Fig. 1. Frequency response of a liquid-filled catheter-transducer system (CT) compared with a reference catheter-tipped pressure transducer to sine pressure waves of increasing frequencies. (A ) For a 1-Hz frequency sine pressure wave, there was no difference in amplitude or phase between the CT and the reference transducer pressure signals. (B ) For a 14.6-Hz frequency sine pressure wave, the difference in amplitude between the CT and the reference transducer pressure signals was maximal, defining resonant frequency, F^r. There was also a phase lag. (C ) For a 25-z frequency sine pressure wave, the difference in amplitude between the CT and the reference transducer pressure signals was negative. The phase lag was larger.