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 skin vasomotor reflexes were studied before and after ulnar nerve blockade within the same person, resulting in a temporal complete denervation of the fifth finger and partial denervation of the fourth finger. Skin temperature and laser Doppler flux (LDF) were registrated to measure predominantly arteriove‐nous shuntflow. Measurements were performed on the palmar tip of the second and fifth finger in nine healthy volunteers, at baseline, and during a sympathetic reflex test (i.e. inspiratory gasp) and postural response test. Beat‐to‐beat digital blood pressure was recorded from the third and fourth finger by a Finapres device. Baseline capillary blood cell velocity (CBV) was measured at the nailfold of the second and the fifth finger. After ulnar blockade baseline skin temperature, LDF and CBV increased significantly, with respectively (mean±SE) 3.2±0.9d̀C, 20.9 ±5.9 relative perfusion units and 0.79 ±0.40 mm‐1 s. The percentage LDF decrease of the fifth finger during inspiratory gasp was 48.2 ±5.3% before and 31 ±0.9% after blockade. The postural response test showed a decrease in LDF of the fifth finger with no significant difference before and after blockade, respectively 12.3± 14.7% and 8.0±2.7%, while no difference was found in the increase in digital blood pressure in the denervated fourth finger compared to both the same finger before blockade and to the third non‐blocked finger. It is concluded that ulnar nerve blockade enables the study of sympathetic skin vasomotor reflexes by comparison of a denervated and a non‐denervated vascular bed within the same person. After ulnar blockade arteriovenous shunt flow as well as nutritional capillary blood flow increased significantly. Postural vasoconstrictor response is not abolished by ulnar blockade, suggesting that local regulatory mechanisms are more important.