The combined effects of local contact force and lower arm cooling upon cutaneous blood cell velocity of the fingertip.

This study investigated the effects of finger contact force (FCF) and lower arm cooling upon cutaneous blood cell velocity (CBV) in the index finger. CBV of the distal finger-pad of the index finger was measured in eight participants while they exerted different FCF of 0.5, 1.0, 1.5, 2.0, 4.9 and 9.8 N, at significantly different mean index finger skin temperatures of 8.0 degrees C (SD 0.4), 14.9 degrees C (SD 0.3) and 30.9 degrees C (SD 0.5). These three levels of skin temperature were achieved by lower arm immersion in water at 5, 13 and 32 degrees C, respectively. Main effects in CBV of FCF (P<0.001) and water temperature condition (P<0.001) were evident and a significant interaction (P<0.001) between these factors indicated an exponential decay in CBV as FCF was increased in each water temperature condition. Mean decay constants (d) of three mono-exponential functions were significantly different from each other (P<0.05) and their values for the 5, 13 and 32 degrees C immersions were 2.16 N (SD 0.67), 1.41 N (SD 0.31) and 0.87 N (SD 0.21), respectively. In conclusion, a decrease in CBV in these conditions was evident with increasing levels of FCF and the three separate mono-exponential functions describing this relationship were separated by thermal states of the hand. Although decay constants became progressively greater at lower water temperature conditions, a cooler hand also had a lower initial and subsequently smaller decrements in CBV with increases of FCF.