Hypoxemia vs Sleep Fragmentation as Cause of Excessive Daytime Sleepiness in Obstructive Sleep Apnea* Henri G. Colt, M.D.;t Helmut Haas, M.D., F.C.C.R;+ and Gerald B. Rich, M.D.§

To determine the effects of intermittent hypoxemia on daytime sleepiness in the clinical setting of obstructive sleep apnea syndrome, we enrolled seven patients in a prospective, randomized, crossover study. We had two experimental conditions with NCPAP treatment as follow: (1) to correct apneas, sleep fragmentation, and hyoxemia; and (2) to correct apneas and sleep fragmentation and at the same time, induce intermittent hypoxemia. The outcome variable, daytime sleepiness, was measured objectively with the multiple sleep latency test following completion of baseline and each treatment condition. Compared with sleep latencies in the untreated condition, both experimental treatment arms prolonged sleep latencies (p30). Although the patients were mildly hypoxemic at rest for their age, only patient 6 had severe ventilatory dysfunction by spirometric standards16 and arterial blood gas values. Mean MSLT scores and sleep stage measurements are summarized in Table 3. At the beginning of the study, patients were excessively sleepy as indicated by a mean sleep latency of 2.7 min. Sleep was primarily stage 2 and stage 1 with very little stage REM. The time spent in all sleep stages except stage 4 improved as the mean sleep latency increased to 5.2 min (p=O.09) after NCPAP application (without addition of nitrogen gas) for two consecutive nights. When results of NCPAP with and without the induction of hypoxemia were compared, no statistically significant differences were noted in the percentage of sleep for different sleep stages (except for a small decrease in stage 2 under condition 2), TST, or mean latency to sleep onset. Sleep efficiency increased from 81 percent at baseline to 91 percent in condition 1 and to 84 percent in condition 2. The differences in sleep efficiency between the two experimental conditions did not reach statistical significance. Results of measures of nocturnal Sa02 are summarized in Table 4. Patients had significant nocturnal hypoxemia during baseline polysomnography with 395 (mean) desaturations below Sa02 of 90 percent. An average of 119 min were spent below SaO! of 85 percent. These measures improved strikingly with the application of NCPAP alone. When nitrogen was added to the NCPAP mask, the degree of nocturnal hypoxemia obtained was similar to that which occurred spontaneously during baseline studies. This is dem-

Table 3-Sleep Stage MetJBUrementB and MSLT at Baeline and Each Erperimental Condition· Post-hoc p Values Variable TST, min % Stage 1 % Stage 2 % Stage 3 Stage 4 % Stage REM

'*' 'MSLT, *' SE min

Baseline Study

Condition 1 CPAP

Condition 2 CPAP+N2



Cl vs C2

343 (56)

385 (37) 6 (5) 69 (9) 7 (6) 0.3 (1) 17 (8) 91 (6) 5.2 (2.1)

363 (45) 6 (3) 61 (8) 10 (4) 0.1 (.2) 23 (7) (8) 84 6.2 (3.6)

0.01 0.006 0.02 0.04 ns 0.02 0.01 0.045

ns 0.006 0.0006 0.004 ns 0.0005 ns 0.008


11 (5) 78 (9) 1 (3) 0.4 (.1) 6 (5) 81 (10) 2.7 (1.7)

ns 0.04 its ns ns os ns

*Results of second night study expressed as mean with SD in parentheses.


Excessive Daytime Sleepiness in OSA (Colt, Haas, Rich)

Table 4-Sleep Related Oxygenation Meamres at Baseline and Each Experimental Condition· Post-hoc p Values Condition 1 CPAI'

Baseline Shldy No. desat Av duration of desat

Hypoxemia vs sleep fragmentation as cause of excessive daytime sleepiness in obstructive sleep apnea.

To determine the effects of intermittent hypoxemia on daytime sleepiness in the clinical setting of obstructive sleep apnea syndrome, we enrolled seve...
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