What determines the results of a gas diffusion study?

The diffusion rate is determined by a number of factors, including:

  • The amount of surface area over which diffusion can occur
  • The blood volume in the capillaries
  • The concentration of hemoglobin (the red part of blood cells whose job is to transport oxygen) present in the blood
  • The thickness of the membrane between the alveoli and the capillaries
  • The presence of excess fluid in the alveoli

When a lung disorder affects any of the above, a low rate of diffusion can occur and the person is left with less than maximum oxygen uptake.

What could abnormal results of a gas diffusion study indicate?

Obstructive lung disease

  • Cystic fibrosis (overproduction of mucus, leading to chronic infections in the lungs)
  • Emphysema (an abnormal increase in the size of the air spaces in the lungs, leading to difficult breathing and infection)

Damage to lung tissue

  • Drug reactions
  • Asbestosis or other lung disease caused by repeated exposure to airborne fibers
  • Inflamed alveoli due to allergic reactions
  • Sarcoidosis (clumps of abnormal tissue)

Systemic diseases that affect the lungs

Heart conditions

  • Pulmonary thromboembolism (blockage of a blood vessel in the lung)
  • Heart attack
  • Mitral stenosis (narrowing of the mitral valve of the heart)
  • High blood pressure
  • Pulmonary edema (fluid in the lungs )


Sometimes a gas diffusion study will show a diffusion rate that is higher than normal. In such cases, the following conditions could play a part:

  • Diseases associated with increased blood flow in the lungs
  • Polycythemia (abnormally high number of red blood cells)
  • Exercise
  • Bleeding in the lungs

Last reviewed by a Cleveland Clinic medical professional on 09/27/2018.


  • Enright MP. Office-based DLCO tests help pulmonologists to make important clinical decisions. Respir Investig. 2016;54(5):305-11.
  • National Heart, Lung, and Blood Institute. Pulmonary Function Tests. Accessed 9/28/2018.
  • Miaskiewicz, Joseph J.. "Pulmonary Function Testing." Principles and Practice of Hospital Medicine, 2e McKean SC, Ross JJ, Dressler DD, Scheurer DB. McKean S.C., Ross J.J., Dressler D.D., Scheurer D.B. Eds. Sylvia C. McKean, et al. New York, NY: McGraw-Hill.

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