A new study shows that objectively measured snoring intensity is correlated with subjective sleepiness independent of the apnea-hypopnea index (AHI) in patients with moderate to severe obstructive sleep apnea (OSA).
Results indicate that the sound intensity of objectively measured snoring in patients with OSA is independently correlated with subjective sleepiness as measured by the Epworth Sleepiness Scale (ESS), and subjective sleepiness is better explained by snoring intensity than by AHI. Independent variables such as snoring intensity, desaturation severity, daily sleep time, subjective snoring frequency and nasal obstruction symptoms accounted for 22 percent of the variance in ESS scores. Snoring intensity and AHI together, however, could explain only 15 percent of the variance in ESS scores.
Principal investigator Hiroshi Nakano, MD, PhD, of the department of pulmonology at the Fukuoka National Hospital in Fukuoka, Japan, says that the results of the study indicate that daytime sleepiness is affected not only by the severity of OSA, but also by the loudness of snoring.
"The results were not so surprising, because previous studies in general population have shown an independent relationship between the degree of snoring, by a questionnaire, and sleepiness," said Nakano.
Records of 507 patients who were referred to Fukuoka National Hospital for suspected OSA and who underwent diagnostic polysomnography (PSG) between September 2002 and January 2005 were retrospectively reviewed. Subjective sleepiness was assessed using the ESS, and snoring intensity was assessed using the highest one percentile ambient sound-pressure level attained while asleep during PSG.
Patients were placed into groups of non-to-mild OSA (AHI less than 15) and moderate-to-severe OSA (AHI greater than 15) in order to clarify the effect of OSA severity on the relationship between snoring intensity and sleepiness in subsequent analyses.
Findings suggest that snoring intensity is significantly correlated with age, body mass index (BMI) and AHI. Insufficient sleep in daily life was taken into consideration as a possible cofounder, as it may enhance snoring intensity and sleepiness. Although sleepiness is one of the most important symptoms of OSA, the authors report that the correlation between the degree of sleepiness and the severity of OSA has been found to be relatively weak in many studies.
Because objectively measured snoring is related to sleepiness independent of OSA, the authors conclude that quantitative measurements of snoring are desirable in ordinary sleep studies.
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