Comparison of biaxial mechanical and microstructural properties between human femoral arteries and surrogate models for stent development.

Functional assessment of human femoral arteries after cryopreservation

An established method for cryopreservation that might preserve the vascular and endothelial responses of human femoral arteries (HFAs) to be transplanted as allografts was studied. HFAs were harvested from multiorgan donors and stored at 4 degrees C in saline solution before cryostorage. Thirty HFA rings were isolated and randomly assigned to one control group of unfrozen HFAs (eight rings) and one group of cryopreserved HFAs (22 rings). Cryopreservation was performed in RPMI solution containing dimethylsulfoxide (DMSO) and the rate of cooling was -1 degrees C/min until -40 degrees C and faster rates until -150 degrees C was reached. The contractile and relaxant responses of unfrozen and frozen/thawed arteries were assessed in organ bath by measurement of isometric force generated by the HFAs. After thawing, the maximal contractile responses to the contracting agonist tested (noradrenaline) were in the range of 43% of the responses in unfrozen HFAs. The endothelium-independent responses to sodium nitroprusside were not altered whereas the endothelium-dependent relaxant responses to acetylcholine were weakly altered. The cryopreservation method used provided a limited preservation of contractility of HFAs, a good preservation of the endothelium-independent relaxant responses, and a good preservation of endothelium-dependent relaxation. It is possible that further refinements of the cryopreservation protocol, such as a slower rate of cooling and a more controlled stepwise addition of DMSO, might allow better post-thaw functional recovery.

Autologous vascular tissues with a small diameter, "biotubes," were developed in vivo using a novel concept in regenerative medicine, "in-body tissue architecture technology." The effect of pulsatile flow in vitro was investigated on the structural and functional properties of the biotubes. Silicone rods (diameter, 3.0 mm; length, 35.0 mm), used as molds, were embedded into dorsal subcutaneous spaces of Wister rats. After 4 weeks, the autologous tubular tissues formed around the rods were harvested. Some tissues were incubated for 2 days under pulsatile flow simulating conditions in the human arteries with small caliber (wall shear stress (WSS), 15.5-77.3 dyn/cm(2); circumferential stress (CS), 0.6-4.5 x 10(5) dyn/cm(2)). Upon flow loading, the sparse, randomly oriented collagen fibers in the biotubes became dense and oriented in the regular circumferential direction. Compliances (beta values) of the control (ca. 30) and flow-loaded (ca. 20) biotubes were equivalent to that of the human coronary arteries and femoral arteries, respectively. Further, upon flow loading, the burst pressure significantly increased from ca. 1000 mmHg to ca. 1800 mmHg, along with the alpha-SMA-positive cell ratio. Pulsatile flow loading in vitro for 2 days could induce biotube maturation in terms of collagen structures and mechanical properties.

Functional assessment of human femoral arteries after cryopreservation

This study was done to assess how local changes in vessel size, together with plaque load, determine luminal narrowing in atherosclerotic arteries. Fifty-one human femoral arteries were analyzed: 32 postmortem and 19 in vivo by 30-MHz intravascular ultrasound. Histological and intravascular ultrasound cross sections were examined every 0.5 cm over an arterial segment 10 to 15 cm long. In each cross section we measured the lumen area and the area circumscribed by the internal elastic lamina (the IEL area). In each arterial segment, the cross section that contained the least amount of plaque was the reference site. For each cross section, the lumen area stenosis was expressed as percent of the lumen area in the reference site. Similarly, the IEL area was expressed as percent of the IEL area in the reference site (the relative IEL area). There was a significant negative correlation between the relative IEL area and the lumen area stenosis percentage (r = -.62, P < .001 for histology and r = -.66, P < .001 for intravascular ultrasound). When lumen area stenosis was less than about 25%, mainly compensatory enlargement was observed. When lumen area stenosis exceeded about 25%, however, mainly a decrease of the IEL area was observed, which is consistent with arterial wall shrinkage. Furthermore, the increase in plaque area does not account for the total loss of luminal area. There was a moderate correlation between an increase in plaque area and reduction of the corresponding lumen area (r = .49 and r = .56 for histology and intravascular ultrasound, respectively). The decrease in luminal area cannot be attributed to plaque increase alone. Arterial wall shrinkage is a paradoxical mechanism that may contribute to severe luminal narrowing of the atherosclerotic human femoral artery.

Inhibiting Connexin Channels Protects Against Cryopreservation-induced Cell Death in Human Blood Vessels

Invited commentary

This study was aimed to establish whether the cryopreservation procedure we currently use in clinics can modify arterial homograft antigenicity. To this purpose, we performed an immunohistochemical study on fresh and cryopreserved human arterial homografts to visualize the expression of HLA class I heavy and light chains "in situ" by using the HC-10 and Namb-1 monoclonal antibodies. Human femoral arteries and thoracic aortas were harvested from 18 heart-beating donors and sampled before and after cryopreservation. Arterial segments were frozen in liquid nitrogen vapors in a controlled rate freezing system. After thawing, samples were processed for routine immunohistochemistry. To standardize immunostaining, flow-cytometry indirect immunofluorescence analysis was performed on HUVEC; immunohistochemistry of human ovarian cortical vessels was performed as an additional positive control. Negative controls were performed by omitting tissue incubation with primary antibodies. HLA-class I antigens were markedly expressed by endothelial cells lining surface intima and adventitial vasa vasorum; a moderate expression was found in medial smooth muscle cells. Except for the surface unreactivity caused by loss of endothelium, results from cryopreserved arterial allografts were strictly comparable to those observed in fresh, unfrozen tissues. These results support the view that cryopreserved arterial allografts are immunogenic as their fresh counterparts; apart from smooth muscle cells which retained a moderate expression of HLA class I antigens following cryopreservation, our study suggests that the highly HC-10 positive endothelial cells we found to line the rich adventitial network of vasa vasorum are expected to be one of the major targets of the serological response in the recipient.

In vitro and in vivo intravascular ultrasound imaging.

Endoluminal Atherosclerotic Plaque Debulking Using Enzymatic and Ultrasonic Energy

Intravascular Ultrasound Elastography in Human Arteries: Initial Experience In Vitro

Peripheral artery disease is one among the circulatory problems in the cardiovascular system in which narrowed artery reduces blood to limbs. This paper focus on the effect of peripheral layer thickness on velocity of blood and on the hemodynamic parameters such as wall shear stress and oscillatory shear index in human femoral artery using two-layered model. Owing to the necessity of clinically reliable estimates for hemodynamic parameters, at the time of prognosis and diagnosis of peripheral diseases, in this investigation the physiological pressure gradient of human femoral artery was taken from cardiology literature and is described using McDonalds model. To the best of our knowledge, this is the first primitive study of this kind. Governing equations are solved analytically. Velocity, wall shear stress and oscillatory shear index for different peripheral layer thicknesses are obtained. Dimensional graphs for velocity and wall shear stress are plotted using MATLAB. Quantitative and qualitative analysis shows that the velocity as well as oscillatory shear index in the core region increases as the peripheral layer thickness decreases. Results are interpreted medically which helps to improve the understanding of the state of artery. Comparison of our results with that of single layer model in the literature indicates that single layer model overestimates core region velocity by approximately 65% and underestimates wall shear stress and oscillatory shear index by 84% and 88% respectively. Primitive model employed in the current investigation recommends for more number of subject specific studies before benchmarking the thresholds for the clinically crucial hemodynamic parameters.

Understanding the hemodynamics of the human circulatory system is crucial for diagnosing and treating cardiovascular diseases. To this end, one of the critical vascular analyses involves determining head loss, or pressure drop, in arteries, as it provides substantial insight into vascular health and efficiency. Thus, this work presents an assessment of head loss in the human femoral artery, one of the major blood vessels in the lower body, comprising the common femoral artery, the deep femoral artery, and the superficial femoral artery, which extends to the popliteal artery. Our study modeled this arterial system as a network of elastic circular pipes and, using the proposed theories, calculated the pressurized diameters and head loss in each segment, accounting for minor losses arising from vessel curvature and geometric variations within the arterial network. Because the proposed theories rely on certain assumptions, the validity of the theoretical predictions was assessed by simulating a two-dimensional computational fluid dynamics (CFD) model of an idealized human femoral artery using available clinical data for the model parameters. Pressurized diameters were computed using both the CFD model and the theoretical formulation, and the results were statistically compared. The results showed a statistically significant difference between the two, underscoring the importance of accurately capturing the elastic behavior of the arterial wall. Accordingly, a modified pressurized diameter formulation incorporating a segment-specific correction factor was proposed. Findings showed that this correction factor is comparatively high for the deep femoral arterial segment.

Surgeons have used cryopreserved vascular allografts successfully for many years to treat arterial occlusive disease and to repair arterial aneurysms. Vascular allografts demonstrate high patency rates but contain viable cells, which may evoke a rejection response following implantation. Removing the cells could prevent such a response and negate the need for cryopreservation and ultra-low temperature storage. The objectives of the study were to characterize human common femoral arteries and develop a decellularization protocol with a view to the generation of biocompatible and biomechanically functional vascular grafts for use in vascular bypass and arteriovenous access. The arteries were decellularized by subjecting the tissue to a single freeze-thaw cycle followed by sequential incubation in hypotonic tris buffer and low concentration sodium dodecyl sulphate. Each artery was disinfected using 0.1% (v/v) peracetic acid. Histological analysis demonstrated a lack of cells following decellularization and confirmed the integrity of the tissue histioarchitecture and retention of major structural proteins. There was a >95% reduction in DNA levels. The acellular tissues and extracts were not cytotoxic to either mouse 3T3 or baby hamster kidney cells. Biomechanical properties were determined by burst pressure, compliance, and tensile tests, which confirmed the retention of biomechanical properties following decellularization. In conclusion the study has developed a suitable protocol for the removal of cells from human common femoral arteries without adversely affecting the biochemical or biomechanical properties. These properties indicate the potential use for acellular human common femoral arteries for vascular bypass or arteriovenous access.

In order to characterise the pharmacological properties of postjunctional alpha-adrenoceptors, both the contractile effects of alpha-adrenoceptor agonists and the blocking potencies of selective alpha-adrenoceptor antagonists were studied in isolated human femoral veins and arteries. The veins were more sensitive to noradrenaline than the arteries. Guanfacine had a higher intrinsic activity in veins than in arteries, whereas the reverse was true for phenylephrine. The antagonists rauwolscine and yohimbine were more potent against noradrenaline in the veins than in arteries, while corynanthine was equally potent in either tissue. They antagonised the noradrenaline response in a competitive manner. Prazosin proved to be the most potent competitive antagonist in arteries, while in veins it exerted weak and non-competitive antagonism. The results suggest that the alpha-adrenoceptor population at the postjunctional site differs between human femoral veins and arteries. The veins seem to contain more alpha 2- than alpha 1-adrenoceptors postjunctionally, whereas in the arteries the alpha 1-subtype prevails. The results indicate the possibility of influencing selectively adrenergic reactions in the capacitance and resistance vessels.