There are two groups of methods of respiratory monitoring: direct and indirect. During direct respiratory monitoring the signals are recorded with various Spirometers. Spirometers measure direct in and out air flow. Indirect methods include measuring of body volume variation, pletismography. Each method has its own benefits and failings. Direct measurement is more accurate, but this disrupts normal breath. Pletismography is very accurate but this method requires patients mobilization. Other methods require frequent calibrations etc. Those methods are more suitable for ambulatory monitoring.

But how to monitor respiration when patient is doing exercises, when he is moving and requires more oxygen where direct implements disrupt normal breath. In such cases getting respiratory information is real challenge. It is known that breath has influence in cardiogram. During one respiratory cycle the heart axis is moving and this affects ECG morphology. There are few signal processing algorithms (such as QRS Area calculating method, Vector Cardiogram angle rotation or event heart rate variation) where breath signals are calculated from ECG. But of course during exercises heart rate isnt permanent and breath is dynamical this is why classical methods doesnt give very good results. Better results can be reached by combining different processing algorithms or searching for new ones.