Changes of fluid-dynamic parameters in peripheral stenoses with transcutaneous interventions

Peripheral vessels provide a useful in vivo haemodynamic model allowing evaluation of local intravascular fluid dynamics. Velocity measurements using a 0·018 inch Doppler-tipped angioplasty guidewire, quantitative angiography and laboratory data were gathered from 45 patients with a total of 48 percutaneous transluminal laser assisted angioplasties (PTLA) in the superficial femoral, in the iliac, in the popliteal artery and in the peroneal artery. From these data, blood flow, whole blood viscosity, Reynold's numbers, Womersley numbers and shear stress were calculated, evaluated as to their change post PTLA and correlated with clinical improvement at early follow-up. The clinical result was quantified as categorial improvement according to the American Heart Association guidelines. The primary angiographic results of angioplasty were satisfactory in all patients. Clinically 17/45 patients showed a marked, 6/45 a moderate, 18/45 a minimal, and 4/45 no improvement. The mean values of maximnal peak velocity at stenosis decreased from 235 ± 28 cm.s-1 to 84 ± 8 cm.s-1 after PTLA ( P < 0·01). The minimal intrastenotic cross section increased from 7·7 ± 0·9 to 21·9 ± 1·6 mm2 ( P <0·01). Mean trans-stenotic flow increased after intervention by about 50% ( P < 0·01) and improved further by 135% after administration of adenosine triphosphosphate i.a. ( P <0·01). Reynold's numbers were elevated intrastenotically (1285 ± 198) pre-intervention as compared to values proximal (564 ± 81) and distal (449 ± 66) to the stenosis and were reduced significantly ( P <0·05) at stenosis by PTLA, whereas values proximally and distally increased significantly ( P <0·01) post PTLA (proximal 829 ± 84, intra 773 ± 107, distal 676 ± 98). Shear stress, reflecting mechanical interaction between flow and vessel wall, was elevated at stenosis pre-intervention to 44 ± 8·9 Pa and reduced at post-stenotic vessel sites to 2·4 ± 0·5 Pa. PTLA caused a decrease in stenosis to 6·3 ± 1 Pa ( P <0·01) and an increase distally to 4·6 ± 1 Pa ( P <0·01). Whereas in single stenoses removal of the obstruction was associated with a significant ( P <0·05) increase in trans-stenotic flow and shear stress distally, there was only attenuated increase in trans-stenotic flow in multiple lesions despite an angiographically good PTLA result. Shear stress distally remained low in those parients. Velocities and Reynold's numbers were lower in these vessels even pre PTLA. Residual flow, Reynold's number and minimal cross-section pre-intervention correlated significantly with clinical outcome. Pooling cases with no or minimal, as opposed to those with marked or moderate improvemnenl, 81 % of patient.s were correctly classified using the Reynold's numbers pre- and post-PTLA. Conclusion: Peak velocity monitoring is feasible and safe during angioplasty. Velocity provides clinically relevant physiological information in addition to angiography. Combining quantitative angiography, velocity measurements and laboratory data allow the calculation of blood flow, Reynold's numbers and shear stress; thereby providing complex fluid dynamic information. Thus the evaluation of haemodynamics in single and multiple obstructions before and after intervention is imnproved. Fluid dynamic parameters pre- and post-PTLA are significantly correlated with clinical short-term result.