A photoplethysmogram ( PPG ) is an optically obtained plethysmogram, volumetric measurement of organs. PPG is often obtained by using pulse oximeter that illuminates the skin and measures changes in light absorption. A conventional pulse oximeter monitors the perfusion of blood to the dermis and subcutaneous skin tissues.
With each heart cycle, the heart pumps blood to the periphery. Although the pulse pressure is somewhat muffled when it reaches the skin, it is enough to enlarge the arteries and arterioles in the subcutaneous tissues. If the pulse oximeter is installed without compressing the skin, pressure pulses can also be seen from the venous plexus, as small secondary peaks.
Volume changes caused by pressure pulses are detected by illuminating the skin with light from the light-emitting diode (LED) and then measuring the amount of light transmitted or reflected to the photodiode. Each heart cycle appears as a peak, as seen in the picture. Since blood flow to the skin can be modulated by several other physiological systems, PPG can also be used to monitor breathing, hypovolemia, and other circulatory conditions. In addition, the PPG waveform differs from subject to subject, and varies with the location and the way in which the pulse oximeter is installed.
Video Photoplethysmogram
Site to measure PPG
While pulse oximeters are commonly used medical devices, PPG derived from them is rarely displayed and nominally processed only to determine the heart rate. PPG can be obtained from transmissive absorption (as in fingertips) or reflection (as in the forehead).
In an ambulatory setting, pulse oximeters are usually used on the fingers. However, in cases of shock, hypothermia, etc. The blood flow to the periphery can be reduced, producing PPG without a visible heartbeat. In this case, PPG can be obtained from the pulse oximeter in the head, with the most common sites being the ear, nasal septum, and forehead. PPG can also be configured as multi-site photoplethysmography (MPPG), for example making simultaneous measurements of the right and left ear lobes, large indexes and toes, and offers further opportunities for the assessment of patients with suspected peripheral artery disease, autonomic dysfunction, endothelial dysfunction, and arterial stiffness. MPPG also offers significant potential for data mining, eg. using in-depth learning, as well as various other innovative pulse wave analysis techniques.
PPG can also be obtained from the following sections:
- vagina (photoplethysmograph vagina)
- clitoris (photoplethysmograph clitoris)
- the esophagus
Motion artifacts have proven to be a limiting factor that prevents accurate readings during exercise and free living conditions.
Maps Photoplethysmogram
Usage
Monitor heart rate and heart cycle
Because the skin is very rich in perfusion, it is relatively easy to detect the pulsatile components of the heart cycle. The DC component of the signal is caused by the mass uptake of the skin tissue, whereas the AC component is directly caused by variations in blood volume in the skin caused by pulse pressure from the cardiac cycle.
The height of the AC component of the photoplethysmogram is proportional to the pulse pressure, the difference between systolic and diastolic pressure in the arteries. As shown in the figure showing premature ventricular contraction (PVC), PPG pulses for cardiac cycles with PVC results in low-amplitude blood pressure and PPG. Ventricular tachycardia and ventricular fibrillation can also be detected.
Monitor respiration
Respiration affects the heart cycle by varying the intrapleural pressure, the pressure between the thoracic wall and the lungs. Because the heart is in the thoracic cavity between the lungs, the partial pressure of inhalation and exhalation greatly affects the pressure on the vena cava and the right atrium filling. This effect is often referred to as normal sinus arrhythmias.
During inspiration, intrapleural pressure decreases to 4 mm Hg, which reaches the right atrium, allowing faster filling of the cava vein, improves ventricular preload, but decreases stroke volume. Conversely during expiration, the heart is compressed, lowers heart efficiency and increases stroke volume. As the frequency and depth of respiration increase, venous return is increased, leading to an increase in cardiac output.
Monitoring the depth of anesthesia
Anesthesiologists should often assess subjectively whether the patient is sufficiently sedated for surgery. As shown in the figure, if the patient is not sufficiently anesthetized, the sympathetic nervous system response to the incision can produce a direct response in the PPG amplitude.
Monitor hypo and hypervolemia
Shamir, Eidelman, et al. studied the interaction between inspiration and the removal of 10% of the patient's blood volume for blood banking prior to surgery. They found that blood loss can be detected both from the photoplethysmogram of pulse oximeter and arterial catheter. Patients show a decrease in heart pulse amplitude caused by reduced cardiac preload during breathing when the heart is compressed.
Photoplethysmograph
photoplethysmograph is a device used to obtain optical volumetric measurements of organs.
See also
- Photoplethysmograph clitoris
- Hemodynamics
- Plethysmograph
- photoplethysmograph vagina
References
External links
- Student project: create device to collect PPG
- Free application for photoplethysmogram measurement without contact via Webcam
Source of the article : Wikipedia
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