[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative) › Aviation and space physiology [Physiology](https://durgical.com/en/physiology/) · [Temperature, exercise and metabolism](https://durgical.com/en/physiology/#s-integrative) # 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](https://durgical.com/en/anatomy/pleura/) · [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/) · [Femur](https://durgical.com/en/anatomy/femur/) ## Key points - Pressurized cabin ≈1800–2400 m equivalent altitude: PaO₂ falls, which matters in patients with COPD or severe anemia. - Time of useful consciousness after decompression: seconds at ≈12,000 m; hence the oxygen masks. - +Gz (head to foot): blood pools in the legs; ≈4–6 G cause greyout, then blackout and loss of consciousness. - Microgravity: fluid shift to the head, diuresis, lower plasma volume and orthostatic intolerance on return. - Bone loss of ≈1–2% per month in space, mostly in weight-bearing bones. ## 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. ## Memory aid «Up high, less pressure; in a turn, blood to the feet; in space, blood to the head». ## 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. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/aviation-and-space-physiology/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Pleura](https://durgical.com/en/anatomy/pleura/) - [Left ventricle](https://durgical.com/en/anatomy/left-ventricle/) - [Femur](https://durgical.com/en/anatomy/femur/) ## Related topics - [High altitude and acclimatization](https://durgical.com/en/physiology/high-altitude-and-acclimatization/) - [Diving, decompression and hyperbaric oxygen](https://durgical.com/en/physiology/diving-decompression-and-hyperbaric-oxygen/) - [Physiology of the vital signs (including blood pressure measurement)](https://durgical.com/en/physiology/physiology-of-the-vital-signs/) ## Related conditions - [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/) - [Pneumothorax](https://durgical.com/en/conditions/pneumothorax/) [← All of physiology](https://durgical.com/en/physiology/) 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](https://openstax.org/books/anatomy-and-physiology-2e/pages/22-6-modifications-in-respiratory-functions) (OpenStax (Rice University), 2022); [6.6 Exercise, Nutrition, Hormones, and Bone Tissue](https://openstax.org/books/anatomy-and-physiology-2e/pages/6-6-exercise-nutrition-hormones-and-bone-tissue) (OpenStax (Rice University), 2022); [20.4 Homeostatic Regulation of the Vascular System](https://openstax.org/books/anatomy-and-physiology-2e/pages/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). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/aviation-and-space-physiology/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/aviation-and-space-physiology/