Patent US 4,409,986

An esophageal cardiac pulse probe includes a lumen for insertion into the esophagus, the end of the lumen preferably being closed by a flexible diaphragm. Pressure variations imparted to the fluid within the lumen in response to sounds from the heart and the lungs are transmitted to an electrical transducer which produces an electrical signal proportional to the time-varying frequency and intensity of the pressure variations. This signal is selectively filtered to effectively eliminate signal components due to respiratory noise and audible heart sounds and the resulting signal is fed to an appropriate visual display apparatus. Direct acoustic cardiac sound monitoring is also achievable with an earpiece connected to the lumen. Several probe geometries and a method of cardiac pulse waveform monitoring are also disclosed.