The test involves inhaling fully, then exhaling fully, hard and fast through the mouthpiece (while the machine measures the volume and rate of gas flow). The spirometer compares results with those expected for a normal person of the same weight, sex and height.
The presence of significant restrictive OR obstructive respiratory disease will reduce the chance of a quick loss of consciousness and peaceful death.
The result is that the lungs now have significant residual oxygen and there is not the sudden drop in the oxygen level in the blood travelling to the brain that causes the rapid loss of consciousness. If one takes more breaths of pure Nitrogen from the bag, the residual oxygen in the lungs will eventually drop and cause loss of consciousness. However, this can take some time, and can lead to anxiety, panic and failure.
To eliminate the possibility of such failure, ask your doctor for a spirometry test to measure your lung function. If the measurements differ significantly from normal, this method is not the most suitable for you.
Note: Some restrictive lung disease can be improved significantly with the use of certain drugs. The best example is asthma, where the inhalation of salbutamol (ventolin) prior to the test can sometimes restore values to near normal. If this is the case, the hypoxic method need not be abandoned, but salbutamol should be used immediately before inhaling the Nitrogen to die.