A medical student, whose baseline alveolar PCO2 level was 40 mm Hg, begins to voluntarily hyperventilate for an experiment during his respiratory physiology laboratory. If his alveolar ventilation quadruples and his CO2 production remains constant, approximately what will be his alveolar PCO2?

When you hyperventilate, CO2 is blown off. The amount of CO2 blown off is inversely propoional to alveolar ventilation. This is shown by the alveolar ventilation equation: VA = VCO2/PACO2, where VA = alveolar ventilation VCO2 = CO2 production PACO2 = alveolar PCO2 So, if VCO2 remains the same, and VA quadruples, PACO2 must decrease by 4 fold; 40 mm Hg decreases to 10 mm Hg.