Desaturation - distance ratio: a new concept for a functional assessment of interstitial lung diseases

Clinics (Sao Paulo). 2010;65(9):841-6. doi: 10.1590/s1807-59322010000900005.


Introduction: The functional evaluation has become increasingly important in the understanding and management of patients with interstitial lung diseases. The cardiopulmonary exercise test and the six-minute walk test (6MWT), through their isolated variables, have been used to do this evaluation, with some limitations.

Objectives: We proposed a new composite index (desaturation distance ratio using continuous peripheral oxygen saturation (SpO₂) and the distance walked as a more reliable tool for doing a functional evaluation of these patients.

Methods: 6MWT was performed by interstitial lung diseases patients and controls. Analyzed parameters were walked distance and desaturation area (DAO₂), obtained by taking the difference between maximal SpO₂ possible (100%) and patient's SpO₂ every 2 seconds. desaturation distance ratio was calculated using the ratio between DAO₂ and distance walked.

Results: Forty-nine interstitial lung diseases patients and 11 control subjects completed the protocol. The mean (SD) age was 60 (12) years and 65 (9) years, respectively (p:NS). Data obtained from 6MWT showed a significant statistical difference between interstitial lung diseases patients and controls: mean walked distance (430 and 602 meters, respectively); SpO₂ minimal maintained at least 10 seconds - SpO₂ min (85% and 94%, respectively), and median desaturation distance ratio (10 and 2.5, respectively). A correlation analysis, considering interstitial lung diseases patients, revealed the best correlation between desaturation distance ratio and DLco (r= - 0.72; p<0.001), being the correlation between SpO₂ min and DLco of 0.61 (p<0.001) and among walked distance and DLco of 0.58 (p<0.05).

Conclusion: Desaturation distance ratio is a promising concept and a more reliable physiologic tool to assess pulmonary diseases characterized by involvement of the alveolar-capillary membrane, such as interstitial lung diseases.

MeSH terms

  • Aged
  • Case-Control Studies
  • Cross-Sectional Studies
  • Exercise Test / methods*
  • Female
  • Humans
  • Lung Diseases, Interstitial / diagnosis*
  • Lung Diseases, Interstitial / physiopathology
  • Male
  • Middle Aged
  • Oximetry
  • Oxygen / analysis*
  • Respiratory Function Tests
  • Sensitivity and Specificity
  • Walking / physiology*


  • Oxygen