Biomedical subjects

R Zaslansky

Publications and source records attributed to R Zaslansky.

6 recordsLinked to original sources

PubMed1996

The P300 in pain evoked potentials.

Pain evoked potentials (EPs) have been used in the last two decades as means of obtaining objective measures of pain, in clinical and experimental setups. The possibility that the pain EP wave contains elements of the endogenous P300 potential rather than being a neurophysiological correlate of pain has been raised by a number of authors, but the issue has not been resolved. In this study, two experiments were performed to study the effect of nonmodality-specific factors on the laser EP: (1) a stimulus attend as opposed to a stimulus-ignore condition and (2) counterbalanced oddball and task P300 stimulus presentations. The latter was to permit full examination of the separate and combined influences of each condition on the EP. Stimuli were given to the radial hand of 10 healthy volunteers using a CO2 laser. The positive component of the laser EP was affected by both manipulations relating to (1) attention (P = 0.0146) and (2) the frequency condition (P = 0.003) in the P300 paradigm. The task condition in the second paradigm did not affect the positive wave on its own, although its effect was visible in interaction with frequency (P = 0.033). In conclusion, although the presence of a somatic component in the laser EP cannot be rules out, we suggest that the laser EP contains a definite non-modality-specific P300 component, and is not a pure neurophysiological correlate of pain intensity.

Acoustic Stimulation↗

PubMed1996

Multiple session experimental pain measurement.

Experimental heat pain transients were administered to 30 normal volunteers over four weekly sessions, measuring both heat pain (HP) threshold and suprathreshold magnitude estimation through VAS. Repeatability and bias for these two factors were evaluated. Heat pain thresholds measured through the method of limits were previously shown to have inter-session bias, presumably due to a practice effect. Existence of such a bias between first and second measurement sessions casts doubt on the usefulness of this parameter for pain assessment of individuals over time. In the present study, measurements of normal HP thresholds over four sessions showed that bias exists between the first and successive sessions, but not among sessions other than the first. It is concluded that (i) HP thresholds obtained from a single session are of limited value, and should be carefully interpreted. (ii) Long-term studies that use the HP threshold should take results from the second (or later) session as their baseline. The Visual Analog Scale (VAS) is considered the 'gold standard' for assessment of clinical and suprathreshold experimental pain, and changes in VAS score are regarded as significant evidence of individual response to treatment, placebo, or experimental manipulation. Although its overall group accuracy and precision have been examined for both clinical and experimental pain, and found adequate (Price 1988), the VAS has not been rigorously assessed for repeatability. Stimuli at three pain levels, 1.5, 3 and 4.5 degrees C above each individual's heat pain threshold as determined at each session, were given. Several models of analysis of the VAS were tested and repeatabilities (r) obtained from these analyses demonstrate poor precision for each of the tested analysis models. For example, inter-session repeatabilities for the three individual pain levels ranged from r = 3.8-4.7, effectively providing a confidence interval of 7.6-9.4 for any VAS reading on a 0- to 10-point scale. An examination of intra-session VAS provided somewhat better results. Thus, use of the VAS in similar experimental settings is called into question. The use of the VAS in clinical settings, where individual assessments are necessary, is also called into question, but remains to be specifically tested.

Adolescent↗

PubMed1996

Somatosensory evoked potentials in aphasic patients.

The purpose of this study was to employ evoked potentials to evaluate the function of the somatosensory system in a group of right hemiplegic aphasic patients in whom conventional physical examination was inapplicable. Bilateral somatosensory evoked potentials (SEPs) in response to stimulation of the median nerve were recorded in 20 patients, and unilateral recordings were performed with 20 healthy, aged, matched controls. The major abnormality, present in 13 patients, was absence or reduction of the amplitude of the cortical components N19 and P22 in the lesioned side of the brain. Consequently, the only significant difference between the lesioned versus nonlesioned brain side in patients, and between patients and control subjects was in the amplitude of the cortical components. Since a strong correlation exists between the detected abnormality and impaired somatosensory function, it is concluded that it is highly probable that many aphasic patients suffer somatosensory deficits which, being difficult to assess, are overlooked by the medical personnel.

Aged↗

PubMed1996

Pain-evoked potentials: what do they really measure?

Cerebral evoked potentials (EPs) in response to painful stimuli have been recorded since the 1970s. Based on the apparent relationship of the response amplitude to intensity of stimulation, these potentials are conventionally interpreted as reflecting the sensory-discriminative aspects of pain. As such, pain-EPs provide an objective measure for sensation of pain. An alternative interpretation regards the pain-EP as comprised of at least two overlapping components, one pain-specific, the other, a P300 wave. In the case of pain, the P300 may reflect the degree of discomfort or unpleasantness, thus reflecting the emotional-motivational aspect. To establish the nature of the pain-EP, mini doses of a benzodiazepine, counterbalanced with placebo, were given to 6 normal volunteers. Benzodiazepines decrease anxiety, and so diminish the emotional response to pain, but they have no analgesic effect. In all subjects, pain perception was unchanged, while the EP wave was almost completely obliterated. We conclude that the pain-EP reflects the emotional-motivational response to pain rather than the sensory-discriminative. Thus, it provides a useful neurophysiological tool for studying the emotions associated with pain.

Adult↗

PubMed1995

Heat pain thresholds: normative data and repeatability.

Measurement of thresholds for heat-induced pain was performed on 106 normal subjects, at thenar eminence and foot dorsum, using the reaction time-inclusive method of limits. Tests were repeated 2 weeks following the first test for most of the subjects. After determination that there were no outlying data points and that there was no systematic relationship between magnitude and variability of test scores, data from between 72 and 76 subjects were used to define normal upper and lower ranges by age, as well as repeatability coefficients. This was done through ANOVA-based procedures that extend standard repeatability assessment methods. Normative data tables are presented, with measures of repeatability for the various sites and modalities. For the conventional test range, reaching 55 degrees C, measurement of heat pain thresholds can define both hyper- and hypoalgesia. Application of repeatability coefficients allows for intra-individual inter-session comparison in longitudinal studies.

Adult↗

PubMed1994

Variance of sensory threshold measurements: discrimination of feigners from trustworthy performers.

Sensory threshold measurements are criticized as subjective and therefore not to be relied upon in clinical diagnostic practice, particularly when deliberate deception by the patient is suspected. In an attempt to devise a method which permits dependable sensory threshold interpretation, individual variability of thresholds was examined in normal and neuropathic subjects. Normals were also instructed to feign sensory impairment resulting from hypothetical injury. For each subject, a number of threshold readings were averaged, yielding individual means and variances. Feigning normal subjects evidenced a larger variance compared to trustworthy normal and neuropathic subjects. Thus, alertness to variance reinforces the psychophysical analysis: small variance values suggest trustworthy normal or pathological results, whereas large variance calls the interpreter's attention to feigned results or inattentive test performance.

Cold Temperature↗