Smokers have severely disturbed peripheral micro-circulation.

AIM: The aim of this study was to determine the effect of smoking a single cigarette on the blood flow rates in capillaries and arteriovenous anastomoses (AVAs) in light and heavy smokers in: a) the skin fold between the first and second fingers, and b) the pulp of the thumb. METHODS: Five light (10-12 cigarettes/day) and 5 heavy (>20 cigarettes/day) chronic smokers participated (4 men and 6 women, median age 40.5 years). The blood flow rates were measured by the (133)Xenon local washout method (capillaries, skin fold) and the heat washout method (AVAs, thumb pulp), respectively, before, during, and after smoking of a single Prince cigarette (0.9 mg nicotine). RESULTS: The blood flow rate (f) in mL(100 g(min)(-1) [standard error, SE] in skin capillaries of light smokers was 24.4 [9], 8.9 [1.8], and 10.4 [3.3] before, during, and after smoking of one cigarette; in heavy smokers, f was 23.6 [10.9], 16.1 [5.3], and 7.1 [2.9]; f in pulp AVAs of light smokers was 130.6 [14.9], 49.2 [24.8], and 119.7 [20.9] before, during, and after smoking; in heavy smokers, the corresponding results were 134.4 [19.1], 136.2 [13.5], and 143 [15.3]. Thus, the blood flow rate in capillaries of both light and heavy smokers was higher before smoking the test cigarette than previously observed in non-smokers. In light smokers blood flow rate in AVAs decreased during smoking with a factor of 2.6, and it returned to the pre-smoking level immediately after the end of smoking the cigarette. In heavy smokers, f remained unchanged before, during, and after smoking. CONCLUSIONS: Smokers have severely disturbed peripheral microcirculation.

Haemodynamic properties of PTFE femoropopliteal bypass grafts as determined by a new magnetic resonance technique.

OBJECTIVES: To apply the automatic three dimensional paraboloid (3DP) method for measurement of wall shear stress (WSS), blood flow, blood velocity, and cross sectional graft lumen area to magnetic resonance phase contrast velocity mapping data acquired from polytetrafluoroethylene (PTFE) suprageniculate 6 mm femoropopliteal bypass grafts to determine the biomechanical and haemodynamic properties immediately and three years after implantation. MATERIALS AND METHODS: Two patient cohorts, each of ten patients, with intermittent claudication were investigated by the 3DP method, one group (A) within 36 h after implantation of a femoropopliteal graft and the other group (B) 35 months after implantation. RESULTS: The mean blood flow was 5.9 ml/s (SD: 1.6), and WSS at peak systole was 2.2 N/m2 (SD: 0.6) 5 cm upstream to the distal anastomosis for group A, and 3.7 ml/s (SD: 1.9) and 1.9 N/m2 (SD: 0.4) for Group B. The WSS varied according to the angular position of the graft circumference. The implanted grafts were not circular but had a slightly elliptical circumference with a greater anterior/posterior diameter. CONCLUSION: The 3DP method is a precise tool with subpixel resolution for determining the biomechanical and haemodynamic properties of implanted PTFE grafts, and it can be used to assess graft function immediately after implantation. It is potentially applicable for routine graft surveillance.

Determination of wall shear rate in the human carotid artery by magnetic resonance techniques.

OBJECTIVES: to measure wall shear rates around the circumference of the human carotid bifurcation throughout the heart cycle. DESIGN: prospective, open study. Materials eight healthy volunteers. METHODS: wall shear rates were determined at the carotid bifurcation using magnetic resonance techniques with high resolution and individually adjusted velocity encoding for imaging and haemodynamic mapping. Wall shear stresses were calculated assuming a constant value of 4 centiPoise. RESULTS: data suitable for postprocessing were obtained in all subjects. The main findings were: unidirectional wall shear rate waveforms and high wall shear rate (775 s(-1)+/-167 s(-1)) at the flow divider; low wall shear rate (60 s(-1+/-40 s(-1)) and a high oscillation index with huge interindividual variation (85+/-65) at the lateral wall. CONCLUSION: these are the first in vivo data describing, in detail, the forces of the blood acting on the wall of the carotid bifurcation. The results do not contradict the hypotheses associating low and oscillating wall shear stress with the development of atherosclerosis.)

Is non-specific aneurysmal disease of the infrarenal aorta also a peripheral microvascular disease?

OBJECTIVES: to examine whether aneurysmal disease of the aorta has a functional component in the peripheral microIvasculature. MATERIALS: ten normal persons; and 15 patients who had been operated on for ruptured non-specific infrarenal aortic aneurysm months to years previously were studied. METHODS: blood flow rates were measured: (a) in the subcutaneous adipose tissue of the forefoot by the(133)xenon local washout method (perfusion through nutritive capillaries supplied by arterioles with elastin in the tunica media); and (b) in the arteriovenous anastomoses of the pulp of the first toe as measured by the heat washout method (perfusion predominantly through thick-walled tubes without elastin). Perfusion rates were measured in supine subjects at heart level, at 30 cm above and at 30 cm below heart level. RESULTS: in subcutaneous adipose tissue, the capillary blood flow rate was four times higher in patients with aneurysmal disease than in normal subjects. Both groups exhibited autoregulation of blood flow and a normal veno-arteriolar sympathetic axon reflex. Blood flow rates in the arteriovenous anastomoses of the pulp did not differ between aneurysm patients and normal subjects. Autoregulation and the axon reflex were absent in the arteriovenous anastomoses of normal subjects as well as in aneurysm patients. CONCLUSIONS: non-specific aneurysmal disease of the infrarenal aorta has a peripheral functional component affecting arterioles but not arteriovenous anastomoses.

Distribution of early atherosclerotic lesions in the human abdominal aorta correlates with wall shear stresses measured in vivo.

OBJECTIVES: to study the relationship between wall shear stresses measured in vivo and early atherosclerotic lesions in the abdominal aorta. MATERIALS: eight young volunteers for in vivo wall shear-stress measurements. Abdominal aortas from 10 young adults without signs or history of atherosclerotic disease were obtained by autopsy for histomorphometric measurements. METHODS: wall shear stresses were measured in the abdominal aorta above and below the renal arteries using a magnetic resonance technique with high resolution for imaging and blood velocity mapping. At identical abdominal aortic locations, intimal thickness was measured blindly using histomorphometric techniques and correlated to wall shear-stress variables using linear-regression analysis. RESULTS: intimal thickness showed a linear decrease with mean wall shear stress (r=-0.90, p<0.01) and with maximum wall shear stress (r=-0.86, p<0.01). CONCLUSIONS: intimal thickness in the normal abdominal aorta is associated with mean, maximum and oscillating wall shear stresses. These in vivo data corroborate previous in vitro studies suggesting that low and oscillating wall shear stresses are localising factors for intimal thickening and hence the early development of atherosclerosis.

Peripheral blood flow rates and microvascular responses to orthostatic pressure changes in claudicants before and after revascularisation.

OBJECTIVES: To study the effect of arterial reconstruction for occlusive atherosclerotic disease with intermittent claudication on blood flow rate during rest and on microvascular responses to orthostatic pressure changes in the pulp skin of the first toe where arteriovenous anastomoses are numerous. MATERIAL: Eleven patients with Fontaine IIa claudication (ankle blood pressure index > 0.30) before and 7 (range: 2-11) months after intervention. METHODS: Blood flow rate was measured by the heat washout method with the toe at heart level and after passive lowering to 50 cm below this level using a Clark type electrode with thermostatically controlled cap that was fixed to the pulp of the first toe by adhesive tape. RESULTS: At heart level, blood flow rate was lower in claudicants before reconstruction as compared to a group of previously published control subjects (p = 0.0076, Wilcoxon), blood flow rate increased in claudicants from before to after intervention (p = 0.0128), and postoperative blood flow rate was like that of normals (N.S.). Before surgery, blood flow rate in claudicants increased in median with a factor of 1.79 during lowering (p < 0.0051). CONCLUSIONS: The disturbance of the microcirculatory responses to orthostatically induced pressure changes in claudicants reverted towards normal after arterial reconstruction.

Quantitation of circumferential subpixel vessel wall position and wall shear stress by multiple sectored three-dimensional paraboloid modeling of velocity encoded cine MR.

Methods are lacking for accurate, noninvasive circumferential edge detection and wall shear stress calculation. Using standard MR phase contrast sequences, parts of the velocity profiles were fitted to a multiple sectored three-dimensional paraboloid model enabling exact calculation of vessel wall position and wall shear stress in 24 locations evenly distributed around the luminal vessel wall. The model was evaluated by in vitro scans and computer simulations and applied to the common carotid artery of humans. In vitro, the luminal area of a glass tube was assessed with an error of 0.9%. Computer simulations of peak systolic data revealed errors of +/-0.9% (vessel area) and +/-3.25% (wall shear stress). The in vivo results showed substantial difference between anterior and posterior wall shear stress values due to skewed velocity profiles. A new noninvasive method for highly accurate measurement of circumferential subpixel vessel wall position and wall shear stress has been developed.

Effect of nitrendipine on renal function and on hormonal parameters after intravascular iopromide.

PURPOSE: To evaluate the effect of the low-molecular nonionic radiographic contrast agent iopromide (Ultravist) on renal function, vasoactive peptides (angiotensin II, aldosterone, arginine vasopressin, and atrial natriuretic factor (ANF)), and blood pressure, and to evaluate the influence of the calcium antagonist nitrendipine on these parameters. The findings were evaluated in a prospective double-blind and placebo-controlled randomized study. MATERIAL AND METHODS: Twenty-six patients undergoing routine aortofemoral arteriography for peripheral atherosclerotic disease were treated with nitrendipine tablets (10 mg) or placebo twice daily for a week. Angiography was performed on the fifth day of medication. Efficacy variables were determined on the day before and 2 days after arteriography. The glomerular filtration rate and renal plasma flow were measured by the constant infusion technique. Renal tubular function was estimated from the clearance of lithium. Hormones were measured by radioimmunoassays. RESULTS: Arteriography with iopromide did not change renal function. No differences between the nitrendipine and placebo groups were found in renal hemodynamics, tubular sodium handling, or blood pressure. Nitrendipine changed ANF (26.1%) compared to placebo (1.5%), whereas the other hormones were not affected. CONCLUSION: The use of iopromide for angiography did not affect renal function in normotensive patients with peripheral atherosclerotic disease. Short-term treatment with nitrendipine may lower the plasma levels of ANF but it had no effect on renal function or blood pressure. Treatment with calcium antagonists prior to arteriography with iopromide is not indicated in these patients.

Accurate noninvasive quantitation of blood flow, cross-sectional lumen vessel area and wall shear stress by three-dimensional paraboloid modeling of magnetic resonance imaging velocity data.

OBJECTIVES: We present a new method in which a priori knowledge of the blood velocity fields within the boundary layer at the vessel wall, combined with acquisition of high resolution magnetic resonance imaging (MRI) blood velocity data, allow exact modeling at the subpixel level. BACKGROUND: Methods are lacking for accurate, noninvasive estimation of blood flow, dynamic cross-sectional lumen vessel area and wall shear stress. METHODS: Using standard acquisition of MRI blood flow velocity data, we fitted all data points (n = 69) within the boundary layer of the velocity profile to a three-dimensional paraboloid, which enabled calculation of absolute volume blood flow, circumferential vessel wall position, lumen vessel area and wall shear stress. The method was tested in a 8.00 +/ 0.01-mm diameter glass tube model and applied in vivo to the common carotid artery of seven volunteers. RESULTS: In vitro the lumen area was assessed with a mean error of 0.6%. The 95% confidence interval included the specified tube dimensions. Common carotid mean blood flow was 7.42 ml/s, and mean (standard error) diastolic/systolic vessel area was 33.25 (0.72 [2.2%])/43.46 (0.65 [1.5%]) mm2. Mean/peak wall shear stress was 0.95 (0.04 [4.2%])/2.56 (0.08 [3.1%]) N/m2. CONCLUSIONS: We describe a new noninvasive method for highly accurate estimation of blood flow, cross-sectional lumen vessel area and wall shear stress. In vitro results and statistical analysis demonstrate the feasibility of the method, and the first in vivo results are comparable to published data.

Physical and mechanical properties of ePTFE stretch vascular grafts determined by time-resolved scanning acoustic microscopy.

OBJECTIVES: Determination of physical and mechanical characteristics and properties of thin-walled (0.39 mm) expanded polytetrafluoroethylene stretch vascular prostheses by time-resolved scanning acoustic microscopy (TR-SAM). MATERIALS AND METHODS: Samples of Stretch Gore-Tex were mounted on polymethylmethaacrylate substrate, and ethyl alcohol was used as acoustic couplant. A 10 MHz ultrasound transducer mounted on a SAM50 scanning acoustic microscope generated short, pulsed sound waves. Reflected signals were used for imaging and for computer analysis of time resolved wave forms acquired by a digital sampling oscilloscope to calculate physical and mechanical characteristics of the material. RESULTS: Graft wall thickness: 0.395 (0.352/0.401) mm; graft wall sound wave penetration velocity: 1111 (1083/1129) ms-1; acoustic impedance: 3.685 (2.975/4.370) 10(6) kg m-3s-1; attenuation coefficient: 0.144 (0.096/0.229) dB mm-1 MHz-1; material density: 3360 (2712/3982) kg m-3; elastic stiffness: 4.06 (3.35/4.83) GPa (median and (25/75) percentiles; n = 8 samples, 10 measurements spaced 100 microns apart in each sample). CONCLUSIONS: TR-SAM can effectively quantify ePTFE graft wall properties, and new data on graft properties have been provided. The acoustic impedance and elastic stiffness of the ePTFE graft wall are 2.2 and 1.6 times higher, respectively, than in human coronary arteries, and it is highly reflective of ultrasound.

Automatic accurate non-invasive quantitation of blood flow, cross-sectional vessel area, and wall shear stress by modelling of magnetic resonance velocity data.

OBJECTIVES: To apply a new, automatic and non-invasive method for quantification of blood flow, dynamic cross-sectional vessel area, and wall shear stress (WSS) by in vivo magnetic resonance velocity mapping of normal subjects. DESIGN: Prospective, open study. MATERIALS: Six young volunteers. METHODS: A three-dimensional paraboloid model enabling automatic determination of blood flow, vessel distensibility and WSS was applied to blood velocity determinations in the common carotid artery. Blood flow was also determined by a manual edge detection method. RESULTS: Using the new method, the common carotid mean blood flow was 7.28 (5.61-9.63) (mean (range)) ml/s. By the manual-method blood flow was 7.21 (5.55-9.60) ml/s. Mean luminal vessel area was 26% larger in peak systole than in diastole. Mean/peak WSS was 0.82/2.28 N/m2. Manually and automatically determined flows correlated (r2 = 0.998, p < 0.0001). WSS and peak centre velocity were associated (r2 = 0.805, p < 0.0001). CONCLUSIONS: Blood flow, luminal vessel area dilatation, and WSS can be determined by the automatic three-dimensional paraboloid method. The hypothesis of association between peak centre velocity and WSS was not contradicted by the results of the present study.

In vivo wall shear stress measured by magnetic resonance velocity mapping in the normal human abdominal aorta.

OBJECTIVE: To apply a new non-invasive method for quantification of in vivo wall shear stress (WSS) by magnetic resonance (MR) FAcE velocity mapping and measure WSS in the human abdominal aorta. DESIGN: Prospective, open study. MATERIAL: Six volunteers. METHODS: MR FAcE velocity method was developed for measurements of mean, maximum, minimum WSS and oscillating shear index (OSI) values at the anterior and posterior walls of suprarenal and infrarenal abdominal aorta. RESULTS: The mean, maximum and minimum WSS values were 0.63/0.28, 4.07/2.72 and -0.71/-1.00 N/m2, respectively, in the suprarenal/infrarenal aorta. The mean WSS was 0.35 N/m2 (p < 0.001) and the maximum WSS was 1.36 N/m2 (p < 0.0001) lower in the infrarenal aorta than in the suprarenal aorta. Mean, maximum minimum WSS and OSI values in the infrarenal position differed (p < 0.01) between the anterior and posterior walls. CONCLUSION: WSS can be determined in vivo by MR FAcE velocity technique. Since the lowest WSS values were measured in the infrarenal, posterior blood-to-wall interface, the theory of more pronounced atherosclerosis development in low and oscillating WSS domains was not contradicted by the results of the present study.

Blood flow rate during orthostatic pressure changes in the pulp skin of the first toe.

OBJECTIVES: Determination of the local regulation of cutaneous blood flow through nutritive capillaries and through arteriovenous anastomoses of the pulp of the first toe in response to passively induced orthostatic blood pressure changes in normal subjects and in patients with occlusive atherosclerotic disease. MATERIAL: Six normal subjects, seven patients with unilateral, crural intermittent claudication and six patients with unilateral, chronic critical ischaemia. METHODS: Blood flow rates were measured in supine subjects by the heat washout method (the sum of blood flow rate in arteriovenous anastomoses and blood flow rate in nutritive capillaries) and by the 133Xenon washout method (blood flow rate in nutritive capillaries) after local, atraumatic labelling. Measurements were made with (a) the toe passively elevated to 50 cm above heart level, (b) at heart level and (c) passively lowered to 50 cm below heart level. RESULTS: Autoregulation of nutritive blood flow was present in normal subjects and in claudicants, but the local sympathetic veno-arteriolar axon reflex was absent in both groups. In patients with critical ischaemia blood flow rate was the same in the supine position and during lowering in arteriovenous anastomoses and in nutritive capillaries. The arteriovenous anastomoses had distinct and characteristic reaction patterns in response to lowering in each of the three examined groups and to elevation in normal subjects and in patients with intermittent claudication (not measured in patients with critical ischaemia). CONCLUSIONS: The microvascular responses to changes of orthostatic blood pressure differed among the three groups (normal subjects, patients with intermittent claudication, patients with critical chronic leg ischaemia). The heat washout method may be used to detect the functional significance of occlusive atherosclerotic disease.

Effect of felodipine on renal function and vasoactive hormones in infrarenal aortic surgery.

We have examined the possible renoprotective effect of felodipine 5 mg orally, given daily for 5 days before operation, in 29 patients undergoing elective infrarenal aortic surgery in a randomized, blinded and placebo-controlled study. Effective renal plasma flow (ERPF), glomerular filtration rate (GFR), urine output, fractional sodium clearance and plasma concentrations of angiotensin II, aldosterone, arginine vasopressin and atrial natriuretic peptide did not differ between the felodipine and placebo groups. ERPF and GFR were not reduced after operation in the placebo group. In the felodipine group, GFR was higher 24 h after operation compared with before operation. We conclude that increased GFR in the felodipine group, measured 24 h after operation, may indicate a beneficial effect of felodipine but in the present context this was not clinically important. Felodipine had no significant effect on vasoactive hormones.