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Biomedical subjects

S C Sun

Publications and source records attributed to S C Sun.

At least 91 records · Page 5Linked to original sources
PubMed1989

Sequentially paced heterotopic heart transplant in the left chest provides improved circulatory support for the failed left ventricle. A potential biologic bridge to orthotopic transplantation.

Acute experimental transplantation of an allograft heart in a heterotopic position was performed in 14 sheep. The donor heart was implanted in the left side of the chest with left atrial, aortic, and pulmonary artery anastomoses. Hemodynamic studies were performed to evaluate the physiologic effects of the procedure, particularly when recipient left ventricular failure was produced by inflow and outflow obstruction. Pacing techniques were developed and tested to coordinate the rhythm of the two hearts either synchronously or sequentially with variable intervals between depolarization of the two hearts. Hemodynamic studies were performed to evaluate the rhythm that would most optimize the physiology. The cardiac index remained essentially unchanged when the dominant circulatory support was shifted from recipient left ventricle to donor left ventricle by producing recipient left ventricular failure (3.79 +/- 0.6 to 3.30 +/- 0.8, p = no significant difference). Consistent and reliable paced rhythms were achieved in each case. The cardiac index was significantly higher when the hearts were paced sequentially rather than synchronously (3.76 +/- 0.5 versus 3.29 +/- 0.5, p less than 0.04). Allograft donor hearts small in size or slightly inadequate otherwise, which may be unsuitable for orthotopic heart transplantation, may still be used heterotopically for short-term support. Their use would maximize the use of all donor organs and the survival of patients awaiting a suitable organ. Further, it may also be possible to use sequentially paced xenografts heterotopically for short-term left ventricular assistance as a bridge to orthotopic heart transplantation.

Animals↗
PubMed1988

Effects of antegrade cardioplegic infusion with simultaneously controlled coronary sinus occlusion on preservation of regionally ischemic myocardium after acute coronary artery occlusion and reperfusion.

This study was conducted to assess the protective effects of antegrade infusion of cardioplegic solution with simultaneously controlled coronary sinus occlusion on regionally ischemic myocardium after acute coronary occlusion and reperfusion. Twelve sheep were subjected to 1 hour of occlusion of the distal left anterior descending coronary artery. Sheep in group I (n = 6) were subjected only to infusion of potassium crystalloid cardioplegic solution into the aortic root, whereas in group II (n = 6) a stitch was snared around the proximal coronary sinus for its subsequent occlusion during antegrade infusions of cardioplegic solution. All animals were placed on cardiopulmonary bypass. Five hundred milliliters of cardioplegic solution at 4 degrees to 8 degrees C was administered in three divided doses during the total cross-clamp period of 30 minutes. The occlusion of the left anterior descending artery was then released, and the animals were weaned from bypass and studied for an additional 4 hours. Coronary sinus pressure, myocardial temperature, regional function assessed by pairs of ultrasonic crystals, global function assessed by rate of rise of left ventricular pressure and cardiac output, and the area at risk and area of necrosis were determined. The heart was excised at the end of the experiment and stained. Animals treated by the technique of antegrade infusion combined with coronary sinus occlusion had more homogeneous myocardial cooling during cardioplegic infusions and better recovery of the first derivative of left ventricular pressure and regional segment shortening at 90 and 270 minutes of reperfusion than those treated with antegrade infusion alone (p less than 0.01 and p less than 0.05, respectively). The group treated by antegrade infusion of cardioplegic solution combined with coronary sinus occlusion had an area of necrosis/area at risk ratio of 40.5% +/- 1.2%; the antegrade infusion group, 58.3% +/- 4.1% (p less than 0.01). These data suggest that antegrade infusion combined with coronary sinus occlusion may be an improved method of global and regional myocardial protection in the presence of an occluded coronary artery.

Animals↗
PubMed1988

Effects of diltiazem cardioplegia on global function, segmental contractility, and the area of necrosis after acute coronary artery occlusion and surgical reperfusion.

We investigated the effects of diltiazem cardioplegia on myocardial function and infarct size in the region of the left anterior descending artery after acute occlusion and reperfusion during cardiopulmonary bypass. Sheep (30 kg) were subjected to 1 hour of regional myocardial ischemia by occlusion of the left anterior descending artery and assigned to a control (n = 8) or experimental group (n = 5). Control animals were placed on cardiopulmonary bypass and the heart arrested with potassium cardioplegia. The left anterior descending artery was released and two additional doses of 100 ml of cardioplegic solution were infused during the total cross-clamp time of 30 minutes. The animals were then weaned from bypass after 1 hour and beating, working reperfusion maintained for an additional 4 hours. The experimental group followed the same protocol except that the cardioplegic solution contained diltiazem (1.4 mg/L). Segmental myocardial function was determined by pairs of ultrasonic crystals in the area at risk, control segment, and minor axis. Global contractility was determined from maximum derivative of left ventricular pressure and cardiac output. The area at risk was determined by injecting monastral blue dye into the left atrium with the left anterior descending artery briefly reoccluded, and the area of necrosis was determined by measuring with a planimeter non-triphenyltetrazolium chloride stained areas in the sectioned left ventricle. After 5 hours of reperfusion, not only did the diltiazem group demonstrate better global contractility as defined by the derivative of left ventricular pressure (1853 +/- 292 versus 979 +/- 191, p = 0.05) but, in addition, the systolic shortening in the ischemic area improved significantly when compared with the control group (9.4 +/- 4 versus 2.13 +/- 0.77, p = 0.05). The group receiving diltiazem cardioplegia had an area of necrosis to area at risk ratio of 31.4% +/- 3%, which was significantly better than this ratio in the control group of 60.75% +/- 7% (p = 0.01). Diltiazem cardioplegia results in improved global and segmental contractility and limits the infarct size after occlusion of the left anterior descending artery and surgical reperfusion.

Animals↗
PubMed1986

The role of obstetric factors in perinatal mortality trends.

In the Perinatal Unit of the New Jersey Medical School, Newark the combined neonatal mortality and stillbirth rates declined from more than 51 per 1000 to less than 17 per 1000 between 1971 and 1983. This change is comparable to the reduction of perinatal mortality rates nationwide since the Second World War. Because the improvement in the fetal and neonatal survival rates occurred in a static population and against well identifiable changes in the structure, equipment, policies and management patterns of the obstetric unit, it was possible to assess the impact of various factors upon perinatal outcome. In the environment of this institution adherence to conservative concepts of obstetric management, avoidance of manipulative and extraction procedures, an increase of the rate of cesarean sections from about 7 to 15% and emphasis upon infection control appeared to be the crucially important factors. Antepartum sonography and fetal stress and non-stress testing significantly impacted upon the results. The role of intrapartum electronic monitoring was less clearly definable and seemed to be effective only in the hands of experienced physicians. The results did not seem to be adversely affected by the fact that the program de-emphasized invasive procedures, including fetal scalp pH sampling.

Adolescent↗
PubMed1978

Effect of Intralipid-induced lipaemia on the arterial oxygen tension in preterm infants.

10% Intralipid was infused (1 g/kg body wt.) intravenously for 15 min with Razel pumps to each of eight selected newborn preterm infants whose general condition and pulmonary status were stable for at least 24 h before study. Six of the eight infants showed greater than 10 mmHg reduction in oxygen tension of umbilical arterial blood. These reductions were correlated with elevated triglyceride concentrations. The findings suggest that Intralipid-induced lipaemia has the potential to lower the oxygen tension of the blood and hence patients with pre-existing pulmonary insufficiency may be at risk from hypoxaemia.

Fat Emulsions, Intravenous↗
PubMed1977

Myocardial lesions produced by external heat or cold exposure in rats.

Three groups of Sprague-Dawley rats were kept at the ambient temperatures of 8, 24 and 32 degrees C respectively for 3 to 7 days. These animals maintained their rectal temperatures within normal limits. However, the animals of either the heat-stressed or the cold-stressed group yielded not only the functional but also the organic effects to their hearts when compared to those of the control group (24 degrees C exposure). Heat exposure produced a lower heart rate and higher cutaneous temperature, while cold exposure produced a higher heart rate and a lower cutaneous temperature. In addition, the ECG recordings showed a predominant S wave and probably a depressed S-T segment in response to either heat or cold exposure. At the end of either 3-day or the 7-day thermal exposure, the animals were subjected to decapitation. Their hearts were sampled for both light and electron microscopic examinations. It was found that the heat-stressed animals shared with the cold-stressed animals a common picture of the myocardial changes. The subcellular changes in the myocardium in response to external heat or cold were characterized by the mitochondrial hypertrophy, the intracellular edema, the destruction of myofibrils, the dilatation of the intercalated discs, and some abnormalities in their capillaries. The data demonstrate that a short term (3 to 7 days) of moderate heat (32 degrees C) or cold (8 degrees C) exposure produces myocardial lesions in rats, although they maintain their body temperatures within normal limits.

Animals↗
PubMed1977

Cardiac lymphatic obstruction: ultrastructure of acute-phase myocardial injury in dogs.

Cardiac lymphatics exist as a network of intercommunicating channels in the myocardium and heart valves, and chronic obstruction of these vessels may result in endomyocardial fibrosis and mucoid degeneration of heart valves. The acute effects of experimental cardiac lymphatic obstruction were studied in the dog. Subendocardial edema and hemorrhage occurred within 150 minutes of the ligation of cardiac lymphatics. Ischemia-type myocardial injury was also observed. Attional changes detectable ultrastructurally included lymphangiectasia, myofibrillar degeneration, disruption of Z-band and intercalated disks, and various mitochondrial derangements. The spottiness of the changes was attributable to the known anatomic variability of lymphatic distribution in the heart. The findings reinforce the belief that greater attention should be focused on the role of cardiac lymphatics in the pathogenesis of a multitude of myocardial and vavular heart diseases.

Animals↗
PubMed1976

Ultrastructure of ischemic contracture of the left ventricle ("stone heart").

Myocardial biopsies from two patients who had developed "stone heart" (myocardial rigor mortis; ischemic contracture of the left ventricle) were studied by electron microscopy. The ultrastructure of tissue in stone heart, though ischemic in nature, differed from that of classic myocardial infarction in some respects. Apart from depletion of glycogen and distension of the sarcoplasmic reticulum and T-tubules, myofibrillar degeneration was much more widespread. Mitochondrial degeneration with active lysosomal autodigestion, disruption of the microcirculation, and lymphedema were prominent changes also observed. In the light of known clinical and experimental observations, our findings suggest that stone heart is an accelerated form of ischemic injury occurring in vulnerable (hypertrophied) hearts and is probably related to ischemia-triggered release of endogenous catecholamines.

Capillaries↗
PubMed1975

Hepatitis B antigen in infants born to mothers with chronic hepatitis B antigenemia in Taiwan.

Hepatitis B antigen (HB Ag) was detected by complement fixation (CF) in serum samples of 7.5% of 1,106 pregnant Chinese women tested in Taipei, Taiwan. HG Ag persisted in all but one of 42 women followed for 1 to 18 months (average, nine months) after delivery, and 27 of the 43 infants (63%) born to those women became antigen-positive. Persistance of the antigen was more common than transient or intermittent antigenemia. Twelve had antigenemia when first tested, while 15 later developed antigenemia, usually during the first six months of life. Only one infant developed antibody to HG Ag (anti-HB Ag), and this occurred after transient antigenemia. The HB Ag was found in two of 32 (6%) fathers, and in 18 of 27 (67%) older siblings. The antigen was more common among siblings of antigen-positive than among those of antigen-negative infants. These findings demonstrate that in Taiwan, infants born to mothers who are asymptomatic carriers of HB Ag commonly become infected by heaptitis B (HB) virus. Exposure of infants near the time of birth may be important maintaining the high, chronic HB Ag carrier rate in Taiwan.

Carrier State↗