Biomedical subjects

Yanina Zócalo

Publications and source records attributed to Yanina Zócalo.

7 recordsLinked to original sources

PubMed2007

Functional properties of fresh and cryopreserved carotid and femoral arteries, and of venous and synthetic grafts: comparison with arteries from normotensive and hypertensive patients.

The ideal arterial graft must share identical functional properties with the host artery. Surgical reconstruction of the common carotid artery (CA) is performed in several clinical situations, using expanded polytetrafluoroethylene prosthesis (ePTFE) or saphenous vein (SV) grafts. At date there is interest in obtaining an arterial graft that improves the results of that nowadays available. The use of a fresh or cryopreserved/defrosted artery appears as an interesting alternative. However, if the fresh and cryopreserved/defrosted arteries allow an adequate viscoelastic and functional matching with the host arteries needs to be established. The aims were to compare the viscoelastic and functional performance of: (1) conduits used in CA reconstruction (SV and ePTFE) with those of the fresh and cryopreserved/ defrosted CA and femoral arteries (FA), and (2) normotensive and hypertensive patients' arteries with those of the arterial substitutes in vitro analyzed. Pressure, diameter and wall thickness of the CA were recorded in 15 normotensive and 15 hypertensive patients (in vivo studies), and in SV, fresh and cryopreserved/defrosted CA and FA (obtained from 15 donors), and ePTFE segments (in vitro studies). From stress-strain relationship we calculated elastic and viscous modulus, and the characteristic impedance. The local buffer and conduit functions were quantified as the viscous/elastic quotient and the inverse of the characteristic impedance. Fresh and cryopreserved/defrosted CA and FA were more alike, both in viscoelastic and functional levels, respect to normotensive and hypertensive patients' arteries, than the ePTFE and SV grafts. CA and FA cryografts could be considered an important alternative for carotid reconstruction.

Adult↗

PubMed2006

Cryopreservation procedure does not modify human carotid homografts mechanical properties: an isobaric and dynamic analysis.

The viscoelastic and inertial properties of the arterial wall are responsible for the arterial functional role in the cardiovascular system. Cryopreservation is widely used to preserve blood vessels for vascular reconstruction but it is controversially suspected to affect the dynamic behaviour of these allografts. The aim of this work was to assess the cryopreservation's effects on human arteries mechanical properties. Common carotid artery (CCA) segments harvested from donors were divided into two groups: Fresh (n = 18), tested for 24-48 h after harvesting, and Cryopreserved (n = 18) for an average time of 30 days in gas-nitrogen phase, and finally defrosted. Each segment was tested in a circulation mock, and its pressure and diameter were registered at similar pump frequency, pulse and mean pressure levels, including those of normotensive and hypertensive conditions. A compliance transfer function (diameter/pressure) derived from a mathematical adaptive modelling was designed for the on line assessment of the arterial wall dynamics and its frequency response. Assessment of arterial wall dynamics was made by measuring its viscous (eta), inertial (M) and elastic (E) properties, and creep and stress relaxation time constant (tauC and tauSR, respectively). The frequency response characterization allowed to evaluate the arterial wall filter or buffer function. Results showed that non-significant differences exist between wall dynamics and buffer function of fresh and cryopreserved segments of human CCA. In conclusion, our cryopreservation method maintains arterial wall functional properties, close to their fresh values.

Carotid Arteries↗

PubMed2006

Regional differences in vein wall dynamics under arterial hemodynamic conditions: comparison with arteries.

Factors that explain the different results among veins, and causes of the superior performance of vein grafts for small arterial reconstructions, remain unclear. The aim was to compare the biomechanical behavior of veins and arteries from different regions and sizes under arterial conditions. In vitro pressure and diameter were measured in four different veins and three different ovine arteries. A diameter-pressure transfer function was designed, and compliance, viscous, and inertial indexes, and viscous energy and buffering function were calculated. Regional differences in vein mechanical behavior and energy dissipation were found. Veins and arteries vary in mechanical properties and buffering, but the differences were lesser when considering the smallest artery. The differences among veins' viscosity, compliance, and energy dissipation, but not in the buffering capability, could be related to different performances of veins when used as arterial grafts. The major biomechanical matching could contribute to explain veins with better results in small arteries reconstruction.

Animals↗

PubMed2006

[Viscoelastic and functional similarities between native femoral arteries and fresh or cryopreserved arterial and venous homografts].

INTRODUCTION AND OBJECTIVES: It is not yet known whether cryopreservation enables vessels to retain their viscoelastic properties or whether cryopreserved homografts are biomechanically more like native arteries than currently used vascular prostheses. The study objectives were: a) to determine whether our cryopreservation methodology enables arterial and venous homografts to retain their viscoelastic and functional properties; and b) to assess similarities between patients' femoral arteries, homografts, and other vascular prostheses in common use. METHODS: The pressure and the diameter and parietal thickness of 15 muscular (femoral) arteries were measured in patients using tonometry and echography, both noninvasive techniques. In addition, the pressure in and diameter and parietal thickness of 15 fresh and 15 cryopreserved human muscular (femoral) artery segments, saphenous veins, and 15 expanded polytetrafluoroethylene (ePTFE) vascular prostheses were measured in vitro under hemodynamic conditions similar to those in patients. A Kelvin-Voigt model of the segment wall was used to derive elastic (Epd, mm Hg/mm) and viscous (Vpd, mm Hg x s/mm) pressure-diameter indices, the buffering function (Vpd/Epd), and the conduit function (1/Zc, where Zc is the characteristic impedance). The incremental Young modulus, the pressure-strain elastic modulus, and pulse wave velocity were also calculated. RESULTS: No difference was observed between either the viscoelastic or functional properties of fresh and cryopreserved homografts. Arterial homografts were the most similar to the patient's arteries. CONCLUSIONS: Cryopreservation enabled venous and arterial homografts to retain their viscoelastic and functional properties. Of all the grafts investigated, arterial homografts were most similar, both biomechanically and functionally, to the patient's femoral arteries.

Blood Vessels↗

PubMed2005

Femoral arteries energy dissipation and filtering function remain unchanged after cryopreservation procedure.

The aim was to evaluate our cryopreservation method effects on the mechanical properties and filtering function of human superficial femoral arteries (SFA). SFA segments from 10 multiorgan donors were divided into two groups: fresh, tested 24-48 h after harvesting, and cryopreserved/defrosted, tested after 1 month of cryopreservation. The cooling process was carried out in three steps: 2 degrees C/min until -40 degrees C; 5 degrees C/min until -90 degrees C and finally a rapid cooling by transferring the bag to vapour phase of liquid nitrogen (-142 degrees C). Thawing was made in two steps, a slow warming time by exposing the bag to 20 degrees C during 20 min, followed by a rapid warming by immersion in a 40 degrees C warm bath until defrost. In a circulation mock, arterial pressure [Pressure signal (P)] and diameter [Diameter (D)] were registered at similar stretch-frequency, P and flow levels. A compliance transfer function (D/P) was used for the on-line assessment of the arterial wall elastic (E), viscous (eta), and inertial (M) properties. To evaluate the arterial wall filter function, the arterial wall D/P frequency response was characterized, the cut-off frequency (fc) was quantified, and the viscous energy dissipation (Weta) was calculated. After cryopreservation, there were not significant changes in E, eta, M, Weta, and fc.

Adult↗

PubMed2005

Reduced elastic mismatch achieved by interposing vein cuff in expanded polytetrafluoroethylene femoral bypass decreases intimal hyperplasia.

BACKGROUND: Wall shear stress, arterial wall elasticity, and intimal hyperplasia are related. The aim of this study was to investigate the in vitro mechanical properties of ovine femoral arteries, jugular veins, and expanded polytetrafluoroethylene conduits, and to evaluate postoperative intimal hyperplasia. METHODS: Arterial, venous, and ePTFE mechanical properties were studied in a circulating loop at isobaric systemic pressures. Histological studies of intimal hyperplasia in ePTFE-bypassed femoral arteries with and without Miller cuffs were performed at the 40th and 120th day. RESULTS: The incremental elastic modulus of veins was significantly higher than that of femoral arteries (P < 0.05), but significantly lower than that of ePTFE graft conduits (P < 0.05). Intimal hyperplasia was significantly less in Miller-cuff-bypassed arteries both at the 40th and 120th day (P < 0.01). CONCLUSIONS: The Miller cuff acts as a mechanical adapter enhancing wall shear stress and the elastic matching between ePTFE and the native artery, resulting in an early decrease of intimal hyperplasia.

Animals↗

PubMed2005

[Regional differences in viscosity, elasticity and wall buffering function in systemic arteries: pulse wave analysis of the arterial pressure-diameter relationship].

INTRODUCTION AND OBJECTIVES: Regional variations in the incidence of vascular diseases have been related to regional differences in arterial viscoelasticity. The aim of this study was to characterize the differences in the elastic and viscous modulus and in wall buffering function between central and peripheral systemic arteries, through a time-series analysis of the pressure-diameter relationship. MATERIAL AND METHOD: Pressure and diameter were measured in seven arterial segments (carotid, brachiocephalic trunk, ascending aorta, proximal, middle and distal descending thoracic aorta, and femoral artery) from six sheep. Each segment was mounted on an in vitro mock circulatory system and perfused with Tyrode solution, with a pulse frequency of 1.8 Hz and systemic pressure levels. We used the Kelvin-Voigt model to calculate the pressure-diameter elastic (Epd, mmHg/mm) and viscous (Vpd, mmHg.s/mm) modulus, and to quantify the local wall buffering function (Vpd/Epd). We also calculated the incremental Young's and pressure-strain elastic modulus and pulse wave velocity for each segment. RESULTS: The elastic and viscous modulus increased from proximal to distal segments. The wall buffering function did not differ significantly between arteries. The lower rigidity of the central arteries compared to the distal ones may indicate that the systolic arterial compliance function is concentrated in the central arterial segments. On the other hand, the greater viscosity in the distal segments may indicate that viscous energy loss is concentrated in these segments. CONCLUSIONS: Arterial elasticity and viscosity can be interpreted as properties that are dependent on the region of the vessel, whereas wall buffering function can be considered region-independent.

Animals↗