Flow limitation in Sleepyhead

[Sleepster]

OK, I think I might be finally starting to understand this. Respiration can be represented by a sinusoidal waveform, where inspiration levels off gradually as your lungs get full, and expiration levels off gradually as your lungs become empty. The flow is greatest in the middle of inspiration or expiration, which can be represented by the rising and falling signature of the sine wave. The top peak represents when your lungs are essentially full, and the bottom peak or nadir represents when your lungs are essentially empty.

The top peak represents the instant when you were inhaling at the highest flow rate, that is, the highest number of liters per minute. Your lungs have not yet stopped filling with air, as that happens when the flow rate drops to zero and starts to become negative.

My best guess is that the xPAP does this by constantly measuring the back pressure from the patient's breathing system against what it knows the therapeutic pressure to be at any particular moment (even with a steady or fixed therapeutic pressure, as you breath in the system pressure naturally lowers a bit, and as you breath out it increases a bit), and that can be graphed as a respiration waveform.

It's much simpler than that. It makes use of a flow rate meter and simply measures the flow rate. The number of liters per minute of air flowing through the hose towards your face.

There is an adjustment of the reading to establish the zero, which is the machine's best guess at when the patient's lungs have made a transition from positive air flow (inhalation) to negative (exhalation).

[justMongo]

Observation of my own flow waveform data indicate that normal inspiration looks much like the positive portion of a sine wave. Expiration looks less sine wave and more like a trapezoidal waveform. Expiration goes to negative flow rather quickly then decays like an exponential. However, I am using a Bilevel that switched to 5 cm-H2O lower when expiration is detected.

When I see flow limitation, the top of the "sine" is indeed clipped. But, it is a ragged clip (wiggles.) The amplitude is diminished by the "clip."
It means the airway is partially collapsing. I sometimes see a ragged flow on expiration with a wiggle in the exponential decay portion.

[ppowers]

Thanks everyone for all your knowledge. Excellent information from all. I will look at my FL graph with a little more ease now. Anything helps when you are dealing with Sleep Apnea!