Ventilation-perfusion matching in long-term microgravity

We studied the ventilation-perfusion matching pattern in normal gravity (1 G) and short- and long-duration microgravity (muG) using the cardiogenic os cillations in the sulfur hexaflouride (SF6) and CO2 concentration signals d uring the phase III portion of vital capacity single-breath washout experim ents. The signal power of the cardiogenic concentration variations was asse ssed by spectral analysis, and the phase angle between the oscillations of the two simultaneously expired gases was obtained through cross-correlation . For CO2, a significant reduction of cardiogenic power was observed in muG , with respect to 1 G, but the reduction was smaller and more variable in t he case of SF6. A shift from an in-phase condition in 1 G to an out-of-phas e condition was found for both short- and long-duration muG. We conclude th at, although the distribution of ventilation and perfusion becomes more hom ogeneous in muG, significant inhomogeneities persist and that areas of high perfusion become associated with areas of relatively lower ventilation. In addition, these modifications seem to remain constant during long-term exp osure to muG.