Biology:Hypoxic drive
The hypoxic drive is a form of respiratory drive in which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle. Normal respiration is driven mostly by the levels of carbon dioxide in the arteries, which are detected indirectly by central chemoreceptors when carbon dioxide crosses the blood–brain barrier, forming detectable hydrogen ions, and directly by peripheral chemoreceptors, and very little by the oxygen levels. An increase in carbon dioxide will cause chemoreceptor reflexes to trigger an increase in ventilation. Hypoxic drive normally accounts for 10% of the total drive to breathe. This increases as the PaO2 drops to 70 torr and below, while hypoxic drive is no longer active when PaO2 exceeds 170 torr. The hypoxic drive is so weak that unconsciousness will develop before respiratory distress is noted and is therefore a risk for pilots flying at high altitudes. For this reason, supplemental oxygen is required by Federal Aviation Regulations[1] for pilots flying above an altitude of about 12,500 feet in unpressurized airplanes.
It was initially believed that in cases where there are chronically high carbon dioxide levels in the blood such as in COPD patients, the body will begin to rely more on the oxygen receptors and less on the carbon dioxide receptors. Consequently, it was believed that providing high flow oxygen to chronic COPD patients caused respiratory depression and apnoea by decreasing the hypoxic drive. However, this has since been disproven, and the respiratory depression in high flow O2 to chronically hypoxaemic patients is instead known to be caused by a combination of the Haldane Effect reducing the affinity of haemoglobin to carbon dioxide and ventilation/perfusion mismatch from alveolar capillary dilation in shunted alveoli that are unable to ventilate effectively.[2][3][4]
See also
- Respiratory system
- Homeostasis
References
- ↑ FAR 91.211
- ↑ Abdo, W; Heunks L (2012). "Oxygen induced hypercapnoea in COPD: myths and facts". Critical Care 16 (5): 323. doi:10.1186/cc11475. PMID 23106947.
- ↑ Lumb, AB (2000). Nunn's Applied Respiratory Physiology (5th ed.). Butterworth Heinemann. p. 533. ISBN 0-7506-3107-4.
- ↑ "Archived copy". Archived from the original on 2013-10-06. https://web.archive.org/web/20131006154255/http://www.mstherapycentrenotts.co.uk/Downloads/COPD/COPD-Schmidt---Hall.aspx. Retrieved 2014-11-30.
- Brady. Anatomy and Physiology for Emergency Care
External links
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