Timing of pulmonary and systemic blood flow during intermittent high intrathoracic pressure cardiopulmonary resuscitation in the dog

Abstract

Simultaneous compression-ventilation Cardiopulmonary resuscitation has been shown to produce high peripheral arterial pressure and flows in comparison with conventional Cardiopulmonary resuscitation. To evaluate further the mechanisms responsible for blood flow during the large cyclical changes in intrathoracic pressure with simultaneous compression-ventilation Cardiopulmonary resuscitation this study assessed (1) the timing of blood flow from the lungs toward the aorta and periphery, and (2) the timing and mechanisms of return of blood from the periphery to the heart and lungs. After induction of ventricular fibrillation in dogs, radionuclide angiography was performed and pulmonary flow velocity measured during simultaneous compression-ventilation Cardiopulmonary resuscitation with each high (70 to 100 mm Hg) intrathoracic pressure phase lasting from 0.9 to 3.6 seconds. The abdomen was bound. Carotid flow during resuscitation was 27 ± 5 percent (mean ± standard error of the mean) of the value before cardiac arrest. With injection of technetium-99m albumin into the right atrium, the radionuclide activity cleared the right atrium only during periods of tow intrathoracic pressure between the high intrathoracic pressure periods. There was a simultaneous increase in lung activity during the periods of low pressure. Thus, blood left the right atrium and entered the lungs during these low pressure periods. Flow velocity recordings in the pulmonary artery confirmed that pulmonary flow occurred mainly during low intrathoracic pressure. There was negligible retrograde pulmonary flow during high intrathoracic pressure. This feature, together with a lack of increase in right atrial counts, suggests that the pulmonary valve was probably closed during high intrathoracic pressure. After injection of technetium-99m albumin into the distal pulmonary bed through a wedged catheter, 29.7 ± 8 percent (probability [p] < 0.005) of the activity cleared the lung during the first period of high intrathoracic pressure with no further clearance in the next period of low intrathoracic pressure (2 ± 8 percent, difference not significant). A parallel and simultaneous increase in activity in the left ventricle and aorta indicated that blood flowed from the lung, through the left ventricle, to the aorta during periods of high intrathoracic pressure. Therefore the mitral valve and aortic valves must be open during these periods.Thus, with simultaneous compression-ventilation Cardiopulmonary resuscitation, blood flow into the lungs occurs during periods of low intrathoracic pressure and from the lungs into the left ventricle and aorta during periods of high intrathoracic pressure. The heart functions merely as a passive conduit for blood flow to and from the lungs.