Ultrasound velocity in human fingernail and effects of hydration: validation of in vivo nail thickness measurement techniques

Abstract

Distal nail thickness was measured using an electronic micrometer and both distal and proximal nail ultrasound times were recorded in 20 volunteers (10 male, 10 female), aged 20-39. The fingernail ultrasound velocity was 2.26 X 10(3) m/s (subject range 2.03-2.69) (analysis of variance technique). The proximal ultrasound transit time was greater than distal ultrasound transit time. In three volunteers, five micrometer and one distal midline ultrasound measurement of five nails were repeated on 10 occasions over 2 weeks. For the micrometer readings the average coefficient of variation was 5.3% (SD +/- 2.4%), and for the ultrasound reading the average coefficient of variation was 4.0% (SD +/- 1.3%). To assess the influence of hydration, in five volunteers the distal nail micrometer thickness and the distal nail ultrasound transit time were measured on five nails before and after 30 min of immersion in water initially at 37 degrees C. The mean distal ultrasound transmission time increased from 0.20 +/- 0.04 microseconds to 0.22 +/- 0.04 microseconds (P less than 0.001) after water immersion. The micrometer measurements and ultrasound velocity did not change significantly (mean ultrasound velocity = 2.01 X 10(3) m/s before, 2.04 X 10(3) m/s after immersion).