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Biomedical subjects

L H Tan

Publications and source records attributed to L H Tan.

At least 19 recordsLinked to original sources
PubMed2002

Anaesthetic considerations for lung volume reduction surgery--a case report.

INTRODUCTION: This case describes some of the unique problems faced by the thoracic anaesthesiologists during anaesthesia for lung volume reduction surgery. CLINICAL PICTURE: The usual pulmonary function requirements for lobectomy are normally not met in these patients with severe emphysema. TREATMENT: Maintenance of the functional residual capacity of the lung and normocapnia during anaesthesia are not as important. Instead problems due to barotrauma and dynamic hyperinflation from positive pressure ventilation are. OUTCOME: Modification of ventilation strategy and providing an anaesthetic tailored towards early extubation is the cornerstone of the anaesthetic plan. CONCLUSION: A good understanding of the respiratory physiology in patients with severe emphysema is essential.

Aged↗
PubMed2001

An fMRI study with written Chinese.

Event-related functional magnetic resonance imaging (ER-fMRI) was used to investigate how the human brain processes phonology and transforms a word's visual form (orthography) into phonological form during reading in logographic Chinese, a writing system that differs markedly from alphabetic languages. We found that reading aloud of irregular words produced larger MR signal intensity changes over extensive regions involving left infero-middle frontal cortex, left motor cortex, right infero-frontal gyri, bilateral anterior superior temporal areas, and anterior cingulate cortex. Right superior parietal lobule, the cuneus in bilateral visual cortex, and thalamus participated in the processing of irregular, but not regular, words. These findings were discussed in comparison to neuroimaging findings from alphabetic languages, as well as in relation to models of reading.

Adult↗
PubMed2001

The neural system underlying Chinese logograph reading.

Written Chinese as logographic script differs notably from alphabets such as English in visual form, orthography, phonology, and semantics. Thus, research on the Chinese language is important to advance our understanding of the universality and particularity of the organization of language systems in the brain. In this study, we examine the neural systems associated with logographic reading using functional magnetic resonance imaging. Two experimental tasks were devised, one based on semantic decision and the other on homophone decision. Compared to the fixation baseline, peak activations resulting from semantic as well as homophony decisions were localized in the left middle frontal gyrus (BA 9). Left inferior frontal cortex also mediated Chinese processing. In addition, more right hemisphere cortical regions (i.e., BAs 47/45, 7, 40/39, and the right visual system) were involved in reading Chinese relative to reading English. This is attributed to the square shape of the logograph which requires an elaborated analysis of the spatial information and locations of various strokes comprising the logographic character. We suggest that the left middle frontal area (BA 9) coordinates and integrates the intensive visuospatial analysis demanded by logographs' square configuration and the semantic (or phonological) analysis required by the present experimental tasks. Our study has implicated brain regions common to both logographic and alphabetic languages as well as brain regions specialized in processing logographs.

Adult↗
PubMed2001

Cerebral hemodynamic response in Chinese (first) and English (second) language processing revealed by event-related functional MRI.

Comparative functional neuroimaging studies using the block design paradigm have previously demonstrated that there are no significant differences in the location of areas of cerebral activation when native Chinese speakers independently process single words or sentences in both the Chinese (first) and English (second) languages. While it has also been documented that significant domains of brain response include the inferior to middle left frontal lobe, the latency, amplitude and duration of the associated hemodynamic changes during isolated neural processing of Chinese and English languages still remain unknown. The aim of this study, therefore, was to examine the characteristics of the hemodynamic alterations in the above-mentioned regions with event-related functional MRI (ER-fMRI) when native Chinese speakers performed verb generation tasks in both the Chinese (first) and English (second) languages. Our results demonstrate the presence of a similar neural activity-induced hemodynamic response in the inferior to middle left frontal lobe during both tasks. Further, there were also no statistically significant differences among the variables that described the hemodynamic response curves. These findings strongly imply that the underlying neural mechanism for Chinese (first) and English (second) language processing may be similar in native Chinese speakers.

Adult↗
PubMed2001

2-octylcyanoacrylate-assisted microvascular anastomosis: comparison with a conventional suture technique in rat femoral arteries.

Standard microvascular anastomosis using only sutures is a well-established and successful technique; however, it is time-consuming and may cause vessel narrowing, needle trauma, and tissue reaction. The authors' hypothesis was that 2-octylcyanoacrylate could simplify microvascular anastomosis and reduce wall trauma and reaction. End-to-end anastomoses of the femoral arteries were performed in 20 adult rats. Each animal served as its own control. The time taken for each anastomosis (from first stitch to release of clamps) was noted, and the patency assessed. At day 7, the anastomoses were reassessed for patency, and the vessels evaluated histologically. 2-octylcyanoacrylate reduced the need to insert more sutures. Anastomotic time in the study group was statistically significantly shorter (p < 0.001), and the patency rate was 90 percent, compared to 85 percent with the standard suture technique. There was also less intense inflammatory reaction, with fewer foreign-body granulomata. This is the first report on the use of 2-octylcyanocrylate, currently approved for cutaneous use, for vessel anastomosis. Further work on the biomechanics and long-term histologic effects will be carried out. 2-octylcyanoacrylate has the potential for simplifying and improving the patency rates of arterial microanastomosis.

Anastomosis, Surgical↗
PubMed2000

Reading Chinese characters for meaning: the role of phonological information.

Two experiments with the Stroop paradigm were conducted to investigate the role of phonological codes in access to the meaning of Chinese characters. Subjects named the ink color of viewed characters or color patches. Key items were color characters, their homophones with the same tone, homophones with different tones, and semantic associates. Apart from finding the usual Stroop interference effect, homophones produced significant interference in the incongruent condition, provided that they had the same tone as the color characters. The interference effect from homophones, however, was significantly smaller than that from color characters. Semantic associates generated an interference effect in the incongruent condition, an effect of the same magnitude as the effect from the same-tone homophones. Finally, in the congruent conditions, all the key items yielded facilitations compared to neutral controls, though the facilitation from color characters was larger than the facilitations from other types of characters. These findings suggest that phonological codes in Chinese are activated obligatorily and provide early sources of constraint in access to meaning.

Cognition↗
PubMed2000

The role of phonological codes in integrating information across saccadic eye movements in Chinese character identification.

Prior research has generally assumed either that phonological codes do not contribute to Chinese character identification or that they do so only through a look-up process at the character level. In 3 experiments, a homophone seen parafoveally aided the identification of a target character that was fixated following an eye movement to the preview location. Moreover, high-frequency phonetically regular characters were named faster than high-frequency, phonetically irregular characters. Thus, both lexical and sublexical phonological codes of Chinese characters are involved early in the process of character identification. Orthographic information from the preview was also used in character identification, as orthographically similar previews facilitated target identification as well. The evidence for the extraction of semantic information from parafoveal previews was mixed, as synonym previews facilitated in Experiment 2 but not in Experiment 1.

Adult↗
PubMed2000

Rosai-Dorfman disease of the breast: a mimic of breast malignancy.

Rosai-Dorfman disease (RDD) or sinus histiocytosis with massive lymphadenopathy (SHML) is primarily a nodal-based, idiopathic, benign proliferative disorder of histiocytes with 43% of these cases also involving extranodal sites. The breast is an unusual site of occurrence of RDD. We report two cases of this exceptional event. The first represents an intramammary nodal Rosai-Dorfman disease, while the second is an extranodal disease with sole involvement of the breast. In both, the possibility of malignancy was raised. Histological examination of the two breast lesions revealed sheets of characteristic large histiocytes displaying emperipolesis, a microscopic hallmark of this disease. Immunohistochemical and ultrastructural studies were also performed; the former showed cytoplasmic staining of histiocytes for S-100 protein, while histiocytes that engulfed lymphocytes and plasma cells were identified on electron microscopy.

Adult↗
PubMed2000

Phonology matters: the phonological frequency effect in written Chinese.

Does phonology play a role in silent reading? This issue was addressed in Chinese. Phonology effects are less expected in Chinese than in alphabetical languages like English because the basic units of written Chinese (the characters) map directly into units of meaning (morphemes). This linguistic property gave rise to the view that phonology could be bypassed altogether in Chinese. The present study, however, shows that this is not the case. We report two experiments that demonstrate pure phonological frequency effects in processing written Chinese. Characters with a high phonological frequency were processed faster than characters with a low phonological frequency, despite the fact that the characters were matched on orthographic (printed) frequency. The present research points to a universal phonological principle according to which phonological information is routinely activated as a part of word identification. The research further suggests that part of the classic word-frequency effect may be phonological.

Adult↗
PubMed2000

Brain activation in the processing of Chinese characters and words: a functional MRI study.

Functional magnetic resonance imaging was used to identify the neural correlates of Chinese character and word reading. The Chinese stimuli were presented visually, one at a time. Subjects covertly generated a word that was semantically related to each stimulus. Three sorts of Chinese items were used: single characters having precise meanings, single characters having vague meanings, and two-character Chinese words. The results indicated that reading Chinese is characterized by extensive activity of the neural systems, with strong left lateralization of frontal (BAs 9 and 47) and temporal (BA 37) cortices and right lateralization of visual systems (BAs 17-19), parietal lobe (BA 3), and cerebellum. The location of peak activation in the left frontal regions coincided nearly completely both for vague- and precise-meaning characters as well as for two-character words, without dissociation in laterality patterns. In addition, left frontal activations were modulated by the ease of semantic retrieval. The present results constitute a challenge to the deeply ingrained belief that activations in reading single characters are right lateralized, whereas activations in reading two-character words are left lateralized.

Adult↗
PubMed1999

The Internal Medicine Center--an integrated solution for information on internal medicine on the World Wide Web.

The World Wide Web (WWW) has grown from being a resource center for a select group of scientists to a large database of information that is available to both professionals and public. The amount of medical information on the Web has been increasing exponentially and thus, it has become increasingly difficult for anyone to be able to search for a specific quantum of information among this mass. Even in mid 1996, it was noted that the amount of information on internal medicine was growing rapidly. Hence, on 21 March 1997, the Internal Medicine Center (IMC) was created and launched. The IMC is an unique concept and it represents the first time that medical data on the web has been organized into a form that intimately parallels clinical medicine. The rationale behind the creation of the IMC can be summarized in three words: information, speed and convenience. The interface used by this center reflects these goals because overuse of large image files are avoided, hence decreasing the access time and yet keeping the information in an easily comprehensible manner. In conclusion, the IMC serves as a useful tool for the layman as well as the expert because the comprehensive information that it offers can be accessed rapidly and conveniently.

Information Services↗
PubMed1998

Effects of perinatal diazepam exposure on the liver of rats.

Diazepam is routinely used in obstetrics in the treatment of maternal eclampsia or as anesthetic induction during deliveries or cesarean sections. We investigated here the effects of perinatal diazepam treatment on the liver of Sprague Dawley rats. From 15th day of gestation to birth pregnant rats were treated daily in the first experimental group (DZ1) with 2.5 mg DZ/kg b.w., s.c., the second (DZ2) with 5 and the third (DZ3) with 10 mg DZ/kg b.w. After birth respective treatment was continued to the pups till 5th day postnatal. One half of pups from DZ2 and control was sacrificed at 12th day, the other were raised to 120th day and then sacrificed. After fixation in formaldehyde serial paraffin sections were processed with proliferating cell nuclear antigen (PCNA), autofluorescence of lipofuscin and Elastica v. Gieson staining. Livers from 12 day old rats showed increased levels of PCNA marked hepatocytes and lipofuscin containing cells. Livers from 120 day old animals exhibited increased levels of PCNA cells especially with weakly stained nuclei, the number of lipofuscin containing cells were decreased in DZ1 and DZ2 but reached in DZ3 the similar number as control. Statistical analysis showed that quantification of Kupffer cells lacked significance. To conclude livers of 12 day old animals demonstrated a stimulated DNA synthesis and an accumulation of nondegradable residues. Livers from 120 day old rats demonstrated an increase in number of potentially proliferating hepatocytes by increased levels of weakly stained PCNA nuclei. At lower dosage DZ seems to inhibit lipofuscinogenesis, at highest dosage DZ accumulates non-degradable residues. Elastica v. Gieson staining was not suitable to quantify Kupffer cells with certainty.

Animals↗
PubMed1996

Erythropoietin production in rats with post-ischemic acute renal failure.

To study the role of erythropoietin (Epo) in the pathogenesis of anemia in acute renal failure (ARF), organ Epo mRNA was measured by RNase protection assay in rats with ARF induced by a one hour-occlusion of the left renal artery. Hematocrit was significantly decreased two hours, 24 hours and one week after renal artery occlusion. A significant reduction in serum haptoglobin at two hours and an increase in serum LDH at 24 hours indicated that hemolysis was the likely cause of the initial fall in hematocrit. However, despite the reduced hematocrit, serum Epo concentrations were not significantly different from controls, suggesting that the anemia is maintained because of lack of an appropriate Epo response. Right renal Epo mRNA levels were not significantly different in all groups, but Epo mRNA levels in post-ischemic kidneys were 50 to 67% lower than in contralateral kidneys. However, Epo mRNA in the post-ischemic kidney was increased sixfold by acute hemorrhage, a rise comparable to the ninefold increase observed in contralateral kidneys. In ARF rats exposed to 7.5% O2 for four hours, right kidney Epo mRNA increased 200-fold over normoxic levels, to a value similar to sham-operated hypoxic controls. Epo mRNA in the post-ischemic kidney also increased 200-fold, to 50% of the level in the contralateral kidney. Hepatic Epo mRNA levels were elevated to comparable levels in both groups. In this ARF model, mild anemia is associated with relative Epo deficiency. In the post-ischemic kidney, a substantial capacity for Epo production is retained but the sensitivity of the Epo response to blood oxygen availability is significantly reduced.

Acute Kidney Injury↗
PubMed1995

Assessment of competence in technical clinical skills of general practitioners.

Technical clinical procedures constitute an important part of the work of general practitioners. Assessment of competence in the relevant skills is important from the perspective of quality assurance. In this study, the psychometric characteristics of three different methods for assessment of competence in technical clinical skills in general practice were evaluated. A performance-based test (8 stations), a written knowledge test of skills (125 items) and a self-assessment questionnaire (41 items) on technical clinical skills were administered to 49 GPs and 47 trainees in general practice. The mean scores on the performance-based test and the written knowledge test of skills showed no substantial differences between GPs and trainees, whereas the GPs scored higher on the self-assessment questionnaire. While the correlation of the score on the knowledge test of skills with the score on the performance-based test was moderately high, the score on the self-assessment questionnaire showed a rather low correlation with the performance-based test. Although performance-based testing is obviously the best method to assess proficiency in hands-on skills, a written test can serve as a reasonable alternative, particularly for screening and research purposes.

Clinical Competence↗
PubMed1993

Infant mortality statistics do not adequately reflect the impact of short gestation.

OBJECTIVE: To determine the accuracy of National Center for Health Statistics cause-specific infant mortality data. The National Center for Health Statistics compiles these data by applying World Health Organization (WHO) selection rules to death certificate data. The WHO rules arrange medical entities into a hierarchical order and select a single underlying cause of death (ULCD). DESIGN: A comparison was made between ULCD assigned to a cohort of 335 infant death certificates by (1) a neonatologist panel, and (2) application of WHO selection rules by the Florida State Office of Vital Statistics (OVS). RESULTS: Among the 146 infants with birth weights 1500 to 4649 g, agreement between neonatologists and OVS was 88%, while among the 189 infants with birth weights 0 to 1499 g (very low birth weight), agreement was just 41%. Neonatologists selected short gestation as the underlying cause of death for 82% of very low birth weight infant records, vs 25% by OVS. Due to the application of specific WHO selection rules, OVS frequently selected immediate causes of death, such as "cardiac arrest," as the ULCD, even when the medical certifier had indicated short gestation as the ULCD. In vital statistics reports, many of these immediate causes are reported as "other respiratory conditions of newborn," or "all other perinatal conditions." CONCLUSION: WHO ULCD selection rules should be modified to allow short gestation to have a higher priority over immediate causes of infant death.

Birth Weight↗