A THEORETICAL STUDY OF THE COMPOSITION OF THE ALVEOLAR AIR AT ALTITUDE

Abstract

A diagram is presented in which alveolar CO2 tensions are plotted against alveolar O2 tensions. When breathing pure O2, each altitude is represented by a diagonal line. The location of the alveolar air on this line depends upon the CO2 output and the alveolar ventilation. When breathing air each altitude is represented by a family of diagonal lines, one line for each value of the R.Q. Equations are developed permitting the calculation of the alveolar gas tensions in terms of altitude, inspired gas tensions, R.Q. and ventilation rate. Two sets of isoventilation lines can be drawn on the chart, one for constant O2 intake and one for constant CO2 output. Limits can be set graphically for acapnia, anoxia, CO2 narcosis and poisoning by high N2 or high O2. The position of the normal alveolar air and lines of equal arterial saturation are also charted. The value of the diagram in predicting the advantages of hyperventilation or CO2 inhalation when breathing air are demonstrated and discussed. The changes which occur with diminishing N2 content of the inspired gases are also explained.