Hypoxic drive
Encyclopedia
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 central chemoreceptors
, and very little by the oxygen levels. An increase in carbon dioxide will cause chemoreceptor reflexes to trigger an increase in respirations. Hypoxic drive accounts normally for 10% of the total drive to breathe. This increases as the PaO2 goes 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and below, while hypoxic drive is no longer active when PaO2 exceeds 170 torr.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 high altitude flying pilots. For this reason, supplemental oxygen is required by Federal Aviation Regulations for pilots flying above about 12,500 feet altitude in unpressurized airplanes.
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 rate of respiration.
Recent studies have proven that COPD patients who have chronically compensated elevated levels (known as " Retainers") are not in fact dependent on hypoxic drive to breathe. However, when in respiratory failure and put on high inspired oxygen, the in their blood may increase via three mechanisms, namely the Haldane Effect
, the Ventilation/Perfusion mismatch (where the regional pulmonary hypoxic vasoconstriction is released) and by the removal or reduction of the hypoxic drive itself.
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
drive in which the body uses oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
chemoreceptors instead of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
receptors to regulate the respiratory cycle.
Normal respiration is driven mostly by the levels of carbon dioxide in the arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
, which are detected by central chemoreceptors
Central chemoreceptors
Central chemoreceptors of the central nervous system, located on the ventrolateral medullary surface, are sensitive to the pH of their environment....
, and very little by the oxygen levels. An increase in carbon dioxide will cause chemoreceptor reflexes to trigger an increase in respirations. Hypoxic drive accounts normally for 10% of the total drive to breathe. This increases as the PaO2 goes to 70 torr
Torr
The torr is a non-SI unit of pressure with the ratio of 760 to 1 standard atmosphere, chosen to be roughly equal to the fluid pressure exerted by a millimetre of mercury, i.e., a pressure of 1 torr is approximately equal to 1 mmHg...
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 high altitude flying pilots. For this reason, supplemental oxygen is required by Federal Aviation Regulations for pilots flying above about 12,500 feet altitude in unpressurized airplanes.
In the past, it was believed that in cases where there are chronically high
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
carbon dioxide levels in the blood such as in COPD
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...
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 rate of respiration.
Recent studies have proven that COPD patients who have chronically compensated elevated levels (known as " Retainers") are not in fact dependent on hypoxic drive to breathe. However, when in respiratory failure and put on high inspired oxygen, the in their blood may increase via three mechanisms, namely the Haldane Effect
Haldane effect
The Haldane effect is a property of hemoglobin first described by the Scottish physician John Scott Haldane. Deoxygenation of the blood increases its ability to carry carbon dioxide; this property is the Haldane effect. Conversely, oxygenated blood has a reduced capacity for carbon...
, the Ventilation/Perfusion mismatch (where the regional pulmonary hypoxic vasoconstriction is released) and by the removal or reduction of the hypoxic drive itself.