PURPOSE: We have previously shown that patients with COPD who desaturate with normal daily activity have lower activity levels than patients who do not desaturate. Desaturation was defined as the time O2 saturation <90% but did not take into consideration the severity of desaturation. The purpose of this study was to determine whether patients with more severe oxygen desaturation walked less than patients with less severe desaturation while living freely in their home environment.
METHODS: 41 patients with COPD underwent daytime ambulatory monitoring: accelerometers defined walking activity and oximetry measured duration and nadir of O2 desaturation linked to walking. Walking time was compared between patient groups defined by duration and severity of desaturation.
RESULTS: Scatter plot of walking and desaturation duration showed a clear and obvious threshold: patients who desaturated for ≥25% of time walked had less walking activity than patients who desaturated for <25%. No relationship was found between walking time and O2 nadir. 4 groups were established: mild dipper (nadir >87%, duration <25%), mild persister (nadir >87%, duration >25%), severe dipper (nadir <87%, duration <25%) and severe persister (nadir <87%, duration >25%). A strong dichotomy (p=.0004) was found between groups: mild and severe persisters walked less than mild or severe dippers. Walking time was similar between GOLD stages.
CONCLUSION: The prevalence of walking is decreased in relation to desaturation duration rather than severity. The relationship between duration of O2 desaturations and walking time is not linear, but there is a threshold of desaturation above which patients engage in minimal walking activity.
CLINICAL IMPLICATIONS: The duration of desaturation in COPD predicts trends in walking capacity better than the severity of desaturation, as defined by nadir from the baseline. Measures to reduce duration of desaturation, such as optimal O2 prescriptions using ambulatory techniques, may significantly improve functional performance in COPD.
DISCLOSURE: Miriam Cohen, Consultant fee, speaker bureau, advisory committee, etc, Nonin, Medical.