Evaluation of Cardiac Adaptation in Patients Undergoing Passive Leg Raising (PLR) Maneuvers: Inferior Vena Cava Study

Passive leg raising (PLR) maneuver is a non-invasive and effective technique to assess fluid responsiveness, particularly useful in monitoring cardiac preload. Unlike intravenous administration, which involves direct fluid introduction and potential associated risks, PLR allows immediate assessment by simulating the effect of a fluid load without actual infusion. In this study, thirteen healthy subjects (5 men and 8 women, mean age 27 ± 9.5 years) underwent two consecutive PLR maneuvers. Each maneuver was assessed through a sequence of three events: pre-maneuver (baseline), during PLR and immediately post-maneuver. The segmentation of the inferior vena cava (IVC) has been performed using a software developed by Viper s.r.l., which included the use of a GUI in MATLAB for data analysis. A graphical user interface (GUI) was developed in Python, using the PyQt6 library, to further facilitate the. Segmentation allowed the analysis of parameters indicative of hemodynamic behavior, such as IVC diameter, caval index (CI), cardiac caval index (CCI), and respiratory caval index (RCI). During the first maneuver, the mean diameter of the inferior vena cava increased from a baseline value of 14.4 ± 4.7 mm to 16.6 ± 4.1 mm during PLR, subsequently decreasing to 14.9 ± 5.1 mm after the maneuver. Accordingly, the caval index (CI) showed an inverse change, decreasing from 0.35 ± 0.13 to 0.26 ± 0.01 during PLR and returning to 0.34 ± 0.12 after the maneuver. For the second maneuver, the inferior vena cava diameter increased from 13.7 ± 5.0 mm (before the maneuver) to 16.8 ± 5.3 mm during PLR, then decreased to 13.3 ± 4.4 mm after the maneuver, with a corresponding decrease in CI from 0.33 ± 0.13 to 0.26 ± 0.01, and then returned to 0.34 ± 0.13. The mean interval between the two maneuvers was 23.82 ± 3.47 minutes. This study evaluated the correlations between pulsatility indices and mean diameters in various observational periods using two-way ANOVA and two-sample t-tests. The two-way ANOVA revealed significant differences between time states, indicating that these states significantly influence both pulsatility indices and diameters. However, no significant intra-subject differences were observed. The two-sample t-test demonstrated significant differences between parameters calculated during both PLR maneuvers and their respective baselines, as well as with respect to the immediately following intervals, but no significant differences were found between parameters calculated during the two maneuvers. In conclusion, the results indicate that the passive leg raise (PLR) maneuver does not lead to physiological adaptation, affirming that the PLR is a consistent, reliable, and repeatable measure over time. This analysis suggests that the PLR can effectively assess fluid responsiveness in clinical settings without the influence of previous tests.