Effect of pulsatile arterial diameter variations on blood flow estimated by Doppler ultrasound

High-resolution measurements of common carotid and femoral arterial diameters have been performed by ultrasound echo devices. When combined with pulsed Doppler measurements of cross-sectional averaged velocity in the same vessels, exact calculations of flow were made possible. The median peak-to-peak pulsatile diameter variations were 0.19 mm (2.8 per cent) in the femoral artery and 0.49mm (6.7 per cent) in the common carotid artery. Flow values were calculated either by taking the time-averaged diameter as a constant value, or by taking into account the dynamic variations in diameter. In comparing the two values, a quantification of the magnitude of error introduced by the averaging of the diameter was made possible. An error in the range 1.5–3.8 per cent was found for the femoral artery, whereas the error in the common carotid artery was in the range 0.4–3.6 per cent despite the larger amplitude of the pulsations in this vessel.     

Influence of transmural pressure on myogenic responses of isolated cerebral arteries of the rat

We examined the diameter responses of isolated and pressurized posterior cerebral artery branches to various static and dynamic pressure alterations. These vessels, dissected from an anatomically identifiable location in the rat brain, developed tone when placed in a normal calcium physiological salt solution (1.6 mM Ca-PSS). Following a series of transmural pressure steps (Δp) of 25 or 50 mm Hg completed in 1–2 s and made every 5 min, they attained additional tone resulting in a mean luminal diameter of 139 μm at 100 mm Hg which was 35% less than their relaxed size measured in 1 mM EGTA-PSS. Continuous measurements of wall thickness and lumen diameter were obtained using a video electronic system in 1–2 mm long arterial segments, and autoregulatory gain factors calculated. Myogenic responses were obtained from each of 6 vessels taken from 6 WKY rats. Diameters following the step pressure changes were usually stable within 2–4 min. The data defined a myogenic regulatory pressure range from 49–145 mm Hg. Gain values averaged about 17% of that necessary for these arteries to maintain perfect flow autoregulation. Our results for myogenicity are comparable with the pressure range for blood flow autoregulation reported by others for the rat. We conclude that myogenic mechanisms, at least in this size artery, are partly responsible for flow autoregulation, and that they are supplemented by metabolic mechanisms operative in the intact rat brain. Research supported by grant HL 17335 from the NHLBI.     

Local elasticity imaging of vascular tissues using a tactile mapping system

This study aimed to map the elasticity of a natural artery at the micron level by using a tactile mapping system (TMS) that was recently developed for characterization of the stiffness of tissue slices. The sample used was a circumferential section (thickness, approximately 1 mm) of a small-caliber porcine artery (diameter, approximately 3 mm). Elasticity was measured with a probe of diameter 1 μm and a spatial resolution of 2 μm at a rate of 0.3 s per point, without significant sample invasion. Topographical measurements were also performed simultaneously. Wavy regions of high elasticity, layered in the circumferential direction, were measured at the tunica media, which was identified as an elastin-rich region. The Young’s modulus of the elastin-rich region in the media was 50.8 ± 13.8 kPa, and that of the elastin-rich region of the lamina elastica interna was 69.0 ± 12.8 kPa. Both these values were higher than the Young’s modulus of the other regions in the media, including smooth muscle cells and collagen fibrils (17.0 ± 9.0 kPa). TMS is simple and inexpensive to perform and allows observation of the distribution of the surface elastic modulus at the extracellular matrix level in vascular tissue. TMS is expected to be a powerful tool in evaluation of the maturation and degree of reconstruction in the development of tissue-engineered or artificial tissues and organs.     

Modelling the sampling volume for skin blood oxygenation measurements

The absolute quantified measurement of haemoglobin skin blood saturation from collected reflectance spectra of the skin is complicated by the fact that the blood content of tissues can vary both in the spatial distribution and in the amount. These measurements require an understanding of which vascular bed is primarily responsible for the detected signal. Knowing the spatial detector depth sensitivity makes it possible to find the best range of different probe geometries for the measurements of signal from the required zones and group of vessels inside the skin. To facilitate this, a Monte Carlo simulation has been developed to estimate the sampling volume offered by fibre-optic probes with a small source-detector spacing (in the current report 250 μm, 400 μm and 800 μm). The optical properties of the modelled medium are taken to be the optical properties of the Caucasian type of skin tissue in the visible range of the spectrum. It is shown that, for a small source-detector separation (800 μm and smaller), rough boundaries between layers of different refractive index can play a significant role in skin optics. Wavy layer interfaces produce a deeper and more homogeneous distribution of photons within the skin and tend to suppress the direct channelling of photons from source to detector. The model predicts that a probe spacing of 250 μm samples primarily epidermal layers and papillary dermis, whereas spacings of 400–800 μm sample upper blood net dermis and dermis.     

Implantation mechanics of tungsten microneedles into peripheral nerve trunks

50 μm tungsten microneedles have been used as a means to introduce longitudinal intra-fascicular electrodes (LIFE) into small peripheral nerve fascicles. However, recent attempts to implant LIFEs into larger, human sized nerves with the same needles resulted in buckling failure of the introducer needle. In the present study, the implantation mechanics (penetration forces and penetration dimple depth) of electrosharpened tungsten microneedles ranging in diameters from 50 to 200 μm into freshly excised porcine peripheral nerve trunks between 3 and 5 mm in thickness was characterized to understand the implantation mechanics and to find the minimum needle diameter that would result in successful penetration. The implant success rate was found to be highest with needles having diameters between 80 and 120 μm. The force of successful penetration ranged from 7.2 ± 0.6 to 71.8 ± 19.5 mN, and increased monotonically with needle diameter. It also had a tendency to increase with increasing tip angles. The dimple depth for successful penetrations varied between 1 and 1.5 mm, and also tended to increase with increasing tip angles, although it was generally not affected by increased needle diameter. Only the smallest penetration dimple depth was found to be different from the others and was associated with the smallest diameter needle (50 μm). Analysis based on the critical buckling force and the measured implantation forces indicated a 15 mm long needle of 80 μm diameter would be necessary and sufficient to penetrate medium to large sized nerves.     

Accuracy of Microvascular Measurements Obtained From Micro-CT Images

Early changes in branching geometry of microvasculature and its associated impact on the perfusion distribution in diseases, especially those in which different branching generations are affected differently, require the ability to analyze intact vascular trees over a wide range of scales. Micro-CT offers an excellent framework to analyze the microvascular branching geometry. Such an analysis requires methods to be developed that can accurately characterize branching properties, such as branch diameter, length, branching angle, and branch interconnectivity of the microvasculature. The purpose of this article is to report the results of a study of two human intramyocardial coronary vascular tree casts in which the accuracy of micro-CT vascular imaging and its analysis are tested against measurements made through an optical microscope (used as the “gold-standard”). Methods related to image segmentation of the vascular lumen, vessel tree centerline extraction, individual branch segment measurement, and compensating for the non-ideal modulation transfer function of micro-CT scanners are presented. The extracted centerline accurately characterized the hierarchical structure of the vascular tree casts in terms of “parent–branch” relationships which allowed each interbranch segments’ dimensions to be compared to the optical measurement method. The comparison results show a close to ideal 1:1 relationship for both length and diameter measurements made by the two methods. Combining the results from both specimens, the standard deviation of the difference between measurement methods was 19 μm for the measurement of interbranch segment diameters (ranging from 12 to 769 μm), and 172 μm for the measurement of interbranch segment lengths (ranging from 14 to 3252 μm). These results suggest that our micro-CT image analysis method can be used to characterize a vascular tree’s hierarchical structure, and accurately measure interbranch segment lengths and diameters.     

Simulating coronary arteries in x-ray angiograms

Clinical validation of quantitative coronary angiography (QCA) algorithms is difficult due to the lack of a simple alternative method for accurately measuring in vivo vessel dimensions. We address this problem by embedding simulated coronary artery segments with known geometry in clinical angiograms. Our vessel model accounts for the profile of the vessel, x-ray attenuation in the original background, and noise in the imaging system. We have compared diameter measurements of our computer simulated arteries with measurements of an x-ray Telescopic-Shaped Phantom (XTSP) with the same diameters. The results show that for both uniform and anthropomorphic backgrounds there is good agreement in the measured diameters of XTSP compared to the simulated arteries (Pearson's correlation coefficient 0.99). In addition, the difference in accuracy and precision of the true diameter measures compared to the XTSP and simulated artery diameters was small (mean absolute error across all diameters was < or = 0.11 mm +/- 0.09 mm).     

Spherometer measurements of human hip-joint geometry

The accuracy of sphericity measurements on human hip joints was studied with two types of 3-legged micrometer gauges. Initial calibration work on metal cylinders (30–65 mm diameter) achieved an error range of 4–8%. Correction was then made for this degree of error on a nomogram which reduced the errors in subsequent measurements to 0·–1·5%. The problem was that the percentage error in the micrometer reading was directly reflected in the percentage error in diametrical calculation. To achieve an acceptable accuracy of ±1%, the micrometer readings had to be accurate to within ±(15–23) μm, i.e. 0·0006–0·0009 in. (average of five measurements). This was only achieved in the metal calibration studies ±(0–15) μm, but not for the hip joint or its replicas, ±(7–109) μm. It was concluded that 3-legged gauges were a very unreliable method of taking diametrical measurements from human joint surfaces.     

Usefulness of polyurethane for small-caliber vascular prostheses in comparison with autologous vein graft

 For long-term patency of small-caliber vascular prostheses, antithrombogenicity and microporous structure are very important. We have developed a new technique to give a microporous structure to a polyurethane vascular prosthesis that has favorable antithrombogenicity. A solution of tetrahydrofuran/dimethylformamide (1 : 1) containing 13 wt% of segmented polyurethane (PTMG + MDI) and calcium carbonate (mean particle size, 8 μm) was dipcoated on a glass mandrel 3 mm in diameter and placed into distilled water. After the glass mandrel was removed, the polyurethane tube was placed into hydrochloric acid, and a microporous polyurethane vascular prosthesis was produced. Prostheses made in this fashion, and autologous jugular vein grafts were implanted into the femoral artery and the carotid artery of mongrel dogs. Patency was recognized on the arteriogram and duplex scanning (ultrasonography), and the removed grafts were inspected macroscopically and microscopically. This prosthesis was similar in elasticity to a vein graft. Patency was defined 8 weeks after implantation, and this prosthesis showed less intimal hyperplasia than the autologous vein graft. The new polyurethane prosthesis might be useful for small-caliber vascular reconstruction. Received: December 18, 2000 / Accepted: January 28, 2002     

Simulation of intraluminal gas transport processes in the microcirculation

This study attempts to measure the hyperthermic response of individual microvessels in skeletal muscle tissue subject to local heating and then to predict the enhancement in thermal conductivity that results from the observed changes in vascular diameter and flow. In contrast to existing studies, which have tried to relate changes in tissue thermal conductivity to local blood perfusion using thermal clearance and self-heated thermistor techniques, we have developed a two-dimensional muscle tissue preparation in which the hyperemic response has been quantified by measuring thein vivo changes in diameter and blood flow of 1A to 4A generation vessels of rat cremaster muscle when the temperature was raised in 2° increments from 34 to 42°C. Only 3A and 4A vessels showed vasodilation when subject to hyperthermia, indicating that the measured increase in flow in the 1A and 2A vessels was the result of a decrease in downstream resistance. Our cremaster muscle preparations have also been used to obtain the first detailed anatomic measurements of the number density and length of countercurrent vessel pairs between 50–200 μm diameter. These combined measurements have been used to establish the limits of validity of the Weinbaum-Jiji theory. Our experimental data indicate that the Weinbaum-Jiji expression forK _eff is valid in cremaster muscle and cat mesentery tissue for both normal and hyperthermic conditions provided the largest vessels are <200 μm in diameter. The theory predicts that significant enhancements ink _eff start to occur for vessels that are 70 μm in diameter or larger, that a 2.5-fold increase ink _eff can be achieved for a maximally dilated 200 μm diameter 1A vessel pair in cremaster muscle of larger rats, and a 6-fold increase is predicted for maximally dilated 200 μm diameter vessels in the cat mesentery. The experiments also show that maximally dilated 1A to 4A vessels in the microcirculation closely satisfy the conditionQ(flow)/(2a)³=constant, which is consistent with the hypothesis that there is an adaptive regulation of vessel diameter which keeps the wall shear stress nearly constant during temporal changes in flow.     

Can blood flow in separate small tubes be quantitatively assessed by high-resolution laser Doppler imaging?

A method is suggested for quantitative flow assessment of whole-blood perfusing tubes with diameters in the range from 500 μm to 1.5 mm, for velocities below 9 mm s⁻¹. The algorithm is based both on the Doppler broadening of backscattered laser light and the magnitude of the diameter of the perfused tube. A bandwidth-modified high-resolution laser Doppler perfusion imaging system is used to record the Doppler broadening. A flow model, consisting of a linearly narrowing tube (inner diameter 620–1330 μm), is connected to a precision infusion pump and perfused by human whole blood of volume flows ranging from 0 to 6.6 mm³ s⁻¹. empirical data are fitted into a regression model, and the parameters of the algorithm can be determined, resulting in a correlation coefficient of 0.975 between the predicted and true volume flows. Using this algorithm, volume flows in tubes of inner diameters of 500 μm, 750 μm and 1.4 mm are predicted, with accuracies corresponding to correlation coefficients of 0.994, 0.993 and 0.996.     

Comparative study of femoral diaphyseal morphometry in two male populations, in France and a French West Indies island: an example of clinical relevance of comparative anatomy for orthopedic practice

Our aim, through a comparative study of two populations, one European and the other Afro-Caribbean, was to find out whether there were differences in radiographic measurements of femoral diaphyseal canal diameter, thickness of the medial and lateral cortex, and global diaphyseal diameter. We studied the nailed femurs of adult males in a population of 54 Europeans and 52 Afro-Caribbeans. Both populations were comparable in terms of age, height and weight. The measurements were taken with a ruler on the narrowest area of the hourglass, the isthmus, on an antero-posterior radiograph. The diameter of the femoral canal was classified into three intervals: <13 mm, 13–14 mm and >14 mm. The femoral canal diameter was significantly larger in the European patients, 14.3 (11–19) versus 13.4 (11–15.6), while the thickness of the lateral cortex was significantly larger in the Afro-Caribbean patients, 8.50 (6–12) versus 7.72 (5.4–11.5). Patient distribution according to the intervals was different in both groups: 59% of the Afro-Caribbeans were in the average interval versus 24.1% of the Europeans. For nearly 53.7% of the Europeans, the diameter of the femoral canal fell in the last interval versus 15.4% of the Afro-Caribbeans. The fact that the femoral canal is narrower in the Afro-Caribbean population may be linked to a thicker lateral cortex. The diameters of the nails used were larger in the European population, 12.6 mm (10–15) versus 12.1 mm (11–14) in the Afro-Caribbean population. The global diameters of both populations’ femurs were similar (28.9 mm for the European sample vs. 29 mm). The present study may have an impact on the implants used in the orthopedic surgery (intramedullary nailing, arthroplasty implants). The range of usable implants must be complete and there must be precise pre-operative planning. A study of computed tomography scans could complement our measurements.     

Static and dynamic changes in carotid artery diameter in humans during and after strenuous exercise

Arterial baroreflex function is altered by dynamic exercise, but it is not clear to what extent baroreflex changes are due to altered transduction of pressure into deformation of the barosensory vessel wall. In this study we measured changes in mean common carotid artery diameter and the pulsatile pressure: diameter ratio (PDR) during and after dynamic exercise. Ten young, healthy subjects performed a graded exercise protocol to exhaustion on a bicycle ergometer. Carotid dimensions were measured with an ultrasound wall-tracking system; central arterial pressure was measured with the use of radial tonometry and the generalized transfer function; baroreflex sensitivity (BRS) was assessed in the post-exercise period by spectral analysis and the sequence method. Data are given as means ± s.e.m . Mean carotid artery diameter increased during exercise as compared with control levels, but carotid distension amplitude did not change. PDR was reduced from 27.3 ± 2.7 to 13.7 ± 1.0 μm mmHg⁻¹. Immediately after stopping exercise, the carotid artery constricted and PDR remained reduced. At 60 min post-exercise, the carotid artery dilated and the PDR increased above control levels (33.9 ± 1.4 μm mmHg⁻¹). The post-exercise changes in PDR were closely paralleled by those in BRS (0.74 ≤ r ≤ 0.83, P < 0.05). These changes in mean carotid diameter and PDR suggest that the mean baroreceptor activity level increases during exercise, with reduced dynamic sensitivity; at the end of exercise baroreceptors are suddenly unloaded, then at 1 h post-exercise, baroreceptor activity increases again with increasing dynamic sensitivity. The close correlation between PDR and BRS observed at post-exercise underlies the significance of mechanical factors in arterial baroreflex control.     

介入治疗股骨头缺血性坏死的应用解剖

目的 介入治疗股骨头缺血性坏死提供解剖学基础.方法 选用经乳胶灌注防腐成人下肢标本20侧及新鲜成人下肢标本2侧,观察股深动脉的起点方位及分支类型,测量股深动脉及各分支长度和外径以及各分支起始部的角度.结果 股深动脉主要从股动脉后方(36.4％)和后外侧方(36.4％)发出,旋股内侧动脉从股深动脉发出(72.7％),从股动脉发出(27.3％).各主要血管的长度为:股深动脉(19.22±10.19) mm,其根部距腹股沟韧带的距离为(38±11.78)mm;旋股内侧动脉(12.56±6.17) mm;旋股外侧动脉(13.93±11.04) mm.各主要血管的外径为:股深动脉(5.20±1.57)mm,旋股内侧动脉(3.64±0.99) mm,其升支(2.66±0.99)mm;旋股外侧动脉(4.48±1.19) mm,其升支(2.12±0.59) mm.旋股内侧动脉升支以与主干成接近90°的夹角;旋股外侧动脉与其升支间约呈115.82°夹角.结论 熟悉股动脉应用解剖,有利于完善这种治疗方法.     

Development of microporous self-expanding stent grafts for treating cerebral aneurysms: designing micropores to control intimal hyperplasia

Treatment of large (diameter 12–25 mm) or giant (diameter >25 mm) cerebral aneurysms with a broad neck in the cranio-cervical area is difficult and carries relatively high risks, even with surgical and/or endovascular methods. To this end, we have been developing a high-performance, self-expanding stent graft which consists of a commercially available NiTi stent (diameter 5 mm, length 20 mm) initially covered with a thin microporous segmented polyurethane membrane fabricated by the dip-coating method. Micropores are then created by the excimer laser ablation technique, and the outer surface is coated with argatroban. There are 2 types of micropore patterns: circular-shaped pore type (pore: diameter 100 μm, opening ratio 12.6%) and the bale-shaped pore type (pore: size 100 × 268 μm, opening ratio 23.6%). This self-expanding stent graft was tested on side-wall aneurysms of both canine carotid arteries that were experimentally induced using the venous pouches from the external jugular veins, with the self-expanding stent graft on one side and a bare self-expanding stent on the other side. All carotid arteries were patent and free of marked stenosis after 1 month. All aneurysms were occluded by stent grafts, while patent in those treated with bare stents. Histologically, the stent grafts with bale-shaped micropores and a high opening ratio were associated with less intimal hyperplasia (187 ± 98 μm) than the bare stents (341 ± 146 μm) or the stent grafts with circular micropores and a low opening ratio (441 ± 129 μm). A pore ratio of 23.6% was found to control intimal growth.     

Flow-driven Diameter Response in Rat Femoral Arteries Perfused In Vitro

The effects of flow and flow changes on arterial diameter were investigated in vitro on isolated rat femoral arteries. Segments of femoral arteries were excised, mounted on microcannulas, and perfused with Tyrode's solution (37°C). Perfusion pressure was kept constant at 90 mm Hg. The mean external diameter after equilibration at a transmural pressure of 90 mm Hg was 720 ± 50 m (n=12). Vessels were then constricted with norepinephrine (1 M in the superfusion solution) to 77% ± 13% of the resting diameter; acetylcholine was used to check endothelial function. The external diameter was measured continuously using video microscopy. The arteries were subjected to two different types of flow variations: (a) step changes in flow (increase and decrease, n=6) and (b) low-frequency sinusoidal flow variations (frequencies ranging from 0.002 to 0.1 Hz, n=11). Flow ranged from 0 to 800 l/min (shear stress ranging from 0 to 15 dyn/cm²). All measured vessels constricted as flow increased. Flow steps induced exponential-like contractions (flow increase) or relaxations (flow decrease) with mean characteristic time constants 31 ± 4 and 22 ± 2 s, respectively. Sinusoidal flow oscillations induced sinusoidal diameter oscillations with a time delay. An increase in the frequency of the flow led to a decrease of both the amplitude of the flow-induced diameter oscillations and the phase shift between flow and diameter. The dynamic diameter response to flow changes could be characterized by a first-order low-pass filter with a time constant of 22 s. © 1998 Biomedical Engineering Society. PAC98: 8745Hw     

Multi-branched model of the human arterial system

A model of the human arterial system was constructed based on the anatomical branching structure of the arterial tree. Arteries were divided into segments represented by uniform thin-walled elastic tubes with realistic arterial dimensions and wall properties. The configuration contains 128 segments accounting for all the central vessels and major peripheral arteries supplying the extremities including vessels of the order of 2·0 mm diameter. Vascular impedance and pressure and flow waveforms were determined at various locations in the system and good agreement was found with experimental measurements. Use of the model is illustrated in investigating wave propagation in the arterial system and in simulation of arterial dynamics in such pathological conditions as arteriosclerosis and presence of a stenosis in the femoral artery.     

Ultrathin-wall vascular grafts for endovascular surgery

 The purposes of this study were to develop ultrathin-wall grafts suitable for stent-graft procedures and to examine the feasibility of the grafts from the physical point of view. We fabricated ultrathin-wall grafts with a wall thickness of 42 to 137 μm, using 50 denier polyester threads consisting of 72 polyester monofilaments. We studied the following physical properties of the ultrathin wall: the surface structure of the grafts, the longitudinal tensile strength of the grafts, the water permeability of the grafts, and the size of introducers through which the stent grafts can pass. In ultrathin-wall grafts with a wall thickness of 75 μm or more, a regular surface structure with zero planimetric porosity was recognized. In those with a thickness less than 64 μm, the porosity increased as the wall thickness decreased. The longitudinal tensile strengths of the 75 μm and 64 μm grafts were 13.1 ± 0.9 and 9.5 ± 0.9 kg, respectively. The water permeability of the 75-μm grafts was 380 ml/min, and that of the thinner grafts increased as the wall thickness decreased. Stents with a diameter of 40 mm covered with the ultrathin-wall grafts could pass through introducers with an inner diameter of 18 French. We conclude that the newly developed ultrathin-wall grafts are physiologically suitable for endovascular surgery. Received: December 4, 2000 / Accepted: August 13, 2001     

Zschokkella egyptica n. sp. (Myxosporea: Bivalvulaida) infecting the gallbladder of the eel catfish Plotosus lineatus Thunberg, 1787 and the freckled goatfish Upeneus tragula Richardson, 1846 in the Red Sea, Egypt

A new myxosporean, Zschokkella egyptica n. sp. was found in the gallbladder of two hosts: the eel catfish Plotosus lineatus and the freckled goat fish Upeneus tragula from the Red Sea at Suez City, Egypt. The plasmodia were polysporic, kidney to elliptical shaped with hairy holdfast projection and measured 109 × 70 μm. Mature spores were fusiform with 9 to 11 longitudinal striations. The mean spore dimensions were 13.0 × 10.5 μm. Spherical polar capsules are 4.8 μm in diameter; the polar filament showed four turns and were arranged perpendicular to the longitudinal axis of the capsule.     

Time course of the enhanced blood pressure response to reinduction of renal artery stenosis in unclipped renal hypertensive rats

Moderate or severe hypertension was induced in rats by application of a clip 0.25 or 0.20 mm internal diameter) to the left renal artery leaving the contralateral kidney intact. Removal of the clip 6, 13 or 24 days after the induction of the hypertension was followed by a rapid decrease in blood pressure. A near normotensive level was reached after 2–6 h. Reapplication of the clip to the unclipped renal artery after 1 day caused an enhanced blood pressure response. The preoperative hypertensive levels were reached within 2 h. This enhanced response was related to the level of blood pressure before the removal of the clip. Lengthening the interval between removal and reapplication of the clip gradually reduced the enhanced response of blood pressure, which had disappeared 8 days after the removal of the clip. Reapplication of the clip to the contralateral renal artery was not followed by an enhanced response in rats with previous moderate or severe hypertension.