Diffusing capacity, of lung

The diffusing capacity of the lung for carbon monoxide (CO) is a measure of the ability of the alveolar capillary membrane to transfer or conduct gases from the alveoli to the blood. This transport process is entirely a passive one brought about by diffusion. As described previously in Section 2.2, the barriers for diffusion consist of surfactant, alveolar epithelium, interstitital fluid, capillary endothelium, plasma, and the red blood cell membrane. 

So far the mechanical components of airflow through the lungs have been discussed. Another important parameter is the diffusing capacity of the lung, the rate at which oxygen or carbon dioxide travel from the alveoli to the blood (or vice versa for carbon dioxide) in the pulmonary capillaries. Diffusion of gas across a barrier is directly related to the surface area of the barrier and inversely related to the thickness. Also, diffusion is directly proportional to the solubility of the gas in the barrier material and inversely related to the molecular weight of the gas. 

Ogilvie, C. M., R. E. Forster, W. S. Blakemore, and J. W. Morton, 1957, A Standardized Breath Holding Technique for the Clinical Measurement of the Diffusing Capacity of the Lung for Carbon Monoxide, J. Clin, Invest., 36 1-17. 

In patients with type 2 diabetes, in whom AIR insulin with meals n = 221) was compared with insulin glargine alone (n = 223) or AIR insulin in combination with insulin glargine (n = 115) for 52 weeks, there was also a reduction in carbon monoxide diffusing capacity of the lungs in those who used AIR insulin [13 =]. 

Ohno Y, Hatabu H, Takenaka D, Van Cauteren M, Fuji M, Sugimura K. Dynamic oxygen-enhanced MRI reflects diffusing capacity of the lung. Magn Reson Med 2002 47 1139-1144. 

Lamberto C, Nunes H, Le Toumelin P, et al. Membrane and capillary blood components of diffusion capacity of the lung for carbon monoxide in pulmonary sarcoidosis relation to exercise gas exchange. Chest 2004 125(6) 2061-2068. 

Hamada K, Nagai S, Tanaka S, et al. Significance of pulmonary arterial pressure and diffusion capacity of the lung as prognosticator in patients with idiopathic pulmonary fibrosis. Chest 2007 131(3) 650-656. 

Lung function tests are also of diagnostic value in allergic alveolitis and, if possible, should be carried out in all cases. It is useful to follow the lung function during the recovery phase. The preferable methods are static and dynamic spirometry and measurement of the diffusion capacity of carbon monoxide (DLCO). The latter is the most sensitive test and the capacity can still be reduced after the chest X-ray has become normalized (Tukiainen et al. 1980 Kokkarinen et al. 1993). 

A suspected diagnosis of COPD should be based on the patient s symptoms and/or history of exposure to risk factors. Spirometry is required to confirm the diagnosis. The presence of a postbronchodilator FEV,/FVC ratio less than 70% [the ratio of FEV, to forced vital capacity (FVC)] confirms the presence of airflow limitation that is not fully reversible.1,2 Spirometry results can further be used to classify COPD severity (Table 12-1). Full pulmonary function tests (PFTs) with lung volumes and diffusion capacity and arterial blood gases are not necessary to establish the diagnosis or severity of COPD. 

Decrease in lung capacity, alveolar volume, and diffusing capacity for carbon monoxide values remained depressed for at least 72 h after last exposure. Persistent inflammation of proximal portion of alveolar ducts and adjacent alveoli. 

Changes in pulmonary function have been observed in a variety of species after short-term exposure to ozone, including alterations in the elastic behavior of the lungs, increased resistance to flow, and decreased carbon monoxide diffusion capacity. 

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