- Haldane effect
The Haldane effect is a property of
hemoglobinfirst 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 dioxide. This is a consequence of the fact that reduced (deoxygenated) hemoglobin is a better proton acceptor than the oxygenated form.
In red blood cells, the enzyme
carbonic anhydrasecatalyzes the conversion of dissolved carbon dioxide to carbonic acid, which rapidly dissociates to bicarbonateand a free proton:
CO2 + H2O → H2CO3 → H+ + HCO3-
Le Chatelier's principle, anything that stabilizes the proton produced will cause the reaction to shift to the right, thus the enhanced affinity of deoxyhemoglobin for protons enhances synthesis of bicarbonate and accordingly increases capacity of deoxygenated blood for carbon dioxide. The majority of carbon dioxide in the blood is in the form of bicarbonate. Only a very small amount is actually dissolved as carbon dioxide, and the remaining amount of carbon dioxide is bound to hemoglobin.
In addition to enhancing removal of carbon dioxide from oxygen-consuming tissues, the Haldane effect promotes dissociation of
carbon dioxidefrom hemoglobin in the presence of oxygen. In the oxygen-rich capillaries of the lung, this property causes the displacement of carbon dioxide to plasma as venous blood enters the alveolusand is vital for alveolar gas exchange.
The general equation for the Haldane Effect is:H+ + HbO2 ←→ H+.Hb + O2
In patients with lung disease, lungs may not be able to increase
alveolar ventilationin the face of increased amounts of dissolved CO2.
This partially explains the observation that some patients with
emphysemamight have an increase in PaCO2 (partial pressure of arterial dissolved carbon dioxide) following administration of supplemental oxygen even if content of CO2 stays equal.cite journal | last=Hanson | first=CW | coauthors= Marshall BE, Frasch HF, Marshall C | title=Causes of hypercarbia with oxygen therapy in patients with chronic obstructive pulmonary disease | journal=Critical Care Medicine | volume=24 | issue=1 | pages=23–28 | date=January 1996 | pmid=8565533 ]
Alkalosis causes a left shift in the oxygen dissociation curve, which enhances the ability of hemoglobin to pick up oxygen in the lungs but makes it less available at the tissue level. ["Mechanical Ventilation, physiological and clinical applications", Author Susan P Pilbeam, 1998; Mosby Inc.]
* [http://physiology.umc.edu/themodelingworkshop/Integrative%20Model/Low%20Level/Haldane%20Effect/Haldane%20Effect.HTML Overview at umc.edu]
* [http://www.people.vcu.edu/~mikuleck/courses/resp2/sld017.htm Overview at vcu.edu]
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