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Biomedical subjects

C N Chen

Publications and source records attributed to C N Chen.

At least 73 records · Page 4Linked to original sources
PubMed1989

Psychosis in sleep apnoea.

A 30-year-old man presenting with intellectual impairment and recurrent psychotic episodes was subsequently found to have suffered from a chronically untreated obstructive sleep apnoea syndrome. Polysomnography revealed sleep fragmentation, slow wave sleep deprivation and abnormal arterial oxygen desaturation. Tonsillectomy led to complete resolution of sleep apnoea and remission of psychosis at 2 years' follow-up, but his apparent intellectual impairment persisted. The limited literature on psychosis associated with sleep apnoea is briefly reviewed.

Adult↗
PubMed1989

Sleep apnea--an overview.

Though distressing and potentially dangerous, sleep apnea may be an under-recognized disease in many countries. The obstructive type, which usually presents with loud snoring and excessive daytime sleepiness, is by far the commonest form. It causes a great deal of medical, social and psychological morbidity as well as an increased mortality. Doctors of different specialties have an important role in detecting and referring suspected patients for early assessment and treatment. Multidisciplinary management in a general hospital and accurate assessment with polysomnography are essential as modern and sometimes effective methods of treatment are becoming available.

Humans↗
PubMed1986

The field dependence of NMR imaging. I. Laboratory assessment of signal-to-noise ratio and power deposition.

A method is proposed for measuring on the bench the NMR signal-to-noise ratio of rf probes, (over the range 1-100 MHz) and also the power deposited in patients during the imaging experiment. The technique is based on the principle of reciprocity, in that a direct relationship exists between the magnetic field generated (upon transmission) by a matched probe coil and the signal-to-noise ratio delivered by the same coil when used as a receiver. The construction and use of a calibrated sense coil for measuring the field is described, and the precautions and theory necessary for accurate measurement and understanding are outlined. Finally, the method is verified by comparison with a direct spectral measure of sensitivity obtained from a small doped water sample placed in NMR imaging equipment.

Calibration↗
PubMed1986

The field dependence of NMR imaging. II. Arguments concerning an optimal field strength.

Some of the factors involved in the choice of field strength for NMR imaging are examined. The influences of relaxation times and chemical shift upon image quality and signal-to-noise ratio are highlighted, and power deposition is introduced as a significant factor which may limit the flexibility and information available at higher fields as long as 180 degrees echo pulses continue to be necessary. Chemical-shift imaging is examined and found wanting as a means of coping with chemical-shift artifacts, and the use of multiple echoes (albeit with research) in conjunction with multiple-slice techniques is advocated as representing an efficient data-gathering scheme which can improve image signal-to-noise ratio. With such use, a medium field strength (0.5-1 T) is presented as representing, for general purpose imaging of head and torso, the best current compromise when imaging time is of major importance, with the important caveat that new techniques may always invalidate this conclusion.

Fourier Analysis↗
PubMed1986

Molecular analysis of cDNA clones and the corresponding genomic coding sequences of the Drosophila dunce+ gene, the structural gene for cAMP phosphodiesterase.

We have isolated and sequenced cDNA clones representing portions of the polyadenylylated transcripts of the dunce+ gene. These define an open reading frame of 1086 bases and some of the 5'- and 3'-untranslated regions of the transcripts. The deduced amino acid sequence is strikingly homologous to the amino acid sequence of a Ca2+/calmodulin-dependent cyclic nucleotide phosphodiesterase isolated from bovine brain and more weakly related to the predicted amino acid sequence of a yeast cAMP phosphodiesterase. These homologies, together with prior genetic and biochemical studies, provide unambiguous evidence that dunce+ codes for a phosphodiesterase. In addition, the dunce+ gene product shares a seven-amino acid sequence with a regulatory subunit of cAMP-dependent protein kinase that is predicted to be part of the cAMP binding site. We also identify a weak homology between a region of the dunce+ gene product and the egg-laying hormone precursor of Aplysia californica. The open reading frame is divided in the genome by four introns.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Quadrature detection in the laboratory frame.

A theory of quadrature detection in the laboratory frame is developed. It is shown that the geometry of the two orthogonal coil systems needed for quadrature detection is radically different from that used with saddle-shaped coils, and that the homogeneity of the B1 field produced upon transmission is marginally better. The opposing quadrature phase shifts needed for transmission and reception are emphasized, and the use of a quadrature hybrid is advocated as a simple and inexpensive means of interfacing the transmitter, probes, and preamplifier. Experimental results are presented which confirm the theoretical predictions, and show that up to a 40% improvement in sensitivity and a twofold reduction in transmitter power are possible, particularly in those instances where the sample is conductive--namely, imaging of humans and in vivo spectroscopy.

Humans↗
PubMed1984

A parallel algorithm for rotating-frame zeugmatography.

An algorithm, which utilizes a high degree of parallel processing, has been developed for two-dimensional rotating-frame zeugmatography so that a picture of 256 X 256 pixels can be generated with a minicomputer system 2 sec after data accumulation. An array processor is employed as a second processor and, the refresh memory of a display unit is used as a fast data storage entity. Approximately half the calculations are carried out in the array processor during the nuclear relaxation period. Data movement to and from the display memory occurs largely during, and in parallel with, the array processing. The sequence can be run at a repetition rate of 35 msec per free induction decay and the algorithm can be implemented in any two-dimensional experiment of the Fourier transform genre.

Data Display↗
PubMed1983

Reproductive hormone changes during weight gain in male anorectics.

Plasma LH, FSH, testosterone and sex-hormone-binding globulin have been measured in a total of ten male anorectics. There was no significant correlation between body weight and FSH levels or body weight and SHBG levels. Both LH and testosterone concentrations were significantly correlated with body weight. They were well below the adult normal range at low body weight and rose with weight gain although in many cases neither hormone reached normal levels at target weight. The plasma LH and FSH response to 50 micrograms LHRH was measured in five male anorectics on twelve occasions, and compared with the responses of twelve normal adult males. The anorectic patients showed a FSH response which was normal on eleven occasions and slightly raised on one occasion. The LH response was below normal at weights below 40 kg, exaggerated between 45 kg and 50 kg and within normal limits at other weight ranges. These results are compared with previous findings in female anorectics.

Adult↗
PubMed1980

The use of clomipramine as an REM sleep suppressant in narcolepsy.

Clomipramine is known to suppress REM sleep, and this property may be of value in treating certain features of narcolepsy. In a case reported here, clomipramine produced relief of cataplexy, sleep paralysis and hallucinations with considerable subjective improvement. Although the sleep attacks were little changed, the time spent asleep increased, leaving clearer intervals of wakefulness.

Clomipramine↗
PubMed1978

Pharmacokinetic model for salicyclate in cerebrospinal fluid, blood, organs, and tissues.

The developed pharmacokinetic model, an extension of the Bischoff--Dedrick model, simultaneously predicts the kinetic behavior of salicylate in cerebrospinal fluid, blood, organs, and tissues. The model, which is entirely different from conventional compartment models, is derived from basic considerations of drug distribution with biochemical and physiological meaning. The dog was studied at three different dosages of salicylate: therapeutic, moderate intoxication, and severe intoxication. The predicted kinetics of salicylate in cerebrospinal fluid, blood, plasma, liver, muscle, and adipose tissue by the model agreed well with the experimental data. The effectiveness of hemoperfusion treatment for the severely intoxicated dog by albumin-coated activated carbon and its effect on the kinetic behavior of salicylate in cerebrospinal fluid, blood, organs and tissues were studied. The model was also applied to predict the kinetic changes of salicylate in the body during and after the extracorporeal treatment. The predicted results also agreed with the experimental data.

Adipose Tissue↗
PubMed1977

Early morning migraine. Nocturnal plasma levels of catecholamines, tryptophan, glucose, and free fatty acids and sleep encephalographs.

Nocturnal plasma catecholamine, tryptophan, glucose, and free fatty acid levels have been measured in 19 subjects who regularly awoke from sleep with migraine. All-night polygraphic sleep recordings were also made. 13 subjects were studied on a second occasion allowing within-subject control as well as group comparison. Plasma total catecholamine and specifically plasma-noradrenaline levels were significantly higher in the three hours before the subjects awoke with migraine. No differences were found in plasma tryptophan, glucose, insulin, and free fatty acid levels in the migraine/no-migraine categories. Waking with migraine occurred significantly more often from rapid-eye movement (REM) sleep. There were no other differences in sleep pattern in the migraine/no-migraine categories.

Adult↗
PubMed1976

Pharmacokinetic model for simultaneous determination of drug levels in organs and tissues.

An extension of the Bischoff-Dedrick pharmacokinetic model is presented. This model is derived from basic considerations of drug distrubition with physiological and anatomical meaning. The Bischoff-Dedrick model can simultaneously predict drug distribution with time in blood, organs, and tissues of pharmacological interest. The parameters are applied to a 15-kg standard dog. The experimental kinetic data of thiopental in brain, plasma, liver, lean tissue, and adipose tissue in a dog are used to demonstrate the feasibility of the model. Allowable variations in the parameters are determined. In general, the kinetics of drug distribution in blood, organs, and tissues depend on the drug dosage, lipid solubility, partition coefficients, metabolism rate, excretion rate, protein binding, route of administration, sizes of organs and tissues, and blood flow rates through organs and tissues. These factors enter the kinetic model separately and explicitly so their effects on the kinetics of drug distribution can be studied to provide valuable information for optimal therapy.

Animals↗
PubMed1975

Isocaloric diet changes and electroencephalographic sleep.

Electroencephalographic (E.E.G.) sleep changes were studied in eight young healthy male subjects who were given a normal balanced diet or a high-carbohydrate/low-fat or low-carbohydrate/high-fat isocaloric diet, according to an experimental design. Significantly less slow-wave sleep (S.W.S.) was found after consuming a high-carbohydrate/low-fat diet than after consuming a normal balanced diet or a low-carbohydrate/high-fat diet. The latter two diets did not differ in terms of the amounts of S.W.S. Both high-carbohydrate/low-fat and low-carbohydrate/high-fat isocaloric diets, especially the former, were associated with significantly more rapid-eye-movement (R.E.M.) sleep than was the normal balanced diet. These findings emphasise the importance of daily diet for the following night's sleep.

Diet↗
PubMed1974

Plasma tryptophan and sheep.

Free, bound, and total plasma tryptophan (F.P.T., B.P.T., and T.P.T.) levels have been measured throughout the night in six young female volunteers. All-night polygraphic sleep recordings were also made. No direct temporal relationship was found between plasma tryptophan levels and specific sleep stages. The mean F.P.T. levels, however, were found to have a positive correlation with rapid-eye-movement (R.E.M.) sleep and a negative correlation with non-R.E.M. sleep. An inverse relationship existed between the F.P.T. and B.P.T. levels. There appeared to be a diurnal variation in F.P.T. levels, with high readings in the first half of the night.

Adrenal Cortex Hormones↗