Normal variation in cutaneous blood content and red blood cell velocity in humans

This study was designed to determine normal variations in cutaneous blood content, red blood cell content and skin thickness in healthy human volunteers. The blood content (BC) of human skin and the velocity of red blood cells (RBV) has been comprehensively mapped over 30 anatomical sites in 28 volunteers between the age of 7 and 77 years using reflectance spectrophotometry (RFS) and laser Doppler (LD) techniques respectively. Total skin thickness, which may have a relationship with blood content, has been mapped at the same anatomical sites in six of the volunteers using two-dimensional array, 12 MHz ultrasound equipment. The major determinant of BC and RBV was found to be anatomical site. Regardless of age, gender or prior sun exposure, anatomical sites above the waist produced higher readings than below. BC and RBV were found to be dependent on age and gender at most sites with higher readings being observed in males and younger volunteers. The largest difference was seen in males under 55 years whose RFS readings above the waist were significantly higher than in older males or females of any age. Heavy prior sun exposure and skin thickness could not be demonstrated to impact on either RFS or LD readings independently of the effects of anatomical site, gender or age. In general, RFS and LD readings paralleled one another and correlated linearly at most anatomical sites. While RFS readings tended to decrease in the cranio-caudal direction, LD readings were relatively uniform across the body except for the head and groin where they were higher, and the abdomen where they were lower. The site-to-site variations in RFS readings observed in this study correspond well to capillary density variations noted in previous studies.