If the partial pressure of oxygen in the atmosphere was halved, what effect would this have on the amount of oxygen that would now dissolve in the alveolar fl uid? It would

B: The amount of gas that will dissolve in water is proportional to its partial pressure (Henry’s law). Hence if the partial pressure in the atmosphere halves, the partial pressure in the alveoli will be approximately half, so the amount that will dissolve will also approximately halve.