The Severity Of Individual Breathing Cessation Events In Diagnostics Of Obstructive Sleep Apnea - Towards Enhanced And Individualized Estimation Of OSA Severity

Obstructive sleep apnea (OSA) is a prevalent nocturnal breathing disorder characterized by complete (apnea) and partial (hypopnea) breathing cessations during sleep 1. OSA is connected to cardiovascular disease, increased mortality rate and impairment of quality of life 2-4. Its prevalence has been estimated to be 9-27 % among middle-aged population and the prevalence is expected to increase in the future 5,6.

Currently, the most commonly used diagnostic parameter for OSA is apnea-hypopnea index (AHI) based on number of apneas and hypopneas during sleep, neglecting their durations and also durations and depths of related desaturation events. In adults OSA is diagnosed if patient has 1) AHI≥5 events/h with associated symptoms (e.g. excessive daytime sleepiness (EDS)) or medical or psychiatric disorder (e.g. hypertension or mood disorder) or 2) AHI≥15 events/h 7.

Previously, the investigators have introduced novel parameters called as obstruction severity, obstruction duration, desaturation severity, desaturation duration, and adjusted-AHI incorporating number, duration and morphology of individual obstruction events (i.e. apneas, hypopneas, and oxygen desaturations) 8,9.we have shown that these parameters can enhance the severity estimation of OSA and that the individual breathing cessation event severity is more strongly connected to increased mortality and cardiovascular morbidities than conventional AHI8,10,11. The potential of these parameters to enhance the assessment of severity of OSA has been previously investigated only using ambulatory polygraphic recordings without EEG registration. Therefore, the parameters do not take into account hypopneas followed by arousal (but not desaturation). In addition, parameters do not take into account apneas not followed by desaturation and novel parameters need to be refined to take into account also such events in order to further increase their prognostic value.

It is known that age and body mass index (BMI) are positively related with the prevalence of OSA12,13. Furthermore, AHI is higher and apneas longer in supine position compared to lateral position14-16. However, it is not thoroughly explored whether the severity of individual obstruction events progress over time and which factors affect to this progression.

EDS is a common symptom of OSA and it can be measured in various methods. The most widely used methods are Epworth Sleepiness Scale (ESS) questionnaire which measures subjective sleepiness and Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT) which measure sleepiness objectively. However, the correlation between ESS score and the severity of OSA (i.e. number of obstruction events) have been shown to be poor 17. Furthermore, albeit MSLT and MWT have been shown to have better correlations with daytime functions than ESS their correlations with AHI and arousal index still remainsweak18. Therefore, it needs to be investigated whether the severity of individual breathing cessation events is correlated better with MSLT and MWT and thus, explaining with more accuracy the daytime symptoms.