Bier's spots reconsidered: a tale of two spots, with speculation on a humerus vein.

It is a widely accepted opinion that some of the spots produced on the forearm and hand by external compression of the brachial artery are the visible evidence of an intraosseous shunt in the humerus. These spots were first evaluated systematically by Bier in 1898. Additional studies were conducted by Rehberg and Carrier in 1922 and by Wolf in 1924, the latter's conclusions providing the currently accepted view. We examined these spots with laser Doppler velocimetry and found no differences in cutaneous perfusion among spots of different coloration. Further, there was no difference between any of the spots produced by occluding the brachial artery and values obtained from the forearm of postmortem subjects. It appears that the differences in coloration are not due to an intraosseous vascular shunt at the level of the mid humerus but, instead, are due to a capacitance phenomenon with venodilation in the dark areas and venoconstriction in the pale areas.