• J Ducas, C Roussos, C Karsardis, and S Magder.
• Chest. 1983 Oct 1; 84 (4): 446-51.

AbstractThe importance of intrathoracic pressure in generating blood flow during cardiopulmonary resuscitation has recently been emphasized. The purpose of this study was to investigate the factors involved in generating intrathoracic pressure. Studies were performed in anesthetized paralyzed dogs with the circulation intact. Balloon-tipped catheters were placed in the abdomen and esophagus for measurement of intra-abdominal and intrathoracic pressures and cannula placed in the airway for airway pressure. The following four maneuvers were studied: (1) chest compression with open airway; (2) chest compression with closed airway; (3) pulmonary inflation to transpulmonary pressure (TP) of 30 cm H2O (TP = 30); and (4) chest compression plus pulmonary inflation (TP = 30). We found that under static conditions, chest compression alone produced small positive intrathoracic pressures (9 +/- 8 cm H2O), but these could be increased by closing the airway pressure (18 +/- 6 cm H2O) or inflating the lungs (15 +/- 7 cm H2O). The combination of inflating the lung and compressing the chest produced the highest intrathoracic pressure (48 +/- 18 cm H2O; p less than 0.001). The pressure developed was highly variable and the distribution of pressures within the thorax was not uniform. As the intrathoracic pressure became large, a pressure gradient developed from thorax to abdomen, and the diaphragm everted; this pressure gradient could divert blood from the brain.

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