A positive pressure mechanical ventilator most likely inflates the lungs by directly:


A.increasing intrapleural pressure.[22%]

B.decreasing intrapleural pressure.[33%]

C.increasing alveolar pressure.[35%]

D.decreasing alveolar pressure.[7%]

Can someone explain the answer (C) to this question to me? "In normal inspiration, the diaphragm contracts to reduce intrapleural pressure, which results in lung expansion. In positive pressure ventilation, an external pump directly increases alveolar pressure by pumping air into the lungs to inflate the lungs." I don't understand how increasing alveolar pressure causes the lungs to inflate.

I think the logic is that in regular breathing, high atmospheric pressure causes our diaphragm contracts which increase the volume of our lungs. Increasing volume decreases pressure which means O2 will flow down the concentration gradient into our lungs. If youre on a ventilator, its probably because your body is not capable of contracting the diaphragm and doing all that stuff. Instead, the ventilator essentially takes initiative and pumps air directly into your system. This means pressure will increase which then forces our lungs to inflate in order to increase volume (otherwise your lungs would burst). Normally you would increase pressure in intrapleural space and O2 moves down the gradient into alveolar, but because we're using a ventilator, I think it directly effects the alveolar pressure. Hope that helps!
edited by on 6/8/2019