INPUT IMPEDANCE OF REVASCULARIZED SKELETAL-MUSCLE, RENAL, AND MESENTERIC VASCULAR BEDS

Input impedance describes the relationship between pressure and flow i n a vascular system and, hence, characterizes the outflow bed. The pur pose of this investigation was to measure input impedance spectra in v ascular reconstructions of skeletal muscle, renal, and mesenteric beds . Input impedance was measured in 107 vascular reconstructions in 96 p atients. Reconstructions were performed at the aortofemoral/aortoiliac (AF, n = 20), femoropopliteal (FP, n = 18), femorodistal (FD, n = 41) , infrapopliteal-inframalleolar (IM, n = 6), renal (REN, n = 16), or m esenteric (MES, n = 6) level. Grafts were constructed from autologous vein in all cases except AF bypasses in which bifurcated woven Dacron grafts were employed. Input impedance was measured intraoperatively af ter reperfusion. For impedance calculation, simultaneously acquired in traluminal pressure (transducer-tipped pressure catheter) and blood fl ow (electromagnetic probe) waveforms of ten- second duration were digi tized at 200 Hz and subjected to Fourier transformation in near real-t ime. AF grafts exhibited the highest blood flow (443 +/- 72.8 mL/minut e) followed by MES (300 +/- 30.4), REN (172 +/- 43.9), FP (91.6 +/- 20 .0), FD (59.3 +/- 5.09), and IM grafts (22.4 +/- 5.44 mL/minute). A si milar (inverse) trend was observed with respect to resistance (R(in)), ie, MES approximate to AF < REN < < FP < FD < < IM (15.7 +/- 2.2 appr oximate to 23.7 +/- 6.5 < 69.2 +/- 12.2 < < 120 +/- 31.9 < 137 +/- 13. 0 < < 337 +/- 75.8 x 10(3) dyne . s . cm(-5)). As expected, AF grafts exhibited the lowest characteristic impedance (Z(0) 3.5 +/- 0.8 x 10(3 ) dyne . s . cm(-5)). However, the Z(0) of REN (20.2 +/- 3.7 x 10(3) d yne . s . cm(-5)) grafts exceeded that of FP and MES grafts (10.5 +/- 1.1 and 12.4 +/- 4.0 x 10(3) dyne . s . cm(-5)) and more closely appro ximated that of FD (22.2 +/- 2.2 x 10(3) dyne . s . cm(-5)). The highe st Z(0) was seen in IM grafts (42.1 +/- 15.8 x 10(3) dyne . s . cm(-5) ). Therefore, the highest ratios of Z(0)/R(in) were observed with MES (0.75 +/- 0.23) and REN (0.33 +/- 0.04) grafts as compared with the ot her groups (AF 0.23 +/- 0.03, FP 0.12 +/- 0.13, FD 0.19 +/- 0.02, IM 0 .16 +/- 0.06). As expected, R(in) of vascular reconstructions follows the general trend of MES approximate to AF < REN < < FP < FD < < IM. H owever, examination of the high-frequency components of the impedance spectra reveals that Z(0) follows a different pattern, AF < FP approxi mate to MES < FD approximate to REN < < IM and the ratio of Z(0)/R(in) is highest in REN and MES vascular beds compared with skeletal muscle beds. Thus, although the REN and MES beds are ''privileged'' tie, max imally dilatated with low arteriolar tone), the intrinsic properties o f the graft and larger blood vessels are no different than those of a femorodistal bypass.