A new look at fetal phonocardiography using a transducer of improved sensitivity and bandwidth

Publisher Summary This chapter discusses a phonocardiographic technique that is common place in postnatal studies and could now be applied to the fetus. The wealth of information potentially available from fetal heart sounds has not been exploited so far because of the weak, narrowly filtered signal that has been produced by machines designed primarily for heart rate determination. When the total acoustic phono signal (TAPHO) can be obtained, the detailed changes of valve closure times become visible in a similar manner to that postnatally. The TAPHO signal, thus, provides a simple, non-invasive tool to study not only changes in heart rate and systolic timing but changes in fetal blood flow, distribution, or pressure, which are reflected in the forcefulness or timing of valve closures, heart recoil, or blood turbulence. The signal obtained is a series of shock excited pressure wave trains that are generated when the various valves snap shut. Changes in the relative timing of the component parts of the heart sounds are also of value. An increase in atrial pressures will delay closure of the corresponding inlet valves. On the other hand, increases in aortic or pulmonary pressures will cause the corresponding outlet valves to close earlier. At present. it is not known as to which valves are delayed or as to which are early, or both, but such changes indicate a possible means of non-invasively monitoring cardiovascular changes in the fetus.