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M C Yang

Publications and source records attributed to M C Yang.

At least 91 records · Page 5Linked to original sources
PubMed1993

Change detection on longitudinal data in periodontal research.

Longitudinal data of attachment level (AL) or the alveolar bone level are often used to assess the progression of periodontal disease. This paper tries to identify the most efficient method to detect the changes of AL in a general periodontal research environment; that is, a sequential decision based on multiple sites. Several existing methods suggested in the periodontal research literature such as the tolerance, running median, cusum, and regression methods as well as change-point detection methods in the statistical literature are examined. It is found that the regression method is most convenient among the several methods that are equally effective in change detection. Formulae, tables and their usage are discussed in detail.

Decision Support Techniques↗
PubMed1993

The strategy and advantage in use of an electronic probe for attachment measurement.

Attachment level has been used as the "gold standard" for assessment of the progression of periodontal disease. However, the measurement of attachment level by periodontal probing can be subject to a large number of error sources. Recently, we have designed experiments by using an electronic probe to identify the magnitude of error components due to the instrument, gingival tissue condition, position or probing angle, and time interval between replicate probings. Even with a very careful clinical setting, a few percent of uncontrollable large errors or outliers could not be avoided. A previously used 'option-3' probing scheme to reduce the unexpected large error is justified from the mathematical viewpoint.

Analysis of Variance↗
PubMed1992

Responsiveness to synthetic parathyroid hormone in the portal vein of portal hypertensive rats.

In addition to its hypotensive action, the parathyroid hormone also decreases portal pressure in portal hypertensive rats. The purpose of this study was to characterize the vascular effects of the parathyroid hormone on the portal vein of portal vein-stenosed rats. When intravenously infused at the rate of 1.62 x 10(-11) mol/kg per min, the parathyroid hormone lowered portal pressure (15.1 +/- 0.7 vs. 14.0 +/- 0.8 mmHg) without affecting systemic blood pressure. With the portal vein isolated, the parathyroid hormone shifted the dose-response curves of KCl and acetylcholine to the right. However, the vasodilator effect of the parathyroid hormone was significantly less in portal hypertensive rats (EC50 of KCl increased 129.2% and acetylcholine 199.3%), compared to sham-operated rats (EC50 of KCl increased 158.7% and acetylcholine 270.2%). Similar results were found for the vasodilator action of verapamil (10(-9)-10(-6) M). On the other hand, the vasodilator effect of forskolin was similar for both groups. These results suggest that decreased responsiveness to the parathyroid hormone may be associated with calcium utilization by vascular smooth muscles.

Animals↗
PubMed1992

Effects of endothelin in portal hypertensive rats.

1. Effects of endothelin-1 on systemic arterial blood pressure, heart rate and portal venous pressure were compared in normal Sprague-Dawley rats and rats with portal hypertension induced by CCl4 and partial portal vein ligation. 2. Endothelin-1 produced biphasic effects on systemic blood pressure and portal venous pressure in all three groups of rats. However, the magnitude of the changes in blood pressure was less in portal hypertensive rats. 3. The ability of endothelin-1 to increase the portal venous pressure was also significantly diminished in portal hypertensive rats. On the other hand, the initial decrease in portal pressure was augmented in rats with partial portal vein ligation, and disappeared at higher dosage in CCl4-treated rats. 4. In accordance with the pressure recording in vivo, the dose-response vasoconstrictive activity of endothelin-1 was significantly attenuated in the intrahepatic vasculature. 5. The plasma immunoreactive endothelin concentration was significantly higher (5.55 +/- 0.81 fmol/ml) in Sprague-Dawley rats than in CCl4-treated rats (2.83 +/- 0.56 fmol/ml) and rats with partial portal vein ligation (2.68 +/- 0.53 fmol/ml). 6. It was concluded that a lower plasma level of endothelin and a reduced vascular responsiveness may contribute, at least in part, to the hyperdynamics of portal hypertension.

Animals↗
PubMed1992

Predictive power of various models for longitudinal attachment level change.

Several statistical models that have been suggested in the periodontal literature for describing longitudinal attachment level changes, such as the gradual loss, single-burst, multiple-burst, and random walk models as well as other models introduced in this paper are compared by their power to predict future attachment loss. The data used in this analysis is from 1061 sites of 8 subjects, with moderate to severe periodontal disease, monitored monthly for about a year. This study found that none of the suggested models could significantly outperform the naïve mean predictor, which predicts the future attachment level from the past mean. It was also found that no single model, such as the burst, gradual, or random walk, together with measurement error can fully explain the variation in the data. These results indicate that in the course of one year, the attachment level change may not follow the same model. Consequently, a model that fits well to past data cannot be accurately extended to the future.

Disease Susceptibility↗
PubMed1992

Reproducibility of an electronic probe in relative attachment level measurements.

4 probing designs have been employed to investigate the reproducibility of the Florida Probe. 3 groups (each composed of 10 subjects) were selected for the study: healthy adults, gingivitis subjects, and periodontitis subjects. The 4 probing designs were as follows: (a) the probe tip was left in the sulcus between successive probings; (b) the probe tip was removed from the gingival margin between probings but the next probing followed immediately; (c) successive whole-mouth probings were interrupted by a 5-min interval and a mouthrinse; (d) there was a 4-week interval between each probing. 3 measurements were taken for each design. The main purpose of this study was to identify variance components in the attachment level variation. The maximum probing error standard deviation was found to be around 0.3 mm, which is considerably smaller than that found in most previous studies. The errors associated with the periodontal condition and probing effect were also estimated. The variance components obtained here can be used for determining the sample size in controlled clinical studies.

Adult↗
PubMed1992

Measuring clinical attachment: reproducibility of relative measurements with an electronic probe.

During the past few years, improvements in detecting longitudinal changes in clinical attachment or alveolar bone density have been introduced. For example, constant-force electronic probes and computer-assisted subtraction analysis of longitudinal radiographs have been reported to be more sensitive and reproducible in detecting changes in clinical attachment or alveolar bone density, respectively. Use of these new technologies requires that sources of measurement error be identified and their contribution quantified. This study investigated the reproducibility of a constant-force electronic probe in a careful clinical setting. Measurements were performed from individually fabricated acrylic stents. Three groups of subjects were selected for the study: 10 adults without oral disease, 10 adults with gingivitis, and 10 adults with moderate periodontitis. Four probing designs were employed to investigate the reproducibility of the probe. In design A, the probe tip was left in the sulcus between successive probings. In design B, the probe tip was removed from the gingival margin between probings but the next probing followed immediately. In design C, successive whole-mouth probings were interrupted by a 5-minute interval and a mouth rinse. In design D there was a 4-week interval between each successive probing. Three measurements were taken at each site for each design. The main purpose of this study was to identify variance components in the attachment level variation. The maximum probing error standard deviation ranged from 0.2 to 0.3 mm depending on the periodontal health of the subject. This level of variation is considerably smaller than that found in most previous studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Evaluation of statistical methods for monitoring periodontal disease.

Three methods for detecting the progression of periodontal disease based on the change in attachment level on teeth are compared from a statistical point of view. Regardless of gradual or burst disease progression theories, the regression method is found to be the most efficient way to detect changes. The exact false alarm rate is computed when the decision is based on the maximum regression coefficient at all sites during several visits.

Epithelial Attachment↗
PubMed1991

Electrooculography and discriminant analysis in Duane's syndrome and sixth-cranial-nerve palsy.

Eye-movement recordings may be helpful in the differentiation of Duane's syndrome from sixth-cranial-nerve palsy. Voluntary horizontal saccades were recorded and quantitated by electrooculography in 18 patients with unilateral type I Duane's syndrome and in 25 patients with sixth-nerve palsy. When ranges of abduction were matched, the peak velocities of abducting saccades in affected eyes were decreased equally in both groups. However, the peak velocities of adducting saccades in sound eyes were slowed in patients with Duane's syndrome. Because the standard deviations in saccadic velocities are large, computer-based, stepwise discriminant analyses were performed to identify the variables that proved to be useful in differentiating the two disorders. By entering these variables into the discriminant functions that were created, we could distinguish Duane's syndrome from sixth-nerve palsy in a statistically significant manner.

Abducens Nerve↗
PubMed1991

Correlation between low-temperature immunosuppression and the absence of unsaturated fatty acid synthesis in murine T cells.

1. Studies were performed to determine if the inability of murine T cells to provide primary helper function at low temperature (27 degrees C) could be correlated with their inability to synthesize unsaturated fatty acids (UFAs). 2. In the absence of exogenous oleic acid (18:1), splenocytes responded to a T-dependent (TD) Ag (trinitrophenyl-keyhole limpet hemocyanin, TNP-KLH) at 37 degrees C but not at 27 degrees C. The addition of 150 microM 18:1 almost completely restored plaque-forming cell (PFC) responses to TNP-KLH at 27 degrees C but markedly suppressed PFC responses to the TD Ag at 37 degrees C. 3. During incubation at 27 degrees C, B cells converted 3- to 5-fold more stearic acid (18:0) to 18:1 and showed a greater accumulation of monounsaturated phospholipid molecular species than did T cells. 4. Following incubation in the presence of a rescuing dose of 18:1 (150 microM), both B and T cells accumulated large amounts of dioleoyl PC. 5. It is proposed that the absence of 18:1 synthesis in T cells is responsible for the unique low temperature susceptibility of this lymphocyte population.

Animals↗
PubMed1991

cAMP and vascular action of endothelin.

Endothelin, a potent vasoconstricting peptide, induced maximal contraction of the rat tail artery within 3 min of administration. Endothelin also caused a dose-dependent decrease in tissue levels of cAMP. Concentrations of cAMP decreased about 60% 1 min after endothelin (10(-8) M) administration, but returned to basal levels in 5 min. By contrast, tissue levels of cGMP were not changed by endothelin. Modulation of cAMP production may provide one mechanism for the vascular action of endothelin.

Animals↗
PubMed1991

Lung deposits of lipiodol in normal and cirrhotic rats.

The distribution of Lipiodol in the liver and lungs following arterial or portal injection was studied in normal (n = 55) and cirrhotic rats (n = 20). Using magnified xeroradiography and radioisotope labeled tracers, it was found that Lipiodol was deposited mainly in the liver and lung after either arterial or portal administration. In control rats after arterial injection, deposits in the lung peaked after 2 hours and gradually declined over 48 hours; whereas after portal injection, the deposit steadily increased for 48 hours. Twenty-five percent of cirrhotic rats demonstrated a Lipiodol-induced military pattern in the lung. An increased number of portosystemic shunts in cirrhotic rats was also noted. These results suggest that cirrhosis of the liver may be a potential risk factor for developing pulmonary complications after Lipiodol administration.

Animals↗
PubMed1990

The hypotensive and negative chronotropic effects of dehydroevodiamine.

The cardiovascular effects of dehydroevodiamine, an alkaloid isolated from Evodia rutaecarpa Jussieu, were studied in both in vivo and in vitro experiments. The in vivo experiments revealed that i.v. administration of dehydroevodiamine elicited a slight but significant reduction in blood pressure and a marked decrease in heart rate which was confirmed by an increased cycle length of the electrocardiogram. However, a hemodynamic experiment with microspheres showed that the total peripheral resistance was not altered by dehydroevodiamine. The blood flows of various organs were not significantly changed except those of kidney and skin, in which blood flow was decreased. In vitro, the spontaneously beating atria were significantly suppressed by dehydroevodiamine in a dose-dependent manner. These findings suggested an important effect of dehydroevodiamine in suppressing the heart, which may largely contribute to the hypotensive effect of this alkaloid. However, its vasodilator effect on hindquarter muscles cannot be neglected.

Alkaloids↗
PubMed1990

Effects of endothelin and vasopressin on portal pressure of rats.

Endothelin is a vasoconstrictor peptide which has recently been isolated and sequenced from the vascular endothelial cells. It was reported to increase blood pressure in vivo and produce a prolonged contraction with a slow onset in vitro. The purpose of this study was to investigate whether endothelin can lower the portal pressure as another endogenous vasoconstriction peptidevasopressin (AVP) can. Heart rate, systemic blood pressure, portal pressure, and portal vein blood flow were measured. Effects of endothelin on these parameters were compared with those of AVP. Endothelin 10(-10) mol/Kg significantly decreased all of the parameters mentioned. At the higher dose (5 x 10(-10) mol/Kg), however, the portal pressure and blood pressure were increased and portal vein blood flow was unchanged. On the other hand, AVP decreased the portal pressure and portal vein blood flow but elevated the systemic blood pressure. In vitro experiments revealed that endothelin contracted both tail artery and portal vein of rat and vasopressin contracted only tail artery. We concluded that although both are endogenous vasoconstricting peptides, endothelin and AVP affect differently on arterial and venous vascular beds as well as on portal pressure.

Animals↗
PubMed1990

Castration may not affect the penile erection ability in terms of peripheral neurocavernous mechanism in dogs.

The penile erection ability (PEA) was assessed in 27 dogs with intact orchids (Group I), seven dogs with bilateral orchidectomy for one month (Group II) and four dogs with bilateral orchidectomy for three months (Group III). PEA was indicated by the increase of the intracorporeal pressure (ICP) upon electrical stimulation of the cavernous nerves. PEA was significantly decreased in both orchidectomized groups. However, when reduction in the blood pressure was considered, the difference in PEA between Group I and the orchidectomized group was no longer significant. Before the orchidectomy, plasma testosterone level of 22 adult male dogs varied widely from 105 to 6302 pg./ml. At one or three months after the orchidectomy in 11 dogs, it decreased to a level below 100 pg./ml. There was no significant change in the body weight in the post orchidectomy period. These findings indicate that the castration and/or the resulting low plasma testosterone level does not directly affect PEA through the peripheral neural and cavernosal mechanism.

Animals↗
PubMed1990

Identifying families at high risk of cardiovascular disease: alternative work site approaches.

By examining coverage, concordance, and costs, this project evaluated four methods of cardiovascular disease (CVD) risk screening at a work site with 1821 central office employees of an energy company in Houston, Tex. Screening methods included a health risk appraisal mail questionnaire (HRA), an HRA plus brief physical assessment, an analysis of medical claims data, and an analysis of absenteeism data. Coverage ranged from 99% of employees for the absenteeism method to about 30% for the HRA method. Combining the first three screening methods, 18% of families had at least one member with a CVD or related diagnosis or one of four major CVD risk factors. The absenteeism method yielded 12.1% of the central office employees with 9 or more days absent. Although the absenteeism method identified high-cost families, only 9% had a heart disease or related diagnosis. This lack of concordance also occurs with other methods. For example, only 9.4% of families identified with the claims data were also identified by the HRA. Therefore, the methods identify different groups of high-risk families. Findings are discussed in relation to costs and other factors important to firms' selection of screening methods.

Absenteeism↗
PubMed1990

Effect of parathyroid hormone on portal pressure in portal hypertensive rats.

Conflicting results have been common in the pharmacological treatments of portal hypertension. In an attempt to seek better management of portal hypertension, we studied the effect of the synthetic parathyroid hormone (PTH) fragment, [bPTH-(1-34)], in portal hypertensive rats (partial portal vein ligation). PTH, 10 U/kg, administered via the jugular vein resulted in a reduction of both mean arterial blood pressure (MAP) and portal pressure (PP) to a similar extent (18.9% and 16.9%, respectively). A higher dose (40 U/kg) of PTH lowered the PP by 27.8% and MAP by 43.2%. Hemodynamic experiments, performed with labelled microspheres, demonstrated that PTH decreased the blood flow of the splanchnic and hepatic portal collateral vascular beds. To determine whether there is a direct vasodilatory effect on the venous vasculature, the effect of PTH on the isolated portal vein was examined. PTH was capable of inhibiting both spontaneous and drug (methacholine 10(-7) mol/l or KCl 40 mmol/l-induced contraction in a dose-dependent manner. Therefore, it can be assumed that some of the effect of PTH on portal pressure is due to a selective effect on the portal vein.

Animals↗