Noninvasive measurement of lower limb outflow resistance andimplications for stenting

Abstract

AIMS: Stenting to relieve iliac vein obstruction is now practical and safe. However, the rates of ulcer healing, pain, and edema relief are 76%, 52%, and 42% respectively. In addition, a high ulcer recurrence (up to 86%) has been reported. Currently, patient selection depends on symptoms, imaging methods, and intravascular ultrasound (IVUS) for the assessment of iliac vein stenosis without consideration of the collateral circulation. The aim of this article is to present the results of a noninvasive method of measuring lower limb outflow resistance (LOR) and also to test the hypothesis that LOR is extremely variable in limbs with iliac obstruction and that some patients with iliac stenosis may have a LOR close to that of normal limbs as a result of a well-developed collateral circulation.MATERIALS AND METHODS: LOR was measured at different venous pressures from 60 to 25 mmHg using air-plethysmography in 15 limbs without and 15 limbs with iliac vein obstruction. Reflux in ml/sec (venous filling index [VFI]) and venous clinical severity score (VCSS) were also measured in all limbs. RESULTS: The LOR at 25 mmHg (LOR25) was found to be the most discriminating measurement between the two groups. The area under the receiver operating characteristic curve was 0.973 (95% confidence interval [CI] 0.923–1.000). The range of LOR25in limbs without obstruction was 0.0043–0.038 mmHg/ml/min and 0.0170–0.330 mmHg/ml/min in limbs with obstruction. By plotting VFI against LOR25, a subgroup of limbs was identified with iliac obstruction that had a high VCSS (5–12) and a near-normal LOR25(0.050 mmHg/ml/min) presumably as a result of a well-developed collateral circulation but a high VFI in the range of 5–14 ml/s. Another subgroup of limbs with iliac obstruction and a high VCSS (5–18) had a high LOR25 (0.100–0.330 mmHg/ml/min) presumably from a poorly developed collateral circulation. CONCLUSION: The noninvasive measurement of LOR25provides a quantitative estimation of overall lower LOR. It can indicate which limbs are compensated by the development of a good collateral circulation and which are not. The combination of LOR25with VFI enables the clinician to determine the relative contribution of reflux and obstruction in individual limbs. A low LOR25in the presence of severe iliac stenosis or occlusion is an indication of a well-developed collateral circulation and suggests that stenting would provide little benefit if any. However, this hypothesis needs to be verified by future prospective studies.

Keywords

• lower limb outflow resistance
• noninvasive measurement
• implications for stenting