Letter Regarding the Review by Zhang et al. of Portable Recording for the Diagnosis of Obstructive Sleep Apnea in Commercial Motor Vehicle Drivers

The primary purpose of this letter is to point out an error in an article reviewing portable diagnostic devices for identifying obstructive sleep apnea (OSA) in commercial motor vehicle (CMV) drivers.¹ The error occurs in Table number 4 (page 1487), a comparison of the sensitivity, specificity, and data loss for various portable sleep apnea diagnostic systems (PMs) found in published studies. For the Westbrook et al. 2005 study,² Zhang et al. list a data loss rate for the ARES of 25%, an inaccurate figure, and list an N/A entry for the later Ayappa et al. 2008 study.³ In neither publication was a data loss number explicitly stated, but in both information is given that allows easy calculation of data loss or technically inadequate recordings.

In the Westbrook et al. study, the ARES data loss was 1% (bad ARES oximeter recordings in 3/287 subjects) for the simultaneous in-lab PSG-ARES Unicorder comparisons and 2.1% (insufficient ARES valid recording time in 4/191 subjects) in the lab versus in-home comparison.

In the Ayappa et al.³ study the ARES data loss rate in the home versus lab comparison was either 1.1% (1/89 Unicorder failure), 6.4% (1+5/94 Unicorder not tolerated at home), or 12% (1+5+6/100 subjects who did not attempt to wear the Unicorder). For the simultaneous lab-ARES comparison, the ARES data loss rate was 3.2% (Unicorder failure in 3/95 subjects). Counting patients not using the mailed device as data loss would be similar to counting patients not showing up for a formal laboratory study (49% for drivers⁴) as data loss by the PSG. Ayappa et al. used the 6.4% data loss rate in oral presentations of their study. In any case, indicating that a data loss number is not available seems insufficiently informative.

Unfortunately the review of PMs is mostly an opinion piece about their real and imagined deficiencies, damning them with vanishingly faint praise. In Table 2 (page 1485), the authors fail to list the availability of a full-disclosure recording. The capability of reviewing raw data by an expert in signal pattern recognition is critical for confirmation of both PSG and PM test validity. The authors also do not list actigraphy in the PM comparison table, although actigraphy is important for the determination of behavioral wake versus sleep states and arousals. Figure 1 (page 1487), “Potential applicability of portable monitors (PM) in 100 high-risk commercial motor vehicle operators,” outlines a hypothetical worst-case scenario unsupported by evidence. I think the authors realize that most of the at-risk CMV license applicants realistically cannot be evaluated with traditional laboratory attended PSG, so what about a best case scenario?

Most of the problems with diagnosing OSA in commercial drivers are political and economic, not technological. Confirming or ruling out sleep apnea is pretty easy with any of a number of full disclosure portable sleep apnea diagnostic systems, and “chain of custody” attachments have and are being developed that can confirm that the signals you see are recorded from the correct person. The difficulty is that the disordered breathing event frequency is poorly correlated with daytime sleepiness, probably due to individual trait variability, so a significant proportion of drivers diagnosed with obstructive sleep apnea will not be measurably sleepy.^5,6 Moreover a significant number of drivers without OSA will be sleepy because of circadian and insufficient sleep issues. Then there is the fact that CPAP is effective treatment in only about half of those for whom it is prescribed because of intolerance and insufficient use.

There are many questions that remain to be answered about the best way to confirm sleep apnea, especially in those who really don't want it confirmed. The topic of the Zhang et al. review is important, and readers deserve information that is as complete and accurate as possible.

CITATION

Westbrook P. Letter regarding the review by Zhang et al. of portable recording for the diagnosis of obstructive sleep apnea in commercial motor vehicle drivers. SLEEP 2013;36(8):1261-1262.

DISCLOSURE STATEMENT

Dr. Westbrook is an employee (Chief Medical Officer) of and shareholder in Advanced Brain Monitoring, Inc., a research and development firm that was originator of the ARES. He is a consultant (Chief Medical Officer) to and shareholder in Watermark Medical, Inc., current owners and purveyors of the ARES technology. He is a consultant to Rotech, Inc. Sleep Central (Medical Director), a business that also uses the ARES. He is a consultant (Chief Medical Officer) to and shareholder in Ventus Medical, Inc., makers of treatment devices for obstructive sleep apnea and snoring. He has participated as an expert witness in a trial involving a CMV driver. The opinions expressed are solely those of the author.