Increased reversal and oscillatory shear stress cause smooth muscle contraction-dependent changes in sheep aortic dynamics: role in aortic balloon pump circulatory support

Impact of a cuff-based device calibration method on the agreement between invasive and noninvasive aortic and brachial pressure

INTRODUCTION

Brachial cuff-based methods are increasingly used to estimate aortic systolic blood pressure (aoSBP). However, there are several unresolved issues.

AIMS

to determine to what extent the scheme used to calibrate brachial records (1) can affect noninvasive obtained aoSBP levels, and consequently, the level of agreement with the aoSBP recorded invasively, and (2) how different ways of calibrating ultimately impact the relationship between aoSBP and cardiac properties.

METHODS

brachial and aortic blood pressure (BP) was simultaneously obtained by invasive (catheterisation) and noninvasive (brachial oscillometric-device) methods (89 subjects). aoSBP was noninvasive obtained using three calibration schemes: 'SD': diastolic and systolic brachial BP, 'C': diastolic and calculated brachial mean BP (bMBP), 'Osc': diastolic and oscillometry-derived bMBP. Agreement between invasive and noninvasive aoSBP, and associations between BP and echocardiographic-derived parameters were analysed.

CONCLUSIONS

'C' and 'SD' schemes generated aoSBP levels lower than those recorded invasively (mean errors: 6.9 and 10.1 mmHg); the opposite was found when considering 'Osc'(mean error: -11.4 mmHg). As individuals had higher invasive aoSBP, the three calibration schemes increasingly underestimated aoSBP levels; and viceversa. The 'range' of invasive aoSBP in which the calibration schemes reach the lowest error level (-5-5 mmHg) is different: 'C': 103-131 mmHg; 'Osc': 159-201 mmHg; 'SD':101-124 mmHg. The calibration methods allowed reaching levels of association between aoSBP and cardiac characteristics, somewhat lower, but very similar to those obtained when considering invasive aoSBP. There is no evidence of a clear superiority of one calibration method over another when considering the association between aoSBP and cardiac characteristics.

Central-to-peripheral blood pressure amplification: role of the recording site, technology, analysis approach, and calibration scheme in invasive and non-invasive data agreement

Background

Systolic blood pressure amplification (SBPA) and pulse pressure amplification (PPA) can independently predict cardiovascular damage and mortality. A wide range of methods are used for the non-invasive estimation of SBPA and PPA. The most accurate non-invasive method for obtaining SBPA and/or PPA remains unknown.

Aim

This study aims to evaluate the agreement between the SBPA and PPA values that are invasively and non-invasively obtained using different (1) measurement sites (radial, brachial, carotid), (2) measuring techniques (tonometry, oscillometry/plethysmography, ultrasound), (3) pulse waveform analysis approaches, and (4) calibration methods [systo-diastolic vs. approaches using brachial diastolic and mean blood pressure (BP)], with the latter calculated using different equations or measured by oscillometry.

Methods

Invasive aortic and brachial pressure (catheterism) and non-invasive aortic and peripheral (brachial, radial) BP were simultaneously obtained from 34 subjects using different methodologies, analysis methods, measuring sites, and calibration methods. SBPA and PPA were quantified. Concordance correlation and the Bland-Altman analysis were performed.

Results

(1) In general, SBPA and PPA levels obtained with non-invasive approaches were not associated with those recorded invasively. (2) The different non-invasive approaches led to (extremely) dissimilar results. In general, non-invasive measurements underestimated SBPA and PPA; the higher the invasive SBPA (or PPA), the greater the underestimation. (3) None of the calibration schemes, which considered non-invasive brachial BP to estimate SBPA or PPA, were better than the others. (4) SBPA and PPA levels obtained from radial artery waveform analysis (tonometry) (5) and common carotid artery ultrasound recordings and brachial artery waveform analysis, respectively, minimized the mean errors.

Conclusions

Overall, the findings showed that (i) SBPA and PPA indices are not "synonymous" and (ii) non-invasive approaches would fail to accurately determine invasive SBPA or PPA levels, regardless of the recording site, analysis, and calibration methods. Non-invasive measurements generally underestimated SBPA and PPA, and the higher the invasive SBPA or PPA, the higher the underestimation. There was not a calibration scheme better than the others. Consequently, our study emphasizes the strong need to be critical of measurement techniques, to have methodological transparency, and to have expert consensus for non-invasive assessment of SBPA and PPA.

Direct estimation of central aortic pressure from measured or quantified mean and diastolic brachial blood pressure: agreement with invasive records

Background

Recently it has been proposed a new approach to estimate aortic systolic blood pressure (aoSBP) without the need for specific devices, operator-dependent techniques and/or complex wave propagation models/algorithms. The approach proposes aoSBP can be quantified from brachial diastolic and mean blood pressure (bDBP, bMBP) as: aoSBP = bMBP2/bDBP. It remains to be assessed to what extent the method and/or equation used to obtain the bMBP levels considered in aoSBP calculation may affect the estimated aoSBP, and consequently the agreement with aoSBP invasively recorded.

Methods

Brachial and aortic pressure were simultaneously obtained invasively (catheterization) and non-invasively (brachial oscillometry) in 89 subjects. aoSBP was quantified in seven different ways, using measured (oscillometry-derived) and calculated (six equations) mean blood pressure (MBP) levels. The agreement between invasive and estimated aoSBP was analyzed (Concordance correlation coefficient; Bland-Altman Test).

Conclusions

The ability of the equation "aoSBP = MBP2/DBP" to (accurately) estimate (error <5 mmHg) invasive aoSBP depends on the method and equation considered to determine bMBP, and on the aoSBP levels (proportional error). Oscillometric bMBP and/or approaches that consider adjustments for heart rate or a form factor ∼40% (instead of the usual 33%) would be the best way to obtain the bMBP levels to be used to calculate aoSBP.

A Systematic Role of Metabolomics, Metabolic Pathways, and Chemical Metabolism in Lung Cancer

Lung cancer (LC) is considered as one of the leading causes of cancer-associated mortalities. Cancer cells' reprogrammed metabolism results in changes in metabolite concentrations, which can be utilized to identify a distinct metabolic pattern or fingerprint for cancer detection or diagnosis. By detecting different metabolic variations in the expression levels of LC patients, this will help and enhance early diagnosis methods as well as new treatment strategies. The majority of patients are identified at advanced stages after undergoing a number of surgical procedures or diagnostic testing, including the invasive procedures. This could be overcome by understanding the mechanism and function of differently regulated metabolites. Significant variations in the metabolites present in the different samples can be analyzed and used as early biomarkers. They could also be used to analyze the specific progression and type as well as stages of cancer type making it easier for the treatment process. The main aim of this review article is to focus on rewired metabolic pathways and the associated metabolite alterations that can be used as diagnostic and therapeutic targets in lung cancer diagnosis as well as treatment strategies.

Aortic systolic and pulse pressure invasively and non-invasively obtained: Comparative analysis of recording techniques, arterial sites of measurement, waveform analysis algorithms and calibration methods

Background: The non-invasive estimation of aortic systolic (aoSBP) and pulse pressure (aoPP) is achieved by a great variety of devices, which differ markedly in the: 1) principles of recording (applied technology), 2) arterial recording site, 3) model and mathematical analysis applied to signals, and/or 4) calibration scheme. The most reliable non-invasive procedure to obtain aoSBP and aoPP is not well established. Aim: To evaluate the agreement between aoSBP and aoPP values invasively and non-invasively obtained using different: 1) recording techniques (tonometry, oscilometry/plethysmography, ultrasound), 2) recording sites [radial, brachial (BA) and carotid artery (CCA)], 3) waveform analysis algorithms (e.g., direct analysis of the CCA pulse waveform vs. peripheral waveform analysis using general transfer functions, N-point moving average filters, etc.), 4) calibration schemes (systolic-diastolic calibration vs. methods using BA diastolic and mean blood pressure (bMBP); the latter calculated using different equations vs. measured directly by oscillometry, and 5) different equations to estimate bMBP (i.e., using a form factor of 33% ("033"), 41.2% ("0412") or 33% corrected for heart rate ("033HR"). Methods: The invasive aortic (aoBP) and brachial pressure (bBP) (catheterization), and the non-invasive aoBP and bBP were simultaneously obtained in 34 subjects. Non-invasive aoBP levels were obtained using different techniques, analysis methods, recording sites, and calibration schemes. Results: 1) Overall, non-invasive approaches yielded lower aoSBP and aoPP levels than those recorded invasively. 2) aoSBP and aoPP determinations based on CCA recordings, followed by BA recordings, were those that yielded values closest to those recorded invasively. 3) The "033HR" and "0412" calibration schemes ensured the lowest mean error, and the "033" method determined aoBP levels furthest from those recorded invasively. 4) Most of the non-invasive approaches considered overestimated and underestimated aoSBP at low (i.e., 80 mmHg) and high (i.e., 180 mmHg) invasive aoSBP values, respectively. 5) The higher the invasively measured aoPP, the higher the level of underestimation provided by the non-invasive methods. Conclusion: The recording method and site, the mathematical method/model used to quantify aoSBP and aoPP, and to calibrate waveforms, are essential when estimating aoBP. Our study strongly emphasizes the need for methodological transparency and consensus for the non-invasive aoBP assessment.

Central Pressure Waveform-Derived Indexes Obtained From Carotid and Radial Tonometry and Brachial Oscillometry in Healthy Subjects (2–84 Y): Age-, Height-, and Sex-Related Profiles and Analysis of Indexes Agreement

Aortic blood pressure (aoBP) waveform-derived indexes could provide valuable (prognostic) information over and above cardiovascular risk factors (CRFs). To obtain aoBP waveform-characteristics, several (i) techniques, (ii) recording sites, (iii) pressure-only waveform analysis mathematical approaches [e.g., pulse wave analysis (PWA), wave separation analysis (WSA)], and (iv) indexes [augmentation pressure and index (AP and AIx), forward (Pf) and backward (Pb) components of aoBP, reflection magnitude (RM), and reflection index (Rix)], were proposed. An accurate clinical use of these indexes requires knowing their physiological age-related profiles and the expected values for a specific subject. There are no works that have characterized waveform-derived indexes profiles in large populations considering: (i) as a continuous, data from different age stages (childhood, adolescence, and adulthood), (ii) complementary indexes, (iii) data obtained from different techniques and approaches, and (iv) analyzing potential sex- and body height (BH)-related differences. In addition, (v) there is a lack of normative data (reference intervals, RIs) for waveform-derived indexes.

Sex- and Age-Related Physiological Profiles for Brachial, Vertebral, Carotid, and Femoral Arteries Blood Flow Velocity Parameters During Growth and Aging (4-76 Years): Comparison With Clinical Cut-Off Levels

Ultrasound-derived blood flow velocity (BFV) levels [e.g., peak systolic velocity (PSV)], intrabeat indexes (e.g., resistive), and intersegment ratios [e.g., internal/common carotid artery (ICA/CCA) PSV ratio] are assessed to describe cardiovascular physiology and health status (e.g., disease severity evaluation and/or risk stratification). In this respect, fixed cut-off values (disregard of age or sex) have been proposed to define “significant” vascular disease from BFV-derived data (parameters). However, the use of single fixed cut-off values has limitations. Accurate use of BFV-derived parameters requires knowing their physiological age-related profiles and the expected values for a specific subject. To our knowledge, there are no studies that have characterized BFV profiles in large populations taking into account: (i) data from different age-stages (as a continuous) and transitions (childhood–adolescence–adulthood), (ii) complementary parameters, (iii) data from different arteries, and (iv) potential sex- and hemibody-related differences. Furthermore, (v) there is little information regarding normative data [reference intervals (RIs)] for BFV indexes.

Aims: The aims of this study are the following: (a) to determine the need for age-, body side-, and sex-specific profiles for BFV levels and derived parameters (intrabeat indexes and intersegment ratios), and (b) to define RIs for BFV levels and parameters, obtained from CCA, ICA, external carotid, vertebral, femoral, and brachial arteries records.

Methods: A total of 3,619 subjects (3–90 years) were included; 1,152 were healthy (without cardiovascular disease and atheroma plaques) and non-exposed to cardiovascular risk factors. BFV data were acquired. The agreement between left and right data was analyzed (Concordance correlation, Bland–Altman). Mean and SD equations and age-related profiles were obtained for BFV levels and parameters (regression methods; fractional polynomials).

Results: Left and right body-side derived data were not always equivalent. The need for sex-specific RIs was dependent on the parameter and/or age considered. RIs were defined for each studied artery and parameter. Percentile curves were compared with recommended fixed cut-off points. The equations for sex, body-side, and age-specific BFV physiological profiles obtained in the large population (of children, adolescents, and adults) studied were included (spreadsheet formats), enabling to determine for a particular subject, the expected values and potential data deviations.

Changes in Body Size during Early Growth Are Independently Associated with Arterial Properties in Early Childhood

Nutritional status in early life stages has been associated with arterial parameters in childhood. However, it is still controversial whether changes in standardized body weight (z-BW), height (z-BH), BW for height (z-BWH) and/or body mass index (z-BMI) in the first three years of life are independently associated with variations in arterial structure, stiffness and hemodynamics in early childhood. In addition, it is unknown if the strength of the associations vary depending on the growth period, nutritional characteristics and/or arterial parameters analyzed. Aims: First, to compare the strength of association between body size changes (Δz-BW, Δz-BH, Δz-BWH, Δz-BMI) in different time intervals (growth periods: 0–6, 0–12, 0–24, 0–36, 12–24, 12–36, 24–36 months (m)) and variations in arterial structure, stiffness and hemodynamics at age 6 years. Second, to determine whether the associations depend on exposure to cardiovascular risk factors, body size at birth and/or on body size at the time of the evaluation (cofactors). Anthropometric (at birth, 6, 12, 24, 36 m and at age 6 years), hemodynamic (peripheral and central (aortic)) and arterial (elastic (carotid) and muscular (femoral) arteries; both hemi-bodies) parameters were assessed in a child cohort (6 years; n =632). The association between arterial parameters and body size changes (Δz-BW, Δz-BH, Δz-BWH, Δz-BMI) in the different growth periods was compared, before and after adjustment by cofactors. Results: Δz-BW 0–24 m and Δz-BWH 0–24 m allowed us to explain inter-individual variations in structural arterial properties at age 6 years, with independence of cofactors. When the third year of life was included in the analysis (0–36, 12–36, 24–36 m), Δz-BW explained hemodynamic (peripheral and central) variations at age 6 years. Δz-BH and Δz-BMI showed limited associations with arterial properties. Conclusion: Δz-BW and Δz-BWH are the anthropometric variables with the greatest association with arterial structure and hemodynamics in early childhood, with independence of cofactors.

Physiological Age- and Sex-Related Profiles for Local (Aortic) and Regional (Carotid-Femoral, Carotid-Radial) Pulse Wave Velocity and Center-to-Periphery Stiffness Gradient, with and without Blood Pressure Adjustments: Reference Intervals and Agreement between Methods in Healthy Subjects (3-84 Years)

In addition to being a marker of cardiovascular (CV) aging, aortic stiffening has been shown to be independently associated with increased CV risk (directly and/or indirectly due to stiffness-gradient attenuation). Arterial stiffness determines the rate at which the pulse pressure wave propagates (i.e., pulse wave velocity, PWV). Thus, propagated PWV (i.e., the distance between pressure-wave recording sites divided by the pulse transit time) was proposed as an arterial stiffness index. Presently, aortic PWV is considered a gold-standard for non-invasive stiffness evaluation. The limitations ascribed to PWV have hampered its use in clinical practice. To overcome the limitations, different approaches and parameters have been proposed (e.g., local PWV obtained by wave separation and pulse wave analysis). In turn, it has been proposed to determine PWV considering blood pressure (BP) levels (β-PWV), so as to evaluate intrinsic arterial stiffness. It is unknown whether the different approaches used to assess PWV or β-PWV are equivalent and there are few data regarding age- and sex-related reference intervals (RIs) for regional and local PWV, β-PWV and PWV ratio.

AIMS

(1) to evaluate agreement between data from different stiffness indexes, (2) to determine the need for sex-specific RIs, and (3) to define RIs for PWV, β-PWV and PWV ratio in a cohort of healthy children, adolescents and adults.

METHODS

3619 subjects (3-90 y) were included, 1289 were healthy and non-exposed to CV risk factors. Carotid-femoral (cfPWV) and carotid-radial (crPWV) PWV were measured (SphygmoCor System (SCOR)) and PWV ratio (cfPWV/crPWV) was quantified. Local aortic PWV was obtained directly from carotid waves (aoPWV-Carotid; SCOR) and indirectly (generalized transfer function use) from radial (aoPWV-Radial; SCOR) and brachial (aoPWV-Brachial; Mobil-O-Graph system (MOG)) recordings. β-PWV was assessed by means of cardio-ankle brachial (CAVI) and BP-corrected CAVI (CAVIo) indexes. Analyses were done before and after adjustment for BP. Data agreement was analyzed (correlation, Bland-Altman). Mean and standard deviation (age- and sex-related) equations were obtained for PWV parameters (regression methods based on fractional polynomials).

RESULTS

The methods and parameters used to assess aortic stiffness showed different association levels. Stiffness data were not equivalent but showed systematic and proportional errors. The need for sex-specific RIs depended on the parameter and/or age considered. RIs were defined for all the studied parameters. The study provides the largest data set related to agreement and RIs for stiffness parameters obtained in a single population.

Maternal nutritional restriction during gestation impacts differently on offspring muscular and elastic arteries and is associated with increased carotid resistance and ventricular afterload in maturity

BACKGROUND

Intrauterine undernutrition could impact offspring left ventricle (LV) afterload and arterial function. The changes observed in adulthood could differ depending on the arterial type, pathway and properties studied. Aim: To analyze whether undernutrition during early and mid-gestation is associated with changes in cardiovascular properties in adulthood.

METHODS

Pregnant ewes were assigned to one of the two treatment groups: (1) standard nutritional offer (high pasture-allowance, HPA; n = 16) or (2) nutritional restriction (50-75% of control intake) from before conception until day 122 of gestation (≈85% term) (low pasture allowance, LPA; n = 17). When offspring reached adult life, cardiovascular parameters were assessed in conscious animals (applanation tonometry, vascular echography).

MEASUREMENTS

Peripheral and aortic pressure, carotid and femoral arteries diameters, intima-media thickness and stiffness, blood flow, local and regional resistances and LV afterload were measured. Blood samples were collected. Parameters were compared before and after adjustment for nutritional characteristics at birth and at the time of the cardiovascular evaluation.

RESULTS

Doppler-derived cerebral vascular resistances, mean pressure/flow ratio (carotid resistance) and afterload indexes were higher in descendants from LPA than in descendants from HPA ewes (p < 0.05). Descendants from LPA had lower femoral diameters (p < 0.05). Cardiovascular changes associated with nutritional restriction during pregnancy did not depend on the offsprings' nutritional conditions at birth and/or in adult life.

CONCLUSION

Pregnant ewes that experienced undernutrition gave birth to female offspring that exhibited increased carotid pathway resistances (cerebral microcirculatory resistances) and LV afterload when they reached the age of 2.5 years. There were differences in the impact of nutritional deficiency on elastic and muscular arteries.

Smooth Muscle-Dependent Changes in Aortic Wall Dynamics during Intra-Aortic Counterpulsation in an Animal Model of Acute Heart Failure

Purpose

Intra-aortic balloon pumping (IABP) may modify arterial biomechanics; however, its effects on arterial wall properties during acute cardio-depression have not yet been fully explored. This dynamical study was designed to characterize the effects of IABP on aortic wall mechanics in an in vivo animal model of acute heart failure.

Methods

Aortic pressure, diameter and blood flow were measured in six anesthetized sheep with acute cardio-depression by halothane (4%), before and during IABP (1:2). Aortic characteristic impedance and aortic wall stiffness indexes were calculated.

Results

Acute experimental cardio-depression resulted in a reduction in mean aortic pressure (p<0.05) and an increase in the characteristic impedance (p<0.005), incremental elastic modulus (p<0.05), stiffness index (p<0.05) and Peterson elastic modulus (p<0.05). IABP caused an increase in the cardiac output (p<0.005) and a reduction in the systemic vascular resistances (p<0.05). In addition, the aortic impedance, incremental elastic modulus, stiffness index and Peterson modulus were significantly reduced during IABP (p<0.05).

Conclusions

Our findings show that IABP caused changes in aortic wall impedance and intrinsic wall properties, improving the arterial functional capability and the left ventricular afterload by a reduction in both. Systemic vascular resistances and aortic stiffness were also improved by means of smooth muscle-dependent mechanisms.

Comparative in vivo analysis of the role of the adventitia and the endothelium on arterial mechanical function: relevance for aortic counterpulsation

PURPOSE

The comparative effect of the intimal and adventitial layers on arterial biomechanics control, in basal and altered conditions, remains to be elucidated. This study aimed (1) to characterize the arterial conduit (CF) and buffering (distensibility) function of the iliac arteries in in vivo animals, in which the intimal and adventitial layers were removed; (2) to determine the effects of intra-aortic ballon pumping (IABP) on simultaneously de-adventitialized (DA) and de-endothelialized (DE) iliac arteries before and after induced heart failure.

METHODS

Pressure and diameter signals were measured in the iliac arteries of sheep (n = 7) in which the adventitial and intima layer were removed. Intra-aortic balloon pump (IABP) assistance was used in a control state and after heart failure induction.

RESULTS

Both DE and DA determined significant changes in arterial diameter, distensibility and CF. Changes were higher after DA than after DE in terms of distensibility and CF (p<0.05). DA followed by DE (DA + DE) showed significant increases in arterial diameter and CF, accompanied by a decrease in distensibility (p<0.05) with respect to intact arteries. Heart failure induction caused significant hemodynamic changes without modifying the already impaired local biomechanical parameters. Nonsignificant improvements in the biomechanical parameters of DA + DE iliac arteries were observed during IABP before and after heart failure induction.

CONCLUSIONS

Biomechanical changes caused by DA of iliac arteries were more important than those observed after DE. The DA + DE arteries showed significant differences with respect to intact arteries and with DA or DE arteries. IABP-related effects on arterial mechanics were absent in DA + DE arteries.

Gαq/11-mediated intracellular calcium responses to retrograde flow in endothelial cells

Disturbed flow patterns, including reversal in flow direction, are key factors in the development of dysfunctional endothelial cells (ECs) and atherosclerotic lesions. An almost immediate response of ECs to fluid shear stress is the increase in cytosolic calcium concentration ([Ca(2+)](i)). Whether the source of [Ca(2+)](i) is extracellular, released from Ca(2+) intracellular stores, or both is still undefined, though it is likely dependent on the nature of forces involved. We have previously shown that a change in flow direction (retrograde flow) on a flow-adapted endothelial monolayer induces the remodeling of the cell-cell junction along with a dramatic [Ca(2+)](i) burst compared with cells exposed to unidirectional or orthograde flow. The heterotrimeric G protein-α q and 11 subunit (Gα(q/11)) is a likely candidate in effecting shear-induced increases in [Ca(2+)](i) since its expression is enriched at the junction and has been previously shown to be activated within seconds after onset of flow. In flow-adapted human ECs, we have investigated to what extent the Gα(q/11) pathway mediates calcium dynamics after reversal in flow direction. We observed that the elapsed time to peak [Ca(2+)](i) response to a 10 dyn/cm(2) retrograde shear stress was increased by 11 s in cells silenced with small interfering RNA directed against Gα(q/11). A similar lag in [Ca(2+)](i) transient was observed after cells were treated with the phospholipase C (PLC)-βγ inhibitor, U-73122, or the phosphatidylinositol-specific PLC inhibitor, edelfosine, compared with controls. Lower levels of inositol 1,4,5-trisphosphate accumulation seconds after the onset of flow correlated with the increased lag in [Ca(2+)](i) responses observed with the different treatments. In addition, inhibition of the inositol 1,4,5-trisphosphate receptor entirely abrogated flow-induced [Ca(2+)](i). Taken together, our results identify the Gα(q/11)-PLC pathway as the initial trigger for retrograde flow-induced endoplasmic reticulum calcium store release, thereby offering a novel approach to regulating EC dysfunctions in regions subjected to the reversal of blood flow.

Hemodynamic analysis of intracranial aneurysms with daughter blebs

BACKGROUND AND PURPOSE

Intracranial aneurysms with daughter blebs appear to have a higher risk of rupture. Whether hemodynamic factors are involved in this phenomenon is not clear.

METHODS

54 patient-specific aneurysms harboring 69 daughter blebs were divided into ruptured and unruptured groups based on their clinical history. Realistic models were retrospectively constructed and analyzed by a computational fluid dynamic method.

RESULTS

There were no differences in the aspect ratio and morphology type of the aneurysms, the size of blebs or other common risk factors between the two groups. The wall shear stress (WSS) was significantly lower while the oscillatory shear index (OSI) was higher in the daughter blebs than in the primary aneurysms. Bleb-bearing aneurysms with a rupture history displayed significantly lower WSS in the daughter bleb. Of the daughter blebs, 73.9% were localized to the impingement region of the inflow jet.

CONCLUSION

These observations indicate that low WSS and high OSI in the daughter blebs might be involved in increasing the risk of rupture. The localized striking force caused by inflow jets may contribute to the development of daughter blebs. However, a precise role of hemodynamics in predicting the future rupture of daughter blebs needs further study.

The endothelium modulates the arterial wall mechanical response to intra-aortic balloon counterpulsation: in vivo studies

Intra-aortic balloon pump (IABP) benefits could depend on variations in the cardiovascular biomechanical properties associated with blood flow-induced endothelium-dependent changes. However, if IABP results in changes in the peripheral artery biomechanics and if the endothelium plays a role in these potential changes remains unknown. The aim of this study is to characterize acute IABP effects on peripheral artery biomechanics in control and acute heart failure (AHF) states and the role of the endothelium in IABP effects on peripheral artery biomechanics. Pressure and diameter were recorded in sheep (n= 7) iliac arteries (IAs), before and during 1:2 IABP, during four states: (i) control with intact IA; (ii) AHF with intact IA; (iii) control with de-endothelialized (DE) (mechanical rubbing) IA; and (iv) AHF with DE IA. Arterial distensibility, elastic modulus, and conduit function (CF) (1/characteristic impedance) were calculated. The results of this study include: (i) during control conditions, IABP resulted in intact IA dilatation, stiffness reduction, and CF increase; (ii) AHF induction determined a reduction in intact IA diameter and CF, and a stiffness increase. These changes reverted during IABP; (iii) the increase in IA stiffness observed after DE remained unchanged during IABP; (iv) in DE IA, AHF did not result in diameter or stiffness changes; and (v) IABP during AHF did not associate changes in diameter or stiffness in the DE IA. In conclusion, during control and AHF states, IABP results in IA dilatation and stiffness reduction. The integrity of the endothelial layer would be critical for the IABP-associated changes in IA biomechanics.

Influence of hemodynamic factors on rupture of intracranial aneurysms: patient-specific 3D mirror aneurysms model computational fluid dynamics simulation

BACKGROUND AND PURPOSE

Hemodynamics factors play an important role in the rupture of cerebral aneurysms. The purpose of this study was to evaluate the impact of hemodynamic factors on the rupture of the MANs with 3D reconstruction model CFD simulation.

MATERIALS AND METHODS

RDSA was performed in 9 pairs of intracranial MANs. Each pair was divided into ruptured and unruptured groups. The hemodynamic factors of the aneurysms and their parent arteries were compared.

RESULTS

There was a significant difference in the WSS at peak systole between the regions of the aneurysms and their parent arteries in the ruptured group (ie, 6.49 ± 3.48 Pa versus 8.78 ± 3.57 Pa, P =.015) but not in the unruptured group (ie, 9.80 ± 4.12 Pa versus 10.17 ± 7.48 Pa, P =.678). The proportion of the low WSS area to the whole area of the aneurysms was 12.20 ± 18.08% in the ruptured group and 3.96 ± 6.91% in the unruptured group; the difference between the 2 groups was statistically significant (P =.015). The OSI was 0.0879 ± 0.0764 in the ruptured group, which was significantly higher than that of the unruptured group (ie, 0.0183 ± 0.0191, P =.008).

CONCLUSIONS

MANs may be a useful disease model to investigate possible causes linked to ruptured aneurysms. The ruptured aneurysms manifested lower WSS compared with their parent arteries, a higher proportion of the low WSS area to the whole area of aneurysm, and higher OSI compared with the unruptured aneurysms.

Linear and nonlinear viscoelastic modeling of aorta and carotid pressure-area dynamics under in vivo and ex vivo conditions

A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from 10 ovine aortas and 10 human carotid arteries. Ex vivo measurements (from both locations) were made in 11 male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates, we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the artery type. Results showed that for the thoracic descending aorta (under both experimental conditions), the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure-area dynamics in this vessel. Results comparing biomechanical properties show that the Kelvin and sigmoid models were able to predict the zero-pressure vessel radius; that under ex vivo conditions vessels are more rigid, and comparatively, that the carotid artery is stiffer than the thoracic descending aorta; and that the viscoelastic gain and relaxation parameters do not differ significantly between vessels or experimental conditions. In conclusion, our study demonstrates that the proposed models can predict pressure-area dynamics and that model parameters can be extracted for further interpretation of biomechanical properties.

How much of the intraaortic balloon volume is displaced toward the coronary circulation?

Objective

During intraaortic balloon inflation, blood volume is displaced toward the heart (V_tip), traveling retrograde in the descending aorta, passing by the arch vessels, reaching the aortic root (V_root), and eventually perfusing the coronary circulation (V_cor). V_cor leads to coronary flow augmentation, one of the main benefits of the intraaortic balloon pump. The aim of this study was to assess V_root and V_cor in vivo and in vitro, respectively.

Methods

During intraaortic balloon inflation, V_root was obtained by integrating over time the aortic root flow signals measured in 10 patients with intraaortic balloon assistance frequencies of 1:1 and 1:2. In a mock circulation system, flow measurements were recorded simultaneously upstream of the intraaortic balloon tip and at each of the arch and coronary branches of a silicone aorta during 1:1 and 1:2 intraaortic balloon support. Integration over time of the flow signals during inflation yielded V_cor and the distribution of V_tip.

Results

In patients, V_root was 6.4% ± 4.8% of the intraaortic balloon volume during 1:1 assistance and 10.0% ± 5.0% during 1:2 assistance. In vitro and with an artificial heart simulating the native heart, V_cor was smaller, 3.7% and 3.8%, respectively. The distribution of V_tip in vitro varied, with less volume displaced toward the arch and coronary branches and more volume stored in the compliant aortic wall when the artificial heart was not operating.

Conclusion

The blood volume displaced toward the coronary circulation as the result of intraaortic balloon inflation is a small percentage of the nominal intraaortic balloon volume. Although small, this percentage is still a significant fraction of baseline coronary flow.

Non-invasive biomechanical evaluation of implanted human cryopreserved arterial homografts: comparison with pre-implanted cryografts and arteries from human donors and recipients

Native vessels-grafts biomechanical mismatch (BM) is related to graft failure. The BM could be reduced using human cryopreserved/defrosted arteries (cryografts), but post-thaw cryografts' recovery could be associated with an impaired biomechanical behavior. In vitro, we demonstrated that our cryopreservation methods do not affect arteries' biomechanics, but only post-implant studies would allow determining the cryografts' biomechanical performance.

AIM

To characterize the biomechanical properties of implanted cryografts, and to compare them with cryografts pre-implant, recipients' native arteries, and arteries from subjects with characteristics similar to those of the recipients and multiorgan donors (MOD) whose arteries were cryopreserved.

METHODS

Native femoral arteries anastomosed to cryografts, implanted cryografts, and arteries from subjects, recipient-like and MOD-like, were studied. In vitro (pre-implant cryografts) and in vivo non-invasive studies were performed. Arterial pressure, diameter, and wall thickness were obtained to quantify local and regional biomechanical parameters, and to evaluate the arterial remodeling.

CONCLUSION

Implanted cryografts were remodeled, with an increased wall thickness, wall-to-lumen ratio, and wall cross-sectional area. The proximal-distal gradual transition in stiffness remained unchanged. Implanted cryografts were stiffer than MOD-like arteries, but more compliant than recipients' arteries. The cryografts-native arteries biomechanical differences were lesser than those described for venous grafts or expanded polytetrafluoroethylene.

Cardiac resynchronization results in aortic blood flow-associated changes in the arterial load components: basal biomechanical conditions determine the load changes

The cardiac resynchronization therapy (CRT)effects on the arterial load components, the mechanisms (i.e.haemodynamic changes-dependence) involved in the load reduction and the factors (i.e. basal load conditions) associated with the load changes after CRT, are to be evaluated.

AIMS

a)to analyze the potential changes in the arterial load components(peripheral resistances, arterial compliance and impedance)associated with the CRT, b) to determine if the load components changes are associated with variations in haemodynamic variables (pressure, heart rate or blood flow), c) to analyze the relationship between the load components basal state and their changes after CRT. To fulfill these aims cardiac and arterial structural and mechanical parameters were non-invasively evaluated in 8 heart failure patients, pre- and post-CRT (23+/-8 days). The main results were that short-term after CRT: 1)there were changes in the static and dynamic determinants of the arterial load; 2) the changes in the load components were not associated with heart rate or pressure variations, but with blood flow changes, and 3) the load components basal levels and their changes after CRT were associated.