Analgesic effect of acetylsalicylic acid and lithium as measured with the CO2-laser stimulator.
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Aspirin↗
Biomedical subjects
R D Treede
Publications and source records attributed to R D Treede.
Human cerebral potentials evoked by CO2 laser stimuli causing pain.
Brief radiant heat pulses, generated by a CO2 laser, were used to activate slowly conducting afferents in the hairy skin in man. In order to isolate C-fibre responses a preferential A-fibre block was applied by pressure to the radial nerve at the wrist. Stimulus estimation and evoked cerebral potentials (EP), as well as reaction times, motor and sudomotor activity were recorded in response to each stimulus. With intact nerve, the single supra-threshold stimulus induced a double pain sensation: A first sharp and stinging component (mean reaction time 480 ms) was followed by a second burning component lasting for seconds (mean reaction time 1350 ms). Under A-fibre block only one sensation remained with characteristics and latencies of second pain. The heat pulse evoked potential consisted of a late vertex negativity at 240 ms (N240) followed by a prominent late positive peak at 370 ms (P370). Later activity was not reliably present. Under A-fibre block this late EP was replaced by an ultralate EP beyond 1000 ms, which in the conventional average looked like a slow halfwave of 800 ms duration. This potential was distinct from eye movements, skin potentials or muscle artefacts. With cross-correlation methods waveforms similar to the N240/P370 were detected in the latency range from 900 to 1500 ms during A-fibre block, indicating a much greater latency jitter of the ultralate EP. Latency corrected averaging with a modified Woody filter yielded a grand mean ultralate EP (N1050/P1250), the shape of which was surprisingly similar to the late EP (N240/P370). The similarity of these components indicates that both EPs may be secondary responses to afferent input into neural centers, onto which myelinated and unmyelinated fibres converge. Such convergence may also explain through the known mechanisms of short term habituation and selective attention, why ultralate EPs are not reliably present without peripheral nerve block.
Adult↗
Pain related cerebral potentials: late and ultralate components.
Brief CO2 laser radiant heat pulses activate both A delta- and C-fibres. In the evoked potential (EP) late and ultralate components can be seen as correlates of first and second pain. Usually the ultralate EP appears to be suppressed. It could be uncovered by a preferential A-fibre block, and in two neurological patients with tabes dorsalis and with a polyneuropathy involving myelinated fibre loss. Due to a strong latency jittering the shape of the ultralate component is distorted in the conventional average. Latency corrected averaging, adaptive filters or parametric spectral estimators are needed to analyze these EP components. As a result the filtered ultralate waveforms look very similar to the late EP components. Clinical application of CO2 laser EPs promises to nonivasively assess A delta- and C-fibre function.
Action Potentials↗
[Increase in somatosensory evoked potentials during anesthesia induction with etomidate].
In 43 patients the time-dependent behaviour of somatosensory evoked potentials (SSEP) before and during induction of anesthesia with 0.3 mg/kg etomidate was studied. The SSEP components could be reliably recorded in one-minute intervals and the modulations of SSEP (early and middle latencies) following bolus injection with its pharmacokinetically non-stationary states could be quantified. The central conduction time (CCT) between the cervical N13- and the cortical N20-component was less prolonged (from 5.6 ms to 6.4 ms) than known from other anesthetics. Middle latency SSEP exhibited a more marked increase and were reduced in amplitude. All patients showed a 2- to 12-fold increase of the primary complex N20/P25 2-3 min after bolus injection. This amplification cannot be explained either by muscle artifacts nor exclusively by activation of muscle afferents. Myoclonia as a side effect of etomidate coincide with the increase of SSEP-components. The combination of myoclonia and SSEP-enhancement is known to be associated with the familial progressive myoclonus epilepsy. This observation therefore may indicate a cortical excitatory or disinhibitory effect, although no spike-wave complexes have been reported in the EEG after etomidate.
Adult↗
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↗
Responses of human cutaneous afferents to CO2 laser stimuli causing pain.
Microelectroneurographic studies in man allow the comparison of stimulus induced activity in the single peripheral nerve unit with the subject's ratings of sensation. Relationships between stimulus intensity, single unit discharges, and pain ratings were investigated using a CO2 laser stimulator which delivers radiant heat pulses of 50 ms duration. Recordings were performed percutaneously from the radial nerve at the wrist. Receptor types were identified by their response to different stimulus modalities and by their reaction delay to electrical test stimuli within the receptive field. Receptive fields of identified units were stimulated with randomised series of different radiant heat intensities between half and double the individual pain threshold (5 to 20 W; stimulation area 64 mm2). The largest receptor class observed to be activated by CO2 laser stimuli were polymodal C-nociceptors. None of them was spontaneously active. High discharge rates up to 75/s were not necessarily associated with pain but, if pain was felt, the impulse trains usually lasted for more than 60 ms. Inter-spike intervals were distributed over a wide range between 8 and 145 ms with a peak at about 25 ms. This peak was only slightly shifted by increasing the stimulus intensity. Higher correlations were found between the number of spikes and stimulus intensity. Measures of Signal Detection Theory indicated that the single unit discharges discriminated stimulus intensities better than the subjects' ratings. These findings underline the importance of temporal summation in the processing of C-fibre input with a considerable loss of information in the nociceptive system.
Humans↗
Nerve fibre discharges, cerebral potentials and sensations induced by CO2 laser stimulation.
Short radiant heat pulses, emitted by a high power CO2 laser, were used to investigate single nociceptor activity, cerebral potentials and concomitant sensations. Stimuli of 20 and 50 ms duration with different intensities were randomly applied to the hairy skin of the hand. Microelectroneurography was performed from the radial nerve at the wrist; 26 stable recordings were evaluated. Pre- and post-stimulus EEG segments were recorded from vertex versus linked ear lobes. Sensation was assessed on an eight-step category scale, an adjective scale, and by reaction times. In some experiments an A-fibre block was applied in order to isolate C-fibre responses. The main results were: Short heat stimuli activate C-units. In addition one of two identified A delta-units responded. None of the 15 A beta-units investigated was activated by the heat pulses. Short heat stimuli evoked cerebral potentials having a main vertex positive component at about 400 ms. These potentials were ascribed to A delta-fibre input. Laser induced pain consisted of an immediate stinging component, followed by a burning pain which often lasted several seconds. Reaction time to first pain ranged from 400-500 ms. Weak laser stimuli induced non-painful sensations mostly of tactile character. High correlations were found between the number of spikes elicited by a given stimulus and the intensity of the evoked sensation. Intensity discrimination, as evaluated by measures of Signal Detection Theory, was better in the peripheral C-units than in the subjective ratings. If conduction of A-fibres was blocked by pressure, A delta-related cerebral potential components vanished.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Evoked cerebral potential correlates of C-fibre activity in man.
CO2 laser emitted radiant heat pulses of 20 ms duration were used to activate predominantly slowly conducting nociceptive cutaneous afferents in man. Stimuli of two-fold individual pain threshold caused stinging and burning pain and elicited cerebral potentials with latencies consistent with A delta-fibre activity. After preferential block of the myelinated nerve fibres by pressure only the burning pain remained with significantly increased reaction time (about 1433 ms). The A delta-fibre-induced evoked potential components disappeared, and a marked ultralate positive component became visible with mean peak latency of 1260 ms, consistent with C-fibre activity.
Afferent Pathways↗
CO2 laser radiant heat pulses activate C nociceptors in man.
Cerebral potentials evoked by noxious CO2 laser stimuli in man have been referred to nociceptive A delta units. This paper shows 1) that ultra short (5 - 50 ms) high power (less than or equal to 50 W) CO2 laser skin stimuli are able to activate nociceptive C units in man, and 2) that these C nociceptors have to be assumed to terminate in the very superficial skin layer (less than or equal to 300 microns depth).
Carbon Dioxide↗
Topography of middle-latency somatosensory evoked potentials following painful laser stimuli and non-painful electrical stimuli.
The aim of this study was to compare cerebral evoked potentials following selective activation of A beta and A delta fibers. In 15 healthy subjects, A beta fibers were activated by electrical stimulation of the left radial nerve at the wrist. A delta fibers were activated by short painful radiant heat pulses, applied to the dorsum of the left hand by a CO2 laser. Evoked potentials were recorded with 15-27 scalp electrodes, evenly distributed over both hemispheres (bandpass 0.5-200 Hz). The laser-evoked potentials exhibited a component with a mean peak latency of 176 msec (N170). Its scalp topography showed a parieto-temporal maximum contralateral to the stimulus side. In contrast, the subsequent vertex negativity (N240), which appeared about 60 msec later, had a symmetrical scalp distribution. Electrically evoked potentials showed a component at 110 msec (N110), that had a topography similar to the laser-evoked N170. The topographies of the N170 and N110 suggest that they may both be generated in the secondary somatosensory cortex. There was no component in the electrically evoked potential that had a comparable interpeak latency to the following vertex potential: for N60 it was longer, for N110 it was shorter. On the other hand, in the laser-evoked potentials no component could be identified the topography of which corresponded to the primary cortical component N20 following electrical stimulation.
Adult↗