Plethysmography

To study vascular tone in medicine, a special technique called plethysmography is used. In the course of this technique, fluctuations in the volume of the human body, an individual organ or part due to their filling with blood are recorded.

In modern medical practice, several types of plethysmography are used, each of which can be performed using certain equipment – plethysmographs. Any plethysmograph includes a receiving and transmitting part, a tape drive mechanism and a recorder.

Technique for research

Plethysmographs serve as devices for measuring graphic changes in volumes in the human body when filled with blood. Equipment for plethysmography is mechanical and electrical. A mechanical plethysmograph indirectly or directly registers the emerging fluctuations in the volumes of the studied objects. An electric plethysmograph helps to assess the filling of vessels over a large study area. Photoelectric plethysmographs are also used, designed to conduct studies on planes, for example, on the patient’s skin, and mechanoelectric devices. But only the one that registers and perceives the change in the volumes of the objects of study, that is, the mechanical apparatus, can be considered directly as a plethysmograph device. All other varieties of technology for this procedure determine volume fluctuations only with additional measurements of the original volume, which often leads to large errors.

A mechanical plethysmograph is a reservoir filled with air or liquids, inside which the area under study is completely isolated from the external environment, and a device for measuring volume fluctuations attached to it. When there is a change in the volume of the studied organ due to blood supply, there is a shift in the transmission medium of the sensitive object used in this plethysmograph. It can be a column of liquid in a tube, a membrane, an air bell, or a bellows. The shift data is captured and recorded by a dedicated device. With a stubborn sensing element, data on changes in volumes can be converted into data on pressure fluctuations. The pressure can be measured with an electromanometer. In the aquatic environment, the transmission of plethysmographs is not used, because they have an increased heat capacity, inertia, and a significant water mass that affects the physiological processes of a person.

The most commonly used mechanical air devices have a compact plethysmographic receptor, high accuracy and sensitivity. Such plethysmographs include the Votchala (finger) plethysmograph, which incorporates a light-beam manometer and sensitive elements connected by rubber tubes with finger caps, which is necessary for the signal recording process itself.

The most accurate of all are mechanoelectric plethysmographs. They are very often used in modern clinical practice. In these devices, the vibrations of the receptors that perceive the signal are converted by means of sensors from mechanical to electrical, are amplified and recorded. One of such sensors is an easily extensible tube, in the cavity of which there is an electrically conductive medium. This tube is connected to an electrical circuit designed to measure vibrations. The tube is superimposed around the object under study, its length, depending on the blood filling of the organ, changes and this is the object of measurement of the plethysmograph.

With the help of electrical plethysmographs, it is customary to measure electrical impedance (or its components, such as capacitance, resistance, inductance). A feature of these plethysmographs is the ability to examine organs without contact – the sensing electrode or coil can be located at a short distance from the study area.

In photoelectric plethysmographs, there is a light source and a photoresistor or diode, which are connected in such a way that, when in contact with the examination area, the photosensitive part perceives the light coming from the source through the tissue of the object. The sensor in such equipment provides information on the optical density of tissues, which depends not only on the fullness of blood, but also on its spectral composition.

To conduct occlusal plethysmography, air devices equipped with special signal-converting sensors are most often used, or mechanoelectric devices with no transmission medium, which have special sets of sensors, occlusal cuffs for different areas of the body, compressors, recorders with automatic data processing capability and the ability to graphically display the obtained data. information. These devices are multifunctional complexes that help measure the average arterial blood flow, the capacity of the venous basin of the extremities, peripheral arterial pressure, and much more, by using multi-mode compression in the areas being examined.

Indications for plethysmography

A plethysmography study should be performed in cases where there are the following medical indications for:

• various vascular diseases;
• numerous circulatory disorders;
• cardiac pathologies;
• vasoconstriction;
• diagnosing Raynaud’s syndrome;
• with varicose veins;
• with thrombosis;
• with disorders of the blood supply to the brain.

Diagnostics allows you to determine the tone of veins, arteries, to monitor the effectiveness of therapy. Plethysmography also allows you to explore conditional vascular reflex states. Moreover, this type of examination is usually prescribed by neuropathologists, therapists, vascular surgeons, and phlebologists. The procedure is carried out in many hospitals and clinics, where equipment and a qualified specialist are provided for this, responsible for the reliability of the data obtained during the diagnosis.

Research progress

The method of conducting a general plethysmography, contraindications to it, as well as the essence of the process of preparing for the procedure, directly depends on which part of the body needs to be diagnosed and what apparatus it will be performed with. A good result is obtained by studies conducted in parallel on the affected and healthy vessels, as well as repeated plethysmography.

To improve the accuracy of diagnosis in the process of plethysmography, thermal and pharmacological tests or samples are taken during periods of physical activity. At the same time, indicators of blood filling before and after manipulations with the studied organ should be recorded. Such tests help to assess the degree and speed of restoration of normal blood flow in the pores.

women’s area. And pharmacological tests make it possible to optimally select the necessary medications that effectively eliminate the pathology diagnosed during the study.

When evaluating the results of plethysmography, it is important to have fast oscillations, provided by the work of the heart and the respiratory system, and slow oscillations, formed in the process of filling the vascular system with blood.

When registering a decrease in blood filling of the vessels of the extremities, doctors can talk about stenosis or obliterating vascular damage. If venous reflux and a small volume of filling of deep veins are detected using the occlusive method, specialists diagnose varicose veins or thrombosis. In any case, all the results of the studies carried out must be transferred to the attending physician, who issued the referral for plethysmography, in order to make the correct diagnosis and prescribe the appropriate treatment.

Impedance examination of limbs

Impedance plethysmography is a non-invasive way to study the blood flow of a patient present in his limbs in modern medicine. During this diagnosis, special electrodes are attached to the hands or feet of the patient, and then resistance changes are recorded, depending on violations of the venous outflow or respiratory procedures.

During the procedure, electrodes are attached to the patient to the area under study (for example, legs), changes in electrical resistance are recorded, which depend on respiratory movements or impaired outflow in the veins.

Impedance plethysmography is used to determine venous disorders in the lower leg, diagnose thrombophlebitis, evaluate the condition of the pulmonary artery, and diagnose thrombophilia. Before the diagnosis, the patient needs to learn about the essence of the study, the need to adhere to a diet before the procedure, it is also important to get acquainted with the specialist who will conduct the diagnosis, so that at the time of plethysmography, you can completely relax and calm down. Before the examination, the patient must empty the bladder and intestines and change into a disposable medical shirt.

During plethysmography, the patient is placed on his back, and the legs should rise in such a way that the elevation angle does not exceed 35 degrees. For better blood flow, the patient’s knees are always placed higher than his heart is at the time of diagnosis. One leg is bent at the knee joint and rotated at the hip joint so that the body weight shifts slightly to its side, which will allow you to attach the plethysmograph electrodes as correctly as possible. With plethysmography, electrodes are placed on the lower leg at a distance of 8 centimeters from one another. In this case, the cuff is placed on the thigh so that it is located higher than the knee. The cuff is inflated to 50-60 centimeters of the water column, while the veins are compressed, but the blood flow is not disturbed, and then loosened. The first recorded data are recorded, which form a curve of venous blood filling and its subsequent decrease when the cuff is loosened. The second leg is subject to a similar procedure. The process can be repeated several times on each leg to obtain reliable data.

Normally, it is believed that short-term compression of the artery should immediately provoke a rush of blood in the veins, and its relaxation will entail the same lightning-fast outflow. If the outflow is disturbed, this often indicates deep vein thrombosis, since when the cuff is inflated, blood is pumped, but the vessels do not increase in diameter. With thrombosis, the outflow is disturbed, the blood filling of the lower leg becomes unstable. With this type of disease, doctors often prescribe appropriate anticoagulant therapy to patients.

Low blood flow due to shock, diseases of the leg arteries, low cardiac output can affect the passage and the results obtained during the study. Also, factors affecting the diagnostic results may be the state of compression of large arteries (for example, tumors), the patient’s excited state, lowering the temperature of the limbs of the body due to the cold air of the room where plethysmography is performed.

A plethysmographic study is especially important to determine the pharmacological dynamics in the treatment of diseases with vasoactive drugs, when it is important to make sure that the prescribed drug does not have a vasodilator, but a tonic effect on the venous network. Thus, when using plethysmographs, the doctor can objectively assess the effect that the therapy prescribed by him produces on the pathological conditions of the patient.