Electronic analysis of foetal breathing movements: a practical application of phase-lock-loop principles

Measurement of foetal breathing movements is becoming more common as a means of monitoring processes occurring in the human foetus. Conventional time-period analysis of breathing movements is prone to error owing to their complexity, and it is laborious to decipher any frequency pattern. The described apparatus has been designed to give an on-line visual indication of the instantaneous frequency of foetal breathing movements when measured by a time-distance recorder connected to an echoscope. It is affected insignificantly by spurious signals, and can be build cheaply with easily-available components. Practical trials suggest that frequency analysis by this device can be of value for examining episodes of continuous breathing movements in the foetus.