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Abstract: Poster Presentations |

DO WE REALLY NEED TO CORRECT FOR LUNG VOLUME WHEN INTERPRETING THE DIFFUSING CAPACITY? FREE TO VIEW

Todd Whitman, MD; David A. Kaminsky, MD*
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University of Vermont College of Medicine, Burlington, VT


Chest


Chest. 2005;128(4_MeetingAbstracts):394S. doi:10.1378/chest.128.4_MeetingAbstracts.394S-a
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Abstract

PURPOSE:  The diffusing capacity of the lung for carbon monoxide (DLCO) is commonly used as a measure of gas exchange. The DLCO is usually reported as both an absolute number (DLCO) and corrected for alveolar volume (DLCO/VA). However, it remains unclear which one to use in interpretation. To resolve this dilemma we determined whether abnormal DLCO or DLCO/VA was more closely associated with abnormal gas exchange as measured by exercise oximetry.

METHODS:  With Institutional Review Board approval, we retrospectively reviewed the charts of all patients who had both DLCO and 6-minute walk/oximetry testing at our University Pulmonary Clinic over a 2-year period. We analyzed the association between abnormal DLCO or DLCO/VA (defined as <75% predicted) and abnormal gas exchange (defined as oxygen desaturation >/= 4%) using Chi-square or Fisher’s exact tests, and calculated sensitivity, specificity, positive and negative predictive values (PPV, NPV) and likelihood ratios (LR). We also measured the association between DLCO, DLCO/VA and oxygen desaturation using Spearman rank correlations.

RESULTS:  A total of 93 patients had valid and complete data. Their average age was 66 years, 54% were women and 60% had interstitial lung disease. The prevalence of oxygen desaturation was 44%. The % predicted values of DLCO and DLCO/VA were highly correlated (rho=0.91, p<0.0001), but both correlated only weakly with oxygen desaturation (rho = -0.37, p=0.0003; rho= -0.42, p <0.0001, respectively). Low DLCO predicted desaturation with a sensitivity of 0.95, specificity of 0.29, PPV of 0.51, NPV of 0.88 and LR of 1.34 (p=0.003). Low DLCO/VA predicted desaturation with a sensitivity of 0.90, specificity of 0.38, PPV of 0.54, NPV of 0.83 and LR=1.45 (p=0.002). The highest LR (1.91) was seen for DLCO/VA of patients with restriction (p=0.04).

CONCLUSION:  There were no differences in the ability of DLCO or DLCO/VA to predict abnormal gas exchange, but patients with abnormal gas exchange were slightly more likely to have an abnormal DLCO/VA than DLCO.

CLINICAL IMPLICATIONS:  Either the DLCO or DLCO/VA may be used to assess gas exchange.

DISCLOSURE:  David Kaminsky, None.

12:30 PM - 2:00 PM


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