[Photoplethysmograph obtained from a small area of human gingiva]

We have established a method to observe circulation in a small area of the human gingiva. Reflected light photo-plethysmographs (RLP) and transilluminated light photo-plethysmographs (TLP) were recorded from healthy gingiva in 2 young adults of twenties. A tungsten-lamp, connected to a stabilized power source, was used to illuminate the gingiva. The reflected or transilluminated light was collected using a fibre-optic bundle. A CdSe photo-conductive cell was used as the photo-detector. The ECG was recorded simultaneously. The results were as follows: 1) RLP and TLP were both synchronous with the heart beat and showed a dicrotic-notched wave form. 2) When the light-collecting fibre was 0.5 mm from the surface of the gingiva, the dicrotic notch with TLP was clearer than that with RLP. 3) When the light-collecting fibre was placed less than 0.5 mm from the gingival surface, clear dicrotic notches were seen in RLP. 4) When the surface of the gingiva was covered with white opaque paint to prevent transilluminated light, definite dicrotic notches were observed with RLP. 5) RLP was produced mainly by the pulsation of the gingival surface, and the pulsatile movement of the tooth had a little effect on RLP. 6) RLP was consisted from the light reflected from the surface of the gingiva and also from the light reflected after penetrating some distance in the gingival tissue.