Plethysmography is a diagnostic method that measures changes in the volume of the body area under study, either from blood circulation or from respiratory movements, such as in the case of the chest. On this basis, the blood flow and pressure in arterial and venous vessels, or the parameters of the respiration process are determined.

Plethysmographyis performed in three areas of the body, ie on the lower limbs (mainly the lower legs), on the upper limbs and on the chest. The limb test measures blood flow, and in the case of the thorax, the respiratory function of the lungs is assessed.

Plethysmography is a non-invasive, painless test that allows you to assess the condition of the peripheral circulatory system and the respiratory system.

Contents:

  1. Plethysmography - indications
  2. Plethysmography - preparation for the examination
  3. Limb plethysmography
  4. Lung plethysmography
  5. Plethysmography - contraindications

Plethysmography - indications

The indication for the examination is the suspicion or presence of symptoms that may indicate poor condition of peripheral vessels resulting from such diseases as:

  • blockage
  • atherosclerosis
  • changes accompanying diabetes
  • obliterating arteritis
  • complications after vascular injuries or surgery
  • deep vein failure
  • phlebitis
  • valvular insufficiency with venous reflux

The indication for lung plethysmography is the suspicion of obstructive changes, reflex bronchiolar stenosis, tuberculosis, pulmonary fibrosis or neoplastic metastases, which may reduce lung capacity.

Plethysmography - preparation for the examination

Before the test, you should give up or reduce to a minimum substances that may disturb blood circulation, e.g. by narrowing or dilating blood vessels, increasing blood pressure or disturbing the heart rhythm. That is why we give up drinking coffee, strong tea, alcohol and smoking.

You should not eat too abundant meals before the test, because the blood flow through the lower leg and through the forearm increases, and the parameters assessed during the test, i.e. venous capacity and maximum venous outflow, increase.

PeopleThe chronically ill and constantly taking medications, e.g. blood thinners, should discuss with the attending physician what dose of the drug can be taken or whether drugs should be taken on the day of the examination.

Limb plethysmography

It is performed using pneumatic cuffs similar to those used to measure blood pressure. They are connected to a precision gauge that records changes in pressure caused by changes in the volume (diameter) of the limb.

Changes in the limb volume result from the fact that after the heart contracts, as the blood wave spreads to peripheral organs, the filling of the arteries with blood increases. Similarly, the amount of blood flowing through the veins is examined.

The basic research technique isclassical plethysmography , which compares the blood flows in the examined limb with the flows in another (upper or lower), considered he althy. If the obtained values ​​are similar, the result is considered correct. A large difference in the observed pressures indicates impaired arterial circulation.

Segmental plethysmographycompares the pressures in individual sections of the limb, eg in the upper and lower parts of the arm and on the forearm. Excessive pressure differences between the proximal and more distal sites suggest that the arteries are not working properly.

Vein plethysmography allows you to evaluate the circulation in the lower extremities. The test is performed using a pneumatic sleeve that is worn over the entire length of the lower leg. When the sleeve compresses the leg, the pressure changes, and its changes allow to assess the blood flow rate and determine whether and to what extent there is reverse blood flow in the superficial veins, i.e. venous reflux.

Another method of examining the venous circulation isphotoplethysmography . During the test, a special probe is placed on the skin, which emits infrared waves. In soft tissues and skin, it is partially reflected, which is recorded by sensors located in the probe.

When the radiation hits a superficial blood vessel, it is absorbed by red blood cells. The maximum light absorption of red blood cells is observed when the patient is sitting or standing still, the blood pressure is high and the veins are filled to the maximum with incoming blood.

As the pressure in the veins drops, light absorption is reduced. Changes in the intensity of impulses returning to the device allow for the assessment of flows and the diagnosis of possible venous reflux.

Lung plethysmography

The test is carried out in a tightly closeda chamber that has connections to pressure sensors. The sensors record changes in the volume of the chest, which are proportional to the degree of air filling in it. The device also records how long each phase of inhalation and exhalation lasts. The processed data allows the physician to estimate the degree of impaired ventilation of the lungs and their respiratory efficiency.

During the test, do not make any movements or tense muscles, as this may disturb the course of the test and give an incorrect result. Depending on the type of plethysmography being performed, your doctor may ask you to get up from the couch and perform appropriate exercises.

After the test, which takes about 30 minutes, the technician removes the sensors. After the examination, you should get up slowly from the couch to prevent dizziness. First you need to sit down and only after a while you can get up. After completing the examination, the doctor will inform you when and where the results can be collected.

Plethysmography - contraindications

The test is safe and can be carried out even in seriously ill people. If the patient suffers from ulcers (extensive and deep), the doctor decides about the examination.

About the authorAnna Jarosz A journalist who has been involved in popularizing he alth education for over 40 years. Winner of many competitions for journalists dealing with medicine and he alth. She received, among others The "Golden OTIS" Trust Award in the "Media and He alth" category, St. Kamil awarded on the occasion of the World Day of the Sick, twice the "Crystal Pen" in the national competition for journalists promoting he alth, and many awards and distinctions in competitions for the "Medical Journalist of the Year" organized by the Polish Association of Journalists for He alth.

Read more articles from this author

Category:

Research