Respiratory Impedence

 (Lower blue lines in the figure above demonstrate the cyclical voltage output observed with respiratory impedance monitoring.)

The impedence across a thoractic cavity will change as the volume of air in the cavity changes.  In general, it will increase during inhalation and decrease during exhalation, leading to a cyclic pattern of impedence that is present during normal breathing.  This principle could be used to determine when an infant stops breathing by employing high frequency (in the range of 50 kHz to 500 kHz)AC between two surface electrodes to detect when the impedence stops changing, and thus breathing has stopped.  The cost of the electrodes for this monitoring would be around $70 (from medical equipment catalogue). Other costs not factored in would be AC volage sources, shirt or fabric that electrode is imbedded in, impedence measuring equipment, etc....

The downfall to this method is that it is somewhat invasive- a small electrical current is passed through the body.

An alternative to this method could be inductive plethysmography. This method uses arrays of sinusoidally arranged wires that carry a high frequency AC current attached to the skin (like that of impedence monitoring). Movement of the chest wall causes a change in the magnetic field produced by the AC currents (Lenz's Law), which is then measured as voltage fluxuations in the wires around the chest.

The downfall to this method is that it could be restricting- the wires would need to be completely wrapped around the infant's chest.