Abstract

There is great practical need for a dependable method of assessing effects of analgesics on experimental pain in man. Past use of threshold pain has not provided such a method. A technique, called here the submaximum effort tourniquet technique, was developed to produce experimental pain in man which simulates the duration and severity of pathologic pain more closely than earlier experimental methods. Pain was produced by having the subject squeeze a hand exerciser 20 times after a tourniquet had been inflated around his upper arm. Under appropriately controlled drug and placebo conditions, 45 male subjects (experiments I, II, III combined) were studied to determine the amount of time required for pain to build up to levels designated as slight, moderately distressing, very distressing and unbearable. Intravenous morphine, 10 mg/70 kg b.wt., was found to allay significantly the development of moderately distressing, very distressing and unbearable pain. There were indications that the 10-mg dosage of morphine might also be capable of allaying development of slight pain and that the 5-mg dosage might be capable of allaying development of unbearable pain, but these effects were not conclusive. Although the effect of 10 mg of morphine was more dependable (i.e., more statistically significant) at the higher pain levels than at the lower levels, the magnitude of the morphine effect was approximately a fixed multiple of the placebo score. Indeed, the largest morphine effect (expressed as percent of the placebo effect) was on the lowest pain level. When averaged for the four pain levels, the 10-mg dosage of morphine prolonged pain tolerance about 70%. It was concluded that appropriate use of the submaximum tourniquet technique produces a type of experimental pain which is responsive to the analgesic effects of 10 mg of intravenous morphine.