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Departments of Medicine and Physiology and Biophysics, The University of Calgary, Calgary, Alberta, Canada T2N 2T9
In the intact animal, it is difficult to
discriminate between the independent effects of series and direct
ventricular interaction (DI) or the individual contributions of the
pericardium and septum to DI. Left ventricular (LV) venous return
(LVVR) and right ventricular (RV) end-diastolic pressure (RVEDP) were
varied independently in a right-heart bypass model. LV minor-axis
diameters were measured, and the product of the two diameters was used
as an index of LV volume (LVVI). At each RVEDP (0, 5, 10, and 15 mmHg),
increased LVVR caused an increased LVVI. When RVEDP was increased,
increased pump output was required to maintain a given LVVI. RV-to-LV
pressure gain (
LVEDP/RVEDP) reflects coupling and DI. With the
pericardium closed, the gain was dependent on RVEDP; when RVEDP was
increased from 0 to 5 mmHg, the gain was not statistically different
from zero, indicating little or no DI. When RVEDP was increased from 10 to 15 mmHg, the gain was not statistically different from 1.0, indicating ~1:1 coupling of the ventricles. Opening the pericardium reduced the gain, but significant interaction remained. When the septal
contribution was accounted for, the remaining interaction was
eliminated. In conclusion, DI substantially affects LVEDP-volume relations. Considerable increases in RV output may be required to
counterbalance increased constraint to LV filling. With the pericardium
closed, RV-to-LV coupling is minimal when RVEDP is low and increases to
1:1 coupling when RVEDP is high. Opening the pericardium reduces DI,
but significant septum-mediated interaction remains.
ventricular interdependence; ventricular mechanics; diastole; diastolic interaction
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