SOMATOTOSENSORY EVOKED-POTENTIALS DURING BARORECEPTOR STIMULATION IN CHRONIC LOW-BACK-PAIN PATIENTS AND NORMAL CONTROLS

Nineteen chronic low back pain patients (aged 19-63) and 17 controls ( aged 20-41) received electrical pain stimuli during manipulation of th eir carotid baroreceptors. The non-invasive mechanical manipulation of baroreceptors, using the PRES technique (Phase Related External Sucti on), simulates the end-effects of phasic blood pressure changes. This technique was developed to assess pain responses induced by changes in blood pressure without the typical shortcomings of pharmacological ma nipulation or lack of a control condition. During maximum baroreceptor activity, there was an unexpected increase in the amplitude of the so matosensory evoked potentials (SEPs) elicited by the electrical pain s timuli condition (N150-P260 peak-to-peak). In most other studies the o pposite effect was found, with decreased pain responses during maximum baroreceptor activity. The chronic pain group reported greater pain d uring highest baroreceptor activation than did the controls. In additi on, the chronic pain group showed lower diastolic blood pressure. To d etermine whether pain and baroreceptor responses observed in the chron ic pain group depended on lower blood pressure levels, a second experi ment with a non-clinical sample was performed. Results showed that low er tonic blood pressures are associated with greater baroreceptor acti vity amplifying pain, while higher blood pressure is associated with p ain dampening during high baroreceptor activity. Data suggested that t he differences in pain responses found in low back pain patients were associated with their lower tonic blood pressure levels. It is propose d that in general, lower blood pressures may be associated with greate r pain during baroreceptor activation. (C) 1997 Elsevier Science B.V.