Physiology · Temperature, exercise and metabolism
Aviation and space physiology !
- Concept
- For completeness
In flight the air has less pressure, accelerations move blood around, and in space the lack of gravity weakens bone and muscle.
Updated 2026-11-01
Also called: G-forces, Microgravity
See it in 3D: Pleura · Left ventricle · Femur
What it is
Aviation exposes people to hypobaric hypoxia, gas expansion (Boyle's law) and accelerations that shift blood. A commercial airliner cabin is pressurized to an equivalent altitude of ≈1800–2400 m, much like living in Bogotá. In space, without gravity, blood shifts to the head, the heart adapts and bone and muscle are lost from disuse.
Key facts
- Trapped gas expands in flight: an undrained pneumothorax worsens, and flying is contraindicated.
- Anti-G manoeuvres (muscle straining, forced breathing) and G-suits boost venous return.
- In space astronauts get puffy faces and thin legs («moon face, bird legs»).
- Without weight-bearing, osteoclasts dominate and urinary calcium rises: a risk for kidney stones.
How it works, step by step
- A +Gz acceleration pushes blood toward the feet and arterial pressure at eye and brain level falls.
- Baroreceptors raise HR and vasoconstriction, but they take a few seconds.
- The retina, perfused against intraocular pressure, loses flow first (greyout); then the brain fails.
- In microgravity blood no longer pools in the legs: the heart and volume receptors «see» excess volume.
- ADH and aldosterone fall and natriuretic peptide rises: diuresis and lower plasma volume.
- Back in gravity, volume is short and the reflex is out of practice: orthostatic hypotension.
Clinical notes
- Flying with severe COPD: PaO₂ can fall to dangerous levels without supplemental oxygen.
- Sea-level residents who fly into Bogotá have already spent hours in mild hypoxia in the cabin.
- Space-flight bone loss resembles that of prolonged bed rest and disuse osteoporosis.
Test yourself
Think of the answer, then tap the question to see it.
Why does a pilot in a tight turn grey out before losing consciousness?
+Gz acceleration lowers arterial pressure at head level; the retina, which must overcome intraocular pressure, loses perfusion before the brain.
Why does an astronaut have orthostatic hypotension on returning to Earth?
In microgravity they lost plasma volume through diuresis and their baroreflex adapted; on standing, blood pools in the legs.
Why does an untreated pneumothorax rule out flying?
By Boyle's law the trapped air expands as cabin pressure falls and can become a tension pneumothorax.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- High altitude and acclimatization
- Diving, decompression and hyperbaric oxygen
- Physiology of the vital signs (including blood pressure measurement)
Related conditions
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 22.6 Modifications in Respiratory Functions (OpenStax (Rice University), 2022); 6.6 Exercise, Nutrition, Hormones, and Bone Tissue (OpenStax (Rice University), 2022); 20.4 Homeostatic Regulation of the Vascular System (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 44). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.