Purposes: Quality of life assessment in obstructive sleep-disordered breathing (OSDB) is increasingly recognized, and the functional outcomes of sleep questionnaire (FOSQ) is a popular instrument. The objective of this study was to apply this questionnaire in Thai patients to assess its reliability, validity, and responsiveness properties.
Methods: A total of 223 subjects were recruited. The scores of FOSQ in 38 healthy volunteers and 40 primary snorers were compared with those of 108 obstructive sleep apnea (OSA) patients diagnosed by polysomnography. Seventy-two subjects answered the FOSQ twice at 2-4 weeks apart to check the test-retest reliability, and 37 patients with OSA who complied well with CPAP therapy answered them again after treatment at 3-6 months. All participants also filled the Epworth sleepiness scales (ESS) to check the concurrent validity.
Results: There were statistically significant differences in all FOSQ subscales including global scores between healthy volunteers (17.3 ± 2.1) and OSA patients (14.5 ± 2.9) (p < 0.001). The internal consistency of the questionnaire was excellent (Cronbach's alpha 0.95), and the test-retest reliability (intra-class correlation coefficients) was 0.70 in global scores. After adequate CPAP therapy, all FOSQ scores increased significantly (p < 0.001) There were significant correlations between all FOSQ scores except sexual relationship and ESS (r -0.48); however, these had only a weak relationship with AHI and minimal oxygen saturation.
Conclusions: The FOSQ can be applied to Thai patients with OSDB with good reliability, validity, and responsiveness properties. It may be the first validated version of FOSQ in East Asian countries which is a very useful tool for future research.