Section 5.1 shows how to correct gas volumes for variations in temperature, pressure, etc., but it is presented more as a study of the general magnitudes of such corrections and of circumstances in which they may be neglected. Sections 5.2 to 5.5 are about oxygen and carbon dioxide in blood, cells and alveoli. From a straightforward treatment of how concentrations of dissolved gases relate to partial pressures, we move on to consider cytoplasmic carbon dioxide tensions (Section 5.3), alveolar gas tensions at altitude (Section 5.4) and why the alveolar arterial carbon dioxide tensions are so much higher in mammals than in fish (Section 5.5). The latter topic is linked to that of Section 5.6 – the loss of water in expired air. Sections 5.7 to 5.9 are about breathing and the structure and dimensions of the lungs. Sections 5.10 to 5.12 are concerned with surface tensions and fluid pressures in the lungs and pleural space, and hence with pulmonary oedema. On the mathematical front, the calculations continue to use little more than simple arithmetic, but the renewal of alveolar gas (Section 5.7) provides an example of an exponential time course (for which, see also Sections 1.4 and 6.3).

Correcting gas volumes for temperature, pressure, humidity and respiratory exchange ratio

When analysing experimental results it is necessary to allow for the effects of temperature, pressure and humidity on gas volumes.