THE INFLUENCE OF ULNAR NERVE BLOCKADE ON SKIN MICROVASCULAR BLOOD-FLOW

Microvascular research is seriously hampered by the great temporal and spatial variability of the measured skin blood flow and variation in sympathetic vasomotor reflexes within and between persons. Therefore s kin vasomotor reflexes were studied before and after ulnar nerve block ade within the same person, resulting in a temporal complete denervati on of the fifth finger and partial denervation of the fourth finger. S kin temperature and laser Doppler flux (LDF) were registrated to measu re predominantly arteriovenous shuntflow. Measurements were performed on the palmar tip of the second and fifth finger in nine healthy volun teers, at baseline, and during a sympathetic reflex test (i.e. inspira tory gasp) and postural response test. Beat-to-beat digital blood pres sure was recorded from the third and fourth finger by a Finapres devic e. Baseline capillary blood cell velocity (CBV) was measured at the na ilfold of the second and the fifth finger. After ulnar blockade baseli ne skin temperature, LDF and CBV increased significantly, with respect ively (mean+/-SE) 3.2+/-0.9 degrees C, 20.9+/-5.9 relative perfusion u nits and 0.79+/-0.40 mm(-1) s. The percentage LDF decrease of the fift h finger during inspiratory gasp was 48.2+/-5.3% before and 3.1+/-0.9% after blockade. The postural response test showed a decrease in LDF o f the fifth finger with no significant difference before and after blo ckade, respectively 12.3+/-14.7% and 8.0+/-2.7%, while no difference w as found in the increase in digital blood pressure in the denervated f ourth finger compared to both the same finger before blockade and to t he third non-blocked finger. It is concluded that ulnar nerve blockade enables the study of sympathetic skin vasomotor reflexes by compariso n of a denervated and a non-denervated vascular bed within the same pe rson. After ulnar blockade arteriovenous shunt flow as well as nutriti onal capillary blood flow increased significantly. Postural vasoconstr ictor response is not abolished by ulnar blockade, suggesting that loc al regulatory mechanisms are more important.