O2 Analysis – Analysis Software for 3He MRI
Regional VA/Q ratios are calculated from the regional measurements of PAO2 by a variation on methods used to calculate PAO2 from a known VA/Q ratio. Steady-state gas exchange in each region is described by a set of mass balances on O2, CO2, and N2, as well as an overall requirement for gas partial pressures to sum to total pressure. It is assumed that the mixed venous inputs to the lung have been measured by venous blood gas analysis, and that the fraction of inspired oxygen, FIO2, is constant and determined by experimental conditions. The system of four equations resulting from these mass balances with four unknowns (PACO2, the ratio of expired ventilation to local perfusion (VA/Q), the ratio of inspired ventilation to local perfusion (VI/Q), and PAN2) is reduced to a single equation with the single unknown, PACO2. This single equation is solved numerically and VA/Q is then calculated from the resulting PACO2.
Screen Shot of the program.