Photoplethysmography

Phlebological method for the determination of volume variations of the subcutaneous venous plexus. A defined area of skin is exposed to infrared radiation of a defined wavelength (800-1000nm). Haemoglobin absorbs the irradiated radiation much more strongly than the surrounding tissue. If the amount of blood in the subcutaneous venous plexus decreases, the absorption becomes lower and the reflection higher. The reflected portion and thus the filling fluctuations in the subcutaneous venous plexus, e.g. during a movement program or a change of position of the leg, are measured. This results in a relative measured value (ratio to the output value) - see below "Quantitative photophlethysmography".

Various photopletysmographic procedures, which differ only slightly in principle, are available:

• Photoplethysmography (PPG)
• Light reflection rheography (LRR after Blazek and Wienert)
• Digital Photoplethysmography (DPPG).

Based on numerous study results related to standardized exercise programs, the following biophysical relationships can be established:

• There is a connection between the pressure changes in the deep vein system and the photopletysmographically measurable filling fluctuations in the superficial vascular networks
• A change in pressure in the venous system always causes an increase in selective dermal light reflection (increase in the PPG signal)
• Standardized muscle pump tests allow, over the time axis and amplitude, definite statements about the venous pumping performance of the functional hemodynamic unit.

The name Photoplethysmography goes back to Hertzman, who called his device "photoelectric plethysmography" in 1938.

1. Blazek V (2010) Venous Photoplethsymography In: T Noppeney, H Nüllen Diagnosis and therapy of varicosis. Springer Medicine Publishing House Heidelberg S 76 -83
2. Hertzman AB (1938) The blood supply of various skinareas as estimated by photoelectric plethysmograph. Amer J Physiol 124: 374-378
3. Saliba Júnior OA et al. (2014)Pre- and postoperative evaluation by photoplethysmography in patients receiving surgery for lower-limb varicose veins Int J Vasc Med doi: 10.1155/2014/562782.
4. Schultz-Ehrenburg U et al (2001) Value of quantitative photoplethysmography for functional vascular diagnostics. Current status and prospects. Skin Pharmacol Appl Skin Physiol 14:316-323.
5. Wienert V (1991) Application errors and misinterpretations in light reflection rheography. Phlebol Proctol 20: 126-130.