Transmural distribution of intramyocardial pressure measured by micropipette technique.

A technique is presented for measuring intramyocardial pressure (IMP) in beating hearts using the servo-nulling pressure transducer equipped with polyethylene micropipettes (ID less than 12 micron). The static and dynamic response characteristics of the system were tested in a pressurized, saline-filled container as well as in a pressurized, hollow, gelatin cylinder. The system was then used to measure IMP in vivo in the hearts of 12 dogs during stable cardiac performance and with aortic constriction. In vitro response characteristics were found to be satisfactory for accurate reproduction of cardiovascular waveforms. Peak systolic IMP was not found to exceed the simultaneously recorded left intraventricular pressure (LVP). Furthermore, the slope of the regression line relating the IMP to LVP during systole is linearly related (slope 0.98) to the depth of the micropipette tip in the ventricular wall, as normalized to total wall thickness. Diastolic IMP ranged between 1 +/- 1 (minimum during the cardiac cycle) and 4 +/- 2 mmHg (end diastolic) at associated LVP of 2 +/- 2 and 5 +/- 2 mmHg (mean +/- SD), respectively.