Physiology ofBloodFlow DuringCardiopulmonary Resuscitation

Background. There aretwocompeting theories ofthemechanism ofblood flowduring cardiopulmonary resuscitation. The"cardiac pump"theory postulates thatbloodflows because theheartissqueezed between thesternumandthespine. The"thoracic pump"theory postulates thatbloodflows fromthe thorax because intrathoracic pressureexceeds extrathoracic vascular pressureandthatflowisrestricted tothevenous-to-arterial direction because ofvenousvalves thatprevent retrograde flowatthethoracic inlet. Todetermine whichmechanism isoperative during actual cardiopulmonary resuscitation, 20 patients wereimaged withtransesophageal echocardiography during resuscitation. Methods andResults. Transesophageal two-dimensional andpulse Doppler echocardiography was begun within 7minutes ofinitiation ofcardiopulmonary resuscitation. Inthe18patients whocould beanalyzed, themitral valve openedduring therelease phase(diastole) andclosed during thecompression phase (systole) ofcardiopulmonary resuscitation. Mitralvelocity-time integral measured 8±3 cm during diastole. Therewas compression ofright andleft ventricular cavities withsignificant reduction in measured left ventricular volumeduring cardiopulmonary resuscitation. Infive patients, mitral regurgitation was present. Conclusions. Transesophageal echocardiography performed during actual cardiopulmonary resuscitationshowing mitral valveopening during cardiac release, reduction ofventricular cavity sizewith compression, andatrioventricular regurgitation support thecardiac pump theory ofcardiopulmonary resuscitation. Thisstudy demonstrates thefeasibility andusefulness oftransesophageal echocardiography during cardiopulmonary resuscitation. (Circulation 1993;88:534-542)