By Mary Bellis
In the 1960s Prof. K. Hammacher and Hewlett-Packard began development of what became the first commercially available non-invasive fetal monitor. The research took place in Boeblingen, Germany. In the spring of 1968, the first HP 8020-A fetal monitors (aptly named " The Babysitters") were supplied to customers. The monitors helped babies by detecting fetal distress during labor. (source Fetal Monitor Inventor)
Hammacher's invention (U.S. Pat. No. 3,318,303) measures heart sounds by use of a contact microphone and provides outputs distinguishing the first and second heart sounds of each heart cycle by generating impulses coincident with each heart sound. While the first and second heart sounds are distinguished and separately analyzed, the first and second heart sounds are not differentiated by the timing relationships between the heart sounds in the overall heart cycle but merely by the state of a flip-flop which changes state upon the detection of each heart sound to thereby output two series of pulses, one for each heart sound in each heart cycle.
The purpose of the Hammacher method and apparatus is to accurately determine heart beat frequency by comparing the periodic rates of each of the pulse trains corresponding to the first and second heart sounds and comparing the heartbeat frequency rate between the two pulse trains. Hammacher also mentions the detection of the first heartbeat by combination with the R-wave of the ECG.
With the invention of the stethoscope in 1810, physicians could hear the fetal heart beat. However, the instrument could not detect subtle changes or provide continuous surveillance. These deficiencies were overcome in 1968 with the development of electronic fetal monitoring.