Kenner T, Leopold H, Hinghofer-Szalkay H
Pflugers Arch. 1977 Jul 29;370(1):25-9. doi: 10.1007/BF00707941.
The "mechanical oscillator" technique for the measurement of the density of fluids is based on the influence of mass on the natural frequency of a mechanical oscillator. The practical application of this principle was worked out by Kratky et al. (1969) and Leopold (1970). It is demonstrated in this study that the method permits the continuous high-precision measurement of the density of flowing blood in anesthetized animals. The accuracy is 10(5) g/ml, the maximum sampling rate 20/min. As found in rabbits and cats during the control state, physiological blood density changes related to spontaneous blood pressure variations are up to 2-10(4) g/ml. The method can be combined with i.v. injections of isotonic and iso-oncotic solutions to determine cardiac output and blood volume on the basis of a "density dilution" principle. Since the density of the interstitial fluid is lower than that of blood, fluid shifts through the capillary walls can be detected. The effects of hypertonic glucose and of hyperoncotic dextran have been examined. Changes in the density of the arterial blood appear within 10 s after i.v. injection of these fluids. Similarly, density changes result from hemorrhage and reinfusion. During and after i.v. administration of vasoactive drugs (noradrenaline, angiotensin II, acetylcholine), marked transient changes in blood density are seen which obviously reflect the effects of fluid shifts through the capillary walls. During hemorrhagic hypotension we found periodic variations in the blood density synchronous with spontaneously occurring Mayer waves. The new method seems to be a promising tool for investigations physiological and pathological capillary fluid dynamics.
用于测量流体密度的“机械振荡器”技术基于质量对机械振荡器固有频率的影响。Kratky等人（1969年）和Leopold（1970年）得出了这一原理的实际应用方法。本研究表明，该方法能够对麻醉动物体内流动血液的密度进行连续高精度测量。测量精度为10⁻⁵g/ml，最大采样率为20次/分钟。在对照状态下的兔子和猫身上发现，与自发性血压变化相关的生理性血液密度变化高达2 - 10⁻⁴g/ml。该方法可与静脉注射等渗和等胶体溶液相结合，基于“密度稀释”原理来测定心输出量和血容量。由于组织间液的密度低于血液，因此可以检测到液体通过毛细血管壁的移动。研究了高渗葡萄糖和高胶体右旋糖酐的影响。静脉注射这些液体后10秒内，动脉血密度就会出现变化。同样，出血和再灌注也会导致密度变化。在静脉注射血管活性药物（去甲肾上腺素、血管紧张素II、乙酰胆碱）期间及之后，可以看到血液密度出现明显的短暂变化，这显然反映了液体通过毛细血管壁移动的影响。在出血性低血压期间，我们发现血液密度的周期性变化与自发出现的迈尔波同步。这种新方法似乎是研究生理性和病理性毛细血管流体动力学的一种很有前景的工具。
