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Biomedical subjects

S Y Tong

Publications and source records attributed to S Y Tong.

At least 19 recordsLinked to original sources
PubMed2003

Layer spacings in coherently strained epitaxial metal films.

Laterally resolved measurements of the quantum size effect (QSE) in electron reflectivity are made with low energy electron microscopy on coherently strained Ag films on a W(110) surface. The evolution of the total film thickness with increasing number of atomic layers is determined accurately by dynamical theory analysis of the QSE features. Combined with a model of layer spacings obtained from first-principles calculations, this provides for a novel approach to determine the buried interface layer spacing, which is inaccessible to other methods.

Journal Article↗
PubMed2003

Small-diameter silicon nanowire surfaces.

Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 x 1) and Si (001)-(1 x 1) surfaces corresponding to SiH3 on Si (111) and SiH2 on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions.

Journal Article↗
PubMed2002

Surface atomic arrangement visualization via reference-atom-specific holography.

We demonstrate the direct reconstruction of 3D atomic images from measured low-energy electron diffraction (LEED) intensity spectra. A multiple-incident angle and multiple-energy integral are first applied to the spectra to obtain a map of interatomic vectors. From this map, a nonbulk interatomic vector is chosen that points to a desired reference atom. A second integral transformation, using the chosen interatomic vector as a filter, is applied to the LEED spectra to produce images of individual atoms in the vicinity of the selected reference atom. This two-step method overcomes the problem of multiple, nonequivalent reference atoms and is applicable to elemental or compound materials.

Journal Article↗
PubMed2001

Surface Patterson function by inversion of low-energy electron diffraction I-V spectra at multiple incident angles.

An accurate Patterson function, free of artifacts, is obtained by transforming low-energy electron diffraction I-V spectra at multiple incident angles. The demonstration is carried out using normal incidence measured spectra and calculated spectra at three angles of incidence. The errors between intensity spots in the Patterson function and known interatomic distances are less than 0.01 A in the horizontal direction and 0.09 A in the vertical direction. The reason for the high accuracy in the horizontal direction is given.

Journal Article↗
PubMed2000

Molecular spectroscopy study of the reaction of nucleic acids with brilliant cresol blue.

The interaction of brilliant cresol blue (BCB) with nucleic acids in aqueous solution has been studied by spectrophotometry and Rayleigh light scattering (RLS) spectroscopy. Under suitable conditions, the RLS spectra of BCB changed significantly due to the presence of nucleic acids. RLS intensity of BCB at 364 nm is greatly enhanced with the addition of nucleic acids, and a new RLS peak is observed at 552 nm. This peak is about half the intensity of that at 364 nm. The results of this study show that BCB interacts with DNA possibly due to the cooperative effect of electrostatic attraction, intercalation, coordination and hydrophobic effect. Under optimum conditions, the increase of RLS at 364 nm of a BCB solution is proportional to the concentration of nucleic acids added. This result is the basis for a new RLS method for determination of nucleic acids. The linear range of ctDNA, fsDNA and yRNA is 0.12-4.70, 0.11-4.64 and 0.43-7.07 microg ml(-1), respectively.

Hydrogen-Ion Concentration↗
PubMed1999

Rayleigh light scattering study on the reaction of nucleic acids and methyl violet.

A new quantitative determination method for nucleic acids in aqueous solutions, based on the enhancement of Rayleigh light scattering of methyl violet by nucleic acids, has been developed. The sensitivity of the assay allows amounts of nucleic acids as little as 100 ng/ml to be quantitated reliably. In addition to its high sensitivity, this method has other advantages: rapidity of reaction (<5 min), simplicity of operation (one-step assay), commonality of spectrofluorimeter and reagents, stability of mixtures formed, and reproducibility. Under the experimental conditions, there is little or no interference from proteins, nucleosides, and most metal ions. Interference by a few metal ions, detergents, and some salts can be minimized by dilution. The method can also be used to determine the total amount of nucleic acids without the arduous choice of standard and difficult separation of DNA and RNA.

Animals↗
PubMed1999

Observation of the correlation of postanaesthesia recovery scores with early postoperative hypoxaemia in children.

To observe the correlation of the postanaesthesia recovery score (PARS) with the incidence, and severity of early postoperative hypoxaemia in children, 1213 infants and children, ASA physical status I, aged three months to 14 years, scheduled for elective plastic surgery were included in this study. Arterial oxygen saturation (Spo2) levels were recorded while children were breathing room air shortly after arrival in the recovery room (0 min), and 5, 10, 15, 20, 30, 40, 50, 60, 120 and 180 min thereafter. The PARS was also determined on all patients when Spo2 levels were recorded in the recovery room. On the basis of different PARS, children were divided into the three groups: Group 1-children having the PARS of < or = 6; Group 2-children having the PARS of 7-9; and Group 3-children having a PARS of 10. The results showed that during the early postoperative period, the incidence and severity of hypoxaemia correlated closely with the PARS. The lower the children's PARS, the higher the incidences of hypoxaemia (Spo2 = 86-90%) and severe hypoxaemia (Spo2 < or = 85%). The incidences of hypoxaemia and severe hypoxaemia were 12.9% and 15.8%, respectively, in Group 1, 20.9% and 2.9% in Group 2, 0.8% and 0% in Group 3. There were significant differences among the three groups. Of the 91 children who required O2 supplementation in the recovery room because of low measured Spo2, 69 had the PARS of < or = 6, and 22 had the PARS of 7-8. It is concluded that if a patient has a PARS of 10, the patient will not need routine oxygen supplement because hypoxaemia will not occur.

Adolescent↗
PubMed1998

A comparative study of the dose-response and time course of action of rocuronium and vecuronium in anesthetized adult patients.

STUDY OBJECTIVES: (1) To compare the dose-response relations of rocuronium and vecuronium in healthy adult patients anesthetized with nitrous oxide-oxygen-fentanyl-thiopental; and (2) to evaluate the time-course of action of two drugs following equipotent doses. DESIGN: Prospective, randomized, clinical comparison. SETTING: Operating room, Plastic Surgery Hospital of the Chinese Academy of Medical Sciences and Peking Union Medical College. PATIENTS: 60 ASA physical status I patients, aged 17-51 years, scheduled for elective plastic surgery. INTERVENTIONS: All patients were randomly assigned to either the rocuronium or vecuronium group. General anesthesia was induced with thiopental 4 to 6 mg/kg and fentanyl 2 to 4 micrograms/kg intravenously (i.v.), and maintained with 60% nitrous oxide (N2O) in oxygen. Further increments of thiopental or fentanyl were given as required. The dose-response relations of rocuronium and vecuronium were determined by the cumulative dose-response technique. MEASUREMENTS AND MAIN RESULTS: Neuromuscular function was assessed mechanomyographically with train-of-four (TOF) stimulation at the wrist every 12 seconds. The percentage depression of first twitch (T1) was used as the study parameter. The cumulative dose-response curve of vecuronium was shifted to the left in a parallel fashion compared with that of rocuronium. As assessed by linear regression, the potency ratio of vecuronium: rocuronium was 1:7.2. There were significant differences in the ED50, ED90, and ED95 between the two drugs. After i.v. administration of equipotent doses of both drugs (2 x ED90), the duration of peak effect, clinical duration, recovery index, and total duration were not significantly different between the two drugs. CONCLUSIONS: Compared with vecuronium, rocuronium is a low-potency, nondepolarizing relaxant, and its neuromuscular blocking potency is approximately 15% that of vecuronium in adult patients anesthetized with N2O and fentanyl. Following equipotent doses, the time-course of recovery for rocuronium is similar to that of vecuronium.

Adolescent↗
PubMed1998

Influence of acute normovolaemic haemodilution on the relation between the dose and response of rocuronium bromide.

The influence of acute moderate haemodilution on the relation between dose and response for rocuronium was evaluated in 60 adult patients, ASA grade I, undergoing elective plastic surgery. The patients were randomly allocated to either the control or the haemodilution group. Following the induction of general anaesthesia, the status of acute moderate haemodilution in the haemodilution group was achieved by draining venous blood, and intravenous infusion of lactated Ringer's solution, 6% dextran or gelofusine, during which the levels of haemoatocrit and haemoglobin dropped from 44% to 27.5% and from 148.3 to 91.3 g L-1, respectively. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12 s and the percentage depression of T1 response was used as the study parameter. The relation between dose and response for rocuronium in the two groups was determined by the cumulative dose-response technique. The results showed that the dose-response curve for rocuronium during acute moderate haemodilution was shifted in a parallel fashion to the left and the potency of rocuronium was increased. There were significant differences in ED50, ED90 and ED95 between the two groups. The ED50, ED90 and ED95 of rocuronium in the haemodilution group was decreased by 28.2%, 35.4% and 38.8%, respectively, compared with the control group.

Adolescent↗
PubMed1998

Influence of surgical technique on early postoperative hypoxaemia in children undergoing elective palatoplasty.

We have assessed the influence of different surgical procedures on the incidence, severity and duration of early postoperative hypoxaemia in 312 healthy infants and children undergoing elective palatoplasty. Group 1 patients underwent von Langenbeck palatoplasty (n = 149), group 2 patients underwent push-back palatoplasty (n = 124) and group 3 patients underwent combined push-back palatoplasty and superior pharyngeal flap surgery (n = 39). Arterial oxygen saturation (SpO2) was recorded while patients were breathing air shortly after arrival in the recovery room (0 min), and at 5, 10, 15, 20, 30, 40, 50, 60, 120 and 180 min thereafter. Patients who underwent more complex surgical techniques for palatoplasty had lower postoperative SpO2 values, slower recovery of SpO2 and a higher incidence of hypoxaemia during the early postoperative period. There were significant differences in postoperative SpO2, values and the incidence of hypoxaemia. The incidences of hypoxaemia and severe hypoxaemia were 27% and 1%, respectively, in group 1, 37% and 12% in group 2, and 36% and 33% in group 3. Hypoxaemia occurred most commonly in the first 15 min in children after von Langenbeck palatoplasty, in the first 40 min after push-back palatoplasty and in the 120 min after combined push-back palatoplasty and superior pharyngeal flap surgery. There were significant associations between low SpO2 values, incidence of hypoxaemia on admission to the recovery room and recovery scores.

Adolescent↗
PubMed1998

Dose-response curve and time-course of effect of vecuronium in male and female patients.

To determine the differences between men and women in the dose-response curve and the time-course of effect of vecuronium, we studied 60 adult patients (30 male and 30 female), ASA I, age 18-51 yr, undergoing elective plastic surgery. Anaesthesia was maintained with nitrous oxide 60% in oxygen; thiopentone and incremental doses of fentanyl were given as required. Neuromuscular function was assessed mechanomyographically using the train-of-four (TOF) stimulation at the wrist every 12 s. The percentage depression of T1 was used as the study variable. The dose-response relationship of vecuronium was determined by a cumulative dose-response technique. The dose-response curve in men was shifted in a parallel fashion to the right, indicating a decrease in the sensitivity to vecuronium-induced neuromuscular block, compared with women. The ED50, ED90 and ED95 of vecuronium were 23.9 (4.7), 45.4 (11.2) and 55.7 (14.3) micrograms kg-1 in men and 18.4 (3.7), 33.5 (7.8) and 39.8 (9.6) micrograms kg-1 in women respectively. There were statistically significant differences in these values between the two groups (P < 0.01 in each instance). After a total dose of vecuronium 80 micrograms kg-1, neuromuscular block was significantly longer in women than in men. The duration of peak effect, clinical duration, and the total duration were 18.7 (7.1), 26.6 (8.8) and 50.6 (16.0) min respectively in men and 26.0 (7.2), 37.1 (11.2) and 65.9 (20.7) min in women. They differed significantly between men and women (P < 0.005 in each case).

Adolescent↗
PubMed1998

The influence of acute normovolemic hemodilution on the dose-response and time course of action of vecuronium.

UNLABELLED: To evaluate the influence of acute isovolemic hemodilution on the dose-response and time course of action of vecuronium, we studied 60 adult patients with and without hemodilution during surgery. The patients with hemodilution underwent major elective plastic surgery with an anticipated surgical loss of more than 600 mL. Anesthesia was induced with thiopental 4-6 mg/kg and fentanyl 2-4 microg/kg i.v. and was maintained with 60% nitrous oxide in oxygen. Further increments of thiopental 2 mg/kg or fentanyl 2 microg/kg were given as required. Acute isovolemic hemodilution in the hemodilution group was induced by drainage of venous blood and an i.v. infusion of lactated Ringer's solution and 6% dextran, during which hematocrit and hemoglobin decreased from 45.7% to 26.2% and from 148.5 g/L to 90.2 g/L, respectively. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12 s, and the percent depression of T1 response was used as the study parameter. The dose-response relationships of vecuronium in the two groups were determined by using the cumulative dose-response technique. The results showed that during hemodilution, the dose-response curve of vecuronium was shifted to the left in a parallel fashion, and the potency of vecuronium was increased. There were significant differences in the 50%, 90%, and 95% effective doses between the two groups. After the i.v. administration of vecuronium 80 microg/kg, vecuronium-induced neuromuscular block was significantly longer in the patients with hemodilution than in the control patients. The duration of peak effect, clinical duration, recovery index, and total duration in the hemodilution patients were significantly different from those in the control patients. We conclude that hemodilution induces significant changes in the pharmacodynamics of vecuronium. IMPLICATIONS: We found that patients with hemodilution were 20% more sensitive to vecuronium and had a longer duration of action after the administration of the same dose than the controls. This should be taken into account when vecuronium is used as a muscle relaxant during acute hemodilution.

Adolescent↗
PubMed1998

Dose-response and time-course of the effect of rocuronium bromide during sevoflurane anaesthesia.

To evaluate the influence of sevoflurane on the dose-response relationship and on the time-course of the effect of rocuronium, 60 adult patients undergoing elective plastic surgery were randomly allocated to either the control or the sevoflurane group. Anaesthesia was maintained with 60% nitrous oxide in oxygen and thiopentone in the control group and with 60% nitrous oxide in oxygen and an end-tidal concentration of 1.75% sevoflurane in the sevoflurane group. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12s and the percentage depression of the first twitch of the train-of-four was used as the study parameter. The dose-response relationship of rocuronium in the two groups was determined by the cumulative dose-response technique. The dose-response curve of rocuronium in the sevoflurane group was shifted to the left compared to the control group, indicating a potentiation of rocuronium-induced neuromuscular block. The effective doses of rocuronium required to produce 50%, 90% and 95% twitch depression in the sevoflurane group were decreased by 30.5%, 26.7% and 25.2%, respectively, compared to the control group. Following the administration of a total dose of rocuronium of 400 micrograms.kg-1, the duration of action of, and the recovery from, rocuronium were both significantly prolonged by sevoflurane. There were significant differences in the duration of peak effect, clinical duration, recovery index and the total duration of action between the control and the sevoflurane groups.

Adolescent↗
PubMed1997

Determination of nanograms of nucleic acids by their enhancement effect on the resonance light scattering of the cobalt(II)/4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene complex.

Using a common spectrofluorometer to measure the intensity of resonance light-scattering, a method for determination of nucleic acids in the nanogram range has been developed. In the pH range 11.5-12.0, the resonance light-scattering of the binary complex of cobalt(II)/ 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) is greatly enhanced by nucleic acids, with the maximum scattering peak located at 547.0 nm. The enhanced intensity of resonance light-scattering is in proportion to the concentration of calf thymus DNA in the range 0-400 ng/mL and to that of fish sperm DNA and yeast RNA in the range 0-300 ng/mL. The limits of detection are 1.4 ng/mL for calf thymus DNA, 0.8 ng/ mL for fish sperm DNA, and 1.3 ng/mL for yeast RNA. Precision at 200 ng/mL for the three nucleic acids is 1.9%, 2.0%, and 0.8%, respectively. Six synthetic samples were determined satisfactorily. Mechanism studies showed that the nature of the reaction is that the binary complex of Co(II)/5-Cl -PADAB reacts with single-stranded nucleic acid, and the enhancement effect of nucleic acids on the resonance light scattering of the binary complex is due to the stacking of the binary complex on nucleic acids, which act as a template.

Hydrogen-Ion Concentration↗
PubMed1997

Enhancement of Rayleigh light scattering of acid chrome blue K by proteins and protein assay by the scattering technique.

Rayleigh light scattering of Acid Chrome Blue K (ACBK) is enhanced greatly by proteins. Based on this, a method for protein assay in aqueous solution was developed. This assay matches the sensitivity of the colorimetric dye-binding method with a linear range of 0.136-10.88 micrograms ml-1. The measurements can be made easily on a common fluorimeter. The reaction between ACBK and proteins is completed in 2 min and the scattered light signal is stable for at lest 3 h. Protein-to-protein variability is encountered in this method as in many other protein assays. There is little or no interference from amino acids, most metal ions and complexing agents (e.g., EDTA). Interferences from salts, urea and detergents can be minimized by dilution.

Coloring Agents↗
PubMed1997

Pharmacokinetics of vecuronium during acute isovolaemic haemodilution.

To evaluate the effect of acute isovolaemic haemodilution on the pharmacokinetics of vecuronium, we studied 13 patients undergoing haemodilution during surgery and 13 control patients. General anaesthesia was induced with thiopentone 4-6 mg kg-1 and fentanyl 2-4 micrograms kg-1, and maintained with enflurane and 60% nitrous oxide in oxygen. The haemodilution patients underwent major elective plastic surgery with an anticipated surgical loss of more than 600 ml. Haemodilution was achieved by drainage of venous blood and i.v. infusion of lactated Ringer's solution and 6% dextran, during which the packed cell volume and haemoglobin concentration decreased from 45% to 28.1% and from 14.7 g dl-1 to 9.1 g dl-1, respectively. After administration of a bolus of vecuronium 100 micrograms kg-1, an improved fluorimetric assay was used to measure the plasma concentrations of vecuronium for 5 h. The results showed that the disposition kinetics of vecuronium were best described mathematically by a three-compartment open model in the two groups. The mean volume of the central compartment and volume of distribution at steady state were 42.3 (SD 11.8) ml kg-1 and 168.4 (31.5) ml kg-1, respectively, in control patients, and significantly greater (55.2 (13.4) ml kg-1 and 225.9 (53.3) ml kg-1) in the haemodilution patients (P < 0.05). The elimination half-life was 50.3 (11.5) min in control patients and significantly greater (68.2 (15.1) min) in the haemodilution patients (P < 0.05). The half-lives of fast distribution and distribution, mean residual time, area under the plasma concentration curve and plasma clearance were unchanged in patients who underwent haemodilution compared with the control group.

Adolescent↗
PubMed1997

Dose-response and time course of effect of rocuronium in male and female anesthetized patients.

UNLABELLED: To determine differences from dose-response and time-course of rocuronium between male and female patients, 60 adult patients (30 male and 30 female), ASA grade I, aged 17-52 yr, undergoing elective plastic surgery were studied. Anesthesia was maintained with 60% nitrous oxide in oxygen, thiopental, and incremental doses of fentanyl as required. Neuromuscular function was assessed mechanomyographically with train-of-four (TOF) stimulation at the wrist every 12 s, and the percentage depression of the T1 response was used as the study variable. The dose-response relationship of rocuronium was determined by a cumulative dose-response technique. The results showed that the dose-response curve of rocuronium in the men was shifted to the right, indicating a decrease in the sensitivity to rocuronium-induced neuromuscular block versus the women. The 50%, 90%, and 95% effective doses of rocuronium were 178.4 +/- 53.7, 358.7 +/- 101.3, and 386.2 +/- 113.4 microg/kg, respectively, in male patients, and 128.8 +/- 42.5, 252.8 +/- 51.7, and 274.4 +/- 59.4 microg/kg in female patients. After an intravenous administration of total dose of 400 microg/kg rocuronium, neuromuscular block was significantly longer in the men than in the women. The duration of peak effect, clinical duration, and total duration were 6.5 +/- 3.0, 12.5 +/- 4.9, and 33.6 +/- 8.7 min, respectively, in male patients, and 11.8 +/- 2.7, 18.5 +/- 5.3, and 46.8 +/- 9.6 min in female patients. We conclude that women were approximately 30% more sensitive to rocuronium compared with men. IMPLICATIONS: The authors found that women were 30% more sensitive to rocuronium than men. This suggests that the routine dose of rocuronium should be reduced in women compared with men.

Adolescent↗