Gravity-induced hyperventilation is caused by a reduced brain perfusion

The suggestion that hyperventilation caused by increased gravity is mediated by a decrease in brain perfusion has led us to propose a mathematical model based on: (1) the CO2 balance equation for the respiratory center (RC), and (2) the relationship between RC blood flow (QRC), foot-to-head acceleration (Gz) and PRCCO2, namely, QRC = [1 - a(Gz - 1)](b X PRCCO2 + c), where the coefficients a, b and c can be calculated from data in the literature. QRC is significantly affected by + GZ only at high PaCO2. The model can be used to calculate oxygen pressure in the RC; the numbers so obtained are in good agreement with measurements of jugular vein PO2 obtained by others.