Positional variation in hemodynamic and morphologic parameters of the iliofemoral venous segment in healthy volunteers.

OBJECTIVE: Iliofemoral venous stenting has become the standard of care for patients with quality-of-life-impairing manifestations of chronic iliac venous obstruction. The initial diagnosis of chronic iliac venous obstruction is through the use of duplex ultrasound (DUS). Here, set diameters are used for each segment (common femoral vein [CFV], external iliac vein [EIV], and common iliac vein [CIV]) to determine if a patient has venous stenosis or not. However, there is concern that DUS measurements obtained in the supine position (standard approach) are different from those when the person is standing, thereby raising the question as to the appropriate positioning for such a study. This study evaluates this possibility through DUS examination of healthy adults.

METHODS: Sixteen limbs (eight healthy volunteers) without any symptoms or signs of chronic venous disease underwent DUS of their right and left CFV, EIV, and CIV segments in the supine and standing positions. Measurements included peak velocity (PV), time-averaged velocity (TAV), and the smallest vein diameter in each segment. Measurements were done for each person across six cohorts: CFV, EIV, CIV, CFV + EIV, EIV + CIV, and CFV + EIV + CIV. Normality of paired differences was assessed using the Shapiro-Wilk test. Variables demonstrating non-normal distributions were analyzed using the Wilcoxon signed-rank test, whereas normally distributed variables were compared using paired t-tests. Effect size was quantified using Cohen's d z. P value ≤.05 was considered significant.

RESULTS: In the CFV, the PV and TAV were both greater in the supine than in the standing position (P < .05), whereas the diameter was smaller in the supine position (mean difference, 1.1 mm; P = .05). In the EIV, a similar finding was observed; however, statistical significance was noted only for PV (P = .02) and TAV (P = .02). In the CIV, no statistically significant change in PV, TAV, or diameter was noted when supine was compared with the standing position. When EIV and CIV segments were combined, a statistically significant decrease in the PV (0.07 cm/s, P = .02) and TAV (0.02 cm/s, P = .03) was noted in the standing compared with supine. An increase in diameter (mean difference, 0.2 mm; P = .39) was noted going from supine to standing position. Effect size analysis (Cohen's d z) demonstrated a moderate to large effect size for PV and TAV and a small effect size for diameter.

CONCLUSIONS: Venous duplex-derived flow velocities in the iliac vein in healthy volunteers demonstrate a moderate to large, statistically significant decrease from supine to standing position without a significant change in the vein diameter. This raises the question about the relevance of any increase in vein diameter from supine to standing, which has become an important contemporary issue. Further study is warranted.