Second derivative of photoplethysmogram in children and young people.
The characteristics of the second derivative of the photoplethysmogram (SDPTG) 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 brachial artery was determined in the resting sitting position and then the fingertip PTG and the SDPTG were automatically measured using a digital photoplethysmograph, 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 blood pressure and height increased (r = 0.52, 0.92). Aging decreased the b/a ratio 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 decreased (r = -0.57, -0.71), whereas the c/a and e/a ratios increased (r = 0.42 and 0.46). In males the SDPTG-AI decreased with age from 3 to 18 years and then increased, and in females it decreased with age from 3 to 15 years and then increased. Overall, the SDPTG-AI decreased with age between 3 and 18 years and then increased, forming a J curve. In the children's and young people's SDPTG, the b/a and SDPTG-AI decreased and the c/a and e/a ratios increased 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 affect the wave pattern.