Lee J S
Department of Biomedical Engineering, University of Virginia, Charlottesville 22908.
Microvasc Res. 1988 Jan;35(1):48-62. doi: 10.1016/0026-2862(88)90049-0.
We used a Fourier transform method to compute from the density fluctuation of aortic blood the changes in the blood volume of pulmonary capillaries and the transit time from the capillaries to the aorta. First the time constants of a lagged normal density function capable of simulating the saline dilution through the central circulation were established. Then we decomposed the Fourier transform of the lagged normal density function to determine an attenuation for the estimation of the density fluctuation in blood leaving the capillaries. Regarding the low hematocrit blood in the capillaries as a density indicator, we deduced from the density fluctuation the percentage change of capillary volume for dogs ventilated mechanically. This change was found to range from 3.8 to 5.8% for frequencies within 6 to 20 cycles per minute. Based on this simulation and the delay time of the density fluctuation from the tracheal pressure, we estimated that the transit time for the density indicator being released from the pulmonary capillaries to the aorta was 45% of the mean transit time of the central circulation, suggesting that the releasing sites are midway of the pulmonary capillaries.
我们采用傅里叶变换方法，根据主动脉血液的密度波动来计算肺毛细血管血容量的变化以及血液从毛细血管到主动脉的传输时间。首先，确定了一个能够模拟生理盐水通过体循环稀释的滞后正态密度函数的时间常数。然后，对滞后正态密度函数的傅里叶变换进行分解，以确定一个衰减值，用于估计离开毛细血管的血液密度波动。将毛细血管内低血细胞比容血液视为密度指标，我们从密度波动中推导出机械通气犬肺毛细血管容积的百分比变化。发现对于每分钟6至20次循环的频率，这种变化范围为3.8%至5.8%。基于此模拟以及密度波动相对于气管压力的延迟时间，我们估计密度指标从肺毛细血管释放到主动脉的传输时间为体循环平均传输时间的45%，这表明释放部位位于肺毛细血管的中间位置。
