ATS Pulmonary Function Laboratory Manual

chapter  10

Figure 10.1  Graphic illustration of the Jones-Meade method for calculating the breath-hold time during the Dl CO maneuver. The breath-hold time starts after 30% of the time it takes to inspire the test gas has elapsed, and ends halfway into the alveolar sample collection. The beginning of inspiration is determined using the back ex- trapolation technique, although it has been recently reported that there are no significant differences between the visual and extrapolation approaches (11).

3.

Any adjustments (e.g., Hb, COHb, Po 2

) should also be reported separately along with the data used to make

the adjustment (7).

4. The average Va (BTPS) should be reported along with the predicted Va (the predicted TLC minus predicted dead space) and % predicted Va. 5. The average Vi at BTPS should be reported.

Procedure notes 1. Various miscellaneous factors may affect this test. 1.1.

A diurnal variation (1.2–2.2% fall/h from 9:30 a.m. to 5:30 p.m.) has been reported in Dl CO (14). How- ever, this fall can be partially explained by increasing COHb and decreasing Hb concentrations (10). 1.2. A 13% change in Dl CO during the menstrual cycle has been reported (17) The highest Dl CO values were observed just before and during menses and the lowest Dl CO values were observed during week 3 (25). 1.3. A 15% reduction 90 minutes after ingesting ethanol has been reported on some analyzers (18). 1.4. Cigarette smoking alters the outcome of this test. 2. An adjustment for COHb is not required but is recommended for interpretation purposes when COHb is clinically elevated. COHb-adjusted Dl CO = measured Dl CO (1 + %COHb / 100) (7). 3. Dl CO increases with increasing altitude (reflects decreased Pi O2 ) (13). Adjustment equation for altitude- induced changes (i.e., Po 2 ) is: Dl CO adjusted for altitude = Measured Dl CO × [1 + 0.0031(Pi O2 – 150)], where estimated Pi O2 = 0.21 (baro- metric pressure −47), or you can adjust the predicted value: Dl CO predicted for altitude = Dl CO predicted / [1 + 0.0031(Pi O2 – 150)] 4. When test specifications are not met, such data should be reported with the warning that the data are suboptimal. 5. Small increases in COHb (about 0.7% per inhalation of test gas) occur when CO is inspired during the Dl CO test.

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