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Biomedical subjects

J Lam

Publications and source records attributed to J Lam.

At least 73 records · Page 4Linked to original sources
PubMed1993

Usefulness of biplane transesophageal echocardiography in neonates, infants and children with congenital heart disease.

A study was performed to assess the feasibility, additional diagnostic value and potential applications of biplane transesophageal echocardiography in neonates, infants and children. One hundred thirty-two consecutive studies were attempted in 111 anesthetized children with congenital heart disease. Longitudinal and transverse planes were compared using 3 methods: (1) separate 7 mm longitudinal and transverse pediatric transducers used sequentially; (2) an experimental 9 x 8 mm biplane pediatric transducer; and (3) a standard adult biplane transducer (12 x 9 or 13 x 9 mm). In all but 1 patient, a probe could be inserted. The longitudinal plane provided superior visualization of both the right and left ventricular outflow tracts, the interatrial septum, the main pulmonary artery, the ascending aorta and the right coronary artery. In 18 patients (16%), the longitudinal plane provided completely new diagnostic information that was not obtained with combined transthoracic and transverse plane transesophageal echocardiography. However, the transverse plane was mandatory for demonstration of the 4-chamber view, short-axis cross sections through the great arteries, the distal right pulmonary artery and bifurcation of the left coronary artery. The longitudinal plane is complementary to the transverse plane, but cannot substitute for it.

Adolescent↗
PubMed1993

Apicectomy of posterior teeth--a clinical study.

Studies evaluating periapical surgery of posterior teeth are relatively few. A retrospective study of 32 apicectomies on posterior teeth using both clinical and radiographic means yielded a success rate of 62 per cent. There were five cases (16 per cent) of failure, the majority of which presented as delayed infection between three and six months following surgery. Post-surgical review of at least six months is recommended. Anatomical considerations for posterior tooth apicectomy and the necessity for retrograde fillings are discussed.

Apicoectomy↗
PubMed1992

Reactivation of unstable angina after the discontinuation of heparin.

BACKGROUND: Heparin is an effective, widely used treatment for unstable angina. Among patients enrolled in a double-blind, randomized, placebo-controlled trial comparing intravenous heparin, aspirin, both treatments, and neither during the acute phase of unstable angina, we encountered patients in whom unstable angina was reactivated after heparin was discontinued. METHODS: The study population included 403 of the original 479 patients in the trial who had completed six days of blinded therapy without refractory angina or myocardial infarction. After the discontinuation of therapy, clinical events, including reactivation of unstable angina and myocardial infarction occurring within 96 hours after hospitalization, were closely monitored. RESULTS: Early reactivation occurred in 14 of the 107 patients who received heparin alone, as compared with only 5 patients in each of the other three study groups (P less than 0.01). These reactivations required urgent intervention (thrombolysis, angioplasty, or coronary-bypass surgery) in 11 patients treated with heparin alone, but in only 2 patients in the other groups combined (P less than 0.01). Four of the six patients who had a myocardial infarction during a reactivation of their disease were in the heparin group. Reactivations in this group occurred in a cluster a mean (+/- SD) of 9.5 +/- 5 hours after the discontinuation of the study drug but were randomly distributed over the initial 96 hours in the other three groups. CONCLUSIONS: Although heparin is beneficial in treating unstable angina, the disease process may be reactivated within hours of the discontinuation of this drug. Concomitant therapy with aspirin may prevent this withdrawal phenomenon.

Acute Disease↗
PubMed1992

Symptom-limited versus low level exercise testing before hospital discharge after myocardial infarction.

OBJECTIVE: This study was undertaken to compare a low level and a symptom-limited test performed before hospital discharge after an uncomplicated myocardial infarction. BACKGROUND: Exercise testing after myocardial infarction provides useful prognostic information. Usually either a low level test is performed before hospital discharge or a symptom-limited test is performed at 3 weeks. METHODS: The study group comprised 202 patients with an uncomplicated myocardial infarction; 58 patients had a non-Q wave infarction and 115 patients had received thrombolytic therapy. Both a low level and a symptom-limited exercise test were performed in 200 of the 202 study patients in randomized order on consecutive days, a mean of 7.4 +/- 2.3 days after infarction. RESULTS: The symptom-limited test required a considerably greater effort than the low level test: exercise duration was 554 +/- 209 versus 389 +/- 125 s (p less than 0.0001), and peak work load was 5.7 +/- 1.8 versus 4.2 +/- 1.1 METs (p less than 0.0001). The peak heart rate was higher during the symptom-limited test (121 +/- 20 vs. 108 +/- 14 beats/min, p less than 0.0001), as was the rate-pressure product. The number of patients who developed ST segment depression greater than or equal to 1 mm increased from 56 during the low level test to 89 during the symptom-limited test (p less than 0.0001). ST segment depression greater than or equal to 2 mm occurred in 22 patients during the low level test and in 41 patients during the symptom-limited test, an 86% increase (p less than 0.0001). The number of patients with either angina or ST depression greater than or equal to 1 mm increased from 66 to 105 (p less than 0.0001) with the symptom-limited test. Exercise test results were similar for patients with a Q wave or a non-Q wave infarction. Exercise duration was longer and exercise-induced ST depression less frequent in patients who had received thrombolytic therapy. CONCLUSIONS: A symptom-limited exercise test performed before hospital discharge after uncomplicated myocardial infarction provides a significantly greater cardiovascular stress than does a low level test and is associated with an ischemic response nearly twice as frequently. The prognostic significance of a positive response at higher work loads has not been defined.

Angina Pectoris↗
PubMed1992

Photosensitization by 2-chloro-3,11-tridecadiene-5,7,9-triyn-1-ol: damage to erythrocyte membranes, Escherichia coli, and DNA.

The natural product 2-chloro-3,11-tridecadiene-5,7,9-triyn-1-ol (1) photosensitized the inactivation of Escherichia coli in the presence of near-ultraviolet light (320-400 nm; NUV) under both aerobic and anaerobic conditions. A series of E. coli strains differing in DNA repair capabilities and catalase proficiency exhibited indistinguishable inactivation kinetics following treatment with the chemical plus NUV. The presence of carotenoids did afford some protection to E. coli against inactivation under aerobic conditions, consistent with the involvement of singlet oxygen. The photosensitized hemolysis of human erythrocytes occurred more rapidly in the absence than in the presence of oxygen. Aerobically, the onset of hemolysis was partially inhibited by NaN3 and by 2,6-di-t-butyl-4-methylphenol (BHT) but not by superoxide dismutase (SOD). The aerobic lipid peroxidation observed in the membranes of erythrocyte ghosts was completely inhibited by BHT, and partially by NaN3, but not by SOD. These results suggest that either lipid peroxidation of the membrane is not the main cause of photohemolysis or that BHT has insufficient access to intact erythrocyte lipids to protect them. Aerobically, crosslinking of membrane proteins was also observed; it was not affected by SOD, but was partially inhibited by BHT and NaN3. The anaerobic photosensitized hemolysis of erythrocytes was more rapid; a radical mechanism was suggested since BHT inhibited the hemolysis to a greater extent than under aerobic conditions. Neither lipid peroxidation nor protein crosslinking was observed under conditions believed to be anaerobic. A light-dependent electron transfer to cytochrome c was obtained under argon but not under oxygen. Although induced mutations were not observed in the experiments with E. coli, 1 was capable of damaging both supercoiled pBR322 and Haemophilus influenzae transforming DNA in a manner that seemed to be equivalent under aerobic and anaerobic conditions. In conclusion, 1 can behave as typical photodynamic molecule under aerobic conditions but, in contrast to most photodynamic molecules, it is also phototoxic under anaerobic conditions. The extent to which the radical reactions detected under anaerobic reactions compete with the photodynamic processes when oxygen is present is not known.

Alkadienes↗
PubMed1991

Newer concepts in the treatment of unstable angina pectoris.

Unstable angina patients should be hospitalized and treated with antianginal drugs to control their symptoms and with aspirin or heparin to reduce the risk of myocardial infarction. Heparin is probably preferable to aspirin acutely, because it also reduces the risk of refractory angina. However, aspirin therapy should be started before heparin is discontinued, to prevent the rebound in symptoms, and continued long-term. Unless specifically contraindicated, coronary arteriography should be performed to identify patients who might benefit from coronary bypass surgery or angioplasty. Control of risk factors is important for long-term outcome.

Angina, Unstable↗
PubMed1991

Neonatal cardiomyopathy and lactic acidosis responsive to thiamine.

A congestive cardiomyopathy was diagnosed in a girl at the age of 4 weeks. In the weeks following she developed general muscle hypotonia and plasma lactate increased to 8.5 mmol/L. Biochemical investigations of a muscle biopsy at the age of 3 months showed a deficiency in the oxidation of all substrates tested: pyruvate plus malate, 2-ketoglutarate and palmitate plus malate. After freezing and thawing of the homogenate and the addition of essential cofactors, the oxidation of the ketoacids normalized. The oxidation defect in the untreated homogenate can be explained by a deficiency in one of the cofactors (such as thiamine pyrophosphate, NAD+ or CoASH), or by a defect in the oxidative phosphorylation. Treatment with thiamine and carnitine resulted in a decrease in blood lactate to normal levels and a dramatic clinical improvement. Suspension of thiamine caused deterioration of her clinical condition and lactic acidaemia. The thiamine therapy was then continued. The girl is now 6 years old and in perfect health.

Acidosis, Lactic↗
PubMed1991

Ultraviolet-dependent biological activities of selected polyines of the asteraceae.

A series of eight polyines, isolated from several plants and containing various furanyl, thiophene, and spiro groups, were evaluated for antibiotic, antiviral, and cytotoxic activities in the presence and absence of long wavelength ultraviolet light, UVA. One compound, a furanopolyine, had impressive activity against a range of microorganisms, and membrane-containing viruses, as well as cytotoxic activity. All of these properties were UVA-dependent. Three other similar compounds had different patterns of UV-dependent activity against the various organisms, but some of these could also be of use in therapy of infectious diseases. In contrast, the dehydromatricaria esters and the two spiro compounds had relatively little biological activity.

Alkenes↗
PubMed1990

Regulation and distribution of Fibrobacter succinogenes subsp. succinogenes S85 endoglucanases.

The distribution of endoglucanase activities in cultures of Fibrobacter succinogenes subsp. succinogenes S85 grown on different carbon sources was examined by a variety of biochemical and immunological techniques. Total culture endoglucanase activity was primarily cell associated and was expressed constitutively, although synthesis of endoglucanase 1 (EG1) was repressed by cellobiose. Western immunoblotting showed that EG1 and EG3 were released into the culture fluid during growth, while EG2 remained largely associated with the cell. Subcellular localization showed low endoglucanase activity in the periplasmic fraction and similar, high levels in the cytoplasmic and membrane fractions. Western immunoblotting showed that EG2 was absent from the periplasmic fraction. Data from immunoelectron microscopy with either polyclonal or monoclonal antibody to EG2 revealed a high density of gold labeling at sites where there was a disruption in the regular features of the cell surface, such as in blebbing or physical tearing of the membrane. When cells were grown on cellulose, there was a high density of labeling on the cellulose but not on the cells, indicating that EG2 has limited exposure at the cell surface. On the basis of these data, export of enzymes from their intracellular locations appears to occur via three different mechanisms: a specific secretory pathway independent of cellulose, a secretory mechanism which is mediated by contact with cellulose, and a generalized blebbing process that occurs irrespective of the carbon source.

Bacteroides↗
PubMed1989

Assessment of bedside umbilical vein balloon septostomy using two-dimensional echocardiographic guidance in transposition of great arteries.

The effectiveness of "bedside" balloon atrial septostomy via the umbilical vein using 2-dimensional echocardiography was compared to the traditional femoral vein approach using fluoroscopy in a series of neonates with transposition of great arteries from March, 1984 to April, 1987. There were 7 neonates who had balloon septostomy performed at the "bedside" (Group I) compared to 13 who had the procedure performed in the catheterization laboratory (Group II). Group II consisted of 7 newborns who had elective femoral vein catheterization under fluoroscopy (Group IIA) and 6 who failed "bedside" umbilical vein balloon septostomy and subsequently had the femoral vein approach under fluoroscopy (Group IIB). Results showed that adequacy of balloon septostomy was not related to the approach used, with 4 of 7 in Group I and 9 of 13 in Group II with an adequate atrial tear and clinical response. The Delay time to septostomy (i.e. time elapsed from initial assessment to commencement of balloon septostomy) and Procedure time (i.e. time taken to complete the balloon septostomy) was significantly shorter for Group I (mean time = 0.7 hours and 0.26 hours respectively) compared with Group IIA (mean time = 2.6 hours and 1.8 hours) and Group IIB (mean time = 2.4 hours and 1.4 hours). Of note, there was no significant increase in Delay time between Group IIA and IIB.(ABSTRACT TRUNCATED AT 250 WORDS)

Catheterization↗
PubMed1987

Comparative antianginal effects of nisoldipine and nifedipine in patients with chronic stable angina.

The acute antianginal effects of 5 mg and 20 mg nisoldipine were compared with 20 mg nifedipine and placebo. Maximal treadmill exercise testing was performed before and 3 hours after drug administration in 10 patients with chronic stable angina. Resting heart rate and systolic blood pressure were unchanged following low-dose nisoldipine, but 20 mg nisoldipine and 20 mg nifedipine increased heart rate and decreased systolic arterial pressure (p less than 0.05). Time (in seconds) to the onset of 0.1 mV ST segment depression was significantly prolonged after 5 mg nisoldipine (+60 +/- 53; p less than 0.05) and 20 mg nisoldipine (+100 +/- 78; p less than 0.01) but not after 20 mg nifedipine (+48 +/- 131; p = NS). Total exercise duration increased significantly following 5 mg and 20 mg nisoldipine (p less than 0.01 and p less than 0.001, respectively) but only slightly following nifedipine (p = NS). The maximal rate-pressure product was increased to a similar degree following doses of both nisoldipine and nifedipine (p less than 0.05). Nisoldipine is an effective antianginal agent which performs well in comparison to nifedipine.

Aged↗
PubMed1987

An infant with the scimitar syndrome and pulmonary hypertension; successful surgical intervention.

The case of an infant with the scimitar syndrome and pulmonary hypertension is presented. After surgical intervention with ligation of the abnormal arterial supply to the hypoplastic lung, the pulmonary hypertension disappeared. This was proven by cardiac catheterization after the operation. The abnormal drainage from the right lung into the inferior vena cava was not corrected. The child has had no complaints since except for recurrent pulmonary infections.

Follow-Up Studies↗
PubMed1987

Prognostic implications of circulating immune complexes and Pseudomonas aeruginosa-specific antibodies in cystic fibrosis.

We re-examined the role of circulating immune complexes (CIC) in cystic fibrosis, by their serial measurement in 16 patients who had advanced lung disease and persistent specific antibodies to Pseudomonas aeruginosa in their serum. CIC were detected by 125I C1q-BA (IgG + IgM-IC) and Raji RIA (IgG-IC), and IgA-IC by a modification of the Raji RIA method. Serum precipitins to Ps. aeruginosa were detected by crossed-immunoelectrophoresis (XIE) and antibodies to alkaline protease (AP), elastase (EL) and exotoxin-A (EA) of Ps. aeruginosa were detected by ELISA technique. CIC were positive in greater than 50% of the samples in 8 patients (group A) and in less than 25% in the other 8 (group B); follow-up averaged 22 mo in group A and 26 mo in group B. The numbers of precipitins to Pseudomonas were equally high, and levels of antibodies to AP, EL, and EA of Ps. aeruginosa were similarly positive, in the 2 groups. In group A the CIC were mostly IgG-IC by Raji RIA (76%) and IgA-IC, whereas in group B C1q-binding IC (79%) and IgA-IC were more prevalent than IgG-IC by Raji RIA. Four group A children died during follow-up, together with one group B child in whom the CIC level had suddenly risen precipitously. We postulate that a high level of CIC in association with persistent specific-antibody response to Ps. aeruginosa heralds a poor prognosis in cystic fibrosis.

Adolescent↗