Scientists from the University of ITMO and FGBU “NMIs. V.A. Almazov “successfully applied the method of spatial plethysmography to the vessels of the face, into which blood comes from carotids. According to the videotapes of the face skin surface, they determined one of the important parameters of the health of the cardiovascular system – the speed of the pulse wave propagation, and also found out that it depends on the position of the human body in space.
In order to draw blood through the body, you need a heart contraction. When the left ventricle of the heart contracts, the blood from it is thrown into the aorta – the largest artery. Its walls, like the walls of other vessels, stretch, so the blood moves through the vessels not uniformly, but by jerks. Exposure to the walls of the vessels increases the pressure on them, so there is a phenomenon such as a pulse wave– a consistent change in pressure from the blood to the walls of the arteries. The rate of movement of blood in different vessels is not the same. The highest is in the arteries, and the slowest of all blood moves along the smallest, narrowest and most numerous vessels – the capillaries. That is, as the blood is removed from the heart through the aorta and the artery to the capillaries, blood flows more slowly.
By how quickly the pulse wave comes from any single artery to the capillaries, and also by the degree of its attenuation, one can determine the functional state of the cardiovascular system. This is done with the help of plethysmography. Special bulbs shine on the capillary, and the device (plethysmograph) records the light reflected or absorbed by this capillary. Then, based on the information received, it determines the volume and velocity of the blood flow and some other parameters.
Russian scientists tried to adapt plethysmography to the face area, fed by capillaries – branching of the carotid arteries. To do this, they connected a video camera equipped with filters for the polarization of light, with eight green LEDs (wavelength 530 nm) and parabolic mirrors. The diodes were shining on the subject’s face, and the video camera registered the radiation reflected from the face. With the help of this plethysmograph, researchers evaluated the speed of pulse wave propagation in 73 healthy subjects. At the time of registration, the volunteers changed the position of the body: for a while they were sitting, some – lying on the right side, some – on the left, etc.
The images of the face that the video camera recorded reflected how the blood filling of the capillaries changes and how the pulse wave passes. But what is even more interesting, its speed depended on the position of the body. For example, if a person was lying on his left side, then the pulse wave to the capillaries of his left side came from the left carotid artery faster than a similar wave to the capillaries in the right side of the face – from the right carotid artery. In addition, the reaction to the change in the position of the body reflected in different ways the velocity of the pulse wave in the same vessels in different subjects.
The work of Russian scientists brings the scientific base to therapeutic yoga . It turns out that different poses can really improve a person’s condition – for example, to reduce the intensity of a headache – due to the fact that they change the local blood flow in the vessels.