Effects of lung inflation on blood flow during cardiopulmonary resuscitation in the canine isolated heart-lung preparation

Using an isolated, fibrillated canine heart-lung preparation, we studied the effects of simultaneous lung inflation and chest compression on blood flow in a model of cardiopulmonary resuscitation. The heart and lungs were placed in an artificial thorax with the great vessels and trachea exteriorized and attached to an artificial perfusion circuit and respirator, respectively. The blood volume of the system was adjusted to obtain various levels of static equilibrium pressure. Blood flow was obtained by cyclically raising and lowering the pressure in the artificial thorax, simulating the changes in pleural pressure that occur during cardiopulmonary resuscitation. Lung inflation during the compression phase caused an increase in cardiopulmonary resuscitation blood flow when the change in pleural pressure was small and when static equilibrium pressure was high. In contrast, lung inflation caused a decrease in blood flow when changes in pleural pressure were high and when blood volume was low. These results suggest that the driving pressure for blood flow during chest compression may be increased by lung inflation when the pulmonary blood vessels are filled with blood. However, blood may become trapped in the right heart and unavailable for transfer to the periphery during chest compression if lung inflation causes the alveolar blood vessels to collapse.