Neco Model Questions Vol1 2018 Biology Question 5

A student at sea level (barometric pressure \(P_B = 760\ \text{mmHg}\)) inhales dry air containing 21 % oxygen (\(F_{iO_2}=0.21\)). The water vapour pressure in the alveoli is \(P_{H_2O}=47\ \text{mmHg}\) and the respiratory quotient is \(R=0.8\). Alveolar ventilation is \(4\ \text{L min}^{-1}\) and carbon dioxide production is \(200\ \text{mL min}^{-1}\). (i) Using the alveolar gas equation \(P_{A O_2}=F_{iO_2}(P_B-P_{H_2O})-\frac{P_{aCO_2}}{R}\) and the relationship \(P_{aCO_2}= \frac{V_{CO_2}\times 0.863}{\dot V_A}\), calculate the alveolar partial pressure of oxygen \(P_{A O_2}\) at sea level. (ii) If the student ascends to an altitude where \(P_B = 600\ \text{mmHg}\), with all other variables unchanged, calculate the new \(P_{A O_2}\). (iii) What is the percentage decrease in alveolar \(P_{O_2}\) caused by the ascent?