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Biomedical subjects

A C Chen

Publications and source records attributed to A C Chen.

At least 109 records · Page 6Linked to original sources
PubMed1986

Psychological preparation influences nitrous oxide analgesia: replication of laboratory findings in a clinical setting.

In an earlier laboratory study, administration of 33% nitrous oxide yielded lower, not higher, pain thresholds when combined with appropriately altered expectations of enhanced creativity and sensitivity. The present study was undertaken in an attempt to replicate this finding in a group of clinical dental patients. It was expected that anxiety would play a significant role in our findings. The present study experimentally confirms that controlled psychological preparation of the clinical subject prior to administration of conventional dental dosages of nitrous oxide can significantly modify the perception of tooth pulp pain, neutralizing and even reversing its analgesic efficacy without increasing anxiety.

Adolescent↗
PubMed1986

Effects of chitin synthesis inhibitors on incorporation of nucleosides into DNA and RNA in a cell line from Manduca sexta (L).

Five putative chitin synthesis inhibitors (CSI) were tested to determine if they inhibited nucleoside incorporation into acid precipitable material in a cell line from Manduca sexta (L.). The results varied. Diflubenzuron (DFB) (100 micron) inhibited cytidine incorporation by 38%; EL-494 (100 micron) inhibited adenosine incorporation by 43%; Bay Sir 8514 (100 micron) inhibited uridine incorporation by 24%. Superdiflubenzuron (100 micron) was the worst inhibitor overall (18-22%) for the benzoylphenyl urea CSI. The triazine CSI, CGA 19255, was the best inhibitor tested with 60% inhibition for cytidine and 49% for adenosine incorporation into DNA and RNA. Examination of cells incubated with diflubenzuron by scanning electron microscopy revealed distinct external morphological changes. Transmission electron microscopy showed that crystalline structures accumulated in the cytoplasm of cells treated with DFB. The crystalline structures were assumed to be diflubenzuron and they persisted even after diflubenzuron was removed from the medium.

Animals↗
PubMed1986

Behavior of myc and ras oncogenes in transformation of rat embryo fibroblasts.

The requirements for transformation of rat embryo fibroblasts (REFs) by transfected ras and myc oncogenes were explored. Under conditions of dense monolayer culture, neither oncogene was able to transform REFs on its own. However, the introduction of a ras oncogene together with a selectable neomycin resistance marker into REFs allowed killing of the normal nontransfected cells and the outgrowth of colonies of ras transformants, 10% of which survived crisis and became tumorigenic. These cells expressed greater than 10-fold-higher levels of ras p21 than tumorigenic cells cotransfected with ras and myc oncogenes. The myc oncogene similarly was unable to induce tumorigenic conversion of REFs unless especially refractile colonies of oncogene-bearing cells, produced by use of a cotransfected selectable marker, were picked and subcultured. Tumorigenic conversion of REFs by single transfected oncogenes appears to require special culture conditions and high levels of gene expression.

Animals↗
PubMed1985

Tonic pain inhibits phasic pain: evoked cerebral potential correlates in man.

In a sample of 10 healthy volunteers phasic pain ratings and evoked cerebral potentials (EPs) elicited by brief electrical skin stimuli were investigated in periods before, during, and after contralateral tonic ischemia pain. In all subjects the phasic pain ratings and the late EP components P80-N150 and N150-P260 were depressed under concurrent tonic pain. The magnitude of the mean reduction (31%, 40%, and 26%) is comparable to morphine analgesia. The early EP components with latencies below 80 ms, which are considered to be correlates of mechanosensitivity, were not influenced. The findings of tonic pain inhibiting phasic pain are discussed on the basis of changes in attention as well as of pain-specific physiological mechanisms like diffuse noxious inhibitory control.

Adult↗
PubMed1985

Sex differences in brain organization: implications for human communication.

This article reviews current knowledge in two major research domains: sex differences in neuropsychophysiology, and in human communication. An attempt was made to integrate knowledge from several areas of brain research with human communication and to clarify how such a cooperative effort may be beneficial to both fields of study. By combining findings from the area of brain research, a communication paradigm was developed which contends that brain-related sex differences may reside largely in the area of communication of emotion.

Adolescent↗
PubMed1984

A pain microcomputer system for clinical and laboratory investigation.

This report describes the design and use of a mobile "Pain Microcomputer System" (PMS). As a mobile clinical and laboratory research tool the PMS integrates four functions: (1) psychophysical measurement of behavioral pain responses; (2) psychophysiologic recording, including brain evoked potentials, cortical power spectrum analysis, EKG and EMG; (3) data acquisition, analysis and display; (4) peripheral communications via modem allows interaction with larger computers for more complex data analyses, extensive graphics, etc. A word processor disk facilitates writing of scientific and clinical reports. Present and future capabilities of the system for comprehensive pain research and patient care are discussed.

Animals↗
PubMed1983

Opiate analgesia and its antagonism in dental event-related potentials: evidence for placebo antagonism.

The analgesic effects of the synthetic opiate fentanyl citrate (0.1 mg) on subjective pain reports (SPR) and late-wave event-related potentials (ERP) recorded during painful dental stimulation were examined in human subjects. Such waves have been shown to reflect the contribution of cognitive variables, such as expectancy and belief, to perception. In addition, the study was intended to demonstrate a dose-related narcotic antagonism with injection of naloxone (1.2 or 0.4 mg) or normal saline (double-blind) following IV fentanyl administration. Fentanyl reduced both ERP waveform amplitudes and SPR as have previously studied analgesic agents, such as nitrous oxide, acupuncture, and aspirin. Naloxone injection reversed both ERP and SPR changes, but surprisingly, a reversal of narcotic analgesia equal to that of 0.4 mg naloxone was seen with saline injection. By chance, all subjects were health-science students or professionals who were knowledgeable in opiate pharmacology, and so placebo reversal was hypothesized. Alternatively, it was hypothesized that fentanyl cleared more rapidly than predicted, thus, producing apparent reveal. In a second experiment involving similarly knowledgeable subjects with identical procedures and testing intervals, subjects received 0.1 mg fentanyl, but no reversal injection. The fentanyl effect was constant across this time period. The data, thus, support the hypothesis where the subjects were knowledgeable in opiate pharmacology, was placebo opiate antagonism.

Adult↗
PubMed1983

Analgesic effects of nitrous oxide with controlled painful stimuli.

This study was designed to provide statistical estimates of the effects of N2O on pain and anxiety associated with tooth-pulp shock in a clinical and in a laboratory setting. Amounts of electric stimulation needed to first feel sensation, amounts to feel pain, and pain tolerance were measured. N2O had a significant effect on raising levels of absolute sensation, pain threshold, and pain tolerance in response to increasing electrical stimulation of teeth. These effects were noted when N2O and pulp stimulation were delivered in a clinical dental setting or in a pain-research laboratory. Subjects also decreased their evaluation of the intensity of the same stimulus as N2O was inhaled at various concentrations; their aversion to the same stimulus tended to be influenced by N2O to a greater extent than perceived intensity. Anxiety levels were reduced to a statistically significant degree.

Adolescent↗
PubMed1983

Cortical power spectral analysis of acute pathophysiological pain.

In the past decade, advances in quantitative EEG methods, such as the analysis of cortical power spectrum, have proven a useful tool for observing changes in brain activity as a function of physiological and behavioral states. The cortical power spectrum (CPS) is a computer-derived analysis of brain electrical activity using mathematical principles of Fast Fourier Transform function. The total energy output of specific cortical areas can be estimated over time, as a function of EEG spectral frequencies. This report describes the study of CPS in pathophysiological pain patients, using acute dental pain as a model. Seven "walk-in" acute pain patients in an emergency dental clinic were recorded during 10 min of pain, before treatment. Approximately one week later, 10 min recordings during nonpain states were obtained as control. Subjective pain scales and other psychological measures were administered to all subjects before and after recording on each visit. Each 10 min stage of continuous CPS recording consisted of 10 spectra per stage, 6 epochs/spectrum, and 10.24 sec/epoch; each spectrum was stored, averaged, transformed, displayed, printed, and plotted by the Pain Microcomputer System. Results show significant cortical power reduction along all frequency bands (0.5-50 Hz) when pain-states are compared to nonpain states. The magnitude of reduction also appears to correspond to subjective pain report. Analysis for rank order may be inversely related to subjective painfulness, indicating that pain and alpha-desynchronization are closely associated. This study demonstrates that the brain activity of clinical pain patients can be measured. The feasibility of developing a pathophysiological objective pain measuring system is discussed.

Acute Disease↗
PubMed1983

Cognitive reversal of expected nitrous oxide analgesia for acute pain.

In a laboratory experiment, the expected analgesic action of 33% nitrous oxide was reversed by creating the expectancy of heightened awareness of bodily sensations. Pain threshold and tolerance of electrical tooth-pulp stimulation were significantly reduced. Results from a control study gave us a basis for comparison of changes in the verbal expression of pain when nitrous oxide was administered without introducing expectancies beyond those already held by the subjects. Contrasting results from the experimental and control studies confirm the powerful role of mental processes in mediating pain experience.

Adult↗
PubMed1982

Effect of nitrous oxide concentration on event-related potentials during painful tooth stimulation.

Effects of inhaling three levels of nitrous oxide in oxygen on event-related brain potentials (ERPs) and pain report were examined in 10 volunteers undergoing painful electrical stimulation of tooth pulp. Previous work by the authors demonstrated that inhalation of nitrous oxide 33 per cent in oxygen, iv injection of 0.1 mg fentanyl, oral administration of 975 mg aspirin, and electrical acupunctural stimulation all reduced ERP amplitudes obtained a vertex during painful tooth pulp stimulation. The authors report here the demonstration of a dose-response relationship between increasing concentrations of nitrous oxide in oxygen and measures of ERP amplitude and pain report. Subjects inhaled room air, nitrous oxide 25 per cent, 37 per cent, and 50 per cent in oxygen while ERPs were recorded and pain reports were given. The procedure was repeated on three separate days with each subject experiencing all levels of treatment on each day. Analyses of variance revealed that both ERP amplitude and pain report significantly decreased as dosage increased, and a significant linear trend was observed for the positive-going ERP wave-form deflection between 160 and 240 ms. Pain report scores decreased significantly (P less than 0.001) and proportionally as dosage increased, but there was not a significant linear trend. Inhalation of nitrous oxide in oxygen increased peak latency for the negative component at 50 ms and the positive component at 90 ms but not for later components. These outcomes demonstrate that amplitude measures of the vertex ERP obtained with dental dolorimetry correlate consistently with pain and analgesia. Simultaneous assessment of brain electrical activity and subjective report appears to be a useful approach for the assessment of analgesia in humans.

Adult↗
PubMed1982

Pain in clinical and laboratory contexts.

Subjects served as their own control when tooth pulp shock was delivered in laboratory and clinical situations. Significantly heightened pain was observed in the clinical dental setting. The dental setting proved more anxiety-provoking and associated with reduced tolerance for pain, suggesting that cognitive contexts of a dental setting may elicit heightened subjective pain responses.

Adult↗
PubMed1981

Cortical power spectrum analysis of hypnotic pain control in surgery.

Cortical power spectrum (CPS) of brain potentials was recorded from the scalp between prefrontal and parietal regions in both right hemisphere (RH) and left hemisphere (LH). A pattern of laterality shift in CPS occurred at different stages during an extensive oral surgery, performed under hypnosis, in a young female patient. Video and audio recordings as well as psychophysiological recordings were obtained through the following 6 stages: Baseline, Hypnosis, Surgery (1 hr, no cortical recording), Immediate Postsurgery Procedure, Hypnotic Re-experience, Hypnotic Rest, and Posthypnotic Baseline. Indications of anxiety and pain scores were reported in writing by the patient through verbal command by the hypnotist. In each stage, 10 min of CPS (10 spectrum/stage, 8 epochs/spectrum, 6 seconds/epoch) were analyzed by a PDP-11 computer. The results of CPS analysis demonstrated significant large total power reduction at different stages. There was significant correlation between both hemispheres at baseline, but dissociation of hemispheric power output occurred during hypnosis stages. LH was more dominant than RH during baseline and presurgery hypnosis, but both were leveled-off immediately following the surgery procedure. However, RH became more dominant during all postsurgery hypnosis stages. Interestingly, this pattern shifted back to the original relationship during the posthypnotic baseline stage. Specific changes of spectral power in theta and alpha of EEG activities in both hemispheres also occurred in conjunction with hypnosis.

Adult↗
PubMed1980

Aspirin analgesia evaluated by event-related potentials in man: possible central action in brain.

The mechanism of aspirin analgesia is still unclear, but it is generally assumed that aspirin exerts its analgesic effect mainly on peripheral nociceptors. In this study, we demonstrate possible brain effects of 975 mg aspirin in man. When brain electrical potentials evoked by painful electrical tooth shocks were examined, aspirin was observed to significantly reduce the amplitude of the late waveform components, but it did not affect the earlier components. Since our earlier findings suggest that early waveform components reflect the energy transmission and the late components manifest the brain activities in an individual's perception of painful information, we postulate that aspirin may act centrally in pain processing.

Adult↗