The photoplethysmography procedure is a hemodynamic examination method used to diagnose and monitor the course of so-called chronic venous insufficiency (CVI). In this disease, the venous vessels are damaged in such a way that the blood is not transported effectively enough to the heart and the blood backs up. This can lead to many secondary conditions such as thrombosis (vascular disease in which a blood clot (thrombus) forms in a vessel).
Photoplethysmography is an instrumental diagnostic method based on the detection of the reflection of emitted infrared light rays. In addition to PPG, there are variants such as light reflectance rheography (LRR) or digital photoplethysmography (DPPG), which differ only in a few details. Because photoplethysmography is a noninvasive method, it is suitable for screening examination (preventive examination of healthy patients for timely detection of disease).
Indications (areas of application)
- The diagnosis of chronic venous insufficiency (CVI, synonyms: chronic venous stasis syndrome, chronic venous insufficiency).
The procedure
Photoplethysmography is based on the following principle: the measuring device is located above the area to be examined and emits infrared light, which is reflected and then registered by a sensor. The infrared light has a specific wavelength and is particularly well absorbed by the hemoglobin (red blood pigment) in the superficial venous plexus (venous plexuses).
During the examination, the patient is instructed to perform simple movements such as dorsiflexion (bending) in the ankle joint or knee flexion. As a result, venous blood is mobilized by the muscle pump and the veins empty (when the calf muscles are tensed, the veins are simultaneously squeezed and blood is pumped towards the heart, this mechanism is called muscle pump). During the subsequent pause in movement, the vessels fill up again. The volume fluctuations in the veins cause parallel fluctuations in the light reflection, which are recorded and evaluated. This results in the refilling time, which provides information about the functional state of the veins: The shorter the refill time, the more severe the damage to the vascular plexuses. Normally, this time period is greater than 25 seconds.
The examination procedure is as follows: The patient is put on the measuring device, which is integrated into a sticker (similar to an ECG electrode) or into a cuff. During the examination, the patient sits and performs a movement program (knee bends, foot tilts, etc.), which is repeated several times. The patient then relaxes and the recovery time is measured. The measurement results are assessed as follows:
| Replenishment time | Rating |
| > 25 seconds | Normal finding |
| 20-25 seconds | Venous dysfunction I. Degree (mild chronic venous insufficiency – CVI) |
| 10-19 seconds | Venous dysfunction II degree (moderate CVI) |
| <10 seconds | III degree venous dysfunction (severe CVI) |
Results are usually documented digitally and are highly reproducible.
