Greenwald S E, Johnson R J, Haworth S G
Cardiovasc Res. 1985 Jan;19(1):44-50. doi: 10.1093/cvr/19.1.44.
The input impedance of the main pulmonary artery in 26 pigs aged from 1 h to 2 weeks has been calculated from measurements of pressure and flow. From these data we have derived estimates of the hydraulic power output of the right heart. The impedance spectra were similar in form to those in many other studies and were consistent with the presence of a single reflection site within the lung. The frequency of the (single) minimum decreased steadily with increasing age as did the corresponding zero crossing point on the phase curve. From estimates of propagation velocity the position of this "reflection site" was found to coincide with the position of the lung periphery in each age group. An overall fall in characteristic impedance with increasing age was found to be due to the increasing diameter of the pulmonary artery rather than to changes in its elasticity. The total power output/body weight of the right heart fell from 10.4 to 4.8 mW X kg-1 from birth to 4 weeks of age. During this period the ratio of pulsatile to steady power fell from 0.5 to 0.31. We conclude that this fall is related to a reduction in the effective reflection of pressure and flow waves within the lung due to increasing attenuation and possibly to a reduction in the magnitude of the lumped reflection coefficient itself.
通过对26头年龄从1小时至2周的猪的压力和流量测量，计算出了主肺动脉的输入阻抗。根据这些数据，我们得出了右心水力功率输出的估计值。阻抗谱的形式与许多其他研究中的相似，并且与肺内存在单个反射点一致。随着年龄的增长，（单个）最小值的频率稳步下降，相位曲线上相应的过零点也如此。根据传播速度的估计，发现这个“反射点”的位置与每个年龄组中肺周边的位置一致。发现特征阻抗随年龄增长而总体下降是由于肺动脉直径的增加，而非其弹性的变化。从出生到4周龄，右心的总功率输出/体重从10.4降至4.8 mW×kg-1。在此期间，脉动功率与稳定功率之比从0.5降至0.31。我们得出结论，这种下降与肺内压力和流量波的有效反射减少有关，这是由于衰减增加以及可能是集总反射系数本身的大小减小所致。
