Effect Of Smooth Muscle Contraction Research Articles

A110 生理的変形状態に置かれた血管壁内ひずみの半径方向分布に対する平滑筋収縮の影響の計測(A1-3 軟組織のバイオメカニクス1)

A110 生理的変形状態に置かれた血管壁内ひずみの半径方向分布に対する平滑筋収縮の影響の計測(A1-3 軟組織のバイオメカニクス1)

A constitutive formulation of arterial mechanics including vascular smooth muscle tone.

A pseudo-strain energy function (pseudo-SEF) describing the biomechanical properties of large conduit arteries under the influence of vascular smooth muscle (VSM) tone is proposed. In contrast to previous models that include the effects of smooth muscle contraction through generation of an active stress, in this study we consider the vascular muscle as a structural element whose contribution to load bearing is modulated by the contraction. This novel pseudo-SEF models not only arterial mechanics at maximal VSM contraction but also the myogenic contraction of the VSM in response to local increases in stretch. The proposed pseudo-SEF was verified with experimentally obtained pressure-radius curves and zero-stress state configurations from rat carotid arteries displaying distinct differences in VSM tone: arteries from normotensive rats displaying minimal VSM tone and arteries from hypertensive rats exhibiting significant VSM tone. The pressure-radius curves were measured in three different VSM states: fully relaxed, maximally contracted, and normal VSM tone. The model fitted the experimental data very well (r2 > 0.99) in both the normo- and hypertensive groups for all three states of VSM activation. The pseudo-SEF was used to illustrate the localized reduction of circumferential stress in the arterial wall due to normal VSM tone, suggesting that the proposed pseudo-SEF can be of general utility for describing stress distribution not only under passive VSM conditions, as most SEFs proposed so far, but also under physiological and pathological conditions with varying levels of VSM tone.

Theoretical study of the effects of vascular smooth muscle contraction on strain and stress distributions in arteries.

To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. Considering that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a ring segment cut out from the artery and exposed to no external load. When the ring specimen is cut radially, it springs open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. During temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level.

Vagal esophageal receptors in anesthetized dogs: mechanical and chemical responsiveness.

This study was performed to evaluate the characteristics of esophageal receptors in anesthetized and artificially ventilated dogs. The electrical activity of the esophageal afferents was recorded from the peripheral cut end of the cervical vagus nerve. A cuffed catheter was inserted into the esophagus at the level of the third tracheal ring and was used to establish the esophageal location of the endings. Most of the receptors were localized in the intrathoracic portion of the esophagus. The majority of the receptors studied (36 of 43) showed a slow adaptation to a maintained stretch of the esophageal wall. Vagal cooling blocked receptor activity at temperatures ranging from 3.5 to 25 degrees C. Twenty-eight of 43 receptors, including 4 rapidly adapting endings (RAR), were challenged with saline, HCl + pepsin (HCl-P; pH 1) and distilled water (8 ml, 37 degrees C). HCl-P solutions specifically stimulated only three receptors; saline or water did not. Five slowly adapting receptors and two RARs were also challenged with topically applied capsaicin; only one RAR was stimulated. To ascertain a possible effect of smooth muscle contraction, 17 receptors were tested with intravenous injections of ACh and/or asphyxia; only 4 were stimulated. These characteristics do not support an important reflexogenic role of the esophagus in response to chemical stimuli.

Conservation of bronchiolar wall area during constriction and dilation of human airways.

We assessed the effect of smooth muscle contraction and relaxation on airway lumen subtended by the internal perimeter (Ai) and total cross-sectional area (Ao) of human bronchial explants in the absence of the potential lung tethering forces of alveolar tissue to test the hypothesis that bronchoconstriction results in a comparable change of Ai and Ao. Luminal area (i.e., Ai) and Ao were measured by using computerized videomicrometry, and bronchial wall area was calculated accordingly. Images on videotape were captured; areas were outlined, and data were expressed as internal pixel number by using imaging software. Bronchial rings were dissected in 1.0- to 1.5-mm sections from macroscopically unaffected areas of lungs from patients undergoing resection for carcinoma, placed in microplate wells containing buffered saline, and allowed to equilibrate for 1 h. Baseline, Ao [5.21 +/- 0.354 (SE) mm2], and Ai (0.604 +/- 0.057 mm2) were measured before contraction of the airway smooth muscle (ASM) with carbachol. Mean Ai narrowed by 0.257 +/- 0.052 mm2 in response to 10 microM carbachol (P = 0.001 vs. baseline). Similarly, Ao narrowed by 0.272 +/- 0.110 mm2 in response to carbachol (P = 0.038 vs. baseline; P = 0.849 vs. change in Ai). Similar parallel changes in cross-sectional area for Ai and Ao were observed for relaxation of ASM from inherent tone of other bronchial rings in response to 10 microM isoproterenol. We demonstrate a unique characteristic of human ASM; i.e., both luminal and total cross-sectional area of human airways change similarly on contraction and relaxation in vitro, resulting in a conservation of bronchiolar wall area with bronchoconstriction and dilation.

Change in Residual Strain in Rat Thoracic Aorta Due to Smooth Muscle Contraction/Relaxation(Positional Variation along the Aortic Tree).

The effect of smooth muscle contraction on strain distribution in the arterial wall was investigated. The opening angle of short, ring-shaped specimens obtained at various longitudinal positions of rat thoracic aortas was measured in an aerated Krebs-Ringer solution (37°C) under smooth muscle contraction induced with norepinephrine and under relaxation induced with sodium nitroprusside. The angle was significantly greater under smooth muscle contraction than relaxation at all positions except the branching site in the aortic arch. There was significant variation of the angle along the aortic tree under both conditions, being highest at the aortic root and generally low in the descending aorta. The angle reached a local minimum at the branching site. In spite of the large angle variation, the amount of increase in the residual strain due to smooth muscle contraction was very similar among the sites investigated except for the branching site, where smooth muscle alignment differed from that of the other sites. These results suggest that the effect of smooth muscle contraction on residual strain is significant and quantitatively similar among the sites in the thoracic aorta with ordinal histology.

Change in intramural strain distribution in rat aorta due to smooth muscle contraction and relaxation.

Effect of smooth muscle contraction on intramural strain distribution in rat thoracic aorta was investigated with residual strain considered. Short segments sliced from the aortas were cut radially to release residual strain in an aerated Krebs-Ringer solution (37 degrees C). Each segment opened up immediately to form an arc. Opening angle was measured at this point and after smooth muscle contraction and relaxation. The angle increased from 97 +/- 11 degrees (means +/- SE, n = 14) to 153 +/- 14 degrees with the contraction and decreased to 68 +/- 9 degrees with the relaxation, indicating increase in residual strain with smooth muscle contraction. Intramural strain distribution at various pressures was calculated from the opening angle and pressure-diameter relations of the aortas. Strain distribution was almost uniform at 55 mmHg under smooth muscle relaxation, whereas this pressure exceeded 200 mmHg because of the increase in residual strain and decrease in vessel diameter under smooth muscle contraction. These results suggest aortic smooth muscle may change its contractile state through myogenic response to keep intramural strain distribution uniform against temporary change in blood pressure and thus maintain mechanical homeostasis in the aortic wall.

Effect of lung inflation and airway muscle tone on airway diameter in vivo.

How normal airway dimensions change with lung volume is of great importance in determining flow limitation during the normal forced vital capacity maneuver as well as in the manifestation of obstructive lung disease. The literature presents a confusing picture, with some results suggesting that airway diameter increases linearly with the cube root of lung volume and others showing a highly nonlinear relation. The effect of smooth muscle contraction on lung-airway interdependence is even less well understood. Recent morphological work explicitly assumes that airway basement membrane is nondistensible, although the lung volume at which this maximal airway size is reached is unknown. With smooth muscle contraction, folding of the epithelium and basement membrane accounts for the changes in luminal area. In this study, we measured the effect of lung inflation on relaxed and contracted airway areas by using high-resolution computed tomography at different transpulmonary pressures, each held for 2 min. We found that fully relaxed airways are quite distensible up to a pressure of 5-7 cmH2O (P < 0.001), where they reach a maximal size with no further distension up to an airway pressure of 30 cmH2O (P = 0.49). Thus relaxed airways clearly do not expand isotropically with the lung. With smooth muscle tone, the airways in different animals responded differently to lung inflation, with some animals showing minimal airway dilation up to an airway pressure of 20 cmH2O and others showing airways that were more easily dilated with lung expansion. However, maximal diameter of these moderately constricted airways was not usually achieved even up to an airway pressure of 30 cmH2O. Thus a transient deep inspiration in vivo would be expected to have only a small effect on contracted airways.

Diameter and Elasticity of the Ascending Aorta during Infusion of Noradrenaline

AbstractThe effect of smooth muscle contraction on diameter and elasticity of the ascending aorta was examined in 18 anesthetized rabbits. Aortic diameter was measured with ultrasonic technique inside the intact thorax, and blood pressure was recorded from a catheter in the right common carotid artery. Control observations were obtained at various blood pressure levels by producing stepwise changes of the blood volume. At diastolic pressures from 40–90 mm Hg, i.v. infusion of noradrenaline (4–6 μg/kg · min) caused a 6.6% average reduction in diastolic aortic diameter. Noradrenaline at low pressures increased the aortic pressure‐strain elastic modulus (Ep) and theoretical pulse‐wave velocity (PWV) by 30–67%. Control values of Ep and PWV were slightly higher for rabbits than those usually found in dogs. It is concluded that at comparable pressures, contraction of aortic smooth muscle tissue, induced by infusion of noradrenaline, produces a small but significant constriction of the ascending aorta, and, at low pressures only, increases dynamic stiffness of the vessel.