Bilevel Therapy Yields Normal Breathing Curves

The tracing below shows normal breathing while on bilevel PAP therapy.

Note how both the inspiratory curve (top portion) and the expiratory curve (bottom portion) are smooth and well rounded or elliptical. Note also that the “change of direction” from inspiration to expiration shows no discontinuity, that is you breathe in and then you simply change direction and breathe out. The diagonal line connecting the two phases has no interruptions or changes in it.

The transition from expiration to inspiration is quite different. Take a moment to feel how you breathe. You’ll notice that when you breathe in, you naturally start breathing out at the end of inspiration with the very smooth transition described above, but when you finish expiration, you’ll notice a different feeling. Most people actually pause or literally stop breathing. Then, they start breathing in again.

It is this pause by the way, known as “end expiration,” where SDB events generally begin. You are already closing the diameter of the “breathing tube” more so during exhalation, and at the very end of breathing out, you are very susceptible to closing it altogether and suffering an apnea.

The smooth and relatively flat line between end expiration and the beginning of inspiration shows this pause in your breathing. In subsequent graphics, we’ll show how this “pause” is one of the prime locations for seeing signs of pressure intolerance as might be seen with a patient on CPAP or APAP, where the “fixed” pressure for any given breath is too high on exhalation.