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Cyanosis is the bluish discoloration of the skin and mucous membranes. It is caused by too little oxygencarrying hemoglobin in the blood that flows through the capillaries. The discoloration usually is most apparent in the fingernail beds and around the lips. Like edema, cyanosis is more a sign of heart disease than it is a symptom. Most people are familiar with cyanosis from historical accounts of the so-called royal blue bloods of England. A common and familiar type of cyanosis is that which occurs when an individual has been outside in the cold for too long.

There are two primary types of cyanosis: central cyanosis and peripheral cyanosis. The first type, from which the term “blue blood” originated, is due to an inherited form of heart disease. In central cyanosis, there is an abnormal mixing of venous blood with arterial blood. Venous blood is normally bluish in color because it is carrying little oxygen, having given HEART DISEASE SYMPTOMS up its oxygen to the tissues. Arterial blood is red because it has become enriched with the oxygen inhaled through the lungs.

Central cyanosis generally occurs when the venous and arterial blood are mixed together in the heart, either because of a congenital opening between the left and right sides of the heart or because of a genetically defective heart in which there is a common mixing chamber. It may also be a result of advanced lung disease, such as emphysema, which prevents arterial blood from absorbing enough oxygen.

Peripheral cyanosis is the type commonly caused by exposure to cold temperatures. This occurs when the body attempts to conserve heat for vital organ functions by constricting the capillaries of the skin and slowing the blood flow. The body tissues respond
by removing excessive amounts of oxygen from the capillary blood. Peripheral cyanosis can occur in anyone following exposure to the cold, but may also occur in people with diseased arteries.

The two types of cyanosis are generally easily differentiated by their observable signs. People with peripheral cyanosis display the bluish discoloration only on skin surfaces, primarily the fingers, cheeks, nose, and outer areas of the lips. The color returns when the areas are warmed. Those with central cyanosis also display discoloration around the conjunctival of the eyes and inside the oral cavity, including the tongue.

In addition to the congenital defects that characteristically cause central cyanosis, it can also be the result of severe heart disease and cardiogenic shock—shock caused by the heart’s failure to pump adequately.

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