Dinno M A, Crum L A, Wu J
Department of Physics, University of Mississippi, University 38677.
Ultrasound Med Biol. 1989;15(5):461-70. doi: 10.1016/0301-5629(89)90099-9.
There are two groups of mechanisms through which ultrasound can affect biological systems, those of thermal origin and others of nonthermal origin. Since in almost every therapeutic application of ultrasound, movement of ions across cellular membranes is involved, it becomes important to study the effect of ultrasound on active and passive ionic conductance. In order to differentiate between thermal and nonthermal effects, a study was conducted on model systems in which the effect of temperature is known. The well-known sodium transporting epithelium, the epidermis of abdominal frog skin, was investigated and the effect of therapeutic ultrasound on its electrophysiological properties was determined. It was found that under open circuit conditions, irradiation of the skin with 1 MHz cw (60-480 mW/cm2) ultrasound caused a significant decrease (5-50%, depending on the applied power) in the transepithelial potential and resistance at room temperature (20-22 degrees C). Under short circuit conditions, also at room temperature, there was an increase in total ionic conductance (20-250%, depending on the applied power) and a decrease in the net actively transported current, measured as the short circuit current. These effects are reversible within the range of powers used. Furthermore, it was found that the magnitude of the observed changes was strongly dependent on the perfusion rate and the gas content of the bathing medium. The effect of ultrasound diminished in the presence of CO2 and was enhanced with faster perfusion rates. Pulsed ultrasound delivered at the same energy (Isata) as that of cw caused a significantly larger effect. At lower temperatures (12-14 degrees C) the effect of ultrasound was reduced. Analysis of the data reveals that the effects of ultrasound on ion transport reported here are not primarily of thermal origin but are probably due to cavitation and related effects, such as microsteaming.
超声影响生物系统有两类机制，一类是热效应机制，另一类是非热效应机制。由于在几乎每一种超声治疗应用中，离子跨细胞膜的移动都涉及其中，因此研究超声对主动和被动离子电导的影响变得很重要。为了区分热效应和非热效应，对温度效应已知的模型系统进行了一项研究。对著名的钠转运上皮组织——腹部蛙皮的表皮进行了研究，并确定了治疗性超声对其电生理特性的影响。结果发现，在开路条件下，用1兆赫连续波（60 - 480毫瓦/平方厘米）超声照射皮肤，在室温（20 - 22摄氏度）下会导致跨上皮电位和电阻显著降低（5 - 50%，取决于施加的功率）。在短路条件下，同样在室温下，总离子电导增加（20 - 250%，取决于施加的功率），而作为短路电流测量的净主动转运电流减少。在所用功率范围内，这些效应是可逆的。此外，还发现观察到的变化幅度强烈依赖于灌注速率和浴液的气体含量。在有二氧化碳存在时，超声的效应减弱，而灌注速率加快时效应增强。以与连续波相同的能量（声强）施加的脉冲超声产生的效应明显更大。在较低温度（12 - 14摄氏度）下，超声的效应减弱。对数据的分析表明，此处报道的超声对离子转运的效应主要不是热效应，而可能是由于空化及相关效应，如微蒸发现象。
