P F C Bayliss

restored by adjustment of sensitivity controls in the normal fashion. Continuous recording of two echoes by time-position is not important because respiratory activity is continuously monitored by chart recorder. The time-position signals are merely used to verify the respiratory origin of the recorded signals. The recording of fetal chest wall velocity provides additional information which may assist in distinguishing between different types of respiratory movement. We make no claim at this stage that this is clinically useful. The capacity of the system to record movements of small amplitude is evidenced in fig 2 (a) in our paper, while the duration of recording available from our chart recorder is similar to that obtained from other systems. We have found that consideration of the comfort of our patients usually limits the duration of recording to a maximum of about 90 minutes. We consider Dr Meire's criteria for a fetal breathing monitoring system to be arbitrary and unsupported by the reference he quotes.