Long-term oxygen therapy (LTOT) improves survival in hypoxemic patients with advanced lung disease. The LTOT prescription is based on an evaluation of oxygen saturation at rest and during exercise, although this evaluation may not reflect the usual daily activity of these patients. The impact of routine daily activity on oxygen desaturation is unknown. We conducted this study to assess the daily activity profile of LTOT patients and its relationship to oxygen saturation.
25 daytime ambulatory oximetry monitoring (AOM) studies were performed on 11 patients with resting hypoxemia on continuous oxygen (COT) and 14 patients who desaturated only with ambulation (AOT). Accelerometers defined 3 categories of activity: walking, active-not-walking, and inactive. Oximetry confirmed desaturation events defined as oxygen saturation <90% for >30 seconds. Using a scoring method similar to polysomnography, a temporal profile of oxygen saturation linked to activity was defined for each patient.
See charts 1 and 2.
Both the COT and AOT patients spent the majority of their time “active-not-walking”. Both groups spent a very small percentage engaged in “walking”. The COT patients spent a significantly more time “inactive” than the AOT patients; the AOT patients spent a significantly more time “active-not-walking”. In both groups, the greatest duration of oxygen desaturation occurred during “active-not-walking”. The COT group desaturated for more minutes when “inactive” compared to AOT. Although both groups desaturated while “walking”, desaturation time linked to walking contributed little to the total time. The severity of hypoxemia for each linked desaturation event was similar.
This is the first detailed study to define the activity profile of patients with advanced lung disease on LTOT. Standard rest and walk testing is a limited evaluation on which to base the LTOT prescription. This approach does not assess oxygen saturation when patients are “active-not-walking” –the most common activity of these patients. AOM with activity monitoring provides patient-specific data on the temporal profile of oxygen saturation linked to usual activity, which may be used to optimize LTOT prescriptions.
Miriam Cohen, Grant monies (from sources other than industry) VA, Veterans Network #3; Grant monies (from industry related sources) Nonin Medical, Inc.
Desaturation Minutes Linked to Activity (mean minutes ± standard error and mean O2 saturation)Total Minutes of Daytime DS (± SE)Walking (min) (± SE)Active-not-walking (min) (± SE)Inactive (min) (± SE)AOT103 (± 31.4)35 (± 9.5) Mean O2 = 8761 (± 23.5) Mean O2 = 877 (± 5.8) Mean O2 = 75COT242 (± 49.2)39 (± 6.6) Mean O2 = 86133 (± 31.6) Mean O2 = 8770 (± 27.1) Mean O2 =78p Value for DS (min)<.02NSNS<.02
Accelerometer Profile of Daytime Activity (% time in activity ± standard error)WalkingActive-not-walkingInactiveAOT3.7 % (± 0.79)89.5 % (± 1.4)6.6 % (± 1.4)COT2.2 % (± 0.39)78.7 % (± 3.1)18.9 % (± 3.2)p ValueNS<.004<.002