ATS Pulmonary Function Laboratory Manual

chapter  10

alveolar gas sample in a bag/chamber, and ( 2 ) measuring exhaled gas concentrations continuously during exhala- tion using a rapid response gas analyzer. Breath-hold with alveolar sample bag/chamber: In this technique, the patient inhales a volume of test gas usu- ally containing 10% helium (He) or 0.3% methane (CH 4 ) as a tracer gas, 0.3% CO, and 21% oxygen (O 2 ) with the balance nitrogen (N 2 ). The test gas is held in the lungs for approximately 10 seconds, and after enough gas is exhaled to wash out the mechanical and anatomical dead space a gas sample is collected in a bag or chamber for analysis. Breath-hold with a rapid response gas analyzer: In this technique, the patient inhales a volume of test gas con- taining 0.3% methane or other tracer gas, 0.3% CO, 21% O 2 , and the balance N 2 . Again the test gas is held in the lungs for approximately 10 seconds, and then during exhalation the tracer gas and CO concentrations are analyzed continuously by a rapid response gas analyzer, eliminating the need to collect gas in a sample bag or chamber (6). While using a single Dl CO value to summarize individual CO uptake properties of millions of lung units is a limitation of this test, measuring an “overall” CO uptake has proved to be clinically useful. In the presence of various systemic disease processes and lung abnormalities that affect alveolar–capillary gas transport, Dl CO can be increased or decreased (7). Increases in Dl CO occur in: • Polycythemia • Pulmonary hemorrhage • Diseases associated with increased pulmonary blood flow

• Exercise • Asthma • Mueller maneuver Decreases in Dl CO

occur in:

• Emphysema • Parenchymal lung diseases (e.g., interstitial pulmonary fibrosis) • Pulmonary involvement in systemic diseases • Diseases or conditions that result in reduced effort or respiratory muscle weakness

• Cardiovascular diseases • Pulmonary embolism • Anemia • Hemoglobin binding changes (e.g., increased COHb) • Valsalva maneuver • Pulmonary edema, vasculitis, or hypertension Indications and Contraindications Some indications for Dl CO are provided in Table 10.1. There are no significant contraindications for the Dl CO

test other than the considerations listed under “Special

safety precautions” below.

Equipment and Supplies 1.

System description (e.g., manufacturer, model, type, accessories, additional features, and software version). The system should meet or exceed recommendations made in the latest ATS/ERS standardization document on Dl CO (7). 2. Cylinder of test gas appropriate for the testing system.

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