Effects of positional changes on inferior vena caval size and dynamics and correlations with right-sided cardiac pressure

Effects of supine and lateral positions on the size and shape of the inferior vena cava (IVC) were studied in 30 normal persons and in 53 patients with cardiac disease undergoing right-sided cardiac catheterization. In normal subjects, mean values for both IVC diameter and area decreased significantly (p <0.01) from the right lateral (22 ± 3 mm and 3.9 ± 0.6 cm², respectively) to the supine position (15 ± 5 mm; 1.8 ± 0.9 cm²) to the left lateral position (7 ± 3 mm; 0.8 ± 0.4 cm²). IVC shape was round in the right lateral, oval in the supine, and slit-like in left lateral position. In the 53 patients, significant differences in IVC diameter and area were also detected in all 3 positions. However, when separated into 2 groups according to right atrial pressure, patients with normal pressure (8 mm Hg or less) had diameter and area values equivalent to those of normal subjects, whereas patients with elevated right atrial pressure (more than 8 mm Hg) had supine and left lateral IVC diameters and areas that were larger than normal, and approximately equivalent: diameters—23 ± 3 mm (right), 18 ± 5 mm (supine) and 17 ± 7 mm (left); areas—4.1 ± 0.8 cm² (right), 3.3 ± 1.2 cm² (supine) and 3.1 ± 1.3 cm² (left). IVC diameters and areas in all 3 positions correlated with mean right atrial pressure, measured subsequently in the supine position, but the left lateral position provided the strongest correlations (r = 0.85, IVC diameter vs right atrial pressure; r = 0.89, IVC area vs right atrial pressure). In the left lateral position, an IVC diameter of more than 10 mm and IVC area of more than 2.0 cm² had sensitivities of 84% and 73%, specificities of 96% and 100% and predictive accuracies of 95% and 100%, respectively, for the diagnosis of elevated pressure. The IVC shape in the short-axis view was round in all 3 positions in patients with high right atrial pressure.