Journal Article

Examination of the Carbon Monoxide Diffusing Capacity (DlCO) in Relation to Its Kco and Va Components

Hughes, J. Michael B., Pride, Neil B.

2012

Overview

Abstract The single-breath carbon monoxide diffusing capacity (DlCO) is the product of two measurements during breath holding at full inflation: (1) the rate constant for carbon monoxide uptake from alveolar gas (kco [minute−1]) and (2) the “accessible” alveolar volume (Va). kco expressed per mm Hg alveolar dry gas pressure (Pb*) as kco/Pb*, and then multiplied by Va, equals DlCO; thus, DlCO divided by Va (DlCO/Va, also called Kco) is only kco/Pb* in different units, remaining, essentially, a rate constant. The notion that DlCO/Va “corrects” DlCO for reduced Va is physiologically incorrect, because DlCO/Va is not constant as Va changes; thus, the term Kco reflects the physiology more appropriately. Crucially, the same DlCO may occur with various combinations of Kco and Va, each suggesting different pathologies. Decreased Kco occurs in alveolar–capillary damage, microvascular pathology, or anemia. Increased Kco occurs with (1) failure to expand normal lungs to predicted full inflation (extrapulmonary restriction); or (2) increased capillary volume and flow, either globally (left-to-right intracardiac shunting) or from flow and volume diversion from lost or damaged units to surviving normal units (e.g., pneumonectomy). Decreased Va occurs in (1) reduced alveolar expansion, (2) alveolar damage or loss, or (3) maldistribution of inspired gases with airflow obstruction. Kco will be greater than 120% predicted in case 1, 100–120% in case 2, and 40–120% in case 3, depending on pathology. Kco and Va values should be available to clinicians, as fundamental to understanding the clinical implications of DlCO. The diffusing capacity for nitric oxide (DlNO), and the DlNO/DlCO ratio, provide additional insights.

• Publisher: Oxford University Press,American Thoracic Society
• Subject: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy / Biological and medical sciences / Blood. Blood and plasma substitutes. Blood products. Blood cells. Blood typing. Plasmapheresis. Apheresis / Carbon monoxide / Carbon Monoxide - pharmacokinetics / Exercise - physiology / Humans / Intensive care medicine / Lung - metabolism / Lung - physiology / Lung Diseases - metabolism / Lung Diseases - physiopathology / Lung Volume Measurements / Medical sciences / Pulmonary Alveoli - metabolism / Pulmonary Alveoli - physiology / Pulmonary Diffusing Capacity - physiology / Respiratory Function Tests - methods / Transfusions. Complications. Transfusion reactions. Cell and gene therapy