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Biomedical subjects

A C Lai

Publications and source records attributed to A C Lai.

At least 19 recordsLinked to original sources
PubMed2002

Haemodynamics during a complete exercise induced atrioventricular block.

The case is reported of an athlete who, during an exercise test, had a complete atrioventricular block without symptoms of cardiac output failure. Heart rate, stroke index, cardiac index, and myocardial contractility were monitored during the episode by an impedance cardiograph. The most important findings of this report are the continuous increase in stroke index, which compensated for the lack of heart rate response, and the normal cardiac index values achieved during the exercise. This stroke index response was mainly due to an increase in myocardial contractility.

Adult↗
PubMed2001

Dynamics of intramural and transmural reentry during ventricular fibrillation in isolated swine ventricles.

The intramural dynamics of ventricular fibrillation (VF) remain poorly understood. Recent investigations have suggested that stable intramural reentry may underlie the mechanisms of VF. We performed optical mapping studies of VF in isolated swine right ventricles (RVs) and left ventricles (LVs). Nine RV walls were cut obliquely in their distal edge exposing the transmural surface. Six LV wedge preparations were also studied. Results showed that intramural reentry was present. In RV, 28 of 44 VF episodes showed reentry; 15% of the activation pathways were reentrant. Except for 4 episodes, reentry was transmural, involving subendocardial structures as the papillary muscle (PM) or trabeculae. In LV, reentry was observed in 27 of 27 VF episodes; 23% of the activations were part of reentrant pathways (P<0.05 compared with RV). All LV reentrant pathways were truly intramural (confined to the wall) and were frequently located at the PM insertion. In both ventricles, reentry was spatially and temporally unstable. Histological studies showed abrupt changes in fiber orientation at sites of reentry and wave splitting. Connexin 40 immunostaining demonstrated intramyocardial Purkinje fibers at sites of reentry in the PM root and around endocardial trabeculae. Our results confirm that reentry is frequent-but unstable-in the myocardial wall during VF. In RV, reentry is mostly transmural and requires participation of subendocardial structures. The LV has a greater incidence of reentry and is intramural. Anisotropic anatomic structures played key roles in the generation of wave splitting and in the maintenance of reentry.

Animals↗
PubMed2001

Diverged evolution of recent equine-2 influenza (H3N8) viruses in the Western Hemisphere.

We reported previously that equine-2 influenza A virus (H3N8) had evolved into two genetically and antigenically distinct "Eurasian" and "American" lineages. Phylogenetic analysis, using the HA1 gene of more recent American isolates, indicated a further divergence of these viruses into three evolution lineages: A South American lineage, a Kentucky lineage, and a Florida lineage. These multiple evolution pathways were not due to geographic barriers, as viruses from different lineages co-circulated. For the Kentucky lineage, the evolution rate was estimated to be 0.89 amino acid substitutions per year, which agreed with the previously estimated rate of 0.8. For the South American lineage, the evolution rate was estimated to be only 0.27 amino acid substitutions per year. This low evolution rate was probably due to a unique alternating Ser138 to Ala138 substitutions at antigenic site A. For the Kentucky lineage, there was a preference for sequential nonsynonymous substitutions at antigenic site B, which was also a "hot spot" for amino acid substitutions. Convalescent sera had minimal cross-reactivity to viruses of different lineages, indicating antigenic distinctions among these viruses. In contrast to human H3N2 viruses, our results suggested that the evolution of equine-2 influenza virus resembled the multiple evolution pathways of influenza B virus.

Amino Acid Sequence↗
PubMed2001

Randomized trial of low-dose misoprostol and naproxen vs. nabumetone to prevent recurrent upper gastrointestinal haemorrhage in users of non-steroidal anti-inflammatory drugs.

BACKGROUND: Prophylactic misoprostol or non-steroidal anti-inflammatory drugs (NSAIDs) with low gastric toxicity (nabumetone) has been shown to reduce mucosal injury. AIM: To compare nabumetone vs. co-therapy of naproxen with low-dose misoprostol for secondary prevention of upper gastrointestinal bleeding in NSAID users. METHODS: NSAID users presenting with upper gastrointestinal bleeding were enrolled if they required long-term NSAIDs. After ulcer healing, they were randomized to receive: naproxen (500-1000 mg/day) and misoprostol (200 microg b.d.), or nabumetone (1000-1500 mg/day) and placebo misoprostol for 24 weeks. The primary end-point was recurrent upper gastrointestinal bleeding. The secondary end-point was the proportion of patients suffering from major gastrointestinal events including ulcer bleeding, symptomatic ulcers and severe dyspepsia. RESULTS: A total of 90 patients were included in the intention-to-treat analysis (misoprostol/naproxen 45, nabumetone 45). Recurrent bleeding occurred in 10 patients (22.2%) receiving misoprostol/naproxen compared with three (6.7%) receiving nabumetone (relative risk 3.33, 95% CI: 0.98-11.32, P=0.069). The proportion of patients suffering from major gastrointestinal events at 24 weeks was 31.1% in the misoprostol/naproxen group and 28.9% in the nabumetone group. CONCLUSIONS: Misoprostol/naproxen is not superior to nabumetone for secondary prevention of upper gastrointestinal bleeding. Neither low-dose misoprostol nor nabumetone is adequate for high-risk NSAID users.

Adult↗
PubMed2001

Dysfunction of oesophageal motility in Helicobacter pylori-infected patients with reflux oesophagitis.

BACKGROUND: Helicobacter pylori infection has been suggested to be protective against gastro-oesophageal reflux disease. However, a significant proportion of patients with gastro-oesophageal reflux disease are infected by H. pylori. AIM: To study oesophageal motor function in H. pylori-infected patients with reflux oesophagitis. METHODS: Patients with erosive reflux oesophagitis were recruited prospectively for stationary oesophageal manometry and 24-h ambulatory oesophageal pH monitoring. H. pylori status was determined by biopsy urease test. Non-reflux volunteers were recruited as controls. RESULTS: Seventy-four patients with erosive oesophagitis (34 H. pylori-positive, 40 H. pylori-negative) and 48 non-reflux patient controls (22 H. pylori-positive, 26 H. pylori-negative) were recruited. There was no difference in severity of oesophagitis (median grade, 1; P=0.53) or oesophageal acid exposure (total percentage time oesophageal pH < 4, 7.6% vs. 6.8%; P=0.57) between H. pylori-positive and H. pylori-negative groups. Compared to H. pylori-negative patients, H. pylori-positive patients had significantly lower basal lower oesophageal sphincter pressure (12.2 mmHg vs. 15.3 mmHg; P=0.03) and amplitude of distal peristalsis (56.9 mmHg vs. 68.4 mmHg; P=0.03). Ineffective oesophageal motility (14% vs. 7%; P=0.02) and failed oesophageal peristalsis were also significantly more prevalent in H. pylori-positive patients. CONCLUSIONS: Among patients with a similar degree of reflux oesophagitis, H. pylori-infected patients have more severe oesophageal dysmotility and lower oesophageal sphincter dysfunction. Oesophageal motor dysfunction probably plays a dominant role in the development of gastro-oesophageal reflux disease in patients with H. pylori infection.

Adult↗
PubMed2001

Bacteriologic analyses of bile and brown pigment stones in patients with acute cholangitis.

BACKGROUND: Bacteria play an important role in the formation of brown pigment stones through adherence and biofilm formation. Scanning electron microscopy of cross sections of these stones reveals a laminated appearance and various bacteria in the different layers. Our postulation was that different bacteria might be involved at different stages of stone formation. METHODS: By using standard bacteriologic cultures, the composition, morphology, and antibiotic sensitivity patterns of bacteria isolated from paired stone were compared with bile samples from 70 patients with acute cholangitis. A further comparison was made between bacteria isolated from the periphery and center of 3 randomly selected brown pigment stones. RESULTS: Ninety-one percent of bile and 99% of stone samples yielded positive cultures, with a total of 151 and 149 bacteria isolated from bile and stones, respectively. In 22 patients (33%), the bacteria isolated from the paired bile and stone samples were totally different. The mean percentage similarity of bacteria isolated from bile and stones was 39% (range 0%-100%). Of the 59 pairs of similar bacteria isolated, the antibiotic sensitivity patterns were different in 24 (41%) cases. Of the 3 brown stones studied, either different bacterial species or the same bacteria but different strains with different antibiotic sensitivities were isolated from the center and periphery of the stones. CONCLUSIONS: Bacteria present in the different layers of brown pigment stones may represent the bacterial flora in bile at different times. Simple bile culture may not identify bacteria trapped inside the stone.

Bile↗
PubMed2001

Indigenization and beyond: methodological relationalism in the study of personality across cultural traditions.

A brief intellectual history of the indigenization movement in Asia leads to the thesis that the generation of psychological knowledge is culture dependent. Indigenous psychologies go further and insist on viewing a target group from the natives' own standpoint. Psychological decentering underlies conceptions of human existence rooted in Asian intellectual traditions, in particular, relatedness between persons predominates in Confucianism. These conceptions demand new approaches to knowledge generation that signify a paradigmatic shift from methodological individualism to methodological relationalism. An implication is that relationships precede situations in the study of personality and social behavior. We define personality as the sum total of common attributes manifest in, and abstracted from, a person's behavior directly or indirectly observed across interpersonal relationships and situations over time. We rely on the notion that there are identifiable levels of cognition to develop a metatheoretical framework for reconstructing selfhood. Confronting the subject-object dichotomy opens the door to investigations of transcendent consciousness; confronting the self-other demarcation underlying Western theories leads to the construction of self-in-relations.

Cross-Cultural Comparison↗
PubMed2000

Relationship between regional cardiac hyperinnervation and ventricular arrhythmia.

BACKGROUND: Sympathetic nerve activity is known to be important in ventricular arrhythmogenesis, but there is little information on the relation between the distribution of cardiac sympathetic nerves and the occurrence of spontaneous ventricular arrhythmias in humans. METHODS AND RESULTS: We studied 53 native hearts of transplant recipients, 5 hearts obtained at autopsy of patients who died of noncardiac causes, and 7 ventricular tissues that had been surgically resected from the origin of ventricular tachycardia. The history was reviewed to determine the presence (group 1A) or absence (group 1B) of spontaneous ventricular arrhythmias. Immunocytochemical staining for S100 protein, neurofilament protein, tyrosine hydroxylase, and protein gene product 9.5 was performed to study the distribution and the density of sympathetic nerves. The average left ventricular ejection fraction was 0.22+/-0.07. A total of 30 patients had documented ventricular arrhythmias, including ventricular tachycardia and sudden cardiac death. A regional increase in sympathetic nerves was observed around the diseased myocardium and blood vessels in all 30 hearts. The density of nerve fibers as determined morphometrically was significantly higher in group 1A patients (total nerve number 19.6+/-11.2/mm(2), total nerve length 3.3+/-3.0 mm/mm(2)) than in group 1B patients (total nerve number 13.5+/-6.1/mm(2), total nerve length 2.0+/-1.1 mm/mm(2), P<0. 05 and P<0.01, respectively). CONCLUSIONS: There is an association between a history of spontaneous ventricular arrhythmia and an increased density of sympathetic nerves in patients with severe heart failure. These findings suggest that abnormally increased postinjury sympathetic nerve density may be in part responsible for the occurrence of ventricular arrhythmia and sudden cardiac death in these patients.

Antibodies↗
PubMed2000

The ligament of Marshall: a structural analysis in human hearts with implications for atrial arrhythmias.

OBJECTIVES: We sought to study the anatomy of human ligament of Marshall (LOM). BACKGROUND: Although the LOM has been implicated in the genesis of focal atrial tachyarrhythmias, its gross anatomic and microscopic features in humans hearts have not been completely defined. METHODS: We studied seven postmortem human hearts from five men and two women with a mean age of 52 +/- 26 years. Four did not have any heart disease. One woman had dilated cardiomyopathy, and two men had chronic atrial fibrillation. A block of tissue encompassing the LOM from the coronary sinus (CS) cephalad, between the atrial appendage and left pulmonary veins, was dissected. Serial sections from this tissue were then stained with hematoxylin and eosin, trichrome, and/or tyrosine hydroxylase. RESULTS: The LOM consists of multiple sympathetic nerve fibers, ganglia, blood vessels and multiple myocardial tracts (Marshall Bundles) insulated by fibrofatty tissue. One or more myocardial tracts was inserted directly into the left atrial free wall and CS. The distance between insertion sites was 7.8 +/- 2.5 mm. Nerve fibers, some tyrosine hydroxylase positive, were present within the fibrofatty matrix and within the myocardial tracts. CONCLUSIONS: Human LOM 1) is innervated by sympathetic nerve fibers; 2) is more complex than the LOM in canine hearts; and 3) has multiple myocardial tract insertions into the left atrial free wall and CS, forming a substrate of reentry. Radiofrequency catheter ablation from the CS may fail to reach the free wall insertion.

Adult↗
PubMed2000

Colocalization of tenascin and sympathetic nerves in a canine model of nerve sprouting and sudden cardiac death.

INTRODUCTION: Sympathetic nerve sprouting after myocardial infarction (MI) may contribute significantly to the occurrence of ventricular arrhythmia and sudden cardiac death. Tenascin-X (TnX), a matrix protein known to be associated with nerve growth in central and peripheral nerves, also may play a role in cardiac nerve sprouting after MI. METHODS AND RESULTS: Immunocytochemical staining techniques were used to identify nerves in 5-microm serial sections from 6 normal dogs and 11 dogs with MI. Among the dogs with MI, 4 also received nerve growth factor infusion to the left stellate ganglion. The time between MI to tissue harvest averaged 35.7 +/- 14.4 days. Tyrosine hydroxylase (TH) stain was used to identify sympathetic nerves, and growth-associated protein-43 (GAP-43) was used to identify growing nerves. Polyclonal antibody was obtained for use in identifying TnX. Nerves were evident in both the infarcted and noninfarcted areas. Many nerves were found around blood vessels. A total of 181 nerves in 69 slides were examined: 89 were from noninfarcted myocardium, 4 from infarct, 13 from infarct border zone, and 75 from perivascular regions. Except in normal dogs, all nerves stained positive for TH also stained positive for GAP-43, indicating sympathetic nerve sprouting after MI. In all dogs, the nerves that stained positive for TH also stained positive for TnX. CONCLUSION: There is a colocalization of TnX, GAP-43, and TH in sprouted cardiac nerves. These results suggest that TnX is important not only in the existing normal myocardial nerve cells but also in cardiac sympathetic nerve sprouting after MI.

Animals↗
PubMed2000

Inhalation transfer factors for air pollution health risk assessment.

To facilitate routine health risk assessments, we develop the concept of an inhalation transfer factor (ITF). The ITF is defined as the pollutant mass inhaled by an exposed individual per unit pollutant mass emitted from an air pollution source. A cumulative population inhalation transfer factor (PITF) is also defined to describe the total fraction of an emitted pollutant inhaled by all members of the exposed population. In this paper, ITFs and PITFs are calculated for outdoor releases from area, point, and line sources, indoor releases in single zone and multizone indoor environments, and releases within motor vehicles. Typical PITFs for an urban area from emissions outdoors are approximately 10(-6)-10(-3). PITFs associated with emissions in buildings or in moving vehicles are typically much higher, approximately 10(-3)-10(-1).

Air Pollutants↗
PubMed1999

Ultrarapid cryopreservation of human embryos: experience with 1,582 embryos.

OBJECTIVES: To demonstrate the effectiveness of ultrarapid cryopreservation in human embryos. DESIGN: Retrospective study. SETTING: An IVF unit of a medical center. PATIENT(S): All cases received ultrarapid freezing (URF) of embryos and frozen embryo transfer. INTERVENTION(S): Embryos were placed in phosphate-buffered saline (PB1) + 20% maternal serum (MS) for 5 minutes. Embryos were loaded to the straws containing PB1 + MS + 0.25 M sucrose (SUC) + 3.5 M dimethyl sulfoxide for 3 minutes, and then were stored in a liquid nitrogen tank. Embryos were thawed in a 37 degrees C water for 6 seconds and then cultured in PB1 + MS + SUC for 10 minutes. Embryos were transferred into PB1 + MS for 5 minutes and were transferred into patients. MAIN OUTCOME MEASURE(S): The embryo grades before and after URF, the survival and transferred embryo numbers, and the pregnancy and abortion rates were analyzed. RESULT(S): A total of 1,582 embryos were thawed, of which 1,273 (80.5%) embryos were transferred and 1,032 (65.2%) embryos survived with > or = 50% intact blastomere. The embryo numbers with grade I or II before and after freezing and thawing were 1,110 (70.2%) and 790 (50.0%). The mean embryo numbers per transfer was 5.0. Twenty-eight pregnancies (11.4% per transfer) were established, which included 5 miscarriages, 1 ectopic pregnancy, 4 preterm and 18 term deliveries. CONCLUSION(S): Ultrarapid freezing is worthy of reconsideration for embryo cryopreservation.

Abortion, Spontaneous↗
PubMed1999

Isolation of avian influenza viruses in central Oklahoma.

Aquatic birds are the natural hosts for influenza virus. It is established that avian influenza viruses provide the gene pool for the generation of new strains of human influenza virus, which can cause pandemic infections. The recent outbreak of an avian influenza virus (H5N1) in Hong Kong not only produced high mortality in chickens, but also resulted in six human fatalities. This outbreak indicates that avian influenza virus can be pathogenic for humans. We surveyed local waterfowl habitats by taking water and fecal samples for virus isolation and identification. We isolated avian influenza viruses from ponds and small lakes in Bartlesville, Lawton, Stillwater, and Tulsa. The density of birds in these sites is small. However, our virus isolation rate is comparable to that found in higher density habitats. The risk of human infection remains to be determined. We encourage primary care physicians to submit samples for virus surveillance.

Animals↗
PubMed1998

Does eradication of Helicobacter pylori impair healing of nonsteroidal anti-inflammatory drug associated bleeding peptic ulcers? A prospective randomized study.

BACKGROUND: Despite the widely accepted view that Helicobacter pylori is the most important cause of peptic ulcer disease, recent studies have suggested that the microbe protects against nonsteroidal anti-inflammatory drug (NSAID)-associated gastroduodenal lesions and promotes ulcer healing. We investigated the effects of H. pylori eradication on the healing of NSAID-associated bleeding peptic ulcers. METHODS: Chronic NSAID users presenting with peptic ulcer haemorrhage underwent endoscopy to secure haemostasis and to document H. pylori infection by rapid urease test and culture. They were prospectively randomized to receive either omeprazole (20 mg once daily) for 8 weeks or a 1-week course of triple therapy (bismuth subcitrate 120 mg, tetracycline 500 mg, metronidazole 400 mg, all given four times daily) plus omeprazole (20 mg once daily) for 8 weeks. Endoscopy was repeated after 8 weeks. Final H. pylori status was determined by a 13C-urea breath test that was performed at least 4 weeks after discontinuation of omeprazole. RESULTS: 195 H. pylori-infected NSAID users, complicated by bleeding ulcers, were randomized to receive omeprazole alone (102) or triple therapy plus omeprazole (93). 174 patients returned for second endoscopy at 8 weeks (91 in the omeprazole group, 83 in the triple therapy group). Urea breath test was negative in 14% in the omeprazole group vs. 92% in the triple therapy group (P < 0.001). Complete ulcer healing was achieved in 88 (97%) patients in the omeprazole group and 77 (93%) in the triple therapy group (P=0. 31). On intention-to-treat analysis, ulcers were healed in 86% of the omeprazole group and 83% of the triple therapy group (P=0.50). There was no significant difference in the healing rates of gastric or duodenal ulcers between the two groups. CONCLUSION: Eradication of H. pylori did not impair the healing of NSAID-associated bleeding peptic ulcers.

Adult↗
PubMed1996

Pregnancies after transfer of ultrarapidly frozen human embryos.

PURPOSE: We report our experience of freezing human embryos using an ultrarapid freezing method. METHODS: The patients were superovulated. Oocytes were inseminated and cultured in HTF + 10% serum. A maximum of three embryos was transferred and the rest of the embryos were frozen ultrarapidly after a 3-min equilibration period in PB1 + 3.5 M DMSO + 0.25 M sucrose. Embryos were thawed in a 37 degrees C water bath for 6 sec, then cultured in PB1 + 20% serum for 10 min. The surviving embryos were transferred into patients on the same day of thawing. RESULTS: Sixty-three embryos were thawed, of which 52 embryos (83%) survived with at least one intact blastomere. Nineteen frozen-thawed embryo transfers were made. The mean embryos per transfer was 2.7. Three pregnancies (16%/transfer) were established. One miscarriage occurred in the eighth week of pregnancy. Two pregnancies went to term and three healthy infants were born. CONCLUSIONS: The present data demonstrate that ultrarapid freezing is a method worth consideration in the area of human embryo freezing.

Abortion, Spontaneous↗
PubMed1996

Antigenic and genetic evolution of equine H3N8 influenza A viruses.

Evolution of equine influenza a H3N8 viruses was examined by antigenic and genetic analysis of a collection isolates from around the world. It was noted that antigenic and genetic variants of equine H3N8 viruses cocirculate, and in particular that variants currently circulating in Europe and the USA are distinguishable from one another both in terms of antigenic reactivity and genetic structure of the HA1 portion of the haemagglutinin (HA) molecule. Whilst the divergent evolution of American and European isolates may be due to geographical isolation of the two gene pools, some mixing is believed to occur as 'American-like' viruses have been isolated during outbreaks of equine influenza in the UK. The cocirculation of two antigenically and genetically distinct lineages of equine influenza H3N8 viruses has serious implications for vaccine strain selection.

Amino Acid Sequence↗
PubMed1996

Stress in parents whose children are hepatitis B virus (HBV) carriers: a comparison of three groups in Guangzhou, China.

This study was conducted in Guangzhou, China. It compared the responses on stress scales of three groups of parents: (1) parents of children with HBV attending a special health kindergarten; (2) parents of children with HBV who stayed at home; and (3) parents of healthy children attending ordinary kindergartens. Parents of HBV infected children reported greater problems due to stress. This stress was correlated with parents' general health in the three groups. The groups did not differ in reports of stress arising from life events other than the child's illness.

Adaptation, Psychological↗