The contactless system measures blood flow in the upper limbs. (Credit: ITMO University)
The contactless system measures blood flow in the upper limbs. (Credit: ITMO University)

Researchers have developed a contactless method for measuring blood flow in the upper limbs. The method is based on video recording of the skin surface under green light measuring the absorption of red blood cells.

The experimental results showed that the proposed method is as accurate as the traditional one. However, it is easier in use, cheaper, and fits more patients. Measuring blood flow in the limbs is an important diagnostic indicator. By studying how efficient is the heart in supplying blood to the limbs, we can see whether the cardiovascular system works properly, and evaluate parameters of the blood flow regulation. Currently, the researchers usually use contact (or tensiometric) methods of occlusive plethysmography to measure the blood flow in the limbs. Such an approach is based on recording the changes in the volume or diameter of a limb due to its filling with blood during venous occlusion.

The new method is based on photoplethysmography. This technique is capable of tracking changes in the blood supply of the skin using video recording of the absorption of green light. When the green light hits a red blood cell, the reflected wave changes its polarization. The camera registers only this modified signal and tracks when it gets most intense. The reason for the increase in light absorption during venous occlusion can be explained by the increase in the number of red blood cells, most likely due to the expansion of the small veins of the upper layer of the skin.

To assess the accuracy of measurements using the new system, the scientists conducted a series of experiments and compared the values obtained by traditional and new methods. Experimental measurements were performed on healthy volunteers. The signal was recorded for several cycles of venous occlusion. The results of cold stress effect on the vessels work obtained by the new method almost completely coincided with the results of traditional measurements.