Relation between systemic hypertension and pain perception.

To test the hypothesis that hypertension diminishes pain perception, a study was made that evaluated the relation between arterial blood pressure and thermal pain perception in human subjects. The average mean arterial pressure in all 20 men studied (10 hypertensive, 10 normotensive) proved to be significantly related to both thermal pain threshold (p = 0.05) and tolerance (p = 0.003). The difference between normotensive and hypertensive groups in baseline and posttest plasma levels of beta endorphin was also significant (p = 0.02) and indicated an interaction between endogenous opioids and blood pressure. Other recent studies of hypertension in relation to hypalgesia were also reviewed. An increased pain threshold was found in hypertensive versus normotensive rats. In cats, electrical stimulation of vagal afferent nerves (cardiopulmonary baroreceptors) suppresses nociceptive responses, and both pharmacologic elevation of blood pressure and vascular volume expansion produce antinociception. Together with preliminary findings in human studies, these results indicate an interaction between pain-controlling and cardiovascular regulatory functions that is probably mediated by the baroreceptor system.