Experimental pain in human temporal muscle induced by hypertonic saline, potassium and acidity

The study was aimed at developing a reference model for experimental pain and tenderness in the human temporal muscle by the local injection of hypertonic saline, potassium chloride and acidic phosphate buffer, using isotonic saline as control. The design was randomized and double-blind. Twenty healthy subjects had 0.2 ml test solution injected into one temporal muscle and saline into the other. Following each injection, pain was rated on a 10-point ordinal scale and pressure-pain thresholds were measured every minute for 10 min by a pressure algometer. Hypertonic saline (n = 11) and potassium chloride (n = 12) induced significantly more pain than isotonic saline (ANOVA, p less than 0.0001). Compared to control injections, hypertonic saline and potassium chloride induced a significant reduction in pressure-pain threshold (ANOVA, p less than 0.0001 and p less than 0.05). Forty-eight percent of the injections led to the referral of pain most often to the jaws. A positive correlation between the relative occurrence of referred pain and pain intensity was observed (p less than 0.001) as was a negative correlation between the decrease in pressure-pain threshold and pain intensity (p less than 0.05).