Analysis of inferior vena cava dynamics under controlled breathing conditions

Ultrasonography of the inferior vena cava (IVC) is a technique widely used in clinical practice to assess its size and pulsatility, providing important information on the volemic status of patients. In addition, it is used to predict fluid responsiveness. Finally, it provides a non-invasive estimate of right atrial pressure (RAP), which is usually measured by an invasive procedure called right heart catheterisation (RHC). Non-invasive estimation of RAP is obtained as a function of IVC maximum diameter and Caval Index (CI), defined as the ratio of the difference between the maximum and minimum diameter and the maximum diameter of the IVC. This is achieved by using a respiratory manoeuvre called sniff, which involves a quick, strong inhalation through the nose by the patient, but is non-standardised. The aim of this thesis is to analyse the dynamics of the IVC, in terms of size and pulsatility indices (CI, RCI, CCI), under controlled breathing conditions. To this end, a spirometer was built and 3D printed, starting from a model created in a previous thesis work and attempting to overcome the problems that emerged, through which it is possible to provide visual feedback to the subject. Subsequently, a user interface was developed to facilitate the operator in data acquisition and to display the signal for visual feedback. Finally, an experimental protocol was tested on 10 healthy subjects with the aim of assessing changes in IVC pulsatility in three different breathing modes: light, normal and deep. For the IVC segmentation, necessary to extract information on size and pulsatility indices, the software developed by Viper s.r.l. was used, which is able to follow the vein borders throughout the ultrasound recording. The mean values and standard deviation of the CI, RCI and CCI are 34.30±9.36%, 24.46±8.49% and 16.71±6.62% for the light breathing condition; 45.79±11.72%, 35.36±9.62% and 19.97±9.62% for the normal breathing condition; and 52.30±9.89%, 41.00±9.23% and 20.21±11.45% for the deep breathing condition, respectively. The increase in IVC pulsatility that occurs with increasing exertion by the subject is mainly due to a greater reduction in IVC minimum diameter. The mean value and standard deviation of the minimum diameter are 10.58±3.48 mm, 8.79±3.71 mm and 7.62±2.57 mm for the light, normal and deep breathing conditions, respectively. Friedman's test and the Wilcoxon signed-rank test were used to highlight any statistically significant differences between the normal breathing condition and the other two conditions: both breathing conditions show significant differences. Only weak correlations were observed between IVC parameters and differential pressure values obtained from the sensors connected to the spirometer. The results show that the three conditions tested can induce a different pulsatility of the IVC, even though the effort required of the subject is not excessive. However, this approach has some limitations that could be overcome with future research.