Measurement of Intramyocardial Pressure in the Left Ventricular Wall of Isolated Rabbit Heart.

Intramyocardial pressure (IMP) in an isolated rabbit heart was measured by stretching either the vessel or the myocardial tissue surrounding the interstitial spaces. The vessel was stretched by changing coronary perfusion pressure, and the myocardial tissue was stretched by inflating a balloon in the left ventricle (LV) in noncontracted or contracted state. The IMP was measured with a servo-nulling pressure measurement system through a glass pipette of being less than ten microns. The result showed that IMP was directly related to perfusion pressure both in the noncontracted and contracted states. There was a small effect of LV pressure when the balloon was inflated from 0mmHg to 30mmHg of the LV pressure for the noncontracted state but not for the contracted state. The result indicates that IMP is increased either by internal stretching of the vessel or by external stretching of the myocardial tissue. The LV cavity pressure is not a major determinant of IMP.