Regional lung ventilation in humans during hypergravity studied with quantitative SPECT

- Hypergravity causes arterial desaturation in humans.
- Hypergravity causes anti-gravitational redistribution of lung perfusion.
- We study ventilation during hypergravity using Technegas and SPECT.
- The results show a redistribution of ventilation in the same direction as perfusion.
- We suggest that desaturation is caused by quantitatively different redistributions of regional perfusion and ventilation.

Recently we challenged the view that arterial desaturation during hypergravity is caused by redistribution of blood flow to dependent lung regions by demonstrating a paradoxical redistribution of blood flow towards non-dependent regions. We have now quantified regional ventilation in 10 healthy supine volunteers at normal and three times normal gravity (1G and 3G). Regional ventilation was measured with Technegas (99mTc) and quantitative single photon emission computed tomography (SPECT). Hypergravity caused arterial desaturation, mean decrease 8%, p < 0.05 vs. 1G. The ratio for mean ventilation per voxel for non-dependent and dependent lung regions was 0.81 ± 0.12 during 1G and 1.63 ± 0.35 during 3G (mean ± SD), p < 0.0001. Thus, regional ventilation was shifted from dependent to non-dependent regions. We suggest that arterial desaturation during hypergravity is caused by quantitatively different redistributions of blood flow and ventilation. To our knowledge, this is the first study presenting high-resolution measurements of regional ventilation in humans breathing normally during hypergravity.