Per Respironics:
The “proper” resistance (aka Mask Type) setting is X1. At 50 L/m, pressure drop is 0.9 cmH2O. At 100 L/m that increases to 3 cm/H2O. Note that it does not scale linearly with velocity. This is normal. At higher air velocity, bends and boundary effects at the inner surface of the tube cause turbulence.
When asleep, my peak rate normally drops to around 30. When awake, it’s around 60. In REM or a catch-up breath, I can spike to over 100.
So, let’s go with 50 L/m for simplicity. With both tubes open, the pressure drop is 0.9 cmH2O. With one tube closed, the velocity in the remaining open tube must roughly double to deliver the same volume (not quite that simple, but let’s stay with napkin numbers). That means that the pressure drop in one tube at 50 L/m is roughly comparable to the drop in both tubes at 100 L/m. In other words, closing one tube increases the pressure drop by roughly 2ish cmH2O (from 0.9 to 3ish).
What about my peak flow of roughly 100? The pressure drop starts at 3 for both tubes. With one tube, it’s literally off the chart. Since the curve is asymptotically approaching 100ish with both tubes, it’s clear that forcing 100 L/m through one tube would require significant effort.
Of course, exhaling forcefully may expand the tube a little. Inhaling forcefully (trying to hit that 100 flow number) is going to collapse the tube a little, making the situation worse.

- B03E84EA-5235-450F-82AB-172251E4B423.jpeg (204.57 KiB) Viewed 2711 times

- 53A555EE-C35D-4CEB-9AD9-19307E2039EC.jpeg (161.08 KiB) Viewed 2711 times