The characteristics of the second derivative of the photoplethysmogram (SDP
TG) were clarified in children and young people, and the factors affecting
the SDPTG wave pattern were examined. The study group comprised 775 healthy
subjects aged 3-20 years (mean, 10+/-5). The blood pressure of the left br
achial artery was determined in the resting sitting position and then the f
ingertip PTG and the SDPTG were automatically measured using a digital phot
oplethysmograph, with the sensor located at the cuticle of the second digit
of the right hand. The values used were the b/a, c/a, d/a, and e/a ratios,
and the SDPTG aging index (SDPTG-AI). With increasing age, the systolic bl
ood pressure and height increased (r=0.52, 0.92). Aging decreased the b/a r
atio and SDPTG-AI (r=-0.58, -0.67) and increased the c/a and e/a ratios (r=
0.42 and 0.42). There was no significant correlation between blood pressure
and indices of SDPTG. As height increased, the b/a ratio and SDPTG-AI decr
eased (r=-0.57, -0.71), whereas the c/a and e/a ratios increased (r=0.42 an
d 0.46). In males the SDPTG-AI decreased with age from 3 to 18 years and th
en increased, and in females it decreased with age from 3 to 15 years and t
hen increased. Overall, the SDPTG-AI decreased with age between 3 and 18 ye
ars and then increased, forming a J curve. In the children's and young peop
le's SDPTG, the b/a and SDPTG-AI decreased and the c/a and e/a ratios incre
ased with age. The length of the vascular system and the inner diameter and
wall thickness of vessels may modify the SDPTG wave pattern in the growth
period. Thereafter, as the effects of these factors decrease, the increase
in intravascular pressure and decreasing wall elasticity due to aging may a
ffect the wave pattern.