 0.001) when compared with the diabetic group (r = -0.341, P = 0.011). CONCLUSION: Diastolic relaxation is impaired in diabetes and hypertensive patients. The relationship between TIMP-1 and e' may reflect increased myocardial fibrosis and consequent diastolic dysfunction, which may be more prominent in hypertension.

Aged↗
PubMed2005

Factors predicting the development of metabolic syndrome and type II diabetes against a background of hypertension.

BACKGROUND: The metabolic syndrome (MetS), predicting coronary heart disease (CHD), is a compound of risk factors including diabetes, obesity and hypertension. The relationship between the development of MetS, diabetes and CHD in patients with established hypertension is unclear. We hypothesized that patients with hypertension developing MetS are at increased risk of type II diabetes and CHD compared with patients who do not develop MetS. MATERIALS AND METHODS: We prospectively studied 284 patients (100 with existing/established MetS) with hypertension but without diabetes and CHD over 4 years. MetS and diabetes were diagnosed by the modified NCEP and ADA criteria, and CHD risk by the Framingham risk equation; all patients had annual fasting blood sampling. RESULTS: Over 4 years of follow up, 75 of the 184 patients (41%) initially free of MetS at baseline subsequently fulfilled the criteria for MetS. These patients (i.e. 'developing MetS') had higher baseline BMI, triglycerides and lower HDL cholesterol, with a higher calculated CHD risk (all P <or= 0.001) than those who did not develop MetS. The 4-year odds ratios of developing diabetes in the patients with established MetS (23%) and the patients developing MetS (13.3%) vs. the patients not developing MetS (3.7%, P < 0.001) were 7.8 (95% CI: 2.6-23.5) and 4.0 (95% CI: 1.2-13.4), respectively. CONCLUSIONS: Patients with hypertension developing MetS have an increased CHD risk and risk of developing type II diabetes even before fulfilling the criteria for MetS, and the former is comparable to patients with established MetS. These data suggest a high-risk phase not adequately identified by current diagnostic thresholds for MetS.

Adult↗
PubMed2005

The effect of multi-factorial intervention on plasma von Willebrand factor, soluble E-selectin and tissue factor in diabetes mellitus: implications for atherosclerotic vascular disease.

BACKGROUND: Endothelial abnormalities and a hypercoagulable state may contribute to increased cardiovascular risk in diabetes mellitus, particularly in patients with overt cardiovascular disease (CVD). We sought to determine the effect of intensified multi-factorial cardiovascular risk intervention on indices of endothelial abnormality and hypercoagulability in diabetes, and if patients with overt CVD would derive similar benefit as those without. PATIENTS AND METHODS: We measured plasma von Willebrand factor (vWf, an index of endothelial damage/dysfunction), soluble E-selectin (sE-sel, marking endothelial activation) and tissue factor (TF, an initiator of coagulation) by ELISA in 94 patients with diabetes mellitus (38 with CVD and 56 without overt CVD) and 34 comparable controls. Thirty-three patients with CVD and 31 without overt CVD then participated in multi-factorial cardiovascular risk intervention over 1 year. RESULTS: Plasma levels of vWf (P = 0.009), sE-sel (P < 0.001) and TF (P < 0.001) were significantly higher in diabetic patients compared with controls, with TF highest in patients with overt CVD. Intensive multi-factorial intervention resulted in reductions in glycated haemoglobin (HbA(1c)), total and LDL-cholesterol (all P < 0.05), but no significant weight change. This was associated with reductions in vWf in patients with (by 26%P = 0.003), and without (by 47%, P < 0.001), overt CVD. TF was reduced only in patients without overt CVD (by 45%, P < 0.001). There were no significant changes in sE-sel levels in either group. CONCLUSION: Endothelial abnormalities in diabetes are only partially influenced by contemporary intensified multi-factorial cardiovascular risk intervention. These data suggest the need for earlier and more aggressive risk factor intervention.

Aged↗
PubMed2005

Clinically apparent atherosclerotic disease in diabetes is associated with an increase in platelet microparticle levels.

BACKGROUND: The commonest cause of mortality in patients with Type 2 diabetes is atherothrombosis, which can be related to abnormalities in the coagulation and fibrinolytic pathways, as well as in platelet function. Platelet microparticles (PMPs) may contribute to the prothrombotic state and may promote the progression of atherosclerosis. We hypothesized that PMPs are elevated in Type 2 diabetes and that patients with Type 2 diabetes and clinically apparent atherosclerosis would have the highest levels. Similarly, we hypothesized that soluble plasma P-selectin (sPsel) and CD40L (both molecules which are released by activated platelets), as well as %CD62P (P-selectin) and %CD63 positivity on platelets quantified by flow cytometry, would be highest in patients with Type 2 diabetes and clinically apparent atherosclerotic disease, and might be correlated to PMP levels. METHODS: Venous blood was obtained from 21 Type 2 diabetic patients without atherosclerotic complications, 18 diabetic patients with clinically apparent atherosclerotic disease and 21 non-diabetic control subjects. PMPs, as well as %CD62P and %CD63 positivity on platelets, were quantified by flow cytometry. sPsel and CD40L were measured using ELISA. RESULTS: Patients with Type 2 diabetes and clinically apparent atherosclerotic disease had the highest PMP (P=0.045) and sPsel (P=0.046) levels, compared with patients without complications (who had intermediate PMP levels) and control subjects. Control subjects had the lowest CD40L levels (P<0.001) when compared with patients with Type 2 diabetes, with no difference in sCD40L levels between the two diabetic subgroups. %CD62P and %CD63 positivity did not differ between the groups. PMP levels correlated with %CD62P positivity (P=0.026) but not to %CD63 positivity (P=0.089), sCD40L (P=0.407) or sP-sel (P=0.163); sCD40L levels did not correlate with any other marker of platelet activation. CONCLUSION: PMPs are elevated in Type 2 diabetes. In addition, patients with clinically apparent atherosclerosis had the highest levels of PMPs and sPsel. Thus, PMPs may be a marker of symptomatic atherosclerotic vascular disease in Type 2 diabetes, and may both represent a useful risk stratification tool as well as a novel therapeutic target for anti-thrombotic drugs.

Aged↗
PubMed2003

Brillouin study of the quantization of acoustic modes in nanospheres.

The vibrational modes in three-dimensional ordered arrays of unembedded SiO2 nanospheres have been studied by Brillouin light scattering. Multiple distinct Brillouin peaks are observed whose frequencies are found to be inversely proportional to the diameter (approximately 200-340 nm) of the nanospheres, in agreement with Lamb's theory. This is the first Brillouin observation of acoustic mode quantization in a nanoparticle arising from spatial confinement. The distinct spectral peaks measured afford an unambiguous assignment of seven surface and inner acoustic modes. Interestingly, the relative intensities and polarization dependence of the Brillouin spectrum do not agree with the predictions made for Raman scattering.

Journal Article↗
PubMed2003

Effects of phytase supplementation on the performance, egg quality, and phosphorous excretion of laying hens fed different levels of dietary calcium and nonphytate phosphorous.

An experiment employing a factorial arrangement of two levels (3.0 and 4.0%) of Ca, two levels (0.15 and 0.25%) of nonphytate phosphorus (NPP), and two levels (0 and 300 U/kg diet) of microbial phytase was carried out with 960 ISA-brown layers from 21 to 41 wk of age. There was a significant interaction between NPP level and phytase for egg production. High NPP level and phytase supplementation increased egg production only in the second 10-wk period (31 to 41 wk). High NPP and low Ca increased feed intake, and a significant interaction between levels of NPP and Ca was observed in the first 10 wk. High NPP improved feed efficiency only in the second 10-wk period. Low NPP improved egg specific gravity and eggshell thickness but decreased Haugh units in the first 10-wk period; high NPP decreased the percentage of broken and soft-shell eggs in the second period. Low Ca decreased egg specific gravity, eggshell strength, and eggshell thickness in both periods and increased Haugh units in the second 10-wk period. Phytase supplementation decreased the percentage of broken and soft-shell eggs. High NPP increased fiber availability but decreased Ca availability. High Ca decreased Ca availability, whereas phytase increased availability of dry matter, fiber, and P. High NPP increased retention of P and Fe but also increased excretion of P. High Ca decreased retention of Zn and Fe. Phytase supplementation increased P retention, resulting in decrease of P excretion. In conclusion, supplementation of microbial phytase at a level of 300 U per kg diet of laying hens can improve egg production, decrease broken and soft egg production rate, and P excretion. The effects of phytase supplementation are significantly modified by the level of Ca and NPP.

6-Phytase↗
PubMed2002

Aortic and pulmonary root: are their dynamics similar?

OBJECTIVES: The long-term behavior of the pulmonary autograft in the aortic position (Ross procedure) remains uncertain. Using three-dimensional (3D) sonomicrometry (200 Hz) we compared the dynamics of the aortic and pulmonary roots. METHODS: Twenty-four crystals were implanted in each aortic (eight sheep) and pulmonary roots (six sheep) at: base (3 x 2), commissures (3 x 2), sinotubular junction (3 x 2), ascending aorta (3) and pulmonary trunk (3). Under stable hemodynamic conditions, geometric changes were time-related to left ventricular pressure (LV) and aortic pressure. RESULTS: The expansion of the aortic root is twice that of the pulmonary root. During the cardiac cycle, the aortic root volume increased by 37.7 +/- 2.7% (mean +/- SEM) versus 20.9 +/- 1.0% for the pulmonary root. Both were cone-shaped at end diastole. Because expansion at commissures was twice that of the base, both roots became more cylindrical during ejection. Although both roots started to expand prior to ejection and reached maximal expansion during the first third of ejection, the commissural and sinotubular junction dynamics were different in each root. While in the aortic root, expansion at commissural and sinotubular junction levels was significantly different (63.7 +/- 3.6% versus 37.0 +/- 2.1%), in the pulmonary root, they were similar (29.0 +/- 1.3% versus 27.7 +/- 1.4%). Expansion of the three sinuses was also different (P<0.001). In the aortic root: the right expanded more than the left and more than the non-coronary sinus. In the pulmonary root: the right sinus expanded more than the anterior more than the left. CONCLUSIONS: Dynamic differences might explain the global pulmonary root dilatation when subjected to systemic pressure, particularly at the level of the sinotubular junction which might result in the autograft failure. Differences in the asymmetrical expansion of the aortic and pulmonary roots should be considered for the implantation of the pulmonary autograft in the most physiological position.

Analysis of Variance↗
PubMed2002

A four-dimensional study of the aortic root dynamics.

OBJECTIVE: Although aortic root expansion has been well studied, its deformation and physiologic relevance remain controversial. Three-dimensional (3-D) sonomicrometry (200Hz) has made time-related 4-D study possible. METHODS: Fifteen sonomicrometric crystals were implanted into the aortic root of eight sheep at each base (three), commissures (three), sinuses of Valsalva (three), sinotubular junction (three), and ascending aorta (three). In this acute, open-chest model, the aortic root geometric deformations were time related to left ventricular and aortic pressures. RESULTS: During the cardiac cycle, aortic root volume increased by mean+/-1 standard error of the mean (SEM) 33.7+/-2.7%, with 36.7+/-3.3% occurring prior to ejection. Expansion started during isovolumic contraction at the base and commissures followed (after a delay) by the sinotubular junction. At the same time, ascending aorta area decreased (-2.6+/-0.4%). During the first third of ejection, the aortic root reached maximal expansion followed by a slow, then late rapid decrease in volume until mid-diastole. During end-diastole, the aortic root volume re-expanded by 11.3+/-2.4%, but with different dynamics at each area level. Although the base and commissural areas re-expanded, the sinotubular junction and ascending aorta areas kept decreasing. At end-diastole, the aortic root had a truncated cone shape (base area>commissures area by 51.6+/-2.0%). During systole, the root became more cylindrical (base area>commissures area by 39.2+/-2.5%) because most of the significant changes occurred at commissural level (63.7+/-3.6%). CONCLUSION: Aortic root expansion follows a precise chronology during systole and becomes more cylindrical - probably to maximize ejection. These findings might stimulate a more physiologic approach to aortic valve and aortic root surgical procedures.

Animals↗
PubMed2002

Gestational diabetes mellitus: a call for systematic tracing.

INTRODUCTION: Women with history of gestational diabetes mellitus (GDM) have up to 50% lifetime risk of developing frank diabetes mellitus (DM). They are an ideal group of patients to implement early interventional measures to halt the progression to diabetes. The success of any early intervention programme would depend largely on postpartum follow-up. We set out to study the response rate to postpartum oral glucose tolerance test (OGTT) and to profile the non-responders on 105 women who attended our Gestational Diabetes Joint Clinic (GDJC). MATERIALS AND METHODS: We divided these women into 3 groups according to their response to postpartum OGTT and compared their weights, glycaemic parameters and other clinical characteristics during gestation. Group A comprised non-responders or those who did not turn up for postpartum OGTT; group B comprised responders with a normal postpartum OGTT; and group C comprised responders with an abnormal postpartum OGTT defined as 2-hour plasma glucose equal or more than 7.8 mmol/L. RESULTS: The non-respondent rate to postpartum diabetes screening was 37.1%. The non-responders were found to be significantly heavier, with more severe hyperglycaemia during their pregnancy (in terms of glycosylated haemoglobin and results of antepartum OGTT) and had bigger babies compared to the responders with normal postpartum OGTT. Their features instead resembled those who had failed their postpartum OGTT. CONCLUSION: The group of non-responders was probably at similar risk of developing glucose intolerance postpartum as those who were tested abnormal. A more effective call and recall system and education programme is, therefore, needed to ensure postpartum attendance of all patients with GDM.

Adult↗
PubMed2001

Benefits of micronised Fenofibrate in type 2 diabetes mellitus subjects with good glycemic control.

AIMS: To determine the effects of micronised fenofibrate on lipids and low density lipoprotein (LDL) subfraction in well-controlled diabetic subjects with mild elevations in cholesterol levels. METHODS: Thirty-five male type 2 diabetic subjects with LDL(3) greater than 100 mg/dl and good glycemic control (mean HbA1c 6.7%) were treated with micronised fenofibrate in an open labeled study for 6 months. Anthropometric indices, blood pressure, lipids, glucose, insulin, apolipoprotein A-I and B, and LDL subfraction by density ultracentrifugation were obtained after an overnight fast of 10 h, at the beginning and end of the 6 months treatment period. RESULTS: The blood pressure, waist to hip ratio, body mass index and glycemic control remained unchanged throughout the 6 months study period. Mean serum triglyceride fell from 2.49 to 1.72 mmol/l (33%) whilst HDL cholesterol increased from 0.88 to 0.96 mmol/l (10.8%). There were no significant changes in total or LDL cholesterol. Both LDL(1) and LDL(2) rose significantly whilst the dense LDL(3) fell from a mean of 148 to 85 mg/dl (43% reduction). Fenofibrate changed the LDL subfraction distribution from dense LDL(3) particles towards buoyant LDL(1) and LDL(2) particles in 63% of the subjects. No subjects had elevations in transaminases greater than three-fold or creatine kinase greater than ten-fold from pre-treatment levels. CONCLUSION: Diabetic subjects with mild hypercholesterolemia and good glycemic control may benefit from therapy with micronised fenofibrate because of the reduction in serum triglyceride, elevation in HDL cholesterol and a shift in LDL subfraction towards a non-atherogenic form.

Adult↗