Visual observation was chosen as the reference method for measuring th
e respiratory rate in ten healthy volunteers. The new fibre-optic and
acoustic sensors were simultaneously compared with capnography and tra
nsthoracic impedance plethysmography during normoventilation in the re
spiratory rate range of 6-24 breaths per minute and at a fixed respira
tory rate of 13 breaths per minute. In addition a simulation of centra
l apnoea was performed. All the measurements were recorded on an analo
gue tape recorder and a strip-chart recorder and analysed off line. Th
e analyses of the recordings were performed by a person who was unable
to see the monitoring systems. There was no discrepency in the result
s of these methods. Each of the methods responded rapidly to an apnoei
c event. The new fibre-optic and acoustic sensors correlate well with
more traditional methods such as capnography and transthoracic impedan
ce plethysmography for respiratory rate monitoring.