PROBLEM SESSION ANSWERS: Problem 5

Step 1: Compute the inhaled oxygen concentration

P_I-O2 = 0.21( P_B - P_H2O ) = 0.21 ( 450 - 47 ) = 0.21 x 403 = 85 mmHg

Step 2: Compute the alveolar P_O2 using the alveolar air equation

P_A-O2 = P_I-O2 - P_A-CO2 / R

Assuming P_A-CO2 remains normal (as given) and assuming R = 0.8 gives

P_A-O2 = 85 - 40/0.8 = 85 - 50 = 35 mmHg

Step 3: Blood saturation at 35 mmHg is about 60% (from the Hb dissociation curve).

Conclusion: A normal person could survive at this altitude, although he would probably have to hyperventilate (see next problem), but would have very limited exercise capacity due to the desaturation of systemic arterial blood and the very low P_a-O2.