Biomedical subjects

A C Chen

Publications and source records attributed to A C Chen.

At least 91 records · Page 5Linked to original sources

PubMed1994

Laboratory evaluations of toothbrush interproximal penetration ratios.

Access to interproximal tooth surfaces by toothbrush bristles has been associated with plaque removal. The ability of toothbrushes to assess the interproximal area was assessed with a new laboratory apparatus by measuring the extent of bristle-to-tooth contact in simulated toothbrushing with ink-coated toothbrush bristles. Toothbrush types evaluated were the bi-level trim Advanced Design Reach Soft, the ripple trim Crest Complete Large Soft, the flat trim Colgate Plus Full Head Adult Soft, and the flat trim Oral-B 35. Six replicates of each toothbrush were tested. Denture teeth in a Columbia Dentoform, mounted at 45 degrees, were brushed at a 300 g brushing weight for 15 horizontal strokes. Tooth #15 (upper left second molar) was then removed for measurement and the interproximal distance of ink deposition was determined under 10x magnification from the plane of the buccal contour, along the mesial side of the tooth in the lingual direction at the approximate vertical midpoint of the proximal surface. This was compared in ratio to the same measurement from the buccal contour to the midline. Mean penetration ratios were 0.84 for the Advanced Design Reach, 0.79 for Crest Complete, and 0.78 for both Colgate Plus and Oral-B 35 (overall standard error = 0.01). A one-way ANOVA showed a highly significant difference (p < 0.001) demonstrating that Advanced Design Reach penetrated significantly farther than the toothbrushes with flat or ripple trim bristle patterns. The data suggest the bi-level trim in the Advanced Design Reach toothbrush offers better penetration into the area between teeth, and may provide superior clinical or plaque removal compared to the other toothbrushes tested.

Analysis of Variance↗

PubMed1992

Intraarticular morphine, bupivacaine, and morphine/bupivacaine for pain control after knee videoarthroscopy.

Evidence has accumulated that opioids can produce potent antinociceptive effects by interacting with opioid receptors in peripheral tissues. This study sought to compare the effects of morphine with those of bupivacaine administered intraarticularly upon pain following arthroscopic knee surgery. In a double-blind, randomized manner, 33 patients received either morphine (1 mg in 20 ml NaCl; n = 11), bupivacaine (20 ml, 0.25%; n = 11), or a combination of the two (n = 11) intraarticularly at the completion of surgery. After 1, 2, 3, and 4 h and at the end of the 1st and 2nd postoperative days, pain was assessed by a visual analogue scale, and supplemental analgesic requirements were recorded. Pain scores were significantly greater in the morphine group than in the other two groups at 1 h. There were no significant differences at 2 and 3 h. From 4 h until the end of the study period, pain scores were significantly greater in the bupivacaine group than in the other two groups. Analgesic requirements were significantly greater in the morphine group than in the other groups at 1 h but were significantly greater in the bupivacaine group than in the other groups throughout the remainder of the study period. We conclude that intraarticular morphine produces an analgesic effect of delayed onset but of remarkably long duration. The combination of these two drugs results in satisfactory analgesia throughout the entire observation period.

Adult↗

PubMed1991

Individual differences in human topographic EEG power: hemodynamic and psychological predictors.

Cortical power spectrum (CPS), a derivative of quantitative EEG, has been studied in human development and varieties of brain functions and dysfunctions. From the EEG literature, consistently a high degree (e.g. 6-15x in alpha amplitude) of individual differences in CPS densities is noted. This study examined the potential biopsychological factors contributing to such a wide range of individual differences in CPS. A set of significant inverse functions between systolic blood pressure and differential topographic CPS densities was observed, indicating that hemodynamic baroreceptor regulatory function may partially account for the individual differences in CPS densities. Furthermore, the trait measure of perceptual factor (reducer-augmenter) was correlated positively with other parameters of CPS densities. These results suggest that hemodynamic and psychological factors are predictive of the individual differences in EEG magnitudes.

Brain↗

PubMed1991

Cognitive neuropsychophysiology of thought imagery versus imagination imagery.

The present study was designed to measure patterns of cortical activation during two types of mental imagery: "thought imagery" and "imagination imagery." Topographic cortical power spectrum (CPS) analyses were conducted for 10 subjects during four experimental conditions. EEG was recorded from right and left hemispheres at frontal, temporal, parietal, and occipital leads. Subjects gave rating of visual vividness and quasisensory subjective experience after each imagery condition. Examination of subjects' ratings revealed that they reported significantly greater visual vividness and quasisensory experiences during the imagination imagery condition, as compared to the thought imagery condition. Topographic CPS analyses showed significant individual differences in patterns of brain activation, which were reliable across conditions. Individual differences in lateralization of brain activity were found in terms of an anterior-posterior gradient. Within-subject analyses showed CPS changes as a function of condition. Three major patterns of CPS changes across condition were delineated.

Adult↗

PubMed1991

Double uterus with an obstructed hemivagina and ipsilateral renal agenesis: report of 5 cases and a review of the literature.

Maldevelopment of the Müllerian duct system can result in various uterine, vaginal, and renal abnormalities. Complete or partial absence of Müllerian duct fusion and/or canalization results in a septate, bicornuate or didelphys uterus with various types of hemivaginal obstruction. In addition, unilateral renal agenesis is a common association. Five patients with uterine anomalies and an obstructed hemivagina are described according to the complete or incomplete obstruction between the double vagina and uterus. Early and accurate diagnosis is important, but difficult, due to the variable clinical pictures. Sonographic evaluation can provide valuable diagnostic information. Early diagnosis and excision of the obstructed vaginal septum can completely relieve the symptoms and prevent further sequelae.

Abnormalities, Multiple↗

PubMed1990

Hydrolysis of sphingomyelin and phosphatidylcholine by midgut homogenates of the stable fly.

Qualitative and quantitative analyses were made to characterize the enzymatic degradation of sphingomyelin and phosphatidylcholine by midgut homogenates of the adult stable fly, Stomoxys calcitrans (L.). The results indicated that sphingomyelin was hydrolyzed by an enzyme with sphingomyelinase-like properties, and that phosphatidylcholine was hydrolyzed by an enzyme with properties similar to phospholipase C. The optimum pH for the sphingomyelinase was 7.6, and the rate of hydrolysis of sphingomyelin at that pH was linear from 1 to 4 nmol of substrate and 5 to 25 micrograms of enzyme preparation. Dialysis of the homogenates against Tris-HCl and imidazole buffers resulted in a decrease of sphingomyelinase activity by 59% and 98%, respectively, and the original activity was not restored with the addition of Ca++, Mg++, or Mn++.

Animals↗

PubMed1990

A reassessment of methylcholanthrene transformation in the C3H10T1/2 cell culture system.

We previously demonstrated that four tumorigenic methylcholanthrene (MCA) transformed cell lines derived from C3H10T1/2 cells each contain a common G34----T nucleotide alteration in the c-Ki-ras gene. In contrast, a non-tumorigenic MCA transformant does not contain this mutation. We have now examined 75 newly isolated MCA transformants of C3H10T1/2 cells for their degree of morphological transformation, the presence of the c-Ki-ras G34----T mutation, colony formation in soft agar, and tumorigenicity in nude mice. Although many of these new MCA transformants exhibit morphological characteristics indistinguishable from previously isolated tumorigenic MCA transformants, none contain the G34----T mutation in the c-Ki-ras gene. Only one newly isolated MCA transformant can grow in soft agar. Of 14 tested, none of the new MCA C3H10T1/2 transformants are tumorigenic in nude mice.

Animals↗

PubMed1990

Age distribution of adult female screwworms (Diptera: Calliphoridae) captured on sentinel animals in the coastal lowlands of Guatemala.

The age structure of screwworm, Cochliomyia hominivorax (Coquerel), populations was studied in the Guatemalan lowlands with the pteridine technique of age determination. Flies (95% were 4-15 d old) were captured on sentinel animals. Mean age was 7.5 d. The oldest fly captured was 21 d old. Most flies visiting wounds were reproductively mature females. Of these, about one-half oviposited once, one-third oviposited twice, and 1 in 10 completed three ovarian cycles (assuming a 3-d interval between clutches). Periodicity in adult capture rates may be related to the reproductive cycle. Results suggest that local populations are composed of a high proportion of synchronized cohorts.

Animals↗

PubMed1989

Radical hysterectomy with pelvic lymph node dissection for treatment of cervical cancer: a clinical review of 954 cases.

Nine hundred fifty-four patients, who received a radical hysterectomy and a bilateral pelvic lymphadenectomy, were included in this study which ran from January 1971 to December 1986. The subjects, by in large, ranged in age from 41 to 60. Of these cases, 62.5% were in clinical stage IB, while 26.2% were in stage IIA. Urinary tract fistula formations occurred in 2.4% of the cases and substantially decreased from 6.1% during 1971-1978 to 0.9% in the subsequent period from 1979 to 1986. The operative mortality rate was 0.4%. The follow-up included 438 cases that came from 1971 to 1981, and each was evaluated over a period of 5 years. Of these cases, 28 patients were lost during the follow-up period and were presumed to have died from cancer. The absolute 5-year survival rates for the patients in stage IB, stage IIA, and IIB were 86.1, 71.7, and 60.1%, respectively. The respective 5-year survival rates for patients with stage IB LN(-) and LN(+), i.e., without or with lymph node metastasis, were 87.7 and 73.1%. The survival rates for patients with stage IIA LN(-) and LN(+) were 79.8 and 40.9%, respectively. In retrospect, the 5-year survival rates seem to be related to age, parametrial involvement, and histological type. This study shows that because of improving surgical techniques and anesthesia, acceptable operative morbidity and mortality, as well as favorable 5-year survival rates, radical surgery seems to be the treatment of choice for patients with early invasive uterine cervical, and especially for younger women.

Adolescent↗

PubMed1989

Tumorigenic methylcholanthrene transformants of C3H/10T1/2 cells have a common nucleotide alteration in the c-Ki-ras gene.

The polymerase chain reaction was used to amplify DNA surrounding the codon 12 region of the c-Ki-ras gene from C3H/10T1/2 cells and from a number of 3-methylcholanthrene (MCA)-transformed derivatives of these cells. Sequence analysis demonstrated that tumorigenic MCAC116/39 cells, known by DNA-mediated transfection to contain an activated c-Ki-ras oncogene, had a G----T transversion in the first position of codon 12 of this gene, resulting in a Gly12----Cys mutation. A combination of polymerase chain-reaction amplification and oligonucleotide hybridization demonstrated that three additional tumorigenic MCA transformants of C3H/10T1/2 cells had an identical mutation in the c-Ki-ras gene. In contrast, this mutation was not present in an MCA-induced C3H/10T 1/2 transformant that was not tumorigenic. The molecular specificity of this MCA-induced mutation resulting in C3H/10T1/2 tumorigenic transformants should provide an excellent system in which to study the roles of transcription, replication, repair, and exogenous factors in the establishment and expression of transformation and tumorigenicity.

Animals↗

PubMed1989

Hypnotizability does not predict outcome of behavioral treatment in pediatric headache.

Several adult studies suggest that recurrent headache patients who are highly hypnotizable benefit most from behavioral treatment. We examined the relationship between intrinsic patient factors and clinical outcome in 100 children and adolescents with recurrent headache who were enrolled in our behavioral treatment program. We found no correlation between age, sex, headache type, hypnotizability, and clinical outcome.

Adolescent↗

PubMed1989

Age determination in the adult screwworm (Diptera: Calliphoridae) by pteridine levels.

Fluorescence spectrophotometry was used to assess the possible use of pteridines in the compound eyes to estimate the age of adult screwworms, Cochliomyia hominivorax (Coquerel). Factors affecting the quantities of pteridines include temperature and head size. No difference in pteridine levels was found among flies fed protein or carbohydrate. A regression model for estimating the age of female screwworms was constructed. The model uses head capsule size and relative pteridine quantities and assumes a constant body temperature of 30 degrees C. This regression formula has an r2 of 0.74. Our study extends the use of pteridine accumulation for age determination from obligate sanguinivorous Diptera to an autogenous species that feeds facultatively on nectar and wound exudates. The technique appears to provide a valid means to determine age of these flies.

Animals↗

PubMed1989

Assessment and management of recurrent pain in adolescence.

The pediatrician presented with an adolescent complaining of recurrent or chronic pain should assess the antecedents, sustainers and consequences of the pain syndrome. Particular attention should be paid to the developmental tasks of adolescence and the presence of psychosocial stress in the adolescent's family, school, peer relationships or community. Regardless of its etiology, effective management of recurrent or chronic pain in adolescence involves a balance of cognitive, behavioral and pharmacologic interventions.

Abdomen↗

PubMed1989

Analysis of headache in a Chinese patient population.

One hundred and fifty patients with headache were studied by initial interview, before beginning treatment in the pain clinic. The McGill Pain Questionnaire (MPQ) for Headache and a Bakal Topographic Chart were translated into Chinese and employed to assess the characteristics of the headache. The series included significantly more women than men. The elderly were in low proportion, but teenagers were a significant proportion. Women tended to report a longer headache history than men. Topographically, 50% of patients had bilateral temporal headache, and 18% had unilateral headache, more on the right than on the left. Most of the patients were considered to belong to tension headache and mixed headache types (40% and 26%, respectively). Major aggravators resulting in headache hypersensitivity were overwork, fatigue, insomnia, poor sleep, stress, and tension. Analgesics were the primary means of relief reported in 46% of the patients, while resting and sleeping (44% and 27% respectively) were also found to be significant relief factors. In the McGill Pain Questionnaire, specific subclasses of miscellaneous dimension and sensory description. Chinese patients used different classes and far fewer MPQ words than patients reported in the western literature.

Adolescent↗

PubMed1988

A continuum of transformed phenotypes in C3H/10T1/2 derivatives.

Two-stage transformants have been isolated from C3H/10T1/2 cells exposed to UV-irradiation followed by treatment with TPA. These UV-TDTx cells form foci in co-culture with C3H/10T1/2 cells only in the presence of TPA. In the absence of TPA, UV-TDTx cells are indistinguishable from control C3H/10T1/2 cells in co-cultures. Single-step transformants of C3H/10T1/2 cells isolated after exposure to high doses of chemical carcinogens, however, show TPA-independent focus formation in co-culture with C3H/10T1/2 cells. We now show that three independently isolated two-stage UV + TPA transformants as well as a single-step, high dose methylcholanthrene (MCA) transformant (MCATx1e) isolated in our laboratory are anchorage-dependent and non-tumorigenic. In contrast, another single-step, high dose MCA transformant (MCACl#16/39) known to contain an activated c-Ki-ras gene shows TPA-independent focus formation in mixed culture with C3H/10T1/2 cells, anchorage independence and tumorigenicity. Analysis of UV-TDTx:C3H/10T1/2 and MCACl#16/39:C3H/10T1/2 somatic cell hybrids indicates that a similar percentage of hybrids of each cell type are able to form foci in co-culture with C3H/10T1/2 cells. However, focus-forming UV-TDTx:C3H/10T1/2 hybrids remain dependent on TPA for focus formation in mixed culture.

Animals↗

PubMed1988

Neural perspectives of cerebral correlates of giftedness.

Giftedness is defined as some special endowment or propensity for creativity, skill, and eminent achievement, found in relatively few individuals among the population. A high order of mental power (IQ), creativity, and motivation (task commitment) appear to be the most universally recognized attributes of the gifted. This report summarizes current knowledge of the cerebral correlates of intelligence and creativity, including physiological measures of EEG, cortical power spectrum, brain evoked potentials, and positron emission tomography. Controversy, debates, contentions, formal hypotheses, and research issues are considered. We are especially interested in the formulation of the deterministic function of EEG-brain dynamics. A CHAOS modeling on hierarchy of cognitive organization and cerebral processing in the gifted is suggested.

Adaptation, Psychological↗

PubMed1988

A test of the multiple connections model of reading acquisition.

Within the framework of Society of Mind Theory (Minsky, 1986), learning to read is conceptualized as a process of creating new communication links or neural connections between an existing visual society and an existing linguistic society. Four visual-linguistic connections may become functional: letter-phonemic code, whole word-semantic code, whole word-name code, letter sequence-aural syllabic code. The hypothesis was tested that more than one of these visual-linguistic connections must be taken into account in predicting reading achievement. Results showed that the combination of the composite letter-phoneme variable and the composite whole word-semantic code variable accounted for significantly more variance in oral reading than did either single variable at the end of the first grade. Groups with large absolute discrepancy (1 or more standard scores) or small absolute discrepancy (1/3 standard score or less) on corresponding visual and linguistic skills differed significantly in both oral (whole word-semantic code composite) and silent reading (whole word-semantic code and letter sequence-aural syllabic code composites). There was a relationship between the number of large discrepancies and reading achievement. Results are discussed in reference to neuropsychological models of connectionism (Rumelhart & McClelland, 1986) and working brain systems (Luria, 1973).

Child↗

PubMed1987

Nonsudorific skin potential level: current hypothesis and psychophysiological significance.

Skin potential level has two mechanisms of generation: that due to sweat gland activity (sudorific) and that due to other causes (nonsudorific). These mechanisms have, in the past, been frequently confounded. This paper addresses the importance of discriminating between the two mechanisms and describes two kinds of nonsudorific skin potentials. There is reason to except nonsudorific skin potential level to be an important factor in embryogenesis, tissue regeneration and atypical growth. Early work that associated these potentials with changes in consciousness (e.g., sleep and hypnosis) is inconclusive. The literature concerning physiological and psychological correlates of skin potential levels that have been attributed to nonsudorific mechanisms is reviewed, and the methodological problem of measuring these potentials is considered.

Animals↗