PURPOSE: Standard methods of assessing oxygen desaturation in patients with chronic obstructive lung disease (COPD) include walking the patient at a “normal” pace until tired (“hallway walk test” [HWT]) or a more formal 6-minute walk test (6MWT). We determined the value of these two standard clinical tests to predict oxygen desaturation during usual daily activities.
METHODS: 43 patients with severe COPD (%FEV1<50%) underwent a HWT and 6MWT followed by ambulatory monitoring of oxygen saturation and activity over 2 days. Accelerometers defined 4 activity categories: Walking, Short/Intermittent Walking (SIW), Active-not-Walking (ANW) and Rest. We calculated the negative predictive value (NPV) and positive predictive value (PPV) of O2 desaturation <90% during the HWT and 6MWT to detect desaturation during each of the daily activity categories using ambulatory monitoring techniques, as previously defined by this research team (Walking = O2 <90% for 25% of walking time; SIW, ANW and Rest = O2 <90% for 10% of time spent in each activity). A predictive value of .75 was considered significant.
RESULTS: 6MWT O2 >90% ruled out desaturation during all categories of daily activity (NPV >.75). 6MWT <90% predicted desaturation during walking (PPV>.75), but could not predict desaturation with acceptable precision during SIW or ANW (PPV<.75). HWT O2 >90% could rule out desaturation during SIW and ANW (NPV>.75), but not during walking (NPV<75%). HWT O2 <90% could predict desaturation during walking (PPV>.75), but could not predict desaturation in the other categories (PPV<.75). Of note, neither the 6MWT nor the HWT could predict desaturation during rest.
CONCLUSION: Standard clinical tests commonly used to assess oxygen desaturation predict desaturation during daily walking, but fail to accurately predict oxygen saturation during other daily activity categories.
CLINICAL IMPLICATIONS: The major portion of daily oxygen desaturation occurs in COPD patients when they are active, but not accelerating at the speed of walking (SIW, ANW). Thus, the standard clinical assessments of oxygen desaturation may underestimate the daily desaturation time.
DISCLOSURE: Miriam Cohen, No Product/Research Disclosure Information; Grant monies (from industry related sources) Nonin Medical, Inc