Cemil M. Purut

Myointimal thickening in experimental vein grafts is dependent on wall tension

This study examines the relative contributions of intraluminal pressure, blood flow, wall tension, and shear stress to the development of myointimal thickening in experimental vein grafts. To study these different hemodynamic parameters, several experimental models were created in 30 New Zealand White rabbits separated into six groups: common carotid interposition vein grafts harvested at 4 weeks (VG-4) or 12 weeks (VG-12), common carotid-linguofacial vein arteriovenous fistulas harvested at 4 weeks (AVF-4) or 12 weeks (AVF-12), AVFs with partial outflow obstruction harvested at 4 weeks (AVFobs), and combination VG-AVFs in series harvested at 4 weeks (VGAVF). Blood pressure and flow in the graft or vein were measured by use of a transducer-tipped pressure catheter and electromagnetic flow meter. At harvest, veins were perfusion-fixed and proximal, middle, and distal sections were subjected to computerized morphometric analysis. Vein grafts were characterized by a high mean pressure (VG-4, 51 +/- 4; VG-12, 62 +/- 3 mm Hg), low mean flow (VG-4, 17 +/- 1; VG-12, 16 +/- 4 ml/min), large luminal area (VG-4, 19.7 +/- 2.4; VG-12, 19.3 +/- 3.9 mm2), high wall tension (VG-4, 17.0 +/- 1.5; VG-12, 19.5 +/- 2.4 x 10(3) dyne/cm), low shear stress (VG-4, 0.75 +/- 0.13; VG-12, 0.96 +/- 0.38 dyne/cm2), and a high degree of myointimal thickening (VG-4, 5.89 +/- 0.90; VG-12, 4.72 +/- 0.83 mm2). Arteriovenous fistulas were characterized by a low mean pressure (AVF-4, 5 +/- 1, AVF-12, 6 +/- 2 mm Hg), elevated blood flow (AVF-4, 82 +/- 16; AVF-12, 82 +/- 17 ml/min), small luminal area (AVF-4, 2.43 +/- 0.58; AVF-12, 7.14 +/- 2.68), low wall tension (AVF-4, 0.62 +/- 0.19; AVF-12, 0.89 +/- 0.24 x 10(3) dyne/cm), elevated shear stress (AVF-4, 108 +/- 32; AVF-12, 71 +/- 50 dyne/cm2), and decreased myointimal area (AVF-4, 1.18 +/- 0.26; AVF-12, 1.90 +/- 0.55 mm2). The addition of outflow obstruction to AVFs (AVFobs) resulted in elevated pressure (48 +/- 2 mm Hg), decreased flow (17 +/- 4 ml/min), larger luminal area (8.71 +/- 2.31 mm2), elevated wall tension (10.3 +/- 1.7 x 10(3) dyne/cm), and a degree of myointimal thickening approaching that of vein grafts (3.79 +/- 0.66 mm2).(ABSTRACT TRUNCATED AT 400 WORDS)

Intraoperative Management of Severe Endobronchial Hemorrhage

Endobronchial hemorrhage due to pulmonary artery perforation by a Swan-Ganz catheter developed during coronary artery bypass grafting while weaning from cardiopulmonary bypass. After reinstitution of cardio-pulmonary bypass with pulmonary artery venting, bleeding was localized to the right lower lobe bronchus using fiberoptic bronchoscopy. A Fogarty embolectomy catheter was inflated in the bronchus to tamponade successfully only the right lower lobe. This case illustrates a method of distal bronchial blockade for maximal retention of pulmonary function and avoidance of pulmonary resection.

Effects of Pulsatile Perfusion on Human Saphenous Vein Vasoreactivity: A Preliminary Report

This study examined the effects of exposure to arterial blood pressure and flow on human saphenous vein catecholamine sensitivity. Unused portions of saphenous vein from eight patients undergoing peripheral bypass procedures were mounted parallel in a specially designed organ culture apparatus and perfused with tissue culture medium with 95% CO(2) at 37 degrees C. One segment was fixed between two cannulas while the medium was gently agitated (control) and the other was actively perfused via a pulsatile pump system at a rate of 60 beats/min, peak pressure of 100 mmHg and peak flow of 200 ml/min (pulsed; mean pressure 60 mmHg; mean flow 115 ml/min). After 48 h, vein segments were removed and tested for in vitro isometric contraction in response to KCI, norepinephrine and histamine, and relaxation in response to acetylcholine, calcium ionophore A23187, and sodium nitroprusside. There were no differences in mean(s.e.m.) maximal contraction in response to KCI (control 0.61(0.16) g versus pulsed 0.72(0.27)g; P = n.s.), norepinephrine (control 1.00(0.56) g versus pulsed 1.51(0.54) g; P= n.s.), or histamine (control 1.47(0.85) g versus pulsed 1.95(0.64) g; P= n.s.). However, pulsed veins exhibited increased sensitivity to both norepinephrine (control -logED50 6.20(0.23) versus pulsed mean(s.e.m.) 6.60(0.17); P< 0.05) and histamine (control -logED(50) 5.60(0.27) versus pulsed 6.24(0.20); P = 0.05). Pulsed veins exhibited slightly less acetylcholine-induced relaxation although the difference did not reach statistical significance (control mean(s.e.m.) relaxation at 1 x 10(6)M 9.2(14.0)% versus pulsed -13.3(6.4)%; P = n.s.). There were no differences in relaxation in response to either A23187 (control 1 x 10-(4)M 178(19)% versus pulsed 191(68)% or sodium nitroprusside (control 225(15)% versus pulsed 254(17)%; P = n.s.). The data presented herein indicate that exposure of human saphenous vein to the hemodynamics of the arterial environment for 48 h results in catecholamine supersensitivity while contractile and relaxant function are not affected.

Quantitation of vascular outflow by measurement of impedance

One of the most important determinants of graft patency is the degree and character of vascular outflow. This study was designed to evaluate input impedance as a functional assessment of the outflow bed of vascular grafts. Four distinct outflow environments were created for external jugular vein conduits in 42 New Zealand white rabbits. Vein grafts (n = 14) were fashioned as end-to-side common carotid interposition bypass grafts. Arteriovenous fistulas (n = 15) were created by side-to-side anastomosis of the distal common carotid artery and linguofacial vein. Arteriovenous fistulas with outflow obstruction (n = 7) were fistulas with a metal clip partially obstructing the distal outflow channel (1 mm lumen). Vein graft/arteriovenous fistula combinations (n = 6) consisted of a vein graft and arteriovenous fistula in series. Pressure and flow in the external jugular vein were measured, and input impedance spectra were calculated by Fourier methods. By use of a PC-based acquisition and processing system, impedance results for 20 cardiac cycles could be obtained in approximately 10 minutes. The results revealed that vein grafts typically demonstrated high resistance to steady state flow (Rin = 235 +/- 50 x 10(3) dyne . sec/cm-5) and steadily decreasing impedance to pulsatile flow resulting in a characteristic impedance (Z0; average of fourth to tenth harmonics) of 35.5 +/- 8.0 x 10(3) dyne . sec/cm-5. Phase angle values were usually negative, especially at low harmonics (first harmonic phase angle = -1.11 +/- 0.10 radians) indicating that flow led pressure. In contrast, arteriovenous fistula Rin was minimal (6.3 +/- 1.4 x 10(3) dyne . sec/cm-5; p less than 0.05 compared to vein graft, and the impedance was flat across the frequency spectrum (Z0 = 8.5 +/- 1.5 x 10(3) dyne . sec/cm-5; p less than 0.05) with pressure and flow nearly in phase (first harmonic phase angle = -0.05 +/- 0.10 radians). Creation of outflow obstruction in arteriovenous fistulas resulted in significantly elevated Rin (136 +/- 41 x 10(3) dyne/sec . cm-5; p less than 0.05 compared to arteriovenous fistula and Z0 (23 +/- 9 x 10(3) dyne . sec/cm-5, p less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Pulmonary arterial impedance after single lung transplantation

Single lung transplantation (SLT) is emerging as definitive therapy for end-stage pulmonary disease of varying etiology, yet a complete description of the hemodynamic properties of the transplanted lung has not been reported. In this study, Fourier analysis was used to calculate the pulmonary arterial (PA) impedance spectrum before and immediately after SLT to define precisely the pulmonary pressure-flow relationship. Median sternotomies were performed in 18 dogs (donors): an ultrasonic flow probe was placed around the PA and micromanometers were placed in the PA and left atrium (LA). Control PA pressure and flow (PAQ) and LA pressure were measured during transient occlusion of the right PA. The lungs were harvested using cold modified Euro-Collins solution for preservation. After thoracotomy and pneumonectomy, left SLT was performed in 18 recipient dogs with a mean ischemic time of 179 +/- 6 min. After reperfusion for 1 hr, PA pressure and flow data were again collected. Characteristic impedance (Z0), a measure of resistance to pulsatile flow, was compared to input resistance (Rin), a measure of resistance to mean flow, and pulmonary vascular resistance (PVR), the conventional index. Rin is defined as the zeroth harmonic of the impedance spectrum and Z0 as the mean of impedance moduli from 2-12 Hz. All recipients survived transplantation. Both PVR and Rin increased significantly after transplantation (11 +/- 1 vs 19 +/- 3 Wood U, P less than 0.05, and 1352 +/- 121 vs 1964 +/- 244 dyne.sec.cm-5, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Input Impedance of Revascularized Skeletal Muscle, Renal, and Mesenteric Vascular Beds

Input impedance describes the relationship between pressure and flow in a vascular system and, hence, characterizes the outflow bed. The purpose of this investigation was to measure input impedance spectra in vascular reconstructions of skeletal muscle, renal, and mesenteric beds. Input impedance was measured in 107 vascular reconstructions in 96 patients. 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 mesenteric (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 after reperfusion. For impedance calculation, simultaneously acquired intraluminal pressure (transducer-tipped pressure catheter) and blood flow (electromagnetic probe) waveforms of ten-second duration were digitized at 200 Hz and subjected to Fourier transformation in near real-time. AF grafts exhibited the highest blood flow (443 ± 72.8 mL/minute) 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 similar (inverse) trend was observed with respect to resistance (Rin), ie, MES≈AF<REN<<FP<FD<<IM(15.7 ± 2.2=23.7 ± 6.5<69.2 ± 12.2 < < 120 ± 31.9 < 137 ± 13.0 < < 337 ± 75.8 x 103 dyne•s•cm-5). As expected, AF grafts exhibited the lowest characteristic impedance (Z0 3.5 ± 0.8 x 103 dyne•s•cm-5). However, the Z0 of REN (20.2 ± 3.7 x 103 dyne•s•cm-5) grafts exceeded that of FP and MES grafts (10.5 ± 1.1 and 12.4 ± 4.0 x103 dyne•s•cm-5) and more closely approximated that of FD (22.2 ± 2.2 x 103 dyne•s•cm-5). The highest Z0 was seen in IM grafts (42.1 ± 15.8 x 103 dyne•s•cm-5). Therefore, the highest ratios of Z0/Rin were observed with MES (0.75 ± 0.23) and REN (0.33 ± 0.04) grafts as compared with the other groups (AF 0.23 ± 0.03, FP 0.12 ± 0.13, FD 0.19 ± 0.02, IM 0.16 ± 0.06). As expected, Rin of vascular reconstructions follows the general trend of MES ≈ AF < REN < < FP < FD < < IM. However, examination of the high-frequency components of the impedance spectra reveals that Z0 follows a different pattern, AF < FP MES < FD ≈ REN < < IM and the ratio of ZO/Rin is highest in REN and MES vascular beds compared with skeletal muscle beds. Thus, although the REN and MES beds are “privileged” (ie, maximally dilatated with low arteriolar tone), the intrinsic properties of the graft and larger blood vessels are no different than those of a femorodistal bypass.

Determination of vascular input impedance in near real-time using a portable microcomputer

A method for determining vascular input impedance using a portable laptop computer coupled to more conventional laboratory measurement equipment is described. The major impediment overcome in the clinical implementation of this microcomputer-based system was the rapid Fourier transformation of pulsatile pressure and flow waveforms from time domain to frequency domain. To meet this need, software was written to allow gating of data collection and Fourier analysis in a continually repetitive, alternating manner in synchrony with the cardiac cycle. High computational speed was achieved by using a math coprocessor and limiting the Fourier analysis to hemodynamically important harmonics of heart rate.<<ETX>>

An Improved Apparatus For In Vitro Study Of Mitral Valve Dynamics

A model left ventricle was developed for the study of mitral valve fluid and mechanical dynamics. Freshly excised human and animal mitral valves were mounted in the apparatus and subjected to conditions simulating cardiac disease states. Control was obtained over mitral valve geometry, atrial and ventricular pressure, ventricular afterload (both in terms of resistance and compliance), heart rate, and stroke volume. Dynamic transmitral flow was measured using an electromagnetic flow probe positioned above the valve annulus. Mapping of forward and regurgitant transmitral flow was possible using both pulsed and continuous wave Doppler uleasonography. In addition, dynamic papillary muscle tension was measured using highly sensitive cantilever load cells. This apparatus will allow a more thorough assessment of mitral valve dysfunction in various disease states than has heretofore been possible.