A non-linear solution of the oxygen conductance equation. Applications to performance at sea-level and at an altitude of 7350 ft.

Summary

The process of oxygen transfer from the atmosphere to the working tissues can be described by a non-linear equation of the type

$$\frac{1}{{\dot U}} = \frac{1}{{\dot V_{\text{A}} }} + \frac{B}{{1 - B}}\left( {\frac{1}{{\lambda \dot Q}}} \right) + \frac{1}{{\lambda \dot Q}} + \frac{K}{{1 - K}}\left( {\frac{1}{{\lambda \dot Q}}} \right)$$

where$\dot U$ is the overall conductance,$\dot V_A$ is the effective alveolar ventilation,$\dot Q$ is the maximum effective cardiac output, λ is the slope of the oxygen dissociation curve, andB andK are coefficients of the typee $\frac{{ - D_L }}{{\dot Q}}\int\limits_\circ ^{D_L } {\frac{1}{\lambda }}$ ande $\frac{{ - D_t }}{{\dot Q}}\int\limits_\circ ^{D_t } {\frac{1}{\lambda }}$ where$\dot D_L$ andD _t are the diffusing capacity of the lungs and tissues respectively. A series of isopleths are presented from which$^{D_L} \int\limits_\circ {\frac{1}{\lambda }}$ may be estimated, given the${{\dot D_L } \mathord{\left/ {\vphantom {{\dot D_L } {\dot V_{02} }}} \right. \kern-\nulldelimiterspace} {\dot V_{02} }}$ ratio. At sea level, the dominant term is that relating to blood transport; the second and fourth terms of the equation have a negligible influence on the overall conductance. At 7350 ft., the altitude of Mexico City, the second term is of equal importance with the first and third; however, the decrease in overall conductance is less than would be predicted from the decrease in ambient pressure, since the normal shape of the oxygen dissociation curve has the effect of increasing blood conductance. Mexico City is at a rather critical altitude, and hyperventilation and the shape of the oxygen dissociation curve provide less effective compensation for further decreases in ambient pressure.