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Biomedical subjects

C N Lee

Publications and source records attributed to C N Lee.

At least 109 records · Page 6Linked to original sources
PubMed1994

Pregnancy following cardiac prosthetic valve replacement.

OBJECTIVE: To determine the effect of cardiac valve replacement on pregnancy outcome. METHODS: We reviewed retrospectively 151 pregnancies in 88 women: 56 pregnancies in 31 women with mechanical valves and anticoagulation therapy, and 95 pregnancies in 57 women with porcine tissue valves. Student t, chi 2, and Fisher exact tests were used for analysis. RESULTS: There was a significantly greater rate of fetal loss in patients with mechanical valve replacements than in those with porcine tissue valves (27.7 versus 12.3%, respectively; P < .05). No significant differences were found in prematurity (5.9 versus 7.7%) or small for dates infants (8.8 versus 10.8%). Two congenital anomalies were noted in the mechanical valve group. Maternal complications in patients with mechanical valves included valve dysfunction (three), thromboembolism (three), abruptio placentae (two), postpartum hemorrhage (two), severe oligohydramnios (two), and puerperal fever caused by brain abscess (one). Four cases of valve dysfunction and one of infectious endocarditis complicated the condition of patients with porcine tissue valves. The 10-year graft survival rate in the porcine valve group was lower following two subsequent pregnancies (16.7%) than following one (54.8%). CONCLUSION: Fewer fetal and maternal complications occurred in subsequent pregnancies after porcine valve replacement. However, the need for reoperation is more likely, and pregnancy might accelerate the degenerative process.

Adult↗
PubMed1994

Age-related changes in normal Chinese hearts.

The heart weights, ventricular wall thickness and valve circumferences were measured in 507 autopsy specimens of normal hearts from persons aged from 10 to 90 years. The heart weights increased with age and were greater in the males than in the females, except from the 6th to 8th decades where they were reversed. The body weight was the best predictor of heart weight. The ventricular wall thickness in males did not differ significantly from that in females. The values of the indexed left ventricular wall thickness (i.e. values divided by BSA) in the females exceeded those in the males from the 6th to 9th decades. The mean valve circumference was greater in the males but it was significant (P < 0.05) only for the tricuspid valves at the 9th decade of life. The pulmonary valve circumferences were greater than the aortic for all decades and the ratio of the aortic to pulmonary valve circumference remained constant. In the clinical evaluation of the specimens of Chinese hearts, the absence of the aged-related dilatation of the aorta described in Caucasian hearts should be duly taken into account.

Adolescent↗
PubMed1993

Metabolic profile of patients after elective open heart surgery.

To evaluate the surgical stress of open heart surgery with moderate hypothermic cardiopulmonary bypass (CPB), oxygen consumption (VO2), carbon dioxide production (VCO2), resting energy expenditure (REE), respiratory quotient (RQ), 24 hour-urinary urea nitrogen excretion (UUN), and glucose, fat and protein utilization were determined in 20 patients before and after open heart surgery. Proteins (albumin, prealbumin and transferin) and body weight were measured preoperatively and on 6th postoperative day (POD). Preoperative predicted EE as determined by the Harris-Benedict equation was correlated with measured REE. No significant alteration in VO2, VCO2, REE, 24 hour UUN and protein utilization was observed on the first 6 PODs. RQ decreased significantly on the 1st, 3rd and 4th POD. This was attributed to greater fat utilization due to reduced calorie intake during the early postoperative period. Transport proteins reduced slightly but insignificantly. There was a significant reduction in body weight at the end of the study period due probably to loss of body water. We conclude that patients in the early postoperative period after uneventful open heart surgery are neither hypermetabolic nor hypercatabolic when compared with their stable state before operation.

Journal Article↗
PubMed1993

Flow studies on atriopulmonary and cavopulmonary connections of the Fontan operations for congenital heart defects.

A comparative flow study has been conducted on two configurations of the Fontan operations for congenital heart defects in which the right ventricle is by-passed. The study was made on rigid in vitro models of the atriopulmonary and cavopulmonary connections under steady-flow conditions. It involved using pressure and flow measurements to determine the pressure-drop coefficient, pressure-energy-loss coefficient and total-energy-loss coefficient. The cavopulmonary model was found to have much lower flow losses compared to the atriopulmonary model, especially at flow rates about 5 l min-1.

Anastomosis, Surgical↗
PubMed1993

Environmental stress effects on bovine reproduction.

Environmental stress is not limited to climatic factors but extends to nutrition, housing, and any stimuli that demand a response from the animal to adapt to new circumstances. Low energy and low or excessive protein levels in the diet are detrimental to reproduction. Likewise, high ambient temperatures and humidity alter the intricate balance of endocrine profiles, leading to lower intensity of estrous behavior, anestrus, embryonic death, and subsequent infertility. Most of these stress factors can be managed with modern technologies to achieve maximum production. Further research in vitamins and minerals under heat stress may add to the knowledge of efficient livestock production.

Animal Husbandry↗
PubMed1993

Moderate heat treatment increases the penetrability of zonae pellucidae of salt-stored mammalian oocytes by spermatozoa.

The zona pellucida of mammalian oocytes stored in highly concentrated solutions of neutral salts is known to retain its biological and biochemical properties. However, the zona may become resistant to sperm penetration as the storage period is increased. In cattle and hamsters, the penetrability of zonae of salt-stored oocytes was restored or increased by treating the oocytes with moderate heat without altering the gross morphology of the zona. Although this technique did not work for salt-stored human ova, this may have been due to the use of so-called inseminated-unfertilised ova which (1) may have been fertilised but failed to activate, or (2) were not fertilised because of functionally defective zonae.

Animals↗
PubMed1993

Laser anemometry measurements of steady flow past aortic valve prostheses.

An experimental investigation was conducted in steady flow to examine the fluid dynamics performance of three prosthetic heart valves of 27 mm diameter: Starr-Edwards caged ball valve, Bjork-Shiley convexo-concave tilting disk valve, and St. Vincent tilting disk valve. It was found that the pressure loss across the St. Vincent valve is the least and is, in general, about 70 percent of that of the Starr-Edwards valve. The pressure recovery is completed about 4 diameters downstream. The velocity profiles for the ball valve reveal a large single reversed flow region behind the occluder while those for the tilting disks valves reveal two reversed flow regions immediately behind the occluders. Small regions of stasis are also found near the wall in the minor opening of Bjork-Shiley valve and in the major opening of St. Vincent valve. The maximum wall shear stresses of the three valves at a flow rate of 30 l/min are in the range 30-50 dyn/cm2 which can cause hemolysis of attached red blood cells. The corresponding maximum Reynolds normal stresses are in the range of 1600-3100 dyn/cm2. The Reynolds normal stresses decay quickly and return approximately to the upstream undisturbed level at about 4 diameters downstream while the wall shear stresses decay at a slower rate. The maximum Reynolds normal stresses occur at about 1 diameter downstream while the maximum wall shear stress is at about 2 diameters downstream. In general, the St. Vincent valve has better performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗
PubMed1993

Mutational analysis of the leucine zipper-like motif of the human immunodeficiency virus type 1 envelope transmembrane glycoprotein.

The N-terminal region of the envelope (env) transmembrane protein of human immunodeficiency virus type 1 (HIV-1) has a leucine zipper-like motif. This highly conserved zipper motif, which consists of a heptad repeat of leucine or isoleucine residues, has been suggested to play a role in HIV-1 env glycoprotein oligomerization. This hypothesis was tested by replacing the highly conserved leucine or isoleucine residues in the zipper motif with a strong alpha-helix breaker, proline. We report here that such substitutions did not abolish the ability of env protein to form oligomers, indicating that this highly conserved zipper motif does not have a crucial role in env protein oligomerization. However, the mutant viruses all showed impaired infectivity, suggesting that this conserved zipper motif can have an important role in the virus life cycle.

Amino Acid Sequence↗
PubMed1993

Effects of the purine biosynthesis pathway inhibitors azaserine, hadacidin, and mycophenolic acid on the developing ovine corpus luteum.

De novo synthesis precursors of the purine second messengers adenosine, guanosine and inosine are adenosine, guanosine and inosine monophosphate (AMP, GMP, IMP), respectively. Inhibitors of the de novo purinergic synthesis pathways for AMP, GMP and IMP by hadacidin, mycophenolic acid and azaserine, respectively, or adenosine, guanosine or inosine alone or in combination were given every 4 or 6 hours in vivo. Treatments were given into the ovarian vascular pedicle sheath adjacent to the luteal-bearing ovary in three separate experiments to determine whether purines were involved in development of the corpus luteum. Hadacidin lowered AMP (p < or = 0.01) and azaserine tended to lower IMP and the GMP: AMP ratio (p < or = 01) while mycophenolic acid tended to lower the GMP:AMP ratio (p < or = 0.1) in luteal tissue. Azaserine (150 mg) increased progesterone (p < or = 0.01) on some days but guanosine or inosine had no effect on profiles of progesterone in jugular blood of the developing corpus luteum (p > or = 0.1). Azaserine (500 micrograms) tended to lower progesterone in jugular blood (p < or = 0.1) while profiles of progesterone did not differ among guanosine or inosine or adenosine, guanosine and inosine plus hadacidin, mycophenolic acid and azaserine treatment groups compared to controls (p > or = 0.1). Weights of corpora lutea or composition of cell types in the corpus luteum or their viability were not affected by adenosine, guanosine, inosine, hadacidin, mycophenolic acid or azaserine (p > or = 0.1). Since profiles of jugular progesterone did not differ between treatments during development of the corpus luteum, these results suggest that progesterone production by the developing corpus luteum is a) less dependent on de novo synthesized purines or b) there may be a non-purinergic-dependent second messenger system controlling biosynthesis of steroids in the developing ovine corpus luteum.

Adenosine Monophosphate↗
PubMed1993

Prevalence of peripheral artery disease in patients with coronary artery disease.

The incidence of coronary artery disease in Singapore has shown a rapid rise in recent years, however, there is a subjective impression that the prevalence of atherosclerotic peripheral artery diseases, although sharing common aetiological factors with coronary artery disease, has not shown a similar rise. We set out to determine the incidence of occlusive peripheral artery diseases of the lower limb in a selected population of Asian patients using a non-invasive test and we analysed the risk factors. The overall prevalence of peripheral artery disease of the subjects as determined by an abnormal ankle brachial index less than 0.9 in at least one limb was 19.1%. Increasing age, hypercholesterolemia and smoking were risk factors. In patients with proven coronary artery disease, abnormal ankle brachial indices were present in 21.3% of patients with angiographic evidence of coronary artery disease but in only 13.0% of those without. In this study, the incidence of peripheral artery disease in this selected Asian population was high. With the increasing availability of vascular laboratories and awareness of the diseases, we can expect to see increasing numbers of patients presenting with these problems.

Adult↗
PubMed1993

Sclerosing haemangioma of lung--case report with histologic, immunohistochemical and ultrastructural correlation.

We report a case of a large sclerosing haemangioma of the lung that was found incidentally on roentgenography of an asymptomatic woman presenting for routine health screening. Computed tomographic scan showed a well-defined "coin" lesion with peripheral foci of calcification. The lesion had a variegated histological appearance comprising four major patterns--solid, papillary, haemorrhagic and sclerotic. There appeared to be two populations of cells--distinct round cells with abundant clear cytoplasm constituting the solid component and uniform cuboidal cells with small, dark nuclei lining irregular spaces. Positive immunohistochemical staining for cytokeratin and epithelial membrane antigen, and the ultrastructural demonstration of epithelial characteristics and electron-dense bodies showed that the proliferating cells had features in keeping with type 2 pneumocytes. This is a benign condition and the prognosis is excellent.

Adult↗
PubMed1992

Mitral valve repair in patients on chronic hemodialysis.

Two cases of successful mitral valve repair in patients on chronic hemodialysis are presented. We stress that valve repair is preferable to valve replacement whenever feasible because of improved left ventricular function, reduced complication rate, and freedom from anticoagulation. This especially applies to patients on chronic hemodialysis as they have impaired immunological function, are subjected to repeated fistula punctures with possible bacteremia, and are more susceptible to early calcification and degeneration of tissue valves.

Female↗
PubMed1992

Effect of prostaglandin F2 alpha (PGF2 alpha) on sources of progesterone and pregnancy in intact, ovariectomized and hysterectomized 90-100 day pregnant ewes.

A single dose of 8 or 16 mg of PGF2 alpha per 58 kg body weight was injected intramuscular into intact, ovariectomized or hysterectomized 90-100 day pregnant sheep in three separate experiments. Both doses of PGF2 alpha decreased the weights of the corpora lutea (P less than or equal to 0.05) and the concentration of progesterone in ovarian venous plasma at 72 hr (P less than or equal to 0.05) compared to the 0 hr sample within treatment groups and to control ewes at 72 hr in intact and hysterectomized pregnant ewes. In hysterectomized pregnant ewes, progesterone in jugular plasma declined (P less than or equal to 0.05) from 0 to 72 hr but never fell below 4 mg/ml and this decrease in progesterone after 8 or 16 mg PGF2 alpha was greater than in control hysterectomized ewes (P less than or equal to 0.05). There was a significant decrease in progesterone over time in jugular or uterine venous plasma in the presence of absence of the ovaries in 90-100 day pregnant ewes (P less than or equal to 0.05) but the profiles of progesterone were not different between vehicle and PGF2 alpha-treated ewes (P greater than or equal to 0.05). Uterine venous progesterone never declined below 30 ng/ml in the presence or absence of the ovaries and there was a significant quadratic increase (P less than or equal to 0.05) in uterine venous progesterone toward the end of the 72 hr sampling period indicating an increase in steroidogenic activity of the placenta. PGF2 alpha did not affect the number of abortions in intact or ovariectomized pregnant ewes (P greater than 0.05). Thus, the corpus luteum of sheep at 90-100 days of pregnancy is functional and responsive to PGF2 alpha, placentomes are functional but do not appear to be responsive to the doses of PGF2 alpha tested and PGF2 alpha was not an abortifacient over the 72 hr treatment period.

Animals↗
PubMed1992

Adenosine facilitates the response to HCG, PGE1 or PGE2 and inhibits the response to PGF2 alpha by HCG-stimulated ovine luteal cells in vitro.

Dispersed ovine luteal cells collected on day 7 or 16 postestrus were incubated in vitro with hCG, PGE1 or PGE2 in the presence or absence of adenosine, dipyridamole (inhibitor of adenosine uptake) or PGF2 alpha in two separate experiments. Secretion of progesterone was increased by hCG, PGE1 or PGE2 when incubated with day 7 luteal cells (P less than or equal to 0.05) which was increased further when co-incubated with adenosine (P less than or equal to 0.05). PGF2 alpha alone or in the presence of hCG decreased (P less than or equal to 0.05) the secretion of progesterone by day 7 luteal cells, PGF2 alpha decreased post treatment cell viability with or without hCG (P less than or equal to 0.05) and adenosine reduced (P less than or equal to 0.05) the inhibitory effect of PGF2 alpha on hCG actions and luteal cell viability. Day 16 luteal cells were not functional based on jugular progesterone (P less than or equal to 0.05) and did not respond to hCG, PGE1, or PGE2 in the presence of adenosine or PGF2 alpha (P greater than or equal to 0.05). It is concluded that adenosine enhances the response of functional luteal cells to the luteotropins hCG, PGE1 or PGE2 and adenosine reduces the luteolytic response to PGF2 alpha by hCG-stimulated ovine luteal cells in vitro.

Adenosine↗
PubMed1992

Intravascular hemolysis after mitral valve repair: a word of caution.

The case of a young patient who presented with severe hemolysis after mitral valve repair is presented. Valve repair included chordal shortening, transposition of chordae tendinae, and annular remodelling using a Duran flexible ring. Reoperation and valve replacement were required to control hemolytic anemia. The possible mechanisms leading to such an uncommon complication after plastic repair of the mitral valve are commented on. The scanty literature concerned is reviewed.

Adult↗
PubMed1992

Coronary artery bypass surgery in young patients.

Coronary atherosclerosis is being increasingly observed in young patients. However results of surgery in such patients have so far been disappointing both in terms of operative mortality, symptomatic relief and long-term survival. Reasons given for this include the increased prevalence of risk factors in young patients and a higher incidence of graft occlusion. In the treatment of Asian patients, a further negative factor is the belief that coronary artery disease is more often diffuse and the vessels smaller. Between January 1987 and May 1991, a total of 66 patients under the age of 45 years at the time of surgery had coronary artery bypass grafting performed. The demographic, clinical, angiographic and operative data were analysed. Eighty-nine per cent of the patients were male and their racial distribution was 63% Chinese, 8% Malays, 26% Indians and 3% Others. Their mean age was 40.8 years. The presence of risk factors was high: 45.6% had hypertension; 34.8% were smokers; 21.2% had diabetes mellitus; and 12.1% had hyperlipidaemia. The main indication in these patients was either angina or a previous myocardial infarction (53%). There were no patients with perioperative infarction diagnosed by the presence of new Q wave. There was no hospital death. The stay of the patients ranged from 6 to 28 days with a mean of 10 days. Follow-up ranged from 3 to 54 months. There were no late deaths. It was concluded that there is a high incidence of risk factors among young patients with coronary artery disease, which follows the pattern of many other studies. The operative risk in these patients is low and morbidity is minimal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗