Some science behind the scenes



A capnometer or capnograph  measures ‘end-tidal CO2’ (the partial pressure of carbon dioxide in expired air at the end of expiration) exhaled through the nostril into a latex tube.

A narrow plastic tube is inserted into each nostril and the tubes are taped to the skin near the upper lip.  The machine then continuously monitors ‘end-tidal breath’.  The air from the tubes is analysed by an infrared gas analyser and the signal is then sent to a computer that feeds back the information to a videomonitor.  Most machines can provide hard copy output and also provide statistical analyses of the results.  It is also possible to place a ‘goal wave’ into the machine for comparative purposes.

It is thus a sensitive analyser of the type of breathing. Shallow, rapid, and effortful breathing lowers CO2, while deep, slow, effortless breathing increases it.  You will know from this whether the person has achieved an increase in breathing rate or a decrease.

Biofeedback therapists use capnometric biofeedback to supplement respiratory strain gauge biofeedback with patients diagnosed with anxiety disorders, asthma, chronic pulmonary obstructive disorder (COPD), essential hypertension, panic attacks, and stress.