Relationship between increased blood pressure and hypoalgesia: additional evidence for the existence of an abnormality of pain perception in arterial hypertension in humans.

An association between hypertension and decreased pain perception (hypoalgesia) has been shown in experimental hypertension and confirmed in humans by electrical tooth pulp stimulation. The aim of this study was to confirm, using two other techniques, whether hypertension is associated with hypoalgesia in humans. In 77 untreated essential hypertensive outpatients, 37 normotensive outpatients and 27 normotensive volunteers subjective cutaneous sensitivity was assessed by an electrical stimulator. Thirty-three measurements were repeated after one month. In addition, in eight normotensive volunteers and eight hypertensives the thresholds of the polysynaptic components R2 and R3 of the blink reflex to electrical stimulation of the supraorbitalis nerve were evaluated. Tooth pulp stimulation was done in 85 of the subjects who measured cutaneous sensitivity and in all of the blink reflex study. Cutaneous perceptive, pain and tolerance thresholds were significantly higher in the hypertensives compared with both normotensive groups, with no significant difference between these two. The results were identical when age and sex-matched subgroups were compared and a high reproducibility was found for all three parameters. Similar findings were obtained for the tooth pulp thresholds and highly statistically significant correlations were found between cutaneous and tooth pulp sensitivity and between these indices and blood pressure. The thresholds of R2 and R3 were also significantly higher in the hypertensives and a significant correlation was found between R3 threshold and diastolic pressure. These results confirm that hypertension is associated to hypoalgesia in humans.