Health informatics design for assisted diagnosis of subclinical atherosclerosis, structural, and functional arterial age calculus and patient-specific cardiovascular risk evaluation.

Traditional methods used to assess cardiovascular risk (i.e., the Framingham Risk Score) exhibit clear limitations. To aid in patient-specific risk stratification and diagnosis it has been proposed to evaluate noninvasively structural and functional arterial parameters. A National Public University Center (CUiiDARTE) was created in Uruguay with the aim of developing and applying strategies to improve cardiovascular risk stratification and subclinical vascular disease detection. To this end a health informatics approach and tool was designed, developed, and implemented in CUiiDARTE. Its goals were to: 1) promote screening for subclinical atherosclerosis, 2) develop a centralized database to store information obtained noninvasively from anywhere in our country, 3) develop a biomathematical model integrating values for arterial structure and function into traditional cardiovascular risk assessment, 4) generate a detailed and comprehensive report for the specialist comparing patient data with reference data from the healthy population, 5) generate a similar report (using a structural and functional arterial age calculator) for the patients assessing the state of their arteries. In this paper, we present the main characteristics of the CUiiDARTE health informatics development.

Integrated e-Health approach based on vascular ultrasound and pulse wave analysis for asymptomatic atherosclerosis detection and cardiovascular risk stratification in the community.

New strategies are urgently needed to identify subjects at increased risk of atherosclerotic cardiovascular disease (ACVD) development or complications. A National Public University Center (CUiiDARTE) was created in Uruguay, based on six main pillars: 1) integration of experts in different disciplines and creation of multidisciplinary teams, 2) incidence in public and professional education programs to give training in the use of new technologies and to shift the focus from ACVD treatment to disease prevention, 3) implementation of free vascular studies in the community (distributed rather than centralized healthcare), 4) innovation and application of e-Health and noninvasive technology and approaches, 5) design and development of a biomedical approach to determine the target population and patient workflow, and 6) improvement in individual risk estimation and differentiation between aging and ACVD-related arterial changes using population-based epidemiological and statistical patient-specific models. This work describes main features of CUiiDARTE project implementation, the scientific and technological steps and innovations done for individual risk stratification, and sub-clinical ACVD diagnosis.

Effects of removing the adventitia on the mechanical properties of ovine femoral arteries in vivo and in vitro.

BACKGROUND: The aims were to characterize in muscular arteries (a) the passive and active effects of the adventitia on vessel biomechanical properties and conduit function (CF), and (b) potential differences between the adventitial role in elastic and muscular arteries. METHODS AND RESULTS: Ovine femoral arteries were studied in vivo and in vitro (reduced smooth muscle-tone) in a circulation mock-up during hemodynamic conditions similar to those found in vivo. Pressure and diameter were assessed before and after removing the adventitia. The arterial compliance, distensibility, stiffness beta-index and CF were quantified. Results were compared with those obtained in brachiocephalic trunks. In vivo, after removing the adventitia there was a nonsignificant diameter reduction and an increase in stiffness (P<0.05). The CF decreased in the early recordings (P<0.02). In vitro, there were no biomechanical changes but vascular dilatation after the adventitia removal. Biomechanical changes associated with the adventitia removal were higher in muscular arteries, whereas diameter changes were major in elastic vessels. CONCLUSIONS: After removing the adventitia, (a) the arterial stiffness and CF were modified in vivo only, suggesting the changes could be ascribed to variations in smooth muscle tone, and (b) changes in elastic and muscular arteries were quantitatively different.

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.

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.

Smart damping modulation of carotid wall energetics in human hypertension: effects of angiotensin-converting enzyme inhibition.

Damping is the conversion of mechanical energy of a structure into thermal energy, and it is related to the material viscous behavior. To evaluate the role of damping in the common carotid artery (CCA) wall in human hypertension and the possible improvement of angiotensin-converting enzyme (ACE) inhibition, we used noninvasive CCA pressure (tonometry) and diameter (B-mode echography) waveforms in normotensive subjects (NT group; n=12) and in hypertensive patients (HT group; n=22) single-blind randomized into HT-placebo (n=10) or HT-treated (ramipril, 5 to 10 mg/d during 3 months; n=12). Vascular smooth muscle (VSM) null tonus condition was achieved from in vitro pressure and diameter waveforms (Konigsberg microtransducer and sonomicrometry) measured in explanted human CCA (n=14). Arterial wall dynamics was described by viscous (eta), inertial (M), and compliance (C) parameters, mean circumferential wall stress, viscous energy dissipation (WD), peak strain energy (WSt), damping ratio (xi=WD/WSt), and modeling isobaric indexes CIso and WSt(Iso). The lack of VSM tonus isobarically increased wall stress and reduced eta, CIso, and damping (P<0.01). Wall stress, eta, and WD were greater in HT than in NT (P<0.015) and arrived near normal in HT-treated (P<0.032 respect to HT), with no changes in HT-placebo. Whereas CIso increased in HT-treated (P<0.01) approaching the NT level, xi did not vary among groups. During hypertension, because of the WSt increase, the arterial wall reacts increasing WD to maintain xi. ACE inhibition modulates VSM activation and vessel wall remodeling, significantly improving wall energetics and wall stress. This protective vascular action reduces extra load to the heart and maintains enhanced arterial wall damping.

An in vitro study of cryopreserved and fresh human arteries: a comparison with ePTFE prostheses and human arteries studied non-invasively in vivo.

The surgical options in arterial reconstruction are: the use of autologous arteries; autologous veins; or expanded polytetrafluoroethylene (ePTFE) grafts. However, the development of intimal hyperplasia when using veins or ePTFE grafts has been associated with graft failure. Since autologous arteries are not always available, the use of cryopreserved arteries has to be considered. The aims of this study were: (a) to compare the viscoelastic properties of stored cryopreserved arteries and fresh arteries by in vitro analysis; and (b) to compare the viscoelastic properties of arteries measured non-invasively in normotensive patients, with fresh arteries, cryopreserved arteries, and ePTFE segments. The viscoelastic studies were performed in normotensive patients using stress-strain analysis with non-invasive measurement of pressure and diameter in the common carotid artery, and in vitro measurements of pressure and diameter in arteries and prostheses. The in vitro studies showed that the elastic modulus (E), viscous modulus (eta), Stiffness Index (SI), Peterson modulus (Ep), and the pulse wave velocity (PWV) values for human cryopreserved carotid arteries were similar to the values obtained non-invasively in normotensive subjects (P>0.05) and to human fresh vessels (P>0.05). In vitro, the SI, Ep, PWV, and E values of ePTFE were significantly higher than the observed values in subjects and with fresh and cryopreserved arteries (P<0.05); on the other hand the ePTFE eta values were the lowest (P<0.05). We concluded that cryopreserved arteries have similar viscoelastic properties to those obtained in vivo in the arteries of normotensive subjects and in vitro in fresh arteries. Consequently, we conclude that the cryopreservation procedure does not modify the mechanical properties of the arterial wall.

Pulmonary artery smooth muscle activation attenuates arterial dysfunction during acute pulmonary hypertension.

Acute pulmonary hypertension (PH) may arise with or without an increase in vascular smooth muscle (VSM) tone. Our objective was to determine how VSM activation affects both the conduit (CF) and wall buffering (BF) functions of the pulmonary artery (PA) during acute PH states. PA instantaneous flow, pressure, and diameter of six sheep were recorded during normal pressure (CTL) and different states of acute PH: 1) passively induced by PA mechanical occlusion (PPH); 2) actively induced by intravenous administration of phenylephrine (APH); and 3) a combination of both (APPH). To evaluate the direct effect of VSM activation, isobaric (PPH vs. APH) and isometric (CTL vs. APPH) analyses were performed. We calculated the local BF from the elastic (EPD) and viscous (etaPD) indexes as etaPD/EPD and the characteristic impedance (ZC) from pressure and flow to evaluate CF as 1/ZC. We also calculated the absolute and normalized cross-sectional pulsatility (PCS and NPCS, respectively), the dynamic compliance (CDYN), the cross-sectional distensibility (DCS), and the pressure-strain elastic modulus (EP). The isobaric analysis showed increase of CF, BF, and etaPD (P < 0.01) and decrease of EPD (P < 0.05) during APH in respect to PPH (concomitant with isobaric VSM activation-induced vasoconstriction, P < 0.01). The isometric analysis showed increase of E(PD) and etaPD (P < 0.01), nonsignificant difference in BF (even in the presence of a significant mean PA pressure rise, from 14 (SD 6) to 25 (SD 8) mmHg, P < 0.01), and decrease in CF (P < 0.01) during APPH respect to CTL. Mechanical occlusions (PPH and APPH) reduced BF (P < 0.01) and increased EPD (P < 0.05) with regard to their previous steady states (CTL and APH). Nonsignificant differences were found in EPD between PPH and APPH. VSM activation (APH and APPH) increased etaPD (P < 0.01) respect to their previous passive states (CTL and PPH), but no significant differences were found within similar levels of VSM activation. In conclusion, VSM plays a relevant role in main pulmonary artery function during acute pulmonary hypertension, because isobaric vasoconstriction induced by VSM activation improves both BF and CF, mainly due to the increase in etaPD concomitant with the arterial compliance. CDYN and DCS were the more pertinent clinical indexes of arterial elasticity. Additionally, the etaPD-mediated preservation of the BF could be evaluated by the geometric related indexes (PCS and NPCS), which appear to be qualitative markers of arterial wall viscosity status.