D_LCO is the extent to which oxygen passes from the air sacs of the lungs into the blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

. Commonly, it refers to the test used to determine this parameter. It was introduced in 1909.

Mechanism of The D_LCO Test

This test involves measuring the partial pressure

Partial pressure

In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....

 difference between inspired and expired carbon monoxide. It relies on the strong affinity and large absorption capacity of erythrocytes for carbon monoxide and thus demonstrates gas uptake by the capillaries that are less dependent on cardiac output

Cardiac output

Cardiac output is the volume of blood being pumped by the heart, in particular by a left or right ventricle in the time interval of one minute. CO may be measured in many ways, for example dm3/min...

.. The measurement of D_LCO is affected by atmospheric pressure and/or altitude and correction factors can be calculated online. Expected D_LCO is also affected by the amount of hemoglobin, age and sex and correction factors are available online.

Decrease

D_LCO is decreased in any condition which affects the effective alveolar surface area:

1. Hindrance in the alveolar
   Pulmonary alveolus
   An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...
   
    wall. e.g. fibrosis
   Fibrosis
   Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...
   
   , alveolitis
   Alveolitis
   Alveolitis can refer to two inflammatory conditions. It can refer to inflammation of the alveoli in the lungs, or the dental alveolus in the jaw.Alveolus in the jaw is also known as dry socket...
   
   , vasculitis
   Vasculitis
   Vasculitis refers to a heterogeneous group of disorders that are characterized by inflammatory destruction of blood vessels. Both arteries and veins are affected. Lymphangitis is sometimes considered a type of vasculitis...
   
   
2. Decrease of total lung area, e.g. Restrictive lung disease
   Restrictive lung disease
   Restrictive lung diseases are a category of extrapulmonary, pleural, or parenchymal respiratory diseases that restrict lung expansion, resulting in a decreased lung volume, an increased work of breathing, and inadequate ventilation and/or oxygenation...
   
   .
3. Uneven spread of air in lungs, e.g. emphysema.
4. Pulmonary embolism
   Pulmonary embolism
   Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...
   
   
5. Cardiac insufficiency
6. Pulmonary hypertension
   Pulmonary hypertension
   In medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
   
   
7. Bleomycin (upon administration of more than 200 units)
8. Anemia-due to decrease in blood volume

However, many modern devices compensates for the hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 value of the patient (taken by blood test), and excludes it as a factor in the DLCO interpretation.

Increase

Factors that can increase the D_LCO include polycythaemia, asthma (can also have normal D_LCO) and increased pulmonary blood volume as occurs in exercise or congestive heart failure

Congestive heart failure

Heart failure often called congestive heart failure is generally defined as the inability of the heart to supply sufficient blood flow to meet the needs of the body. Heart failure can cause a number of symptoms including shortness of breath, leg swelling, and exercise intolerance. The condition...

. Other factors are left-to-right pulmonary shunting that occurs in left heart failure, alveolar hemorrhage, and smoking within 24 hours of the test.

Decrease

A D_LCO of less than 60% predicted portends a poor prognosis for lung cancer resection. FEV₁ is of lesser prognostic value for lung resection survival.