Skin blood flow in the human hand in relation to applied pressure

Our aim was to study the relationship between external pressure and skin blood flow (BF) in the area of the palm (P) of the human hand and the relationship between BF and pressure pain thresholds. A special probe was designed for measuring simultaneously the skin BF using a laser Doppler flowmeter and the pressure using an algometer. The normal BF in the distal phalanx of the index finger and in the middle of the thenar musculature was higher than in the middle phalanx of the middle finger and the middle of P. A pressure of 15-33 kPa was required to reduce BF by 50% and 30-52 kPa to reduce by 85% except in P where the pressure had to be much higher; for 50% of the subjects the reduction in BF did not reach 85% even at 100 kPa. After the removal of the pressure the BF was 170%-230% of the normal readings. The BF did not correlate with the pressure pain thresholds. These results indicate that continuously applied pressure in the hand should not be above 50 kPa to avoid tissue damage due to the cessation of BF in the skin.