Correct!
3. Daytime oxygen saturation.

Several physiological factors can contribute to a decrease in oxygen saturation during sleep (Table 1). Most of these changes are more pronounced during rapid eye movement (REM) sleep compared to Non REM (NREM) sleep.

Table 1

Chronic obstructive pulmonary disease (COPD) is associated with diverse sleep disorders. There is a high prevalence of insomnia disorder in patients with COPD (1). The incidence of restless legs syndrome is also higher in those with a history of obstructive lung disease (2).  While the prevalence of sleep apnea does not appear to be higher in those with COPD than in general population (3), nocturnal hypoxemia occurs commonly in patients with COPD (4). The physiologic changes reported in Table 1 are more pronounced in patients with COPD. Pronounced alveolar hypoventilation and ventilation-perfusion mismatch significantly contribute to nocturnal hypoxemia (5,6).

Daytime oxygen saturations (SaO2) play a prominent role in predicting nocturnal hypoxemia (7). Patients with lower daytime saturation, and hence, resting oxygen levels on the steep portion of the oxyhemoglobin dissociation curve, endure a more pronounced drop in oxygen saturation with a similar decrease in arterial oxygen tension (PaO2) as compared to a person with higher resting oxygen levels on the higher, flatter portion of the oxyhemoglobin dissociation curve.

Several studies have been done to identify the predictors of nocturnal desaturation in COPD patients. Many of these have found PaO2 and SaO2 to be independent predictors of desaturation during sleep (8-10). However, not all studies have confirmed this relationship between awake SaO2 and oxygen saturation during sleep (11). Other factors such age, FEVI, radiological severity of COPD have been assessed, but not consistently been found to be strong predictors of nocturnal hypoxemia.

References

  1. Budhiraja R, Parthasarathy S, Budhiraja P et al. Insomnia in patients with COPD. Sleep. 2012;35(3):369-75. 
  2. Budhiraja P, Budhiraja R, Goodwin JL et al. Incidence of restless legs syndrome and its correlates. J Clin Sleep Med. 2012;8(2):119-24.
  3. Sanders MH, Newman AB, Haggerty CL, et al. Sleep and sleep-disordered breathing in adults with predominantly mild obstructive airway disease. Am J Respir Crit Care Med. 2003;167:7–14.
  4. Douglas NJ, Weitzenblum E. Sleep and chronic obstructive pulmonary disease. Eur Respir Mono. 1998;  3: 209–214.
  5. Douglas NJ, Flenley DC. Breathing during sleep in patients with obstructive lung disease. Am Rev Respir Dis. 1990;141:1055-70.    
  6. Fletcher EC, Gray BA, Levin DC. Nonapneic mechanisms of arterial oxygen desaturation during rapid-eye-movement sleep. J Appl Physiol. 1983;54(3):632-9. 
  7. Little SA, Elkholy MM, Chalmers GW, et al. Predictors of nocturnal oxygen desaturation in patients with COPD. Respir Med. 1999;93(3):202-7.
  8. Connaughton JJ, Catterall JR, Elton RA, Stradling JR, Douglas NJ. Do sleep studies contribute to the management of patients with severe chronic obstructive pulmonary disease? Am Rev Respir Dis. 1988;138(2):341-4.
  9. Stradling JR, Lane DJ. Nocturnal hypoxaemia in chronic obstructive pulmonary disease. Clin Sci (Lond). 1983;64(2):213-22.
  10. Lewis CA, Fergusson W, Eaton T, Zeng I, Kolbe J. Isolated nocturnal desaturation in COPD: prevalence and impact on quality of life and sleep. Thorax. 2009 ;64(2):133-8
  11. Vos PJ, Folgering HT, van Herwaarden CL. Predictors for nocturnal hypoxaemia (mean SaO2 <90%) in normoxic and mildly hypoxic patients with COPD. Eur Respir J. 1995;8(1):74-7. 

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