Hypoxic drive

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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 by peripheral chemoreceptors, and very little by the oxygen levels. An increase in carbon dioxide will cause chemoreceptor reflexes to trigger an increase in respirations. Hypxoxic drive accounts normally for 10% of the total drive to breath. This increases as the PaO2 goes to 70 torr and below. Hypoxic drive is obliterated when PaO2 exceeds 170 torr.

In the past it was 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. And that in this case, when there is an increase in oxygen levels, the body will decrease the respirations.

Recent studies have proven that CO2 Retainers--COPD patients whom have chronically compensated elevated CO2 levels, are not in fact "dependent" on hypoxic drive to breath. However, when in respiratory failure and put on high inspired oxygen the CO2 in their blood may increase via 3 mechanisms..

1) Haldane Effect 2) Ventilation/Perfusion mismatch----regional pulmonary hypoxic vasoconstriction is released 3) removal or reduction of hypoxic drive

[edit] See also

• Respiratory System
• Homeostasis

[edit] External links

• The Hypoxic Drive
• Anaesthia Explained

[edit] References

• Brady. Anatomy and Physiology for Emergency Care