Sensitivity and Reproducibility of Inferior Vena Cava Diameter and Superior Vena Cava Flow Velocity Measurements to Changes in Cardiac Preload in Subjects with Hypertension

OBJECTIVES: We investigated the sensitivity and reproducibility of inferior vena cava (IVC) diameters and superior vena cava (SVC) flow velocities in detecting changes in cardiac preload in clinically euvolemic subjects with hypertension. METHODS: Measurements were obtained during passive leg raising (PLR) and lower limb venous occlusion (LVO), interventions which respectively transiently increase and decrease cardiac preload. Measurements were made in 36 subjects and repeated on two separate occasions to examine reproducibility. RESULTS: During PLR, there was no significant change in IVC diameters, but peak flow velocity of the SVC S wave increased by 6.5 (95% confidence interval 1.6–11.3) cm/s (P = 0.01). During LVO, IVC diameter in expiration decreased by 3.2 (1.7–4.7) mm and the SVC S wave decreased by 9.7 (4.4–14.7) cm/s (P < 0.001). Venae cavae-derived indices can be used to assess changes in preload within the physiological range in euvolemia. CONCLUSIONS: Despite suboptimal reproducibility of baseline measurements, high agreeability between the changes in IVC diameter and SVC flow after LVO suggests that these indices can be used to monitor changes in cardiac preload.