How much carbon dioxide is exhaled with each breath?
A. According to the text “Biology” by Claude A. Villee (Third Edition, W.B. Saunders Co., Philadelphia and London, copyright 1957), a person at rest inhales and exhales about 500 ml with each breath. That air consists of 150 ml of recently inhaled air that is in the larger air passages (where no exchange of gases between the lungs and blood stream occurs) and 350 ml of air that has been in the alveoli of the lungs. Thus, 150 ml of the 500 ml may be considered atmospheric air (approximately 0.04% carbon dioxide by volume), and 350 ml of the 500 ml may be considered alveolar air (approximately 5.3% carbon dioxide by volume). The average carbon dioxide content of the 500 ml of exhaled air is thus: [(150 ml)/(500 ml) x 0.04% CO2] + [(350 ml)/(500 ml) x 5.3% CO2] = 3.7% CO2 by volume, which is equivalent to 5.7% CO2 by weight. 22.4 L of air at standard temperature and pressure has a mass of about 28.5 g (the difference in the average molecular weight of atmospheric and alveolar air is trivi
