Measurement of Vascular Input Impedance in Infrainguinal Vein Grafts

n = 40) or claudication (n= 17) were prospectively studied. At the time of revascularization, simultaneously acquired intraluminal pressure and blood flow waveforms were digitized at 200 Hz and subjected to Fourier transformation in near real-time. Input impedance was calculated at baseline (immediately after unclamping) and after stimulation with either papaverine or completion arteriography. Resistance (R _in) was calculated as mean pressure divided by mean blood flow (Q). Characteristic impedance (Z ₀) was calculated as the mean of harmonics 3–10. Intraoperative data acquisition required approximately 5 min, utilized the completion angiography cannula already in place, and was uncomplicated in all patients. Stimulation with either papaverine or arteriography resulted in increased Q (72 ± 7 to 146 ± 11 ml/min, p < 0.001), decreased R _in (126 ± 13 to 52 ± 4 × 10³ dyne · s · cm⁻⁵, p < 0.001), and slightly decreased Z ₀ (18 ± 2 to 15 ± 1, p = 0.002). After a mean follow-up of 20 months, the 2-year primary patency, secondary patency, limb salvage, and survival rates were 61 ± 8%, 74 ± 7%, 76 ± 6%, and 86 ± 6%, respectively. Primary patency was not associated with any of the clinical variables studied including age, sex, smoking history, history of previous vascular surgery, hypertension, coronary artery disease, diabetes mellitus, creatinine, indication for revascularization (claudication versus limb salvage), anesthesia (general versus regional), or level of distal anastomosis (popliteal versus infrapopliteal). Furthermore, there was no association between primary patency and baseline Q, baseline R _in, or stimulated Z ₀. However, using univariate analysis, patency was positively associated with decreased stimulated R _in (p= 0.002), elevated stimulated Q (p= 0.006), and decreased baseline Z ₀ (p= 0.02). Multiple regression analysis identified stimulated R _in as the only independent predictor of primary patency (p= 0.002). Stimulated R _in≥ 50 × 10³ dyne · s · cm⁻⁵ was 71% sensitive and 65% specific for graft failure. It is concluded that 1) vascular input impedance can be simply and reliably measured in the operating room, and 2) elevated stimulated R _in is an independent predictor of primary patency.