Mhm. Ma et al., TRANSESOPHAGEAL ECHOCARDIOGRAPHIC ASSESSMENT OF MITRAL-VALVE POSITIONAND PULMONARY VENOUS FLOW DURING CARDIOPULMONARY-RESUSCITATION IN HUMANS, Circulation, 92(4), 1995, pp. 854-861
Background The mechanisms of blood flow during closed-chest cardiopulm
onary resuscitation (CPR) in humans have been debated since the techni
que was first described in 1960. Two competing models, the cardiac pum
p theory and the thoracic pump theory, have been proposed, and some in
vestigators have used mitral valve position during the downstroke of c
hest compression to distinguish between them. Previous studies using e
ither transthoracic or transesophageal echocardiography have yielded c
onflicting results, and there have been few, if any, hemodynamic or ec
hocardiographic studies on pulmonary venous flow (PVF) during CPR. Met
hods and Results In this study, transesophageal two-dimensional and pu
lsed Doppler echocardiography were used to study mitral valve position
and flow, together with PVF, in 20 adult patients undergoing manual C
PR. In the 17 patients who could be analyzed, the mitral valve closed
in 5 patients (group 1) during chest compression but stayed open or op
ened further in the remaining 12 patients (group 2). Peak forward mitr
al flow occurred during the release phase in group 1 but during the co
mpression phase in group 2. During chest compression, PVF occurred in
the forward direction (from the pulmonary vein to the left atrium) in
8 of the group 2 patients (group 2a) and in the backward direction (fr
om the left atrium to the pulmonary vein) in all group 1 patients and
the remaining 4 patients in group 2 (group 2b). The downtime (time fro
m collapse to CPR) was significantly shorter (P<.05) for those in grou
p 1 (7.0+/-4.4 minutes) than in groups 2a (19.8+/-7.7 minutes) and 2b
(17.8+/-6.8 minutes). Conclusions Transesophageal echocardiography per
formed during manual CPR in humans disclosed three different patterns
of mitral valve position and PVF during chest compression. The presenc
e of an opened mitral valve with forward mitral flow and backward pulm
onary venous flow during chest compression in a small number of subjec
ts underscores this heterogeneity in blood flow and suggests the possi
ble existence of a ''left atrium pump'' in addition to the currently k
nown ''left ventricle pump'' and ''chest pump'' mechanisms.