Deakin Charles D, Sado Daniel M, Petley Graham W, Clewlow Frank
Shackleton Department of Anaesthetics, Southampton University Hospital, N.H.S. Trust, Tremona Road, Southampton SO16 6YD, UK.
Resuscitation. 2004 Feb;60(2):171-4. doi: 10.1016/j.resuscitation.2003.10.001.
Two mechanisms by which firm external paddle force decreases transthoracic impedance (TTI) have been proposed. Decreased impedance at the paddle-skin interface has been assumed to be the primary mechanism, but expulsion of air from the lungs, reducing lung volume is also likely to contribute. The relative contribution of each mechanism is unknown.
Thirty five intubated patients undergoing general anaesthesia for cardiac surgery were studied. TTI across external defibrillation paddles was measured as paddle force was increased to 12kgf. Measurements were performed twice; once allowing the volume of the lungs to change and once with lung volume held at functional residual capacity. TTI with constant lung volume was significantly higher at (P< 0.001), confirming that a reduction in lung volume contributes to the decrease in TTI. At an optimal paddle force of 8kg, the reduction in lung volume contributed to 16.2% of the overall decrease in TTI.
The decrease in TTI seen with increasing external paddle force is due primarily to improved electrical contact at the paddle-skin interface, with a decrease in thoracic volume accounting for no more than 16% of the overall decrease at forces used clinically.
已经提出了两种机制来解释外部硬电极片压力降低经胸阻抗（TTI）的现象。电极片与皮肤界面处阻抗的降低被认为是主要机制，但肺部气体排出、肺容积减小也可能起到了作用。每种机制的相对贡献尚不清楚。
对35例接受心脏手术全身麻醉的插管患者进行了研究。随着电极片压力增加到12千克力，测量了外部除颤电极片的经胸阻抗。测量进行了两次；一次允许肺容积变化，一次将肺容积保持在功能残气量。肺容积恒定时的经胸阻抗显著更高（P<0.001），证实肺容积减小导致了经胸阻抗降低。在8千克的最佳电极片压力下，肺容积减小占经胸阻抗总体降低的16.2%。
随着外部电极片压力增加，经胸阻抗降低主要是由于电极片与皮肤界面处电接触改善，胸腔容积减小在临床使用的压力下对总体降低的贡献不超过16%。
