Nocturnal oxygen desaturation (NOD) has long been recognized in chronic obstructive pulmonary disease (COPD), although its significance remains controversial. In patients with moderate daytime hypoxemia who are not on oxygen therapy, the reported prevalence of NOD is highly variable due, in part, to different definitions of NOD. In addition, oximetry studies in the hospital or sleep lab setting underestimate the duration of desaturation. Home studies demonstrate marked night-to-night variability that may be explained by the disrupted sleep patterns in patients with COPD. Therefore, we propose that measuring oxygen desaturation during the time patients are actually sleeping may be a more accurate method to detect NOD.
We evaluated 11 subjects with COPD and moderate daytime hypoxemia with 15 overnight home studies using a wearable pulse oximeter (WristOx, Nonin Medical Company) and a “sleep watch” (Actigraph, Ambulatory Monitoring, Inc). The actigraph software contained an algorithm that identifies sleep. Pulse oximetry data were then extracted from periods identified as sleep and compared to the oximetry data for the duration of the night study (total-night-study = time asleep + time in bed not sleeping).
a. Subject cohort had variable sleep duration: percent of the total-night-study identified as sleep ranged from 44% to 99%. b. Using standard definitions of NOD: 3 patients desaturated below 90% for at least 30% of the night; 6 patients desaturated below 90% for at least 5 minutes with a nadir of 85% or lower. c. 89.2% of all desaturations occurred during the time identified as sleep. d. Subject cohort desaturated below 90% for 17.5±5.2% of their sleep time (range 0.1-59.3%).
In this patient cohort, oxygen desaturated predominantly occurred during sleep. Actigraphy data enhanced these overnight home oximetry studies by distinguishing when subjects were asleep and when they were awake, thus allowing precise quantification of nocturnal hypoxemia.
Accurate assessment and evaluation of the magnitude of NOD cannot be done with oximetry alone.
M.D. Cohen, Nonin Medical, Inc