Li John K-J, Zhu Ying, Geipel Pamela S
Cardiovascular Engineering Lab, Department of Biomedical Engineering, Rutgers University, 599 Taylor Rd, Piscataway, NJ 08854, USA.
Cardiovasc Eng. 2010 Dec;10(4):170-5. doi: 10.1007/s10558-010-9107-y.
Similar pulse pressure increases and flow reductions have been reported by many investigators, despite dissimilar forms of arterial loading applied. Increased vascular load is most commonly observed due to mechanical and vasoactive interventions. The present study intended to differentiate the hemodynamic contributions of these two forms of arterial loading at closely matched blood pressure levels. To accomplish this, proximal aortic characteristic impedance (Z(o)), total arterial compliance (C), peripheral vascular resistance (R(s)) and time-domain resolved forward (P(f)) and reflected (P(r)) waves were obtained in six anesthetized, thoracotomized and ventilated dogs. Acute loading was accomplished by brief descending thoracic aorta (DTA) occlusion or by intravenous bolus infusion of methoxamine (MTX:5 mg/ml) Systolic pressure increases were matched to a similar extent. Results showed that pulse pressures were drastically increased, reflecting large increases in wave reflections and decreases in arterial compliances. Changes in Z(o), R(s) and C were quantitatively different between the two forms of loading. DTA occlusion primarily increased Z(o) and R(s) with a concurrently large reduction in C. MTX infusion significantly increased small vessel R(s) to the same extent as DTA occlusion, but with a slight decrease in C secondary to an increase in pressure, with Z(o) unchanged. Examination of dynamic loading showed similar increases in reflection coefficients, but P(f) and P(r) were qualitatively different. We conclude that vasoactive methoxamine infusion provides primarily an increased resistive load, while mechanical DTA occlusion provides an increased complex load to the left ventricle. These loads also occur earlier and variably during ventricular ejection.
尽管施加的动脉负荷形式不同，但许多研究人员都报告了类似的脉压升高和血流减少情况。由于机械和血管活性干预，最常观察到血管负荷增加。本研究旨在区分在血压水平密切匹配时这两种动脉负荷形式对血流动力学的影响。为实现这一目标，在六只麻醉、开胸并通气的犬身上获取了近端主动脉特征阻抗（Z(o)）、总动脉顺应性（C）、外周血管阻力（R(s)）以及时域分辨的正向（P(f)）和反射（P(r)）波。通过短暂阻断降主动脉（DTA）或静脉推注甲氧明（MTX：5 mg/ml）来实现急性负荷。收缩压升高的程度相似。结果显示脉压急剧升高，反映出波反射大幅增加以及动脉顺应性降低。两种负荷形式下Z(o)、R(s)和C的变化在数量上有所不同。DTA阻断主要使Z(o)和R(s)增加，同时C大幅降低。MTX输注使小血管R(s)显著增加，幅度与DTA阻断相同，但由于压力升高C略有降低，Z(o)不变。动态负荷检查显示反射系数有类似增加，但P(f)和P(r)在性质上有所不同。我们得出结论，血管活性甲氧明输注主要提供增加的阻力负荷，而机械性DTA阻断为左心室提供增加的复合负荷。这些负荷也在心室射血期间更早且变化地出现。
