Modified Magnetorheography: Measurement of Cardiac Output by a Catheter and an Externally Applied High Magnetic Field

This study is dealt with a design for measuring cardiac output using a catheter and an externally applied magnetic field with the most minimized trauma. Many trials have yielded the following results. When a high static magnetic field is applied externally to the body and a catheter carrying electrodes at the tip is inserted from the carotid artery cutdown, 2 sensing electrodes, across the lumen of the aortic arch, at a little larger electrode distance than the lumen can detect the greatest flow signal. Since the biggest noises in the signal are ECG, they can be cancelled to great extent by the reversed deflection of the ECG which is detected with cancelling electrodes placed at the left chest surface point geometrically symmetrical to the ascending aorta with respect to the center of the heart. Clamping the flow signal to zero level during diastole leads to the remodulation of D-C level in the flow signal and to the reduction of zero drifts. The flow signal produced by giving known volume to the ascending aorta via a catheter can be used for the calibration of the flow measuring system.