Arterial wall mechanics in conscious dogs. Assessment of viscous, inertial, and elastic moduli to characterize aortic wall behavior.

To evaluate arterial physiopathology, complete arterial wall mechanical characterization is necessary. This study presents a model for determining the elastic response of elastin (sigma E, where sigma is stress), collagen (sigma C), and smooth muscle (sigma SM) fibers and viscous (sigma eta) and inertial (sigma M) aortic wall behaviors. Our work assumes that the total stress developed by the wall to resist stretching is governed by the elastic modulus of elastin fibers (EE), the elastic modulus of collagen (EC) affected by the fraction of collagen fibers (fC) recruited to support wall stress, and the elastic modulus of the maximally contracted vascular smooth muscle (ESM) affected by an activation function (fA). We constructed the constitutive equation of the aortic wall on the basis of three different hookean materials and two nonlinear functions, fA and fC: sigma = sigma E + sigma C + sigma SM + sigma eta + sigma M = EE. (epsilon - epsilon 0E) + EC.fC.epsilon + ESM.fA.epsilon + eta. [equation: see text] + M.[equation: see text] where epsilon is strain and epsilon 0E is strain at zero stress. Stress-strain relations in the control state and during activation of smooth muscle (phenylephrine, 5 micrograms.kg-1.min-1 IV) were obtained by transient occlusions of the descending aorta and the inferior vena cava in 15 conscious dogs by using descending thoracic aortic pressure (microtransducer) and diameter (sonomicrometry) measurements. The fC was not linear with strain, and at the onset of significant collagen participation in the elastic response (break point of the stress-strain relation), 6.02 +/- 2.6% collagen fibers were recruited at 23% of stretching of the unstressed diameter. The fA exhibited a skewed unimodal curve with a maximum level of activation at 28.3 +/- 7.9% of stretching. The aortic wall dynamic behavior was modified by activation increasing viscous (eta) and inertial (M) moduli from the control to active state (viscous, 3.8 +/- 1.3 x 10(4) to 7.8 +/- 1.1 x 10(4) dyne.s.cm-2, P < .0005; inertial, 61 +/- 42 to 91 +/- 23 dyne.s2.cm-2, P < .05). Finally, the purely elastic stress-strain relation was assessed by subtracting the viscous and inertial behaviors.

[1]  Joseph P. Murgo,et al.  Age-Related Changes in Left Ventricular/Arterial Coupling , 1987 .

[2]  R. Armentano,et al.  Assessment of elastin and collagen contribution to aortic elasticity in conscious dogs. , 1991, The American journal of physiology.

[3]  C. Ting,et al.  Compliance changes in physiological and pathological states , 1992, Journal of hypertension. Supplement : official journal of the International Society of Hypertension.

[4]  W. Nichols.  McDonald's Blood Flow in Arteries , 1996 .

[5]  A. Rovick,et al.  Influence of vascular smooth muscle on contractile mechanics and elasticity of arteries. , 1969, The American journal of physiology.

[6]  R. D. Bauer,et al.  Separate determination of the pulsatile elastic and viscous forces developed in the arterial wall in vivo , 2004, Pflügers Archiv.

[7]  D H Fitchett.  LV-arterial coupling: interactive model to predict effect of wave reflections on LV energetics. , 1991, The American journal of physiology.

[8]  S. Glagov,et al.  Transmural Organization of the Arterial Media: The Lamellar Unit Revisited , 1985, Arteriosclerosis.

[9]  Sparks Hv.  EFFECT OF QUICK STRETCH ON ISOLATED VASCULAR SMOOTH MUSCLE. , 1964 .

[10]  R. Armentano,et al.  Paradoxically decreased aortic wall stiffness in response to vitamin D3-induced calcinosis. A biphasic analysis of segmental elastic properties in conscious dogs. , 1991, Circulation research.

[11]  F. Yin.  Ventricular/Vascular Coupling , 1987, Springer New York.

[12]  R. Armentano,et al.  Assessment of smooth muscle contribution to descending thoracic aortic elastic mechanics in conscious dogs. , 1993, Circulation research.

[13]  G. Langewouters,et al.  The static elastic properties of 45 human thoracic and 20 abdominal aortas in vitro and the parameters of a new model. , 1984, Journal of biomechanics.

[14]  W. Bayliss.  On the local reactions of the arterial wall to changes of internal pressure , 1902, The Journal of physiology.

[15]  B. J. Winer.  Statistical Principles in Experimental Design , 1992 .

[16]  J. Rüegg,et al.  Smooth muscle tone. , 1971, Physiological reviews.

[17]  Alain Simon,et al.  Mechanical Pressure Versus Intrinsic Effects of Hypertension on Large Arteries in Humans , 1991, Hypertension.

[18]  L Finkelstein,et al.  Validation of simple and complex models in physiology and medicine. , 1984, The American journal of physiology.

[19]  R. Cox.  Effects of norepinephrine on mechanics of arteries in vitro. , 1976, The American journal of physiology.

[20]  E de Forteza,et al.  Real-time pressure-volume diagrams for the evaluation of ventricular function. , 1986, Journal of biomedical engineering.

[21]  L. Lundholm,et al.  Length at Inactivated Contractile Elements, Length‐tension Diagram Active State and Tone of Vascular Smooth Muscle , 1966 .

[22]  E. Bozler.  AN ANALYSIS OF THE PROPERTIES OF SMOOTH MUSCLE , 1936 .

[23]  D. A. Mcdonald.  Blood flow in arteries , 1974 .

[24]  W. Nichols,et al.  Left Ventricular-Systemic Arterial Coupling in Humans and Strategies to Improve Coupling in Disease States , 1987 .

[25]  R H Cox,et al.  Arterial wall mechanics and composition and the effects of smooth muscle activation. , 1975, The American journal of physiology.

[26]  B. J. Winer,et al.  Basic concepts in statistical inference. , 1962 .

[27]  C. Wiederhielm,et al.  Viscoelastic description of a collagenous tissue in simple elongation. , 1969, Journal of applied physiology.

[28]  A. Simon,et al.  Overview on atherosclerotic systolic hypertension. , 1987, International journal of cardiology.

[29]  M Pagani,et al.  Effects of Age on Aortic Pressure‐Diameter and Elastic Stiffness‐Stress Relationships in Unanesthetized Sheep , 1979, Circulation research.

[30]  Lysle H. Peterson,et al.  Mechanical Properties of Arteries in Vivo , 1960 .

[31]  N. Akaike,et al.  Internal perfusion studies demonstrating GABA-induced chloride responses in frog primary afferent neurons. , 1984, The American journal of physiology.

[32]  M Arditi,et al.  Non-invasive estimate of the mechanical properties of peripheral arteries from ultrasonic and photoplethysmographic measurements. , 1991, Clinical physics and physiological measurement : an official journal of the Hospital Physicists' Association, Deutsche Gesellschaft fur Medizinische Physik and the European Federation of Organisations for Medical Physics.