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Biomedical subjects

Y M Liu

Publications and source records attributed to Y M Liu.

102 records · Page 6Linked to original sources
PubMed1984

Contrast sensitivity measured during smooth pursuit movement.

When pursuit eye movement is guided by a light spot which moves at the same velocity as that of a drifting grating, the reciprocal of the threshold contrast (TC) needed for the eye to perceive the grating moving at the same velocity as the auxiliary spot is defined as the guided pursuit contrast sensitivity (GP-CS). GP-CS and flicker (F-) or motion-CS are determined for 20-21 out of 25 possible combinations of 0.75, 1.5, 3, 6 and 12 c/deg grating drifting at 1, 2, 4, 8 or 16 Hz. Up to a drifting velocity of about 5 degrees/s, the GP-CS is near to the pattern recognition (PR)-CS for a stationary grating (+20 to -40%), while the F-CS shows systematic higher (100-200%) to lower (30-60%) values than the PR-CS from low to high spatial frequency (SF) gratings as found by previous investigators. These differences can be most easily seen when the GP-CSF's for gratings drifting at 2, 4 and 8 Hz are plotted and compared with the respective F-CSF's against SF. The general shape of the GP-CSF's shows remarkable similarity to that of PR-CSF at 0 Hz which is generally regarded to be mediated by the so-called sustained system. Apparent motion sensation is inevitably associated with GP. Participation of sustained system in the mediation of motion sensation and the implication of pattern vision during smooth pursuit eye movement are discussed.

Eye Movements↗
PubMed1982

Use of annular artificial pupil in the determination of modulation transfer function of the eye.

According to Ref. [1] primary spherical aberration of the schematic eye would be completely absorbed by an annular aperture when its obstruction ratio epsilon is greater than or equal to 0.60. Consequently the contrast sensitivity function, Tcs, determined with the use of such an annulus, Tcs (A), is the MTF of the retina-brain system, Trb, weighted by the MTF of the annulus, T. . Trb thus obtained can be used to determine the MTF of the eye, Te. Annular apertures of various sizes and obstruction ratios used for the determination of Te have been analysed. It is shown that there are several factors other than incomplete absorption of primary spherical aberration that would prevent the use of annular pupil to derive Trb under unrestrained conditions. This is due to the fact that the apparent T.'s of annuli used in the actual determination of Tcs(A) usually deviate from the theoretical T.'s for the passive eye to different extents. However, it is found that the T. for annulus of o.d. = 2.7 mm and epsilon = 0.60 conforms more or less to the theoretical T. and can be used to derive reasonably accurate Te(2.7). It is also possible to estimate Te(less than 2.7) from Te(2.7) by some empirical correction.

Adaptation, Ocular↗
PubMed1981

Studies on the phenomenon of latent propagated sensation along the channels. I. The discovery of a latent PSC and a preliminary study of its skin electrical conductance.

By combining electrical impulse stimuli with mechanical ones, we are able to trace out a new line of feeling, coincident with the classical channel course. Impulse stimulation was carried out at the Jing point of the Large Intestine or Stomach channel, namely Shangyan or Lidui. With a small rubber nipple, light taps were applied on the skin along the lines perpendicular to the channel and crossing over the acupuncture points; a specific propagational numb feeling at the points of the channel could be found. By linking up these points of specific feeling, an imaginary line which is exactly the classical Large Intestine or Stomach channel can be traced out. This line is called the "latent propagational sensation line along the channels" because, unless through tapping, no prominent sensation of propagation could be felt. Employing an impulsive electrical generator and an all-wave commutating circuit linked to a micro-ammeter, the skin conductance was measured over the latent PSC of the Large Intestine channel lying between the wrist and 5 cm above the elbow joint. Results were compared to those locations of 1 cm apart from the channel course, i.e. the control sites devoid of acupuncture points or channels. At most acupuncture points or any site of the channel course on all of the 10 subjects under examination, there was greater electrical conductance maxima than there was at control sites. This fact indicates that not only the acupuncture points, but the entire course of latent PSC are also of higher electrical conductance.

Acupuncture Therapy↗
PubMed1981

Dynamic pupillary response to positive differential of light stimulus.

Under low background illumination, the pupil responds only to an increase in light intensity by a transient constriction when the extent and rate of the increase exceed a certain values. We term this response the dynamic papillary response in order to differentiate it from the much more sluggish and much less pronounced response moiety that governs the static pupil size according to the level of light adaptation. The characteristics of the dynamic response are studied in some detail. This virtually unidirectional rate sensitivity of pupil to light renders it difficult to be subjected to frequency-response analysis even by small signal approximation. Analysis of the experimental results suggests that this transient response is a light-precipitated confluence of few consecutive hippus.

Adaptation, Ocular↗
PubMedDate not supplied

Chiral separation of amines by high-performance liquid chromatography after tagging with 4-(N,N-dimethylaminosulphonyl)-7-(2-chloroformylpyrrolidin-1-yl)- 2,1,3-benzoxadiazole.

Chiral tagging reagents, 4-(N,N-dimethylaminosulphonyl)-7-(2-chloroformylpyrrolidin-1 -yl)-2,1,3- benzoxadiazole (R(+)-DBD-Pro-COCl and S(-)-DBD-Pro-COCl), react with mirror image enantiomers of amines to produce corresponding diastereomers in the presence of pyridine as a catalyst. The maximal excitation and emission wavelengths of the resulting diastereomers were ca. 450 nm and 560 nm, respectively. The diastereomers derived from some aliphatic amines were resolved by a reversed-phase chromatography with water-acetonitrile or normal-phase chromatography with n-hexane-ethyl acetate as the eluent. The reactivities of both enantiomers of DBD-Pro-COCl to chiral amines were almost comparable, whereas a slight difference of fluorescence intensity was observed with S(-)-DBD-Pro-COCl. When (S-)-DBD-Pro-COCl was used as the derivatization reagent, amines corresponding to S-configuration were eluted faster than R-configuration. The opposite elution order was obtained with the use of R(+)-DBD-Pro-COCl, instead of S(-)-DBD-Pro-COCl. The Rs values obtained from 1-cyclohexylethylamine (CEA) having aliphatic ring structure was larger than those of amines (1-(1-naphthyl)ethylamine (NEA) and 1-phenylethylamine (PEA)) having aromatic ring structures.

Amines↗
PubMedDate not supplied

Bullatacin and bullatacinone: two highly potent bioactive acetogenins from Annona bullata.

Screening of crude extracts of the bark of Annona bullata showed cytotoxic and pesticidal activities. By monitoring with brine-shrimp lethality, two novel, extremely potent acetogenins, bullatacin [1] and bullatacinone [2], were isolated. Spectral and chemical methods identified bullatacin as a diastereomer of asimicin. Bullatacinone represents bullatacin with the lactone cleaved and reformed at the 4-OH. Compounds 1 and 2 show selective cytotoxicities in human tumor cell lines, and certain susceptible cells give ED50 values as low as 10(-12)-10(-15) micrograms/ml. Bullatacin was pesticidal at concentrations as low as 1 ppm, but bullatacinone lacked pesticidal activities. The known compounds liriodenine and (-)-kaur-16-en-19-oic acid were also isolated and were lethal to brine shrimp but were not significantly cytotoxic.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Bullatacin, bullatacinone, and squamone, a new bioactive acetogenin, from the bark of Annona squamosa.

Activity-directed fractionation of the stem bark of Annona squamosa, monitoring with brine shrimp lethality, led to the isolation of the highly bioactive acetogenins bullatacin [1] and bullatacinone [2], thus demonstrating a new abundant plant source for these potent compounds. A new keto-monotetrahydrofuran acetogenin with a ketolactone terminus, as first seen in bullatacinone [2], was also isolated, characterized by spectral analyses, and named squamone [3]. The cytotoxicities of 3 were increased significantly by reduction of the two keto groups to hydroxyls, and the tetrahydrosquamone [7] and bullatacinone [2] both showed selective cytotoxicities to MCF-7 human breast carcinoma. Liriodenine and (-)-kaur-16-en-19-oic acid were also isolated.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Modification of AOAC multiresidue method for determination of synthetic pyrethroid residues in fruits, vegetables, and grains. Part II: Acetone extraction system.

To optimize conditions and to evaluate further a multiresidue method for pyrethroids, various extraction solvents and partitioning conditions were examined. Acetone and acetonitrile (for fruits and vegetables) and acetone-water and acetonitrile-water (for grains) were used as solvents with or without acetonitrile partitioning. Twenty crops fortified with 8 pyrethroid insecticides at low, medium, and high levels were analyzed. For limit of detection (LOD) levels, repeatability tests were completed with acetone-water as extraction solvent. Recoveries of 8 pyrethroid insecticides at LOD levels were 76.2-99.6%, with coefficients of variation (CVs) of 2.08-10.90% for narrow-bore capillary gas chromatography (GC) (n = 6) and 80.1-107.3% with CVs of 3.76-15.38% for wide-bore capillary GC (n = 6). Both acetone or acetone-water extraction with acetonitrile partitioning and acetonitrile or acetonitrile-water extraction with acetonitrile partitioning are suitable for multiresidue analysis of pyrethroid insecticides. However, acetonitrile and acetonitrile-water as extraction solvents were better than acetone and acetone-water at LOD-fortified levels. This finding was confirmed chromatographically with pear, cucumber, and barley control samples.

Acetone↗