To the Editor:

We thank Dr. Kumagai et al. [1] for their interest in our study regarding motor vehicle accidents (MVA) in CPAP-compliant patients with obstructive sleep apnea (OSA) [2]. In a long-term study based on objective data of both CPAP adherence and MVA we found that CPAP-treated patients with high adherence did not have lower MVA incidence than those with poor CPAP adherence, or untreated patients. Our results were contradictory to many previous studies, most of them using self-reports of MVA and/or CPAP adherence.

Kumagai et al. are concerned about driving safety, especially among professional drivers. We share their concern. We agree that combination therapy with CPAP and an oral appliance is worthy of investigating as well as taking advantage of technical solutions to improve driving safety for prevention of MVAs.

However, we still encourage our patients to comply with CPAP therapy. In our study, MVA data were based on a national registry in which data of small, near miss accidents or close shaves on the road were not available. Further, Finland is a sparcely populated country and the effect of CPAP therapy on driving safety may be greater in countries with higher traffic density. Of importance, time to the first MVA was almost three times longer among CPAP-treated than those among controls suggesting some beneficial effect of CPAP treatment.

In summary, we consider further research regarding safety in drivers with OSA to be important. Despite negative results of our study [2], in line with the American [3] and European [4] guidelines we encourage our patients to adhere their CPAP treatment.