On-line measurement of aortic valve ring deformation during the cardiac cycle

An electronic device is described for the measurement of relative changes in segment length within the aortic valve ring during the cardiac cycle. The technique is based on the principle of magnetic induction. A magnetic field generated in one coil induces a voltage in another coil. From the amplitude of this voltage the strain between both coils can be determined because the strength of the magnetic field decreases with distance. In vitro, over a range of 5-25 mm, strains less than or equal to 0.20 strain units can be measured with an accuracy of 0.008 strain units. The frequency response is 0-150 Hz (-3 dB). By varying the generator and receiver assignment at a frequency of 2 kHz and multiplexing the signals of six coils, six strains can be measured simultaneously. As an example, simultaneous recordings of commissure strains in the aortic valve and left ventricular and ascending aortic pressures, as obtained in open-chest dogs, are shown.