Central or generalized cyanosis is due to an insufficient oxygen concentration
Consequently, of oxidized hemoglobin in arterial blood; this can in turn be due to pulmonary diseases that hinder the gas exchange between inspired air and blood in the pulmonary alveoli, as in asthma, chronic bronchitis or pulmonary emphysema; or it may be related to cardiovascular diseases and, more specifically, to cardiac insufficiency or congenital cardiac anomalies.
In the first case, there is a decrease in the velocity of circling of the blood by the capillaries, so that the arteriovenous oxygen difference increases; in congenital malformations, on the other hand, anomalous communication can occur between right and left heart cavities, with a mixture of venous and arterial blood.
Generalized cyanosis can also be recorded when, in the course of poisonous seizures, anomalous hemoglobin particles form, for example in methemoglobinemia or sulfohemoglobinemia.
Cyanosis can also affect a single organic region (localized or peripheral cyanosis), such as the extremities, and in this case is often related to disorders of blood circulation.
State of cutaneous capillaries.
If they are dilated, the skin will harbor a greater amount of dark blood, so the cyanosis will be much more intense than if they are contracted. A considerable increase of the carbon dioxide in the circulating blood results in a dilation of the capillaries; if this circumstance is accompanied by a decrease in oxygen, as occurs in the venous insufficiency of the superficial regions, the cyanosis will be very intense. On the other hand, in the shock, a more serious clinical situation than the previous one, the capillaries are contracted and the cyanosis is apparently less intense.