PHENTOLAMINE EFFECT ON THE SPONTANEOUS ELECTRICAL-ACTIVITY OF ACTIVE LOCI IN A MYOFASCIAL TRIGGER SPOT OF RABBIT SKELETAL-MUSCLE

Objective: To investigate the effect of phentolamine, a sympathetic bl ocking agent, on the spontaneous electrical activity (SEA) recorded fr om a locus of a myofascial trigger spot (MTrS), equivalent to a human trigger point, in rabbit skeletal muscle. Design: Randomized control t rial. Setting: A university medical laboratory. Patients or Other Part icipants: Nine adult New Zealand rabbits. Intervention: In the experim ental group phentolamine mesylate (1 mg/kg) was injected into the exte rnal iliac artery, followed by flushing with normal saline. The contro l group was treated with normal saline instead of phentolamine using t he same procedure. Main Outcome Measures: SEA was recorded from multip le active loci of MTrSs in the biceps femoris muscle: initially SEA in the same locus was recorded before and immediately after phentolamine (or normal saline) injection; then SEA was recorded from 25 different active loci. The mean of the average integrated signal (AIS) of SEA w as analyzed, comparing the effects of phentolamine and normal saline o n SEA. Results: In the same active locus, the AIS of SEA showed statis tically a linear decay with time after phentolamine injection, with a correlation coefficient of .56 at p < .05. However, no statistical rel ationship could be derived for the control group data with time by usi ng regression analysis, probably because of large variations among the rabbits and movement artifacts during the experiment. In 25 different loci in the phentolamine group, the mean of the AIS of SEA (7.92 mu V ) was significantly lower than that of the control group (9.89 mu V) a tp <.05. Conclusions: The results support the hypothesis that the auto nomic nervous system is involved in the pathogenesis of myofascial tri gger points. The application of the AIS as an evaluation index seems t o be feasible in the quantitative measurement of SEA. (C) 1998 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.