The Science Journal of the American Association for Respiratory Care

2002 OPEN FORUM Abstracts

COMPARISON OF TWO DIFFERENT SIZE SINGLE BREATH DIFFUSING CAPACITY COLLECTION TUBES ON THE JAEGER MASTERSCOPE PFT SYSTEM IN PATIENTS WITH REDUCED DLCO VALUES AND BIOLOGICAL CONTROLS.

Carl D Mottram BA RRT RPFT FAARC, Marlene A Edgar CPFT, Scot M Witzke CPFT, Paul D Scanlon MD. Mayo Clinic, Rochester, MN 55905.

Measurement of the single breath diffusing capacity using the Jaeger Masterscope PFT system (Yorba Linda, CA) necessitates a collection tube, which results in a total system deadspace (VD) of 700 ml. Exhaled gas is analyzed at the distal end of this tubing following the standard 10-second breath-hold and exhalation of a predetermined physiologic VD according to ATS recommendations. We noticed an unusual decrease in DLCOSB among patients with previously low values, which had been tested using a different PFT system. Hypotheses: In patients with high V/Q mismatching the alveolar gas sample at the distal end of the standard large tube will be different than at the proximal end resulting in a lower DLCO value. We measured DLCOSB in 18 patients with suspected reduced values based on history and 10 healthy technologists (Bio-QC techs) using both the standard tubing and a smaller tube with a total system VD of 350 ml. The patients were randomized into two groups where the standard tube was tested first followed by the small tube and vice versa to reduce testing bias. The Bio-QC techs were tested twice to satisfy both arms of the testing model. Two measurements were made with each tube (4 total) and the mean values of the standard 700 ml VD versus the 350 ml VD were used in the analysis. A paired Student t-test was used to compare the difference in values.

  18 patients 10 Bio-QC (20 tests)
DLCO standard 700 ml VD (mean) 7.4 ml/mmHg/min +/- 2.93 SD 22.5 ml/mmHg/min +/- 1.9 SD
DLCO 350 ml VD (mean) 9.1 ml/mmHg/min +/- 3.06 SD 23.0 ml/mmHg/min +/- 1.7 SD

P value

0.000004 0.02

In all 18 patients the small tube gave a higher DLCO (range: 0.35 to 4.25 ml/mmHg/min, average = 22.9% greater) when compared to the standard large tube. The Bio-QC group results varied only slightly between the two tube sizes. The small tube results were slightly but significantly higher (range: -1.7 to +2.2 ml/mmHg/min, average = 2.2% greater). These results support the hypothesis. The reduction in the tubing VD yields a higher result, which in separate analysis appears to be more consistent with expected results.

OF-02-154

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