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Dead space examples diseases lungs8/25/2023 ![]() Because anemia can lower Dlco, all calculations of Dlco are adjusted for hemoglobin concentration to standardize measurements and interpretation. CO has a 200 to 250 times greater affinity for hemoglobin than does oxygen. ![]() Inhaled CO is used because of its very high affinity for hemoglobin. Remember, blood in the airways also can bind CO, hence Dlco can rise with hemoptysis and pulmonary hemorrhage. While Dlco serves as a surrogate marker of the available lung surface area and its properties that enable diffusion to take place, blood in the capillaries-or more accurately, unbound hemoglobin-is the essential driver in the diffusion of CO from the alveolar air across the alveolar-capillary membrane barrier into hemoglobin in red blood cells. For example, Dlco is low in chronic obstructive pulmonary disease (COPD) with emphysema, or amiodarone lung toxicity, and it is even lower in ILD with PAH. Overlooking a reduced Dlco can delay early diagnosis and treatment of a disease. Respiratory tract symptoms and abnormalities on chest radiographs and/or chest computed tomography (CT) scans are essential to properly interpret any PFT, including Dlco. Additionally, Dlco may predict mortality in a variety of lung diseases (including cancer), various ILDs (including idiopathic pulmonary fibrosis), and severe PAH.ĭyspnea is the most common reason for ordering a Dlco test, but there are many situations and presentations in which a higher than predicted or lower than predicted Dlco suggests the possible presence of lung or heart disease ( Table 1). ![]() Alone, Dlco is not enough to confirm the presence of or differentiate between the 2 lung conditions. 2 Both PAH and ILD can reduce Dlco, the former by reducing capillary blood volume and the latter by causing fibrosis of the delicate interface necessary for gas diffusion between alveolar air and capillary blood. The specificity and sensitivity of Dlco for specific lung diseases has not been studied extensively until recently, particularly for pulmonary arterial hypertension (PAH) and systemic sclerosis with or without interstitial lung disease (ILD). When Dlco is below the predicted reference range (75% to 140% of predicted) it becomes a clue to the presence of a physiologic problem that ultimately may impair exercise, and even affect long-term survival from common lung diseases and disorders. 1 But has anyone stopped to ask why Dlco measurement is ordered, how it is determined, and what it means when it is reduced or not?ĭlco is a calculated, derived value that indirectly assesses the ability of the lungs to “transfer” oxygen to blood through the use of a test gas (namely, CO) that has a greater affinity for blood hemoglobin. Every clinician knows that Dlco measures the quantity of carbon monoxide (CO) transferred per minute from alveolar gas to red blood cells (specifically hemoglobin) in pulmonary capillaries, and that this value, expressed as mL/min/mm Hg, represents mL of CO transferred per minute for each mm Hg of pressure difference across the total available functioning lung gas exchange surface. 2016 56(5):440-445.Ĭarbon monoxide diffusing capacity (Dlco) probably is the least understood pulmonary function test (PFT) in clinical practice worldwide, even among experienced pulmonologists. Using and interpreting carbon monoxide diffusing capacity (Dlco) correctly. UC Davis Medical Center, Sacramento, California.
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