Search PubMed⌕ Search

Biomedical subjects

G Y Chen

Publications and source records attributed to G Y Chen.

36 records · Page 2Linked to original sources
PubMed1998

Energy dissipation as a key factor for electroporation of protoplasts.

Energy dissipation (epsilon) during electroporation was theoretically determined to be epsilon = 0.5CV02 for the various combinations of capacitance (C) and initial voltage (V0). Experiments on asparagus protoplasts established that electroporation efficiency (EE) and survival rate were directly proportional to energy dissipation during electroporation. A positive linear relationship exists between energy dissipation per unit volume and EE, whereas energy dissipation per unit volume and survival rate of protoplasts are related in a negative linear manner. At the same energy level, longer time constants were more effective at increasing EE. This suggests that energy dissipation approximating rectangular waveforms is more important than that dissipated as sharply decaying exponential waveforms. With energy as the key parameter, the optimization of electrical parameters for efficient electroporation is greatly simplified, is not machine-dependent, and generally applies to all species.

Cell Survival↗
PubMed1998

Clinical experience with orbicularis oculi myocutaneous flaps in the temporal area.

There are many methods to repair facial skin defects in clinical practice. The desired outcome for the surgeon and the patient is the restoration of facial appearance and function. The temporal region is one of the ideal donor sites for the repair of a facial skin defect, because this area is relatively inconspicuous and the skin quality is similar to that of the face. In the past, the temporal region was always used as the donor site of the local flap for repairing the facial skin defect. Because the blood supply of the skin comes from the subjacent tissue mainly rather than from the contiguous tissue, the pedicles of the local flaps are short, limiting the use of this area as a donor site. From 1993 to 1996, the anatomy of the orbicularis oculi myocutaneous flap in five cadavers was studied; what was learned allowed for the use of this flap to repair skin defects of the face in 13 patients. In this paper, the clinical experiences using the orbicularis oculi myocutaneous flaps to repair skin defects of the face and the surgical anatomy of this myocutaneous flap are discussed.

Adolescent↗
PubMed1997

Congenital mitral stenosis: challenge of percutaneous transvenous mitral commissurotomy.

A 26-year-old woman with congenital mitral stenosis and embolic stroke was referred to our hospital. The echocardiogram showed a hypoplastic posterior mitral valve leaflet with short, unbalanced chordal attachments to the posteromedial papillary muscle. The mitral valve area was 0.9 cm2 by the pressure half-time method. There was no left atrial thrombus and spontaneous echo contrast. Percutaneous transvenous mitral commissurotomy was performed since the suggestion of surgical management was refused by her family members. A rupture at the chordae tendinae of the hypoplastic posterior papillary muscle developed during the procedure and needed mitral replacement. We advise that percutaneous transvenous mitral commissurotomy be avoided in adult patients with congenital mitral stenosis having an asymmetric and hypoplastic mitral valve.

Adult↗
PubMed1997

The effect of the lateral decubitus position on vagal tone.

The average person spends about one-third of their time in a recumbent position. However, little is known about the effect of recumbent posture on autonomic nervous activity. Manoeuvres which can increase vagal tone have been sought both in the normal subject and in patients with heart disease. We have studied the autonomic effect of various recumbent positions, namely the supine, left lateral decubitus and right lateral decubitus positions, in healthy subjects by using spectral heart rate variability analysis. Both time- and frequency-domain measures were calculated and compared between the three recumbent positions. The normalised high-frequency power was used as the index of cardiac vagal activity, the normalised low-frequency power as the index of cardiac sympathetic activity and the low-frequency power/high-frequency power ratio as the index of sympathovagal balance. The normalised high-frequency power is highest in the right lateral decubitus position, followed in decreasing order by left lateral decubitus and supine positions. The low-frequency power/high-frequency power ratio has the reversed trend as compared with that of the normalised high-frequency power. These results suggest that cardiac vagal activity is greatest when the right lateral decubitus position is adopted.

Adult↗
PubMed1997

The effect of position on autonomic nervous activity in late pregnancy.

We investigated the effect of three different recumbent positions on autonomic nervous activity in late pregnancy. Thirty pregnant and 24 nonpregnant aged-matched women were studied, and measures of heart rate variability in both time and frequency domains were compared using supine, right and left lateral decubitus positions. In the nonpregnant women, the normalised high-frequency power was greatest in the right lateral decubitus position. In the pregnant women, the normalised high-frequency power was lowest and the low/high-frequency power ratio was greatest in the supine position. Both the percentage decrease of normalised high-frequency power and the percentage increase of low/high-frequency power ratio in the supine and right lateral positions were greater than those in the left lateral position. For women in late pregnancy, the left lateral decubitus position may be beneficial because cardiac vagal activity is least suppressed and cardiac sympathetic activity is least enhanced. Aortocaval compression might be the mechanism underlying the change in cardiac autonomic nervous activity when supine and right lateral decubitus positions are assumed in late pregnancy.

Adult↗
PubMed1996

Application of hemodilution in microsurgical free flap transplantation.

The intra-operative hemodilution and blood auto-transfusion is a blood-saving technique that can be performed when major blood loss is expected. The effects of this technique were studied in 30 microsurgical free flap transplantation patients. Between 400-600 ml blood was collected from the patients before surgery. The patients received dextran, a balanced salt solution, and glucose with the ratio of 3:1 to the collected blood volume, bleeding, and urine before the blood auto-transfusion. There were no significant changes in RBC, HCT, MCV, blood pressure, or heart rate. Of the 30 free flaps, 28 were successful with a 93.3% survival rate. The safety of intra-operative hemodilution and autologous blood transfusion in microsurgery as well as the effect of hemodilution on transplanted flap survival are discussed in this study.

Adult↗
PubMed1995

Thrombus formation on polytetrafluoroethylene surfaces: the importance of von Willebrand factor.

The importance of von Willebrand factor (vWf) in the formation of platelet-fibrin thrombi on expanded polytetrafluoroethylene (ePTFE) surfaces was studied in an in vitro system, perfusing non-anticoagulated human blood over ePTFE grafts for 3 min at varying shear rates (100, 500 and 1500/s shear). Platelet (111In) and fibrin (125I) deposition was assessed on ePTFE surfaces in the presence and relative absence of vWf, achieved by use of polyclonal anti-vWf antibody (anti-vWf Ab). A total of 29 perfusions were performed. Increasing shear rate was associated with greater platelet deposition in the presence of vWf (p < 0.001). This shear-dependent rise in platelet deposition was not observed when vWf was blocked by anti-vWf Ab (P < 0.1), confirming the role of vWf in platelet deposition at high shear rates. Fibrin deposition increased with increasing shear rate in the presence of vWf (P < 0.01). Inhibiting vWf abolished the shear-dependent increase in fibrin deposition. These data suggest that vWf plays a critical role in platelet and fibrin thrombus formation on ePTFE surfaces. These effects are particularly important under conditions of high shear rate. These mechanisms may lead to the observed pathologic thrombus formation and platelet-dependent neointimal processes occurring at areas of high shear rate within the anastomotic regions of ePTFE grafts.

Blood Platelets↗
PubMed1995

Evidence for a high prevalence of spotted fever group rickettsial infections in diverse ecologic zones of Inner Mongolia.

A 3-year study of spotted fever group rickettsial ecology in Inner Mongolia revealed that nearly half of the human population tested had antibodies to Rickettsia sibirica detected by complement fixation test. Infected persons, ticks and a high proportion of seropositive livestock and wild rodents were found in all five vegetation zones (desert, steppe, forest, forest-grassland and grassland).

Animals↗
PubMed1993

A novel quinone antibiotic from Malbranchea cinnamomea TAIM 13T54.

A novel quinone antibiotic named malbranicin was isolated from the culture filtrate and mycelium of Malbranchea cinnamomea TAIM 13T54, a thermophilic fungus. The antibiotic was elucidated to be 6-(1-acetylethyl)-2-methoxy-2,5-cyclohexadiene-1,4-dione by spectral analysis. Malbranicin exhibited antimicrobial and cytotoxic activities against Gram-positive bacteria and mammalian cell lines, respectively.

Animals↗
PubMed1993

[Effects of captopril on myocardial ultrastructure in diabetic rats].

Diabetic rat models were established with intraperitoneal injection of streptozotocin. The animals were randomly divided into four groups: Group 1, normal control (n = 5); Group 2, diabetic control (n = 4); Group 3, diabetics treated with PZI (n = 5); Group 4, diabetics treated with PZI and captopril (n = 5). Specimens taken from free wall of the left ventricle were observed under electron microscope after 10-week treatment, and the volume density (Vv), numerical density on area (Na), numerical density (Nv) and mean volume (V) of mitochondria were measured with stereological quantitation. The results showed that the myocardial changes in Group 4 were much less severe than those in Group 3 and similar to those in Group 1. There was significant difference in Nv (P < 0.05) but not in Vv, Na and V between Group 4 and Group 1. While the changes of Group 3 were relatively obvious. As comparing Group 3 with Group 1, there were significant differences in all of the four parameters (P < 0.05-0.01). It is implied that the renin-angiotensin system may be involved in the pathogenesis of diabetic cardiomyopathy, since captopril can improve and reverse the cardiomyopathy of diabetic rats.

Animals↗
PubMedDate not supplied

Clinical experience and surgical anatomy of 32 free anterolateral thigh flap transplantations.

The anterolateral thigh flap, first described by Song, is one of the septocutaneous flaps in the thigh. Since November 1985 we have transferred 32 anterolateral thigh flaps successfully without any loss. Six of these flaps were performed in Australia. The vascular pedicles are divided into three types: fasciocutaneous perforator (37.5%-12/32), vertical musculocutaneous perforator (56.2%-18/32) and horizontal musculocutaneous perforator (6.6%-2/32). This paper presents the surgical anatomy of the flap and clinical experience.

Adolescent↗