It sounds like using this device always can only help? If the alveoli remain open longer for more O2 transfer, does not this mean they pt can oxygenate and perfused better?
Oxygenation and ventilation are often confused and the concepts used interchangably. They are not the same thing are infact two different physiologic proceses.
The amount of air breathed in is not the amount of oxygen that will reach the brain and tissues.
- Air is about 21% oxygen, yet in Denver it's lower (I don't know the exact forula to figure out how much lower) so altitude plays a part
- The ability to change pressure inside the thorax is also important; if Stanley my immaginary grey pet elephant sits on your chest you will have a very hard time creating a negative pressure gradient to draw air in as you can't expand the throacic cavity enough.
- Just because oxygen is inhailed does not mean it will reach the bronchioles, alveoli, blood, cells and tissues. Any number of obstructions may prevent this - eg choking, hypovolemia, obstructive lung disease/pulmonary edema, carbon monoxide poisioning or a haemothorax.
It is also important to recognise that not all the air inhailed will reach the respiratory zone for the oxygen to diffuse out of the alveoli and into the blood.
The lungs have what is called dead space either anatomical (bronchi and bronchioles that do not have alveoli and pulmonary capillaries, I believe this is the first 20 or 21 divisions of the bronhcial tree) or alveolar; alveolar dead space is any buggered alveoli that can't exchange gas either because they have collapsed or are full of puss or the marbles I ate for dinner.
Dead space is an important concept as about 150ml of air will occupy the anatomical dead space at any one time, this will increase if there is additional alveolar dead space such as in infection or APO/CPE.
This is where PEEP (and I believe also CPAP) are important as they only work on
pulmonary problems by decreasing surface tension and assisting the alveolar surfactant to decrease alveolar dead space and ensure more gas exchange.
Doesn't work on a circulatory issue such as V/Q mismatch or anemia.