Bia Daniel, Zócalo Yanina, Armentano Ricardo L, Camús Juan, de Forteza Eduardo, Cabrera-Fischer Edmundo
Departamento de Fisiología, Facultad de Medicina, Universidad de la República, Montevideo, Uruguay.
Rev Esp Cardiol. 2007 May;60(5):501-9.
Ventricular dynamic afterload depends on arterial viscoelastic and geometric properties. Vasoactive factors produced in the adventitia modulate arterial tone. However, it is still not known whether the adventitia is involved in determining the magnitude of the dynamic afterload. The aim of this study was to investigate the role played by the adventitia, via smooth muscle-dependent mechanisms, in determining dynamic afterload.
The diameter, pressure and flow in brachiocephalic trunks from sheep were measured before and after removal of the adventitia, both in vivo with muscular reactivity preserved (n=8) and in vitro with muscular reactivity abolished (n=8). All studies were performed under similar hemodynamic conditions. Dynamic afterload was determined from elastic and viscous arterial responses, elastic and viscous work, arterial characteristic impedance, and pulse wave velocity. Comparison of in vivo and in vitro findings enabled smooth muscle-dependent changes to be evaluated.
Only in vivo, did removal of the adventitia lead to a reduction in vessel diameter (17.32 [2.02] vs 15.46 [1.28] mm) and to increases in elastic (7.21 [1.39] vs 15.59 [3.00] x 10(6) dyn.cm(-2)) and viscous (5.16 [2.04] vs 9.87 [2.00] x 10(5) dyn.s.cm(-2)) arterial responses, elastic (6.15 [1.08] vs 9.20 [0.76] x 10(-2) J/m2) and viscous work (11.61 [2.25] vs 15.20 [2.37] x 10(-3) J/m2), impedance (223.97 [136.11] vs 396.33 [182.27] dyn x s x cm(-3)), and pulse wave velocity (397.70 [31.21] vs 598.78 [28.04] cm.s(-1)) (P<.05). The reduction in diameter and the increases in elastic and viscous responses are evidence of muscular activation.
The adventitia may contribute to the control of ventricular dynamic afterload by means of mechanisms dependent on muscular tone.
心室动态后负荷取决于动脉的粘弹性和几何特性。外膜产生的血管活性因子调节动脉张力。然而，外膜是否参与确定动态后负荷的大小仍不清楚。本研究的目的是通过平滑肌依赖性机制研究外膜在确定动态后负荷中所起的作用。
在保留肌肉反应性的体内（n = 8）和消除肌肉反应性的体外（n = 8）条件下，测量绵羊头臂干在去除外膜前后的直径、压力和流量。所有研究均在相似的血流动力学条件下进行。根据弹性和粘性动脉反应、弹性和粘性功、动脉特征阻抗和脉搏波速度确定动态后负荷。体内和体外研究结果的比较有助于评估平滑肌依赖性变化。
仅在体内，去除外膜导致血管直径减小（17.32 [2.02] 对 15.46 [1.28] mm），弹性（7.21 [1.39] 对 15.59 [3.00]×10(6) dyn.cm(-2)）和粘性（5.16 [2.04] 对 9.87 [2.00]×10(5) dyn.s.cm(-2)）动脉反应、弹性（6.15 [1.08] 对 9.20 [0.76]×10(-2) J/m2）和粘性功（11.61 [2.25] 对 15.20 [2.37]×10(-3) J/m2）、阻抗（223.97 [136.11] 对 396.33 [182.27] dyn×s×cm(-3)）和脉搏波速度（397.70 [31.21] 对 598.78 [28.04] cm.s(-1)）增加（P<.05）。直径减小以及弹性和粘性反应增加是肌肉激活的证据。
外膜可能通过依赖于肌肉张力的机制有助于控制心室动态后负荷。
