Biomedical subjects

T S Shih

Publications and source records attributed to T S Shih.

At least 19 recordsLinked to original sources

PubMed2003

Predictors of whole-body vibration levels among urban taxi drivers.

To identify a set of important WBV predictors that could be used to develop a statistical instrument for exposure assessment in a large epidemiologic study, a total of 432 WBV measures were taken from a sample of 247 male drivers in Taipei City, Taiwan. In accordance with the ISO 2631-1 (1997) methods, we measured the frequency-weighted vertical acceleration (z-axis) over drivers' seat surface, under conditions representing different types of rides (vacant vs. short vs. long) assigned to random destinations. Mixed effect models were used to analyse the WBV data including repeated measures. For this group of urban taxi drivers regularly exposed to WBV of low intensity (mean = 0.31 ms( - 2), ranging from 0.17 to 0.55 ms( - 2) r.m.s.), our analyses indicated that average driving speed was the primary predictor (p < 0.0001). As average driving speed increased, measured vertical acceleration increased in a quadratic-linear manner (p < 0.0001). Other WBV predictors, after adjusting for the effects of other covariates, included automobile manufacturer (p = 0.02), engine size (p = 0.04), body weight (p = 0.002), age (p = 0.02), use of seat cushion (p = 0.03), and traffic period (p = 0.02). Our study suggests that a similar statistical approach could be employed in future studies to improve the quality and efficiency of WBV exposure assessment in professional drivers.

Acceleration↗

PubMed2001

Collection efficiency and capacity of three samplers for acidic and basic gases.

This paper compares the collection efficiency and capacity of a coated porous metal disk with those of a silica gel tube and an impinger at the acid or basic aerosol concentration of two times the permissible exposure limitation (Taiwan IOSH, Institute of Occupational Safety and Health), relative humidity of 80 +/- 5%, and temperature of 30 +/- 3 degrees C in the laboratory. Using 5% sodium carbonate/glycerin coating, the collection efficiencies of the porous metal disk for nitric acid, hydrogen chloride, and hydrogen fluoride are found to be higher than those of the silica gel tube and the impinger when the sampling time is less than 3.0 h. The gas collection capacity of the porous metal disk coated with 5% sodium carbonate is calculated to be 3.9, 5.8, and >2.5 mg for nitric acid, hydrogen chloride, and hydrogen fluoride, respectively. For ammonia, the porous metal disk coated using 4% citric acid performs slightly better than the impinger, and the corresponding capacity is slightly greater than 33.6 mg.

Aerosols↗

PubMed2000

Field evaluation of a passive sampler for the exposure assessment of 2-methoxyethanol.

OBJECTIVE: This paper presents a field evaluation of 3 M 3500 passive badges for measuring 2-methoxyethanol (ME) in a humid working environment. METHODS: A total of 93 pairs of side-by-side active/passive samples, 48 pairs of duplicate active samples, 52 pairs of duplicate passive samples, and three groups of six replicate active/passive samples were compared. Three groups of six replicate active charcoal/active charcoal tube with drying tube samples were also compared to evaluate the humidity effect. RESULTS: No statistical difference was found between the passive badges and active samplers. Linear regression showed the correlation to be high (r = 0.992, slope = 0.973, n = 93) over the range of 0.17-163 ppm. The mean concentration difference was -0.34 ppm and the mean relative error was 3.50%. The intraclass correlation coefficients of 48 duplicate active samples and 52 duplicate passive samples were 0.994 and 0.989, respectively. The precision of replicate passive, active, and active/drying tube samples (n = 6) were 3.84%, 7.14%, and 5.12%, respectively. CONCLUSIONS: The humidity effect for active samples was insignificant at the low sampling rate (36.3 ml/min). It is therefore concluded that the use of the passive samplers to assess ME exposure produces comparable findings to that of active sampling.

Environmental Exposure↗

PubMed2000

Measurement of percutaneous uptake of 2-methoxy ethanol vapor in humans.

Absorption of vapors through skin has been largely ignored in occupational health, although for ethylene glycol ethers this route of exposure could be more important than inhalation. We used an automated concentration and humidity controlled system to measure real-time percutaneous absorption of 2-methoxy ethanol (ME) vapor in seven volunteers. The exposure concentration (300 +/- 10 ppm or 25 +/- 0.5 ppm), humidity (80 +/- 2%), and temperature (27.5 +/- 0.5 degrees C) were controlled throughout the experiments. Uptakes during 4-hour single-arm exposure at 25 ppm and 300 ppm were 7.0 mg and 65.3 +/- 25.0 mg, respectively, with corresponding uptake rates of 1.36 micrograms/cm2/hr and 13.2 +/- 5.0 micrograms/cm2/hr. Percutaneous absorption was consistent and unsaturated during exposure. Because the permeability constant of ME vapor (14.0 +/- 5.3 cm/hr) was much higher than that of many widely used organic chemicals, we concluded that vapor absorption through skin is a significant contributor to overall ME exposure.

Adult↗

PubMed2000

Haematological and spermatotoxic effects of ethylene glycol monomethyl ether in copper clad laminate factories.

OBJECTIVES: To investigate the effects of ethylene glycol monomethyl ether (EGME) on haematology and reproduction in exposed workers. METHODS: 53 Impregnation workers from two factories that make copper clad laminate with EGME as a solvent were recruited as the exposed group. Another group of 121 lamination workers with indirect exposure to EGME was recruited as the control group. Environmental monitoring of concentrations of EGME in air and biological monitoring of urinary methoxyacetic acid (MAA) concentrations were performed. Venous blood was collected for routine and biochemical analyses. Semen was collected from 14 workers exposed to EGME for sperm analysis and was compared with 13 control workers. RESULTS: Results of haematological examination showed that the haemoglobin, packed cell volume, and red blood cell count in the male workers exposed to EGME were significantly lower than in the controls. The frequency of anaemia in the exposed group (26.1%) was significantly higher than in the control group (3.2%). However, no differences were found between the female workers exposed and not exposed to EGME. After adjustment for sex, body mass index, and duration of employment, red blood cell count was significantly negatively associated with air concentrations of EGME, and haemoglobin, packed cell volume, and red blood cell count were significantly negatively associated with urinary concentrations of MAA. The pH of semen in the exposed workers was significantly lower than in the control workers, but there were no significant differences in the sperm count or sperm morphology between the exposed and control groups. CONCLUSION: It can be concluded that EGME is a haematological toxin, which leads to anaemia in the exposed workers. However, the data from this study did not support the theory of a spermatotoxic effect of EGME.

Adult↗

PubMed1999

Mouse models of tumor development in neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is a prevalent familial cancer syndrome resulting from germ line mutations in the NF1 tumor suppressor gene. Hallmark features of the disease are the development of benign peripheral nerve sheath tumors (neurofibromas), which can progress to malignancy. Unlike humans, mice that are heterozygous for a mutation in Nf1 do not develop neurofibromas. However, as described here, chimeric mice composed in part of Nf1-/- cells do, which demonstrates that loss of the wild-type Nf1 allele is rate-limiting in tumor formation. In addition, mice that carry linked germ line mutations in Nf1 and p53 develop malignant peripheral nerve sheath tumors (MPNSTs), which supports a cooperative and causal role for p53 mutations in MPNST development. These two mouse models provide the means to address fundamental aspects of disease development and to test therapeutic strategies.

Animals↗

PubMed1999

Detection of methyl ethyl ketone in urine using headspace solid phase microextraction and gas chromatography.

Headspace solid-phase microextraction coupled with gas chromatography/flame ionization detection was developed to measure urinary methyl ethyl ketone (MEK). A fused silica fiber coated with 75 microns carboxen/polydimethylsiloxane was used to extract urinary MEK. The optimal extraction conditions were obtained when temperature was 50 degrees C, extraction time was 15 minutes, and ammonium sulfate concentration was 0.5 g/mL. The optimal desorption temperature and time were 200 degrees C and 5 minutes, respectively. The concentration range of calibration curves was 27 to 8000 ng/mL of MEK. The within-day and between-day pooled coefficients of variation (9 concentrations, triplicate samples) were 5.4% and 8.8%, respectively. The limit of detection and limit of quantitation were 4.2 ng/mL and 21.6 ng/mL, respectively. The recovery (+/- standard deviation) of MEK was 100.2% +/- 8.6% (n = 3). MEK in urine was stable for at least 1 month when stored at -20 degrees C. This method proved to be applicable for the analysis of urinary MEK of exposed workers in a plastic material printing plant. We concluded that this new method is sensitive, inexpensive, simple, and reliable for measuring the occupational exposure of MEK.

Adult↗

PubMed1999

Correlation between urinary 2-methoxy acetic acid and exposure of 2-methoxy ethanol.

OBJECTIVES: To examine the correlation between airborne 2-methoxy ethanol (ME) exposures and the urinary 2-methoxy acetic acid (MAA) and to recommend a biological exposure index (BEI) for ME. METHODS: 8 Hour time weighted average (TWA) personal breathing zone samples and urine samples before and after the shift were collected from Monday to Saturday for 27 workers exposed to ME and on Friday for 30 control workers. RESULTS: No correlation was found between airborne exposure to ME and urinary MAA for nine special operation workers due to the use of personal protective equipment. For 18 regular operation workers, a significant correlation (r = 0.702, p = 0.001) was found between urinary MAA (mg/g creatinine) on Friday at the end of the shift and the weekly mean exposures of ME in a 5 day working week. The proposed BEI, which corresponds to exposure for 5 days and 8 hours a day to 5 ppm, extrapolated from the regression equation is 40 mg MAA/g creatinine. A significant correlation was also found between the weekly increase of urinary MAA (Friday after the shift minus Monday before the shift) and the weekly mean exposures of ME (r = 0.741). The recommended value of the weekly increase of urinary MAA for 5 days repeated exposures of 5 ppm ME is 20 mg/g creatinine. No urinary MAA was detected in workers in the non-exposed control group. CONCLUSIONS: The Friday urinary MAA after the shift or the weekly increase of urinary MAA is a specific and a good biomarker of weekly exposure to ME.

Acetates↗

PubMed1999

Improved method to measure urinary alkoxyacetic acids.

OBJECTIVES: To simplify the current preparation of samples, and to improve the specificity and reliability of the conventional analytical methods to measure urinary alkoxyacetic acids. METHODS: Samples containing alkoxyacetic acids including methoxy, ethoxy, and butoxyacetic acids (MAA, EAA, and BAA) were acidified with HCl and extracted with a mixed solvent of methylene chloride and isopropyl alcohol, then analysed by gas chromatography/mass spectrometry (GC/MS). RESULTS: Optimal results were obtained when pH was 1.05-1.45, the ratio of methylene chloride and isopropyl alcohol was 2:1, and when extraction time was 10 minutes. Over the concentration range 0.3-200 micrograms/ml, MAA, EAA, and BAA could be determined with a pooled coefficient of variation (nine concentrations, six replicate samples) of 5.55%, 6.37%, and 6.41%, respectively. Urine samples were stable for at least 5 months and 3 freeze-thaw cycles at -20 degrees C. The limits of detection of MAA, EAA, and BAA were 0.055, 0.183, and 0.009 microgram/ml, respectively. The matrix effect of urine samples was negligible for MAA and EAA, but were marginally significant for BAA. The average recoveries of alkoxyacetic acids were 99%-101%. In urine samples MAA from 15 exposed workers showed a strong linear correlation (r = 0.999, slope = 1.01) between the new GC/MS method and Sakai's GC method. CONCLUSIONS: The simplified non-derivatisation pretreatment of samples coupled with GC/MS can provide a specific, sensitive, simple, safe, and reliable method for the biological monitoring of occupational exposure of ethylene glycol ethers.

Acetates↗

PubMed1998

Development of respirable aerosol samplers using porous foams.

Workplace aerosols must be sampled to assess the degree of health hazard caused by the particulate matter. By adjusting the sampling flow rate, most of the samplers can match the 50% cutoff size, but not the slope of the respirable convention defined by the American Conference of Governmental Industrial Hygienists, the International Organization for Standardization, and the European Committee for Standardization (CEN). Combinations of foams (or other porous material) of different nominal sizes (10-100 ppi) and thicknesses (5-35 mm) were employed to overcome this bias. A foam disk 25 mm in diameter was placed in an asbestos sampling cowl. Dioctylphthalate was the liquid test agent. An aerodynamic particle sizer and an Aerosizer were calibrated against a settling chamber and were employed to measure the aerosol number concentrations and size distributions upstream and downstream of the foams. The sampling efficiency data showed that the 50% cutoff size could be met for foams in series, but that the slope remained sharper than the new definition. Foams in parallel showed great flexibility and many of the parallel combinations flattened the slope, closer to that of the new international respirable convention. For instance, when the total flow rate is set at 10.1 L/min the aerosol penetration through foams in parallel (100 ppi, 20 mm thick, diameter 25 mm + 10 ppi, 20 mm thick, diameter 13 mm) nearly matched the new international standard for respirable fraction. This sampler can be further miniaturized for smaller sampling flow rates to fit the capacity of personal sampling pumps.

Aerosols↗

PubMed1998

Pre-analytical for biological monitoring of manganese.

Manganese is an essential element but it may result in a toxic event if the workers are excessively exposed to this element. Monitoring of biological Mn exposure is therefore important. The careful preparation for Mn analysis is necessary. In order to get a correct protocol for sampling and storage of the biological samples, identification of the possible contamination source is necessary. This study is concerned with the monitoring procedure of manganese especially the sources of contamination sampling, sample transportation and storage. The results of the study shows that some kinds of needles and anticoagulants might be the main sources of contamination of specimen. It is important to avoid these contamination in performing biological monitoring on workers exposed to manganese.

Environmental Monitoring↗

PubMed1997

Automated on-line sample pretreatment system for the determination of trace metals in biological samples by inductively coupled plasma mass spectrometry.

A fully automated on-line sample pretreatment system combining microwave digestion with sample preconcentration/matrix separation for the determination of trace metals (Fe, Ni, Cu, Zn, and Pb) in blood and serum samples by inductively coupled plasma mass spectrometry (ICPMS) was designed and evaluated. The samples were mixed with an appropriate reagent and digested in a flow-through, focused microwave-heated oven. After digestion, the sample solution was transferred on-line to a column packed with iminodiacetate-based resin for separation of matrix elements like Na, K, Ca, Mg, Cl, P, and S that might interfere with the measurement by ICPMS. The analytes chelated on the resin were subsequently eluted and led to ICPMS for multielement determination. The whole sample pretreatment process was automatically controlled by a self-designed expert system. The analytical reliability of data from this on-line system was confirmed to be good with the analysis of SRM samples (Seronorm Whole Blood and NIST SRM 1598 Bovine Serum), and the limits of detection (3 sigma) for Fe, Ni, Cu, Zn, and Pb were 68, 0.34, 3.5, 13.4, and 0.22 microgram/L, respectively. With this fully automated on-line system, the determination of analytes in biological fluid samples down to micrograms-per-liter levels has been proven to be feasible, and the sample throughput can achieve up to 6 samples/h.

Animals↗

PubMed1997

Characteristics of lead aerosols in different work environments.

Air samples were collected to examine physical and chemical characteristics of lead aerosols in different work environments in the airborne lead concentration range from 28-783 micrograms/m3. Size distribution of aerosols was measured using a Marple personal cascade impactor, and lead analysis was conducted using graphite atomic absorption spectrometry. Lead aerosol size distribution was found to be different from that of total particles. Such differences are not negligible and must be taken into account when estimating aerosol deposition within the human respiratory tract. Variation of MMAD (mass median aerodynamic diameter) and GSD (geometric standard deviation) of lead aerosols in the coarse mode wit total airborne concentration was found to be small, and the assumption that lead aerosol distribution is constant is reasonable for establishing the relationship between airborne lead concentration in all work areas of the three plants except the charging area of the capacitor plant. Therefore, it is expected that either total airborne lead or respirable airborne lead concentration can be used to correlate blood lead concentration.

Aerosols↗

PubMed1997

Occupational neurotoxic diseases in Taiwan: a review of the outbreaks and clinical features.

In the past 20 years, several outbreaks of neurotoxic disease due to occupational exposure have occurred in Taiwan. The most notorious outbreaks were 'Yu-cheng' due to contamination of polychlorinated biphenyls in cooking oil, lead poisoning in battery manufacturers and workers in a ship-scrapping yard, tile factory and battery recycling plants, and n-Hexane intoxication in press-proffers and ball-manufacturers. In addition, there were manganese intoxication in ferromanganese smelters, mercury intoxication in lamp-socket workers, carbon disulfide intoxication in viscose rayon workers and hydrogen sulfide intoxication in chemical synthetic plants. Although the incidence of occupational neurotoxic diseases has increased, the real incidence is probably still underestimated. The reasons for the underestimation include: 1) the education for workers in industrial hygiene is inadequate; 2) high risk workers are not screened well; 3) physicians are not well trained in early diagnosis of occupational diseases; 4) material safety data information is not readily available in the factories; and 5) the threshold limit values for toxic substances are relatively high in Taiwan, compared with other developed countries.

Carbon Disulfide↗

PubMed1996

Nf1 gene targeting: toward models and mechanisms.

Patients with neurofibromatosis type I develop multiple benign nerve sheath tumors and are predisposed to a number of malignancies. Since loss-of-function mutations in the NF1 gene appear to be responsible for the disease, NF1 has been classified as a tumor suppressor. Several strategies involving the targeted disruption of the murine homologue have been used in an attempt to establish an animal model for the disease and four types of animals have been generated: (1) Nf1 +/- animals, (2) NF1 -/- embryos, (3) Nf1 -/- chimeras, and (4) mice transplanted with Nf1 -/- hematopoietic stem cells. In addition to yielding mice which mimic various aspects of the human disease, each of these approaches has contributed to a better understanding of the normal function of Nf1.

Animals↗

PubMed1996

Chronic carbon disulfide encephalopathy.

To understand central nervous damage after long-term exposure to carbon disulfide (CS2), 10 patients who had polyneuropathy with various neuropsychiatric symptoms in a viscose rayon plant were studied. Clinical and laboratory examinations including electroencephalography (EEG), brain computed tomography (CT), brain magnetic resonance images (MRI), and carotid duplex sonography were carried out. Clinically, headache, unpleasant dreams, memory impairment, fatigue, anorexia and emotional lability were common in these patients while 2 patients had stroke episodes. EEGs were all normal. Brain CT scan showed mild cortical atrophy in 3 and low density lesions in the basal ganglia in 3. Brain MRI studies also disclosed mild cortical atrophy in 4 and multiple lesions involving the basal ganglia and corona radiata in 4. Carotid duplex sonography revealed mild atherosclerosis with plaques (< 20% stenosis) of extracranial vessels in 6. However there was no significant difference in flow velocities and flow volumes in the extracranial carotid arteries between patients and the normal controls. Interestingly, 2 patients had multiple brain lesions in the subcortical white matter but without strokes. In conclusion, encephalopathy with possible strokes may occur after chronic exposure to CS2, as well as polyneuropathy. The lesions usually involve the basal ganglia and subcortical white matter. Furthermore, MRI study may detect brain lesions particularly in the subcortical white matter areas before the occurrence of stroke.

Brain Diseases↗

PubMed1996

Lipid peroxidation in workers exposed to manganese.

OBJECTIVES: The following hypothesis was tested: plasma manganese concentration is associated positively with the product of lipid peroxidation, and lipid peroxidation is associated negatively with the activities of antioxidants in workers exposed to manganese. METHODS: The plasma manganese concentration of 22 manganese-exposed workers and 45 referents was determined by graphite furnace atomic absorption spectrophotometry. Malondialdehyde, the product of lipid peroxidation, was determined by high-performance liquid chromatography, and the activities of protective enzymes were measured by ultraviolet-visible spectrophotometry. RESULTS: The activities of superoxide dismutase, glutathione peroxidase, and catalase spread widely among the referents. The activity of superoxide dismutase and the concentrations of malondialdehyde and manganese were significantly higher in the manganese workers than in the referents. The concentration of malondialdehyde in the exposed workers was correlated strongly with the manganese level of plasma. CONCLUSIONS: Malondialdehyde can be used as an index of lipid peroxidation induced by manganese exposure.

Antioxidants↗

PubMed1995

Vascular system defects and neuronal apoptosis in mice lacking ras GTPase-activating protein.

The gene encoding p120-rasGAP, a negative regulator of Ras, has been disrupted in mice. This Gap mutation affects the ability of endothelial cells to organize into a highly vascularized network and results in extensive neuronal cell death. Mutati ons in the Gap and Nf1 genes have a synergistic effect, such that embryos homozygous for mutations in both genes show an exacerbated Gap phenotype. Thus rasGAP and neurofibromin act together to regulate Ras activity during embryonic development.

Animals↗