Abstract
Six minute walk test (6MWT) is widely used in the functional evaluation of diffuse parenchymal lung diseases (DPLD). To date, distance walked is the most studied 6MWT parameter.
We focused our study on desaturation index (DI) in 6MWT.
We retrospectively evaluated serial lung functions of 59 consecutive DPLD patients: 28 idiopathic interstitial pneumonia (IIP), 11 connective tissue disease (CTD), 13 sarcoidosis and 7 other DPLD.
DI was calculated as the ratio between the area above the curve, which was created using each peripheral oxygen saturation (SpO2) value obtained every 2 seconds, and the distance walked.
Composite physiologic index (CPI) was used to assess disease severity. Disease progression (“time to irreversible decline” in either FVC levels of 10% from baseline or DLCO levels of 15% from baseline) was quantified from the date of the first 6MWT available, by using proportional hazards analysis.
Of the 59 patients, 38 were females, mean age was 66.3 (±11.8 SD), mean FVC was 90% predicted (±24) and mean DLCO was 55% (±24). Median length of follow up was 24.7 months.
Among 6MWT parameters, only DI (p=0.02), lowest SpO2 (p=0.01) and SpO2 at 1 minute of recovery (p=0.02) significantly differed between IIP and sarcoidosis.
DI showed more correlations with other physiologic variables than distance walked; the strongest one was with DLCO (r=-0.53, p=0.0001).
After controlling for age, gender, smoking status, diagnosis and disease severity, DI remained predictive of disease progression (p=0.04).
DI and SpO2 at 1 minute of recovery are two new promising parameters in the assessment of DPLD. DI is associated with disease progression, independently of disease severity.
- © 2011 ERS