• Charles F Babbs.
• Department of Basic Medical Sciences, Purdue University, 1246 Lynn Hall, West Lafayette, IN 47907-1246, USA. babbs@purdue.edu
• Resuscitation. 2005 Sep 1;66(3):335-45.

UnlabelledAn impedance threshold valve (ITV) is a new airway adjunct for resuscitation that permits generation of a small vacuum in the chest during the recoil phase of chest compression.ObjectivesTo explore in detail the expected magnitude and the hemodynamic mechanisms of circulatory augmentation by an ITV in Standard CPR.MethodA 14-compartment mathematical model of the human cardiopulmonary system--upgraded to include applied chest compression force, elastic recoil of the chest wall, anatomic details of the heart and lungs, and the biomechanics of mediastinal compression--is exercised to explore the conditions required for circulatory augmentation by an ITV during various modes of CPR.ResultsThe ITV augments systemic perfusion pressure by about 5 mmHg compared to any particular baseline perfusion pressure without the ITV. When baseline perfusion is low, owing to either diminished chest compression force, the existence of a thoracic pump mechanism of blood flow, or the presence of an effective compression threshold, then the relative improvement produced by an ITV is significant. With an ITV the heart expands into soft pericardiac tissue, which makes the heart easier to compress.ConclusionsAn ITV can augment perfusion during CPR. The observed effectiveness of ITVs in the laboratory and in the clinic suggests a thoracic pump mechanism for Standard CPR, and perhaps also an effective compression threshold that must be exceeded to generate blood flow by external chest compression.

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