Manipulation of the Indirect Fick Principle by a Digital Computer Program for the Calculation of Exercise Physiology Results

Abstract

Calculations of the results of respiratory and cardiac function studies such as the physiological dead space, cardiac output and venous admixture are time consuming and very susceptible to human error. A digital computer program has been designed to perform these calculations based on the rebreathing method for mixed venous PCO₂ so that cardiac catheter data is not required. The conversion of CO₂ differences to content differences is described and the disturbances of the CO₂ dissociation curve which may occur are discussed and allowed for in the program. Particular attention is given to the graphical ‘bloodless’ solution where arterial PCO₂ is unknown and the program has been designed to print or draw the possible relationships between dead space, cardiac output and arterial PCO₂ under these circumstances. The derivation of all equations are given and the scope and versatility of the actual program is outlined.