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Biomedical subjects

Z X Fang

Publications and source records attributed to Z X Fang.

15 recordsLinked to original sources
PubMed1996

Factors affecting production of compound A from the interaction of sevoflurane with Baralyme and soda lime.

Various alkali (e.g., soda lime) convert sevoflurane to CF2=C(CF3)OCH2F, a vinyl ether called "Compound A, " whose toxicity raises concerns regarding the safe administration of sevoflurane via rebreathing circuits. In the present investigation, we measured the sevoflurane degradation and output of Compound A caused by standard (13% water) Baralyme brand absorbent and standard (15% water) soda lime, and Baralyme and soda lime having various water contents (including no water). We used a flow-through system, applying a gas flow rate relative to absorbent volume that roughly equaled the rate/volume found in clinical practice. Both absorbents, at similar water contents, temperatures, and sevoflurane concentrations, produced roughly equal concentrations of Compound A. Dry and nearly dry absorbents produced less Compound A early in exposure to sevoflurane, and more later, than standard absorbents. Increases in temperature and sevoflurane concentration increased output of Compound A. Both absorbents, especially when dry, also destroyed Compound A, the concentration exiting from absorbent resulting from a complex sum of production and destruction. We conclude that the variability of concentrations of Compound A found in clinical practice may be largely explained by the inflow rate used (i.e., by rebreathing), sevoflurane concentration, and absorbent temperature and dryness. The effect of dryness is complex, with fresh dry absorbent destroying Compound A as it is made, and with dry absorbent that has been exposed to sevoflurane for a period of time providing a sometimes unusually high output of Compound A.

Absorption↗
PubMed1995

Seroprevalence of hepatitis C virus infection and its genotype in Lanzhou, western China.

The seroprevalence of hepatitis C virus (HCV) infection in Lanzhou, Western China was studied. HCV genotypes in 20 patients with HCV infection was determined by genotype-specific primer for polymerase chain reaction (PCR) based on HCV core region and compared with the genotype assigned by sequence comparison and molecular evolutionary analysis based on the same region. Antibody to HCV (anti-HCV) was present in 2.5% of volunteer blood donors and in 35.0% of paid blood donors (P < 0.01). HCV infection is uncommon in patients with liver disease who attended liver clinics in this locality; 4.0% with acute hepatitis and 4.0% with chronic hepatitis, 10.0% with liver cirrhosis, and none with hepatocellular carcinoma were seropositive for anti-HCV. Genotype 1b and 2a were both found to be prevalent. Together, they accounted for 19 of 20 (95%) patients with HCV infection. Sequencing of the HCV core region from two patients showed that the assignment of HCV genotype by genotype-specific primers for PCR matched well with the genotyping results based on sequence comparison and molecular evolutionary analysis. These data showed that HCV is present in Western China, HCV infection is more common in paid blood donors, and HCV genotypes 1b and 2a are both prevalent in Western China.

Amino Acid Sequence↗
PubMed1995

Carbon monoxide production from degradation of desflurane, enflurane, isoflurane, halothane, and sevoflurane by soda lime and Baralyme.

Anecdotal reports suggest that soda lime and Baralyme brand absorbent can degrade inhaled anesthetics to carbon monoxide (CO). We examined the factors that govern CO production and found that these include: 1) The anesthetic used: for a given minimum alveolar anesthetic concentration (MAC)-multiple, the magnitude of CO production (greatest to least) is desflurane > or = enflurane > isoflurane >> halothane = sevoflurane. 2) The absorbent dryness: completely dry soda lime produces much more CO than absorbent with just 1.4% water content, and soda lime containing 4.8% or more water (standard soda lime contains 15% water) generates no CO. In contrast, both completely dry Baralyme and Baralyme with 1.6% water produce high concentrations of CO, and Baralyme containing 4.7% water produces concentrations equaling those produced by soda lime containing 1.4% water. Baralyme containing 9.7% or more water and standard Baralyme (13% water) do not generate CO.3) The type of absorbent: at a given water content, Baralyme produces more CO than does soda lime. 4) The temperature: an increased temperature increases CO production. 5) The anesthetic concentration: more CO is produced from higher anesthetic concentrations. These results suggest that CO generation can be avoided for all anesthetics by using soda lime with 4.8% (or more) water or Baralyme with 9.7% (or more) water, and by using inflow rates of less than 2-3 L/min. Such inflow rates are low enough to ensure that the absorbent does not dry out.

Adsorption↗
PubMed1995

Factors affecting the concentration of compound A resulting from the degradation of sevoflurane by soda lime and Baralyme in a standard anesthetic circuit.

Carbon dioxide absorbents, such as soda lime and Baralyme brand absorbent, convert sevoflurane to CF2 = C(CF3)OCH2F, a vinyl ether called "Compound A," whose toxicity raises concerns regarding the safety of sevoflurane in rebreathing circuits. Because an increased inflow rate to an anesthetic circuit decreases rebreathing, we assumed that an increased rate would proportionately decrease the concentration of Compound A. In the present report, we measured the Compound A concentration resulting from the action of wet (standard) soda lime and wet (standard) Baralyme on 2% sevoflurane in a model anesthetic circuit, using inflow rates (0.5, 1.0, 2.0, 4.0, and 6.0 L/min), ventilations (5 and 10 L/min), and carbon dioxide production/removal (200 and 400 mL/min) found in clinical practice. An increase in inflow rate decreased Compound A concentration to lower levels as inflow rate approached minute ventilation. At lower inflow rates, increasing duration of sevoflurane inflow increased the concentration of Compound A, a finding consistent with a progressive increase in absorbent temperature from absorption of carbon dioxide and consequently greater sevoflurane degradation. There was no material difference between Baralyme and soda lime in the concentrations of Compound A produced at a particular inflow rate. An increase in ventilation increased the concentration of Compound A, having a much greater effect at high rather than low inflow rates. An increase in amount of carbon dioxide absorbed also increased the concentration of Compound A. We conclude that inflow rate, ventilation, and carbon dioxide production are major determinants of the concentration of Compound A.

Absorption↗
PubMed1993

Oxygen radicals in bronchoconstriction of guinea pigs elicited by isocapnic hyperpnea.

The role of oxygen radicals in isocapnic hyperpnea-induced bronchoconstriction (HIB) of guinea pigs was investigated using scavengers of the radicals. In series 1, 50 young guinea pigs were randomly divided into seven groups: control 1, control 2, chlorisondamine, tetrodotoxin (TTX), acute dimethylthiourea (DMTU), tachykinin depletion, and 5% CO2 in air. Animals of the control 2 group received vehicle (saline) infusion while those of the control 1 group did not. Chlorisondamine was used to block ganglionic transmission, TTX to interrupt nerve conduction, DMTU to scavenge hydroxyl radicals, and chronic capsaicin pretreatment to deplete tachykinins. The animals in the last group were ventilated with dry 5% CO2 in air during hyperpnea. In series 2, 13 additional animals were used to test the effects of intratracheal administration of superoxide dismutase and catalase (SOD + CAT) on HIB. Each animal was anesthetized with pentobarbital sodium, cannulated with a tracheal cannula and venous catheter, paralyzed with gallamine triethiodide, and mechanically ventilated. During the baseline period, each animal was ventilated normally with humidified air. Then it was hyperventilated 15 min with a dry gas mixture of 95% O2-5% CO2, except animals in the last group of series 1. Subsequently, all animals returned to normal ventilation with humidified air for 45 min (recovery period). The maximal expiratory flow and dynamic compliance were obtained periodically during the recovery period. The isocapnic hyperpnea using 95% O2-5% CO2, but not 5% CO2 in air, caused bronchoconstriction that was significantly blocked by acute DMTU, acute SOD + CAT, and tachykinin depletion. In an additional group of six animals, acute DMTU did not significantly alter acetylcholine-induced airway constriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Noncholinergic airway constriction: role of axon reflex and oxygen radicals.

In the airways and lungs, activated afferent C-fibers release tachykinins, which induce noncholinergic bronchoconstriction. We have, for several years, focused our research on the role of axon reflex and oxygen radicals in noncholinergic airway constriction in guinea pigs. In this species, the noncholinergic bronchial constriction is not affected by administration of a ganglionic blocking agent, chlorisondamine, indicating that only the afferent C-fiber, not a complete reflex arc, is required for this constriction. Accordingly, we investigated the role of axon reflex by using tetrodotoxin (TTX) and bupivacaine to block impulse conduction in the axon. For the role of oxygen radicals, superoxide dismutase (SOD), catalase (CAT), and dimethylthiourea (DMTU) were employed to scavenge superoxide anion, hydrogen peroxide, and hydroxyl radical, respectively. We used capsaicin, resiniferatoxin (RTX), or hyperventilation to activate afferent C-fibers which, in turn, release tachykinins and lead to noncholinergic airway constriction. The constriction was quantified by measuring the maximal expiratory flow rate (Vmax) and dynamic compliance (Crs). Both capsaicin and RTX caused an immediate decrease in Vmax and Crs, indicating severe bronchoconstriction. This constriction decreased gradually with time. Tachykinin depletion abolished neurotoxin-induced airway constriction, suggesting that tachykinins mediate the constriction. Both TTX and bupivacaine significantly attenuated the constriction at 15-20 min after neurotoxin administration. Therefore, these data suggest that the axon reflex plays an important role in noncholinergic bronchial constriction. In other studies, capsaicin- or hyperventilation-induced bronchoconstriction was abolished by tachykinin depletion, as well as significantly ameliorated by the administration of antioxidants. These data indicate that oxygen radicals modulate the tachykinin-mediated noncholinergic airway constriction.

Animals↗
PubMed1992

Inhibition of [3H]dopamine uptake into rat striatal slices by quaternary N-methylated nicotine metabolites.

The effects of quaternary N-methylated nicotine derivatives were examined on in vitro uptake of [3H]dopamine ([3H]DA) in rat striatal slices. Striatal slices were incubated with a 10 microM concentration of the following compounds: N-methylnicotinium, N-methylnornicotinium, N-methylcotininium, N,N'-dimethylnicotinium and N'-methylnicotinium salts. The results clearly indicated that significant (60%) inhibition of [3H]DA uptake occurred with those compounds possessing a N-methylpyridinium group; whereas, compounds that were methylated at the N'-pyrrolidinium position were less effective or exhibited no inhibition of [3H]DA uptake. The results suggest that high concentrations of quaternary N-methylated nicotine metabolites which are structurally related to the neurotoxin MPP+, and which may be formed in the CNS, may protect against Parkinson's Disease and explain the inverse relationship between smoking and Parkinsonism reported in epidemiologic studies.

Animals↗
PubMed1990

[Use of signal averaging system in the study of ventricular late potentials].

Signal-averaged electrocardiograms (SAECGs) were performed in 93 patients with various heart diseases and 20 dogs with experimental acute myocardial infarction. SA-ECGs were recorded with a high-pass bidirectional digital filter Mode FDS which was made by Shanghai Fudan University and Suzhou Medical College. All the patients and dogs were also examined with ART 1200 EPX recorder. Ventricular late potentials (VLPs) were directly recorded from the epicardium with experimental infarction by using composite electrodes and signal averaging system in late stage of coronary ligation. The results showed: VLPs were detected by body surface SA-ECG only in half of the dogs with VLPs detected by the real time mapping on infarction region, but the abnormal SAECGs did reveal the delayed ventricular activity; the data obtained with FDS or ART SA-ECG were similar.

Adult↗
PubMed1989

On the structure selectivity problem in drug design. A comparative study of benzylpyrimidine inhibition of vertebrate and bacterial dihydrofolate reductase via molecular graphics and quantitative structure-activity relationships.

Quantitative structure-activity relationships (QSAR) have been derived for the action of 68 5-(substituted benzyl)-2,4-diaminopyrimidines on dihydrofolate reductase (DHFR) from Lactobacillus casei and chicken liver. The QSAR are analyzed with respect to the stereographics models of the active sites of the enzymes and found to be in good agreement. Using these QSAR equations, we have attempted to design new trimethoprim-type antifolates having higher selectivity for the bacterial enzyme. The general problem of developing selective inhibitors is discussed.

Animals↗
PubMed1986

Inhibition of chicken liver dihydrofolate reductase by 5-(substituted benzyl)-2,4-diaminopyrimidines. A quantitative structure-activity relationship and graphics analysis.

The inhibition of chicken liver dihydrofolate reductase by a series of substituted benzylpyrimidines has been investigated. From the inhibition constants a quantitative structure-activity relationship has been formulated. This mathematical model is compared with molecular graphics models constructed from the X-ray crystallographic coordinates of trimethoprim and 5-(3,4-dimethoxy-4-isopropenylbenzyl)-2,4- diaminopyrimidine bound to the enzyme. There is good correspondence between the two types of models.

Animals↗