Ventilation-perfusion matching in long-term microgravity

Abstract

We studied the ventilation-perfusion matching pattern in normal gravity (1 G) and short- and long-duration microgravity (microG) using the cardiogenic oscillations in the sulfur hexaflouride (SF(6)) and CO(2) concentration signals during the phase III portion of vital capacity single-breath washout experiments. The signal power of the cardiogenic concentration variations was assessed by spectral analysis, and the phase angle between the oscillations of the two simultaneously expired gases was obtained through cross-correlation. For CO(2), a significant reduction of cardiogenic power was observed in microG, with respect to 1 G, but the reduction was smaller and more variable in the case of SF(6). A shift from an in-phase condition in 1 G to an out-of-phase condition was found for both short- and long-duration microG. We conclude that, although the distribution of ventilation and perfusion becomes more homogeneous in microG, 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 exposure to microG.

Vital capacity, respiratory muscle strength, and pulmonary gas exchange during long-duration exposure to microgravity

“…The iV/Q slope seen over the first half of phase III [the most sensitive indicator of V A/Q inhomogeneity from this test (37)] was slightly elevated in G compared with standing in 1G, lending credence to previous speculation (33) that gravity in fact provides a degree of matching between ventilation and perfusion in the normal upright human lung. The result is also consistent with a previous study in two subjects aboard Mir for ϳ6 mo, which showed that the matching of ventilation to perfusion was unaltered by the time spent in G (44).…”

“…There were only small changes in O 2 uptake (V O 2 ), CO 2 output (V CO 2 ), and end-tidal PO 2 and PCO 2 . The matching of ventilation to perfusion has been reported to remain unaltered in long-duration G (44). However, long-duration bed rest of 113 days showed a reduction VC and diffusing capacity of the lung for CO immediately after bed rest that appeared to persist for up to 2 wk into the recovery period (29).…”

V˙O2max and Microgravity Exposure

“…The distribution of ventilation and pulmonary blood flow (V A /Q ) is also altered in microgravity. V A /Q matching becomes more homogenous in microgravity but seems to return to baseline with return to 1g (86).…”

Physiological, Pharmacokinetic, and Pharmacodynamic Changes in Space

“…Several studies have shown differences between lung function under different gravity conditions, especially regarding perfusion 61–63 . As represented in Figure 4, pulmonary perfusion is believed to be more homogeneous in microgravity, although a residual inhomogeneity is still detected 64–66 . This more even distribution of capillary blood flow leads to a more efficient interface between the gas and the blood in the lungs.…”

“…[61][62][63] As represented in Figure 4, pulmonary perfusion is believed to be more homogeneous in microgravity, although a residual inhomogeneity is still detected. [64][65][66] This more even distribution of capillary blood flow leads to a more efficient interface between the gas and the blood in the lungs. This may explain the improved membrane diffusion capacity observed in microgravity compared to both upright and supine preflight controls.…”