Experimentelle Schmerizinduktion im algesimetrischen Humanversuch

The effect of repeated intramuscular alfentanil injections on experimental pain and abuse liability indices in healthy males

OBJECTIVE

Opioid-induced hyperalgesia (OIH), increased sensitivity to noxious stimuli after repeated opioid exposures, has been demonstrated in preclinical studies. However, there is no accepted, prospective model of OIH after repeated opioid exposures currently available in humans. This study assessed a potential prospective OIH model.

METHODS

Double-blind intramuscular injections of a short-acting opioid (alfentanil 15 mcg/kg; N=8) were compared to active placebo (diphenhydramine 25 mg; N=3) on cold and pressure pain testing and standard abuse liability measures in eight 10-hour sessions (1 injection/session) over 4 to 5 weeks in healthy, pain-free males. Decreases from session baseline pain threshold (PThr) and tolerance (PTol) were calculated to represent hyperalgesia, and were assessed both within and across sessions.

RESULTS

Mean decreases in cold PTol were seen in the alfentanil group at 180 minutes (-3.8 s, ±26.5) and 480 minutes (-1.63 s, ±31.5) after drug administration. There was a trend for differences between conditions on cold PThr hyperalgesia but not for pressure PThr. Alfentanil participants had greater mean ratings on Liking and High visual analog scales at peak effects (30 min), but these scores did not change across sessions.

DISCUSSION

Repeated alfentanil exposures over 4 to 5 weeks resulted in within session decreases in cold pain tolerance from baseline but these differences were not substantially different from diphenhydramine controls. The results did not support the phenomenon of OIH in this model, although definitive conclusions regarding the existence of OIH in humans likely requires a larger sample size or an alternative model.

The second exteroceptive suppression is affected by psychophysiological factors

OBJECTIVE

The second exteroceptive suppression (ES2) is assumed to be an indicator of central antinociceptive processing, although some conflicting data have been produced. We examined the impact of experimentally induced psychophysiological conditions on the latency and duration of the ES2. Also, the association to the subjective evaluation of the painful electrical stimulation by which the ES2 is elicited was studied.

METHODS

ES2 was assessed in 46 healthy volunteers running through four experimentally induced psychophysiological conditions: stress, relaxation, depressed mood, and heterotopic pressure pain. Conditions were presented in a repeated measure design in permuted sequences. Ten stimulation-recording sequences per condition were averaged. ES2 parameters were compared to a baseline condition and correlated to subjective pain perception.

RESULTS

ES2 duration was found to be prolonged and ES2 latency to be shortened under the impact of relaxation and depressed mood. The subjective perception of the painful electrical stimulation was affected by the experimental conditions.

CONCLUSION

Data lend support to the hypothesis that the repeatedly observed limited stability of ES2 parameters might be caused by the variability of individual psychophysiological states. Against expectation, subjective pain perception is not systematically correlated with ES2 parameters. Thus it can be questioned whether the ES2 is directly associated with pain processing at all.

Effects of pain-incompatible imagery on tolerance of pain, heart rate, and skin resistance

Imagery is an important component in strategies for coping with pain. In this study, we examined, whether imagery influences tolerance for pain and whether subjects, trained in pain-incompatible imagery differ in heart rate and skin resistance from these in a control group during a pain-induction session. 39 subjects were randomly assigned to two groups: imagery and control. Both groups had two pain-induction sessions. At intake into the study (t1). Pain Tolerance and Psychophysiological Reaction to Pain were assessed using a pressure algometer. After the first session, the experimental group received 1 hr. of training in pain-incompatible imagery. Seven days later, the session was repeated (t2). The results showed that Pain Tolerance was significantly increased in the group who used pain-incompatible imagery. One might follow the notion that increased Pain Tolerance is associated with increased Psychophysiological Pain Reaction, but results suggest the contrary. Subjects trained in pain-incompatible imagery had lower heart rates during the second pain induction than the control group. Groups did not differ with regard to skin resistance. It can be stated that besides information, cues on coping with pain may be helpful in clinical practice.

Effects of nondirective suggestions on pain tolerance, pain threshold and pain intensity perception

In this experiment, we followed the issue whether nondirective suggestions have an effect on pain threshold, pain tolerance, and perception of pain intensity. 48 healthy subjects consented to take part. At intake into the study (t1), pain threshold and pain tolerance were assessed in all subjects using a pressure algometer. Perception of maximum pain intensity perception was rated on a scale of 0 to 25. Seven days later, the session was repeated (t2). Subjects were randomly assigned to one of two groups. One group received nondirective suggestions as pretreatment. Subjects listened to a tape of 20 min. which consisted of general information about pain theory. In this context, suggestions for coping with pain were placed. The other group served as a control and received no pretreatment. Analysis showed that pain tolerance was significantly prolonged in the group who received nondirective suggestions, while pain threshold and perception of maximum pain intensity did not differ across groups. This study demonstrates that nondirective suggestions are effective in prolonging pain tolerance. It can be stated that, beside information, cues on coping with pain may be helpful in clinical practice.

Post-lumbar puncture headache: the relation between experimental suprathreshold pain sensitivity and a quasi-experimental clinical pain syndrome

The relation between general experimental pain sensitivity and the clinical expression of post-lumbar puncture syndrome (PLPS) was examined in a prospective double-blind study of patients who underwent a lumbar puncture with a 20-gauge spinal needle. In 44 neurology patients randomized pain was induced on the middle phalanges of fingers II-IV of both hands using a tension device on the day before lumbar puncture. Pain intensity was measured using the category sub-dividing procedure. The correspondence between experimental pain stimuli and induced pain intensities could best be described by a logarithmic function. PLPS symptoms were documented in a multi-dimensional quantitative fashion using various scales. Pronounced position-dependent headache occurred in 31% of the patients. There proved to be very significant effects of experimental pain sensitivity on intensity and duration of position-dependent headaches, as well as on vegetative symptoms of PLPS (P less than or equal to 0.01). The results provide an explanation for the varying interindividual manifestation of PLPS symptoms, in addition to factors already identified such as the size of needle used in individual patients.

[Algesimetric experiment on pain sensitivity in the pericranial musculature. Circadian rhythms and corresponding psychic variables.]

Many types of headache that occur in the form of attacks show a notably high incidence at certain times of the day. Attacks are often accompanied by emotional instability, irritability, exhaustion and other impairments of well-being. The cause for the frequent daytime occurrence of attacks is not clear. One possible explanation could be the variability in a person's sensitivity to headache over the course of the day. For this reason we set out to investigate whether pain sensitivity to experimentally-induced headache varies in a circadian manner and whether this variation correlates to changes in the current state of well-being over the course of the day. In 24 healthy, voluntary subjects, headache was induced experimentally at 0200, 0600, 1000, 1400, 1800, and 2200 hours. Blood criculation in both superficial temporal and occipital arteries was reduced by applying a cuff to the head and inflating it to 200 mmHg, thereby producing a continuously increasing, bilateral, dull, frontal headache. The subjects scaled the intensity continually, using the category subdividing procedure ranging from pain threshold to pain tolerance level. In addition, 17 dimensions of the current state of well-being and 12 personality traits were recorded at the above-mentioned times in a standardized quantitative manner. At low levels of headache intensity there were no significant differences in pain sensitivity. Sensitivity to very intense headache, however, varied significantly over the course of the day: sensitivity was greatest at 0200 hours; it decreased at a constant rate until 1400 hours, and increased again continuously until 2200 hours (P</=0.05). Sensitivity to low levels of headache intensity did not prove to be significantly correlated to dimensions of current well-being. By comparison, however, the findings showed significant correlations between sensitivity to very high headache intensities and multiple dimensions of the current state of well-being. These findings show that headache sensitivity follows circadian patterns. Daytime variations, however, are only significant for sensitivity to high intensities. Thus these results may explain, in part, why violent attacks of pain occur predominantly at night and in the early morning.