Changes in venous lumen size and shape do not affect the accuracy of volume flow measurements in healthy volunteers and patients with primary chronic venous insufficiency

PURPOSE: The purpose of this study was the analysis of the rapid changes in the size and shape of the peripheral vein and the associated changes in blood flow velocities and the estimation of their effect on the reliability of the ultrasound scan volume flow (VF) measurements. METHODS: Ten patients with primary chronic venous insufficiency and 10 healthy volunteers were studied. Two duplex scanners were used simultaneously: one for the velocity measurements in longitudinal plane and another for the cross-sectional area (CSA) measurements in transverse plane during quiet respiration, Valsalva's maneuver (VM), pneumatic cuff compression-decompression, and active dorsiflexion. The patients underwent examination in standing and 15-degrees reverse Trendelenburg's (RT) positions. VF was calculated on the basis of real-time CSA and velocity values. RESULTS: Rapid changes in the CSA as much as 130% for 0.2 seconds were observed. In most cases, the changes in CSA and the flow velocity were inversely related, which resulted in near constant VF. With the exception of VM in the RT position, the difference between real-time VF and mean VF was not significant (P >.05). In the RT position, significant changes in CSA were observed during and immediately after VM. These changes resulted in 23% +/- 15% changes in outflow (both groups) and in 24% +/- 13% changes in reflux (chronic venous insufficiency group). CONCLUSION: The CSA of the peripheral vein and the flow velocities undergo rapid changes during time intervals of a fraction of a second. The vein can have a noncircular cross-section. To minimize the potential error, VF measurements should be performed during quiet respiration or with cuff compression-decompression. With these conditions, the rapid changes in velocities and CSA do not significantly affect the accuracy of VF measurements because of their inverse relation. CSA should be measured planimetrically, or the site of the measurements should be where the vein is close to a circular shape.