A systematic review and meta-analysis of pulmonary function in microgravity

Technological advancements have increased the number of human spaceflights, including the advent of space tourism and deep space travel. The structure and function of the pulmonary system are gravitationally dependent, highlighting the importance of understanding functional changes within the pulmonary system during transient and sustained microgravity exposure. This systematic review and meta-analysis provide an overview of effects of microgravity (0G) on various functional outcome measures of the human lungs relative to Earth gravity (1G). Twenty-eight studies comprising parabolic flights (~20 seconds), short- (≤30 days) and long-duration spaceflight (>30 days) were assessed. Outcome measures reported in 1G (before flight) and 0G (in-flight) were extracted. Fixed effects models showed microgravity caused a reduction in elastic work and carbon dioxide production, and increases in pulmonary diffusion capacity, compliance, and pulmonary capillary blood volume. Despite this, the effect sizes were small and likely have little clinical significance in healthy individuals. However, they could impact space tourists who have lower health requirements for space travel, and those with underlying obstructive respiratory disorders. The results demonstrate how traditional functional pulmonary testing provides essential physiological benchmarks that complement high-throughput data collection methods, enabling an integrated understanding of how molecular changes translate into functional respiratory outcomes in microgravity.