Analysis of breathing effect on vena cava

This master thesis aims to correlate breathing and vena cava’s variations. It will be done thanks to a built spirometer and an ultrasound probe used at the same time. It is known that the diameter of IVC (inferior vena cava) varies with cardiac cycle and breathing. Indeed, its diameter tends to increase during inspiration and decrease during inspiration. This happens because of a variation of pressure and the intervention of muscles. Whereas, regarding the cardiac cycle, the diameter is smaller right before atrial systole and it is bigger during atrial contraction. In addition, variation of the IVC is deeply used to analyse and diagnose clinical diseases. For instance, it is possible to evaluate CVP (central venous pressure) via the variation of vena cava. Moreover, its variation of diameter is widely used to analyse the fluid responsiveness of patients with acute circulatory failure. Lastly, it can be used to estimate RAP (right atrial pressure) which, normally, requires an invasive procedure, that can be used in a few cases, by inserting a pressure sensor inside the right atrium: right heart catheterization (RHC). Today the Caval index, the ratio between the difference of maximum diameter and minimum diameter and the maximum diameter, is used in echocardiography as a diagnostic indication to monitor cardiac function and the amount of blood returning to the heart during breathing. To calculate this, very often a technique known as sniffing is used, in which the patient is asked to perform a very strong nose inhalation. As this technique is very dependent on the collaboration of the patient, this thesis sought to find a method to normalise an effort and make it possible for each patient. One of the biggest problems in estimating the diameter of IVC is its movement due to respiration. The greatest movement occurs in the craniocaudal direction. This causes different locations of ICV at different times, resulting in a decrease in its diameter.