Static and dynamic operating characteristics of a pericardial balloon

Previously, we developed a balloon transducer to measure the constraint of the pericardium (i.e., pericardial pressure) on the surface of the heart. I t was validated physiologically in that it was shown to measure a pressure equal to the difference between the left ventricular end-diastolic pressure measured before and after pericardiectomy at the same left ventricular vol ume. To define its static operating characteristics, we loaded the balloon nonuniformly with weights that covered fractions of the balloon surface and found that the balloon accurately recorded the average stress if the stres s was applied over at least 23% of its surface. To test its performance whe n curved, we placed it in large and small cylinders (minimum diameter 31 mm ) and found that the balloon accurately recorded the stress. To define its dynamic operating characteristics, we applied sinusoidal stresses and found that its frequency response was limited only by that of the connecting cat heter. When better dynamic response is required, we introduce a micromanome ter-tipped catheter to obtain a unity-gain frequency response that is flat to 200 Hz.