Long and active life depends on blood vessel state. Vessel disorders are the reason of the most of severe complications, and vice versa: any disorders impact the microcirculation, i. e. capillary net, which consists of the smallest blood vessels. Photoplethysmography is based on this principle.
It is a rapid test method of detection of blood volume in capillary vessels during transillumination of skin area with infrared light. For photoplethysmography by Bioscanner Wellness the same sensor as for pulseoxymetry and calculation of the heart rate variability is used. The sensor is placed on the finger because of intensive capillary blood flow in the fingertip area.
How the method works
The volume of any organ consists of the tissue volume and the volume of blood that fills the organ. Therefore the tissue volume is constant and the blood volume varies according to the phase of cardiac cycle (heart contraction or relaxation). These changes are registered by the sensor and recorded as photoplethysmogram. Upon completing the computerized data processing, the software draws a conclusion with description of detected abnormalities and recommendations.
Principle of method
P1 — beginning of the ejection period of systolic time interval,
P2 — a moment of maximum vasodilatation (time of maximum pulse wave amplitude),
P3 — protodiastolic period
P4 — beginning of diastole,
P5 — end of diastole and end of cardiac cycle.
A pulse wave forms due to the blood output from the left ventricle during heart contraction. A pressure spreads through the aorta and arteries. The pulse wave velocity through vessels depends on lumen width, vessel wall elasticity, thickness of the vessel wall and the heart muscle strength. Photoplethysmography helps to reveal the signs of stenosis (narrowing of the blood vessel) and sclerosis, assess the vascular tone and the heart function.
The pulse wave on a photoplethysmogram consists of two components. Anacrotic phase reflects systole (heart contraction) and dicrotic phase corresponds to diastole (relaxation). The dicrotic peak is a reflection wave when blood goes to lower limbs and returns to aorta. It is considered that pulse wave rate and duration depend on the cardiac function and its shape and peak height depend on the vessel wall state.
The pulse wave of a healthy person is characterized by relatively steep ascendant part of the curve and a relatively high reflection wave. The arteriostenosis leads to the flattening of the ascendant part, lengthening of dicrotic phase duration and decreasing of reflection wave height. There is no reflection wave in significant stenosis.
What it is used for
Photoplethysmography helps to detect vessel changes in diabetes mellitus, atherosclerosis, hypertensive disease. Besides, it allows to control the treatment or rehabilitation efficacy based on the improving of vessel state.
Photoplethysmography in sports medicine helps to develop an individual training program. It is known that intensive physical activity with increase in muscle volume often leads to the vein overpressure and even vessel rupture. Regular monitoring allows to avoid varicosis (abnormally dilated veins) and related complications.
Besides, this method helps to determine contraindications for certain rehabilitation/cosmetic procedures or types of fitness training. This is particularly important when there is an increased tendency for excessive blood clotting. Blood clots most frequently are formed on the walls of lower limbs. A clot in a vein may detach from its point of origin and travel through the heart to other vessels until it becomes wedged, preventing adequate blood flow. Blood clots can be life-threatening, for example, if a pulmonary (lung) embolism occur.
Examination by photoplethysmograph is necessary before training, related to vibration action (for instance, vibration platforms) or other exercises that are associated with the high risk of blood clot detachment. The same applies to use of vibration beds and other gadgets and procedures causing vibrations in the body.
Evaluation of the photoplethysmogram
The photoplethysmogram is interpreted according certain parameters. For example, stiffness index (the normal value is about 5–9 m/s) allows to detect stenosis of large arteries. Wave reflection characterizes arteriola tone. It indicates indirectly if there are atherosclerosis plaques.
The pulse wave shape can be a sign of disorders too. For example, additional waves (like a cock’s comb) on the pulse wave top clearly indicate a stenosis (there are obstacles in the way of blood flow).
How the procedure is performed
Connect Bioscanner to a laptop or a computer and start the program to perform photoplethysmography. An electric shock hazard is excluded, because the device is independent from external power supplies. It is supplied by USB port. Accumulator or batteries also are not required for its operation. Examination can be conducted anywhere if there is a possibility to connect Bioscanner to a laptop.
To conduct measurements you should fix a sensor on the index finger. It is necessary to avoid movements of this hand not to confound data results due to muscle contraction. After completion of the recording, you should choose for analysis the sequence of pulse waves, that consists of at least five consecutive pulse waves without interference and artifacts. Place the marker on the third of them. To more accurate calculation of indices is also advisable to mark the end of the anacrotic wave and the beginning of the dicrotic wave manually.
Photoplethysmography is a safe and painless procedure. There are no contraindications, but a finger on which a sensor is placed must be without skin damage.
It is advisable not to take any drug substances within 24 hours before examination. It is advisable as well to avoid any physiotherapy procedures during this period.
To avoid vessel reaction to the heat or cold, the room temperature should be maintained within + 19 °–23 °С. You should note that at temperature below 16 °С the arteriolospasm occurs.
It is necessary to rest for a several minutes before examination at a convenient seating or lying position to adapt. During measurements sensor shall be protected from the bright artificial light and direct sunlight.