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Biomedical subjects

P Cheng

Publications and source records attributed to P Cheng.

At least 73 records · Page 4Linked to original sources
PubMed1995

Coping and psychological distress of Chinese parents of children with Down syndrome.

Coping and correlates of psychological distress of Chinese parents of children with Down syndrome were examined and compared to parents of children with language delays or no disabilities. Individual parent scores were used for analyses, with groups and gender of child and parent as independent factors. Down syndrome group parents reported the most frequent use of avoidance coping style, followed by parents of the language delay and no disabilities groups. Compared to parents in the no disabilities group, the other parents reported a higher level of psychological distress, were less optimistic, felt less self-efficacious, and engaged in more frequent use of self-reliance coping style. Main effects for parent gender revealed that mothers engaged in more frequent use of self-reliance, avoidance, and seeking social support coping styles. Mothers also reported a higher level of distress but lower levels of optimism and self-mastery. Intercorrelations among variables showed that avoidance coping style and self-mastery emerged as the two robust correlates of parental distress.

Adaptation, Psychological↗
PubMed1994

Time-frequency analysis of the electrocortical activity during maturation using wavelet transform.

In this study, we introduce the wavelet transform (WT) as a method for characterizing the maturational changes in electrocortical activity in 24 fetal lambs ranging from 110-144 days gestation (term 145 days). The WT, based on multiresolution signal decomposition, is free of assumptions regarding the characteristics of the signal. The approximation of the electrocortical activity at resolutions varying from 2j+1 to 2j can be extracted by decomposing the signal on a wavelet orthonormal basis of L2(R). We performed multiresolution decomposition for four sets of parameters D2j, where -1 < j < -4. The four series WT represent the detail signal band-widths: (1) 16-32 Hz, (2) 8-16 Hz, (3) 4-8 Hz, (4) 2-4 Hz. The data were divided into three groups according to gestational age: 110-122 days (early), 123-135 days (middle), and 136-144 days (late). In the early group, the power was highest in the fourth signal bandwidth, with relatively low power in the other bands. Increase in gestational age was characterized by increased power in all four bandwidths. Comparison of the cumulative distribution function of the power in the four wavelet bands confirmed the presence of two statistically different patterns in all three age groups. These two patterns correspond to the visually identified patterns of HVSA (high-voltage slow activity) and LVFA (low-voltage fast activity). The earliest development change occurred in HVSA, with progressive increase in power in the 2-8 Hz band. Later changes occurred in LVFA, with a significant increase in power in the 16-32 Hz band.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Optical spectroscopy of a highly fluorescent aggregate of bacteriochlorophyll c.

Bacteriochlorophyll (BChl) c and a similar model compound, Mg-methyl bacteriopheophorbide d, form several types of aggregates in nonpolar solvents. One of these aggregates is highly fluorescent, with a quantum yield higher than that of the monomer. This aggregate is also unusual in that it shows a rise time in its fluorescence emission decay at certain wavelengths, which is ascribed to a change in conformation of the aggregate. An analysis of fluorescence depolarization data is consistent with either a linear aggregate of four or five monomers or preferably a cyclic arrangement of three dimers.

Bacteria↗
PubMed1993

The role of ultrasound and computed tomography in the evaluation of parotid masses.

A prospective sonographic study of 40 patients with symptomatic parotid masses detected all of their 48 lesions (sensitivity 100%). Computed tomography (CT) detected 47 lesions (sensitivity 97.5%). Ultrasound correctly characterized all benign tumours and inflammatory lesions and four out of five malignant tumours. Deep compartment involvement was accurately delineated in 10 (25%) patients but in two patients the extraparotid tumour origin could only be detected by CT. Ultrasound is a sensitive, non-invasive investigation of parotid masses. Computed tomography (CT) or magnetic resonance should be reserved for lesions that involve the deep compartment of the gland and cannot be separated from the parapharyngeal space or skull base.

Humans↗
PubMed1993

Lifetimes of bacteriochlorophyll fluorescence in Rhodopseudomonas viridis and Heliobacterium chlorum at low temperatures.

Fluorescence lifetimes of isolated membranes of Rhodopseudomonas viridis were measured in the temperature range of 77 K to 25 K. At room temperature, the main component of the fluorescence decay of bacteriochlorophyll (BChl) b had a time constant of 50 ps. In contrast to other purple bacteria, the emission at low temperature was spectrally homogeneous and showed essentially single lifetimes of 140 ps at 77 K and 180 ps at 25 K, with the primary electron donor in the oxidized state. Taking into account the relative fluorescence yields with open and closed reaction centers, we arrive at numbers of 125 ps and 215 ps, respectively, for open reaction centers. These numbers are significantly smaller than expected on the basis of measurements of the efficiency of charge separation, perhaps suggesting that the excitation decay in the absence of reaction centers is considerably faster at low temperature than at room temperature. At least four different spectral components with different lifetimes were observed at 25 K in the emission of Heliobacterium chlorum, a short-wavelength component of about 30 ps and three longer-wavelength components of about 100 ps, 300 ps, and 900 ps. This indicates a strong heterogeneity in the emitting pigment, BChl g-808. The component with the shortest lifetime does not appear to be affected by the redox state of the reaction center and might reflect energy transfer to BChl g species which are connected to the reaction center.

Bacteria, Anaerobic↗
PubMed1993

Redox regulation of energy transfer efficiency in antennas of green photosynthetic bacteria.

The efficiency of energy transfer from the peripheral chlorosome antenna structure to the membrane-bound antenna in green sulfur bacteria depends strongly on the redox potential of the medium. The fluorescence spectra and lifetimes indicate that efficient quenching pathways are induced in the chlorosome at high redox potential. The midpoint redox potential for the induction of this effect in isolated chlorosomes from Chlorobium vibrioforme is -146 mV at pH 7 (vs the normal hydrogen electrode), and the observed midpoint potential (n = 1) decreases by 60 mV per pH unit over the pH range 7-10. Extraction of isolated chlorosomes with hexane has little effect on the redox-induced quenching, indicating that the component(s) responsible for this effect are bound and not readily extractable. We have purified and partially characterized the trimeric water-soluble bacteriochlorophyll a-containing protein from the thermophilic green sulfur bacterium Chlorobium tepidum. This protein is located between the chlorosome and the membrane. Fluorescence spectra of the purified protein indicate that it also contains groups that quench excitations at high redox potential. The results indicate that the energy transfer pathway in green sulfur bacteria is regulated by redox potential. This regulation appears to operate in at least two distinct places in the energy transfer pathway, the oligomeric pigments in the interior of the chlorosome and in the bacteriochlorophyll a protein. The regulatory effect may serve to protect the cell against superoxide-induced damage when oxygen is present. By quenching excitations before they reach the reaction center, reduction and subsequent autooxidation of the low potential electron acceptors found in these organisms is avoided.

Bacteria, Anaerobic↗
PubMed1993

The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching.

Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

Bacteria↗
PubMed1992

Helix-loop-helix transcription factors E12 and E47 are not essential for skeletal or cardiac myogenesis, erythropoiesis, chondrogenesis, or neurogenesis.

E12 and E47 are two non-tissue-specific helix-loop-helix (HLH) transcription factors encoded by the E2A gene. Previous studies suggested that they are involved in regulation of differentiation in many tissue types including muscle, blood, and nerve through direct heterodimer interactions with tissue-specific HLH proteins. To gain further genetic insight into the functions of E12 and E47 during cell differentiation, we mutated both copies of the E2A gene in mouse embryonic stem (ES) cells and then tested the effect on differentiation in vitro. We find that the ES cells lacking functional E12 and E47 are capable of differentiating into both skeletal and cardiac muscle, erythrocytes, neurons, and cartilage that the same extent as wild-type cells. These results indicate that the E2A gene is not essential for differentiation of these cell types and suggest that redundant genes may control these developmental pathways.

Alternative Splicing↗
PubMed1992

The stress distribution of the lumbar spine and disc degeneration.

A three-dimensional finite element model of the lumbar motion segment was developed to study the effect of disc degeneration upon stress distribution in the lumbar spine. The results showed that after degeneration of the intervertebral disc, the stress distribution and load transmission of the lumbar spine are significantly changed. It is concluded that these changes provide a biomechanical basis for understanding the etiology of spinal canal stenosis and nerve root entrapment.

Biomechanical Phenomena↗
PubMed1992

Stress distribution and bone density in the lumbar spine.

The stress distribution of the lumbar spine was analyzed with a mechanical model of the lumbar motion segment constructed by a three-dimensional finite element method, and the results were compared with the corresponding bone density represented by the value of CT. The results showed that the stress levels in the various parts of the lumbar spine were closely related to the CT values. The authors conclude that the dynamic balance of bone growth is maintained in large part by mechanical stress.

Adult↗
PubMed1991

[Measurement of plasma malondialdehyde contents and erythrocyte superoxide dismutase activities in patients with chronic cor pulmonale].

We measured the contents of plasma MDA and erythrocyte SOD activities in patients with chronic cor pulmonale. The contents of malondialdehyde (MDA) increased; the superoxide dismutase (SOD) activities suppressed significantly and reoxygenation caused increases in the SOD activities in patients with acute attacks. But the changes of the contents of MDA and SOD activities did not appear in patients with stationary phase. These results indicate that oxygen free radicals may contribute to the physiopathological process of chronic cor pulmonale.

Adult↗
PubMed1990

Epstein-Barr virus genotypes associated with nasopharyngeal carcinoma in southern China.

We have used probes representing approximately two-thirds of the Epstein-Barr virus (EBV) genome to examine genetic polymorphism of wild-type EBV directly detected in 28 nasopharyngeal carcinoma (NPC) tissues from Southern China. In the hypervariable regions containing reiterated sequences, this analysis showed that while naturally occurring viruses are genetically diverse, only one genotype was detectable in each tumor specimen. Unique variants in NPC were detected in four regions of the EBV genome. Two of these appeared significant in their distribution. The type C variant resulting from loss of a BamHl site between the BamHl W1* and l1* regions was prevalent among isolates from Southern China, but not so common in the United States. An "f" variant having an extra BamHl site in the BamHl F region was almost exclusively detected in only Asian NPC biopsies.

Biopsy↗
PubMed1990

End-point nystagmus and ocular drift: an experimental and theoretical study.

End-point nystagmus (EPN) and ocular drift during eccentric fixation were investigated in five normal subjects. All had EPN during prolonged eccentric fixation, two had sustained EPN within a few seconds of fixating an eccentric target. Our data show that the occurrence of EPN was determined by the velocity of slow phase ocular drift. Drift velocities greater than 1 deg/sec elicited sustained EPN or fatigue EPN while drift velocities lower than 0.3 deg/sec did not elicit EPN. Slow phase drift velocity increased with eccentricity and fixation duration and decreased with visual feedback. Computer simulations and theoretical analysis suggest that the reduction in drift eye movement velocity during fixation of a visible target, as compared to drift eye movement velocity during attempted fixation of a remembered target in darkness, is mainly due to the smooth pursuit system.

Adult↗
PubMed1990

[Anti-anaphylactic pharmacological action of water-soluble constituents of Ginkgo biloba L. episperm].

Water-soluble constituents of Ginkgo biloba episperm 100 or 200 mg/kg po given to mice inhibited passive cutaneous allergic response and the same dose given to rats ip inhibited mast cell degranulation. It antagonized the contractile effect of isolated guinea pig ileum smooth muscles induced by the antigen. It inhibited the deliverance of SRS-A from anaphylactic lung of guinea pig.

Animals↗