1 Departamento de Fisiología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay; 2 Facultad de Ingeniería, y Ciencias Exactas y Naturales, Universidad Favaloro, Buenos Aires, ...Argentina
Submitted 12 April 2004
; accepted in final form 8 October 2004
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 (E PD ) and viscous ( PD ) indexes as PD /E PD and the characteristic impedance (Z C ) from pressure and flow to evaluate CF as 1/Z C . We also calculated the absolute and normalized cross-sectional pulsatility (P CS and NP CS , respectively), the dynamic compliance (C DYN ), the cross-sectional distensibility (D CS ), and the pressure-strain elastic modulus (E P ). The isobaric analysis showed increase of CF, BF, and PD ( P < 0.01) and decrease of E PD ( 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 PD ( 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 E PD ( P < 0.05) with regard to their previous steady states (CTL and APH). Nonsignificant differences were found in E PD between PPH and APPH. VSM activation (APH and APPH) increased PD ( 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 PD concomitant with the arterial compliance. C DYN and D CS were the more pertinent clinical indexes of arterial elasticity. Additionally, the PD -mediated preservation of the BF could be evaluated by the geometric related indexes (P CS and NP CS ), which appear to be qualitative markers of arterial wall viscosity status.
buffering function; arterial wall viscoelasticity; characteristic impedance
Address for reprint requests and other correspondence: D. Bia Santana, Departamento de Fisiología, Facultad de Medicina, Universidad de la República, General Flores 2125, PC 11800, Montevideo, Uruguay (E-mail: dbia{at}fmed.edu.uy )
Background
Several works analyze arterial parameters’ (stiffness levels, wall thickness, etc.) association with variations of body mass index (BMI) in pediatric populations.
However, none integrate ...different arterial parameters as comparable continuous (standardized) variables, in order to assess their association with standardized (age- and sex-independent) BMI scores (zBMI).
Aims
To analyze the association of standardized arterial parameters with interindividual variations of zBMI.
Methods
609 children and adolescents (mean age/range: 12/4–18 years, 45% females) were studied. Body mass index (BMI) was calculated. zBMI scores were derived from population-based tables. Non-invasive arterial assessment was performed: oscillometric measurements of peripheral systolic (pSBP), diastolic (pDBP) and pulse pressure (pPP), and central (applanation tonometry) systolic (cSBP), diastolic (cDBP) and pulse pressure (cPP); ultrasonographic measurements of common carotid (CCA), femoral (CFA) and brachial (BA) diastolic diameters (DD), and CCA intima-media thickness (cIMT). Arterial elastic moduli (EM) were calculated. Arterial parameters were standardized with equations derived from a reference population (no cardiovascular risk factor exposure). Simple linear regression models were obtained for the different standardized arterial parameters with zBMI as the independent variable. Statistical threshold was 0.05.
Results
We found a positive and significant association between zBMI and standardized pSBP (β = 0.210), pPP (β = 0.150), cSBP (β = 0.204) and cPP (β = 0.188), CCA DD (β = 0.145), FCA (β = 0.143), BA (β = 0.210), cIMT (β = 0.135), and CCA EM (β = 0.117).
Conclusions
Higher zBMI associated higher standardized arterial blood pressure, stiffness levels, diameters and thickness. Hemodynamic parameters presented the stronger associations with zBMI variations.
High blood pressure states (HBP) would differ in wave components and reflections indexes, which could associate clinical and prognostic implications. The study aims: 1) to characterize the ...association of aortic wave components and reflection parameters (backward Pb, forward Pf, Pb/Pf ratio and augmentation index AIx) with demographic, anthropometric, hemodynamic and arterial parameters in healthy children and adolescents; 2) to generate multivariate prediction models for the associations, to contribute to understand the main determinants of Pf, Pb, Pb/Pf and AIx; 3) to identify if differences in wave reflection indexes observed in HBP could be explained by differences in the analyzed parameters.
Healthy children and adolescents (n=816, females: 386; Age: 3-20 years) were studied.
central aortic pressure and wave components (Pb, Pf, Pb/Pf and AIx determination with SphygmoCor SCOR and Mobil-o-Graph MOG); anthropometric assessment; regional arterial stiffness (carotid-femoral, carotid-radial pulse wave velocity PWV and PWV ratio); carotid intima-media thickness; carotid and femoral distensbility; cardiac output; systemic vascular resistances (SVR). Simple and multiple regression models were constructed to determine aortic wave parameters; the main explanatory variables. Normotensive and HBP groups were compared. Differences in wave reflection indexes were analyzed before and after controlling for explanatory variables. Equivalences between SphygmoCor and Mobil-O-Graph data were assessed (correlation and Bland-Altman analyses).
There were systematic and proportional differences between the data obtained with SphygmoCor and Mobil-O-Graph devices. Heart rate (HR), peripheral pulse pressure, height and weight were the variables that isolated (simple associations) or combined (multiple associations), showed the major capability to explain interindividual differences in Pf, Pb, Pb/Pf and AIx. Arterial stiffness also showed explanatory capacity, being the carotid the artery with the major contribution. HBP associated higher Pf, Pb, AIx and lower Pb/Pf ratio. Those findings were observed together with higher weight, arterial stiffness and HR. After adjusting for anthropometric characteristics, HR, cardiac output and SVR, the HBP group showed greater Pf and Pb. Then, Pf and Pb characteristics associated with HBP would not be explained by anthropometric or hemodynamic factors. Evaluating wave components and reflection parameters could contribute to improve the comprehension and management of HBP states.
Cardiac resynchronization therapy (CRT) has benefits on left ventricle (LV) performance, but its mid-term effects on LV load and LV-arterial coupling are unknown.
To evaluate CRT mid-term effects on ...LV-arterial coupling, arterial load and its determinants, and the association between CRT-dependent aortic haemodynamic changes and the arterial biomechanics.
Cardiac and aortic echographies were done in 25 patients (age: 61 ± 12 years; 14 men; New York Heart Association functional classes III-IV; LV ejection fraction = 28 ± 7%, QRS = 139 ± 20 ms) before and after (23 ± 12 days) CRT. Standard structural and functional parameters and dyssynchrony indices were evaluated. Ascending aorta flow and diameter waveforms were measured. Central pressure was derived using a transfer function and the diameter calibration method. Calculus: arterial elastance (EA); aortic impedance (Zc) and distensibility (AD); systemic resistances (SVR), total compliance (CT); global reflection coefficient; LV end-systolic elastance (EES); and LV-arterial coupling (EA/EES). After CRT EA diminished (-30%;P = 0.001), EES increased (29%; P = 0.001) and EA/EES improved (pre-CRT: 2.9 ± 0.9, post-CRT: 1.6 ± 0.7; P = 0.001). Arterial elastance changes were associated with changes in arterial properties. Cardiac resynchronization therapy was associated with pressure-independent increase in mean aortic diameter (pre-CRT: 30.0 ± 4.0 mm, post-CRT: 33.0 ± 5.1 mm; P = 0.005) and distensibility (pre-CRT: 3.8 ± 2.6 × 10(-3)mmHg(-1), post-CRT: 6.4 ± 2.5 × 10(-3) mmHg(-1); P = 0.002), and Zc reduction (pre-CRT: 3.5 ± 1.8 × 10(-2)mmHg.s/mL, post-CRT:1.9 ± 0.8 × 10(-2) mmHg.s/mL; P = 0.001) and SVR (pre-CRT:1.7 ± 0.4 mmHg.s/mL, post-CRT:1.0 ± 0.3 mmHg.s/mL; P = 0.001). Changes in EA determinants were associated with changes in aortic flow.
Early after CRT central and peripheral arterial biomechanics improved, determining a pressure-independent increase in aortic diameter and a reduction in arterial load. Left ventricular systolic performance and LV-arterial coupling were enhanced. Arterial biomechanical changes were associated with aortic flow changes.
The increase of arterial stiffness has been to have a significant impact on predicting mortality in end-stage renal disease patients. Pulse wave velocity (PWV) is a noninvasive, reliable parameter of ...regional arterial stiffness that integrates the vascular geometry and arterial wall intrinsic elasticity and is capable of predicting cardiovascular mortality in this patient population. Nevertheless, reports on PWV in dialyzed patients are contradictory and sometimes inconsistent: some reports claim the arterial wall stiffness increases (i.e., PWV increase), others claim that it is reduced, and some even state that it augments in the aorta while it simultaneously decreases in the brachial artery pathway. The purpose of this study was to analyze the literature in which longitudinal or transversal studies were performed in hemodialysis and/or peritoneal dialysis patients, in order to characterize arterial stiffness and the responsiveness to renal replacement therapy.
Aim. To analyze if childhood obesity associates with changes in elastic, transitional, and/or muscular arteries’ stiffness. Methods. 221 subjects (4–15 years, 92 females) were assigned to normal ...weight (NW, n=137) or obesity (OB, n=84) groups, considering their body mass index z-score. Age groups were defined: 4–8; 8–12; 12–15 years old. Carotid, femoral, and brachial artery local stiffness was determined through systodiastolic pressure-diameter and stress-strain relationships. To this end, arterial diameter and peripheral and aortic blood pressure (BP) levels and waveforms were recorded. Carotid-femoral, femoropedal, and carotid-radial pulse wave velocities were determined to evaluate aortic, lower-limb, and upper-limb regional arterial stiffness, respectively. Correlation analysis between stiffness parameters and BP was done. Results. Compared to NW, OB subjects showed higher peripheral and central BP and carotid and femoral stiffness, reaching statistical significance in subjects aged 12 and older. Arterial stiffness differences disappeared when levels were normalized for BP. There were no differences in intrinsic arterial wall stiffness (elastic modulus), BP stiffness relationships, and regional stiffness parameters. Conclusion. OB associates with BP-dependent and age-related increase in carotid and femoral (but not brachial) stiffness. Stiffness changes would not be explained by intrinsic arterial wall alterations but could be associated with the higher BP levels observed in obese children.
Arterial changes associated with children and adolescents high blood pressure (HBP) states would vary depending on the arterial type, arterial indexes considered and/or on blood pressure (BP) levels.
...To determine in children and adolescents: 1) if there is gradual structural-functional arterial impairment associated with gradual peripheral (brachial) systolic BP (pSBP) level or z-score increases, and 2) whether subjects with HBP levels and those with normal BP differ in the profiles of arterial changes associated with pSBP deviations.
1005 asymptomatic children and adolescents were included. Clinical, anthropometric and arterial non-invasive evaluations were performed. Heart rate, brachial BP, aortic BP and wavederived parameters (i.e. augmentation index), carotid and femoral diameters, blood velocities and elastic modulus, carotid intima-media thickness and aortic pulse wave velocity, were obtained. Two groups were assembled: Reference (without cardiovascular risk factors (CVRFs); n=379) and HBP (n=175). Additionally, subjects were ascribed to groups according to their pSBP z-scores (z-score ≤ 0, 0< z-score < 1 or z-score ≥ 1). Age and sex-related mean and standard deviation equations were obtained for each variable (Reference group). Using those equations, data (entire population) were converted into z-scores. Groups were compared (absolute and z-scored variables) before and after adjusting for cofactors (ANOVA/ANCOVA). Linear regression analyses were done considering: pSBP and z-pSBP (independent) and absolute levels and z-scores for hemodynamic and arterial indexes (dependent variables). Differences in hemodynamic and arterial levels and z-scores variations (dependent) associated with variations in pSBP and z-pSBP (independent variable) were assessed. The slopes of the models for Reference and HBP groups were compared.
HBP states associate hemodynamic and arterial changes not explained by exposure to other CVRFs, anthropometric or demographic factors. The higher the pSBP deviations from ageand sex-expected mean value in the Reference group, the higher the hemodynamic and arterial indexes deviation. The pSBP-related variations in hemodynamic and arterial indexes would not differ depending on whether HBP states are present or not.
In this paper, we analyze how elastic and viscoelastic properties differ across seven locations along the large arteries in 11 sheep. We employ a two-parameter elastic model and a four-parameter ...Kelvin viscoelastic model to analyze experimental measurements of vessel diameter and blood pressure obtained in vitro at conditions mimicking in vivo dynamics. Elastic and viscoelastic wall properties were assessed via solutions to the associated inverse problem. We use sensitivity analysis to rank the model parameters from the most to the least sensitive, as well as to compute standard errors and confidence intervals. Results reveal that elastic properties in both models (including Young's modulus and the viscoelastic relaxation parameters) vary across locations (smaller arteries are stiffer than larger arteries). We also show that for all locations, the inclusion of viscoelastic behavior is important to capture pressure-area dynamics.
Despite the clinical utility of echocardiography to measure cardiac target organ injury (TOI) there are scarcities of data about the reference intervals (RIs) and percentiles of left ventricular (LV) ...mass (LVM) and derived indexes (LVMI and LVMI
2.7
), relative wall thickness (LVRWT) and ejection fraction (LVEF) from population-based studies in children and adolescents. The aim of this study was to generate reference intervals RIs of LVM and derived indexes (LVMI and LVMI
2.7
), LVRWT, and LVEF obtained in healthy children, adolescents, and young adults from a South-American population. Echocardiographic studies were obtained in 1096 healthy subjects (5–24 years). Age and sex-specific RIs of LVM, LVMI, LVMI
2.7
, LVRWT, and LVEF were generated using parametric regression based on fractional polynomials. After covariate analysis (i.e., adjusting by age, body surface area) specific sex-specific RIs were evidenced as necessaries. Age and sex-specific 1st, 2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, 97.5th, and 99th percentile and curves were reported and compared with previously reported RIs. RIs showed high concordance and complementarity with what was previously reported for the population of North-American children (0–18 years old). In conclusion, in children and adolescents the interpretation of the LVM, LVMIs, LVRWT, and LVEF RIs requires sex-related RIs. This study provides the largest Argentinean database concerning RIs and percentile curves of LVM, LVMIs, LVRWT, and LVEF as markers of cardiac TOI obtained in healthy children and adolescents. These data are valuable in that they provide RIs values with which data of populations of children, adolescents can be compared.
Background. Adequate fluid management could be essential to minimize high arterial stiffness observed in chronically hemodialyzed patients (CHP). Aim. To determine the association between body fluid ...status and central and peripheral arterial stiffness levels. Methods. Arterial stiffness was assessed in 65 CHP by measuring the pulse wave velocity (PWV) in a central arterial pathway (carotid-femoral) and in a peripheral pathway (carotid-brachial). A blood pressure-independent regional arterial stiffness index was calculated using PWV. Volume status was assessed by whole-body multiple-frequency bioimpedance. Patients were first observed as an entire group and then divided into three different fluid status-related groups: normal, overhydration, and dehydration groups. Results. Only carotid-femoral stiffness was positively associated (P<0.05) with the hydration status evaluated through extracellular/intracellular fluid, extracellular/Total Body Fluid, and absolute and relative overhydration. Conclusion. Volume status and overload are associated with central, but not peripheral, arterial stiffness levels with independence of the blood pressure level, in CHP.
PDF
