Obstructive sleep apnea (OSA) is usually diagnosed from a single night of home sleep apnea testing using the apnea-hypopnea index (AHI). However, the AHI varies substantially from night to night, undermining diagnostic accuracy, and shows only modest correlation with symptoms. This variability further limits its usefulness for predicting cardiovascular and other complications. Besides the traditional AHI, more robust physiological markers are needed.

Several emerging physiological metrics - hypoxic burden, ventilatory burden, heart rate variability, autonomic arousals, and the pulse wave amplitude drop index - capture the physiological impact of OSA more comprehensively and demonstrate stronger associations with cardiovascular risk. Despite this promise, their night-to-night variability has not been studied.

A systematic evaluation of both established and novel OSA metrics across nights is essential to identify reliable, stable parameters suitable for clinical routine. This improves diagnostic precision beyond what traditional metrics can provide, enhances patient selection, reduces costs and patient harm, and may improve treatment outcomes.

Inclusion Criteria:

• Patients with suspected or diagnosed sleep-disordered breathing, irrespective of disease severity, as defined by the indications for home sleep apnea testing in the German guidelines [15]
• No active treatment during sleep recordings or within preceding two weeks (e.g., mandibular advancement devices, positive airway pressure therapy)
• Written informed consent obtained

Exclusion Criteria:

• Age <18 years
• Known or suspected neurological sleep disorder (e.g., narcolepsy, parasomnia)
• Known or suspected psychiatric sleep disorder
• Known or suspected central and complex sleep apnea
• Participants who are unable to perform sleep measurements reliably
• Insufficient knowledge of the project language (German)
• Inability to give consent
• Shift workers (with shift work <2 weeks before testing)

Participants with suspected or diagnosed sleep-disordered breathing of any severity will be recruited at Inselspital University Hospital und University Bern.

No selection or stratification based on sex, gender, or any other patient characteristics is applied during recruitment. Participants are included consecutively based on the clinical indication for home sleep apnea testing, irrespective of sex or gender. Any resulting imbalance reflects the underlying clinical population and does not compromise the scientific validity of the study, as analyses will account for sex and gender as covariates and report their effects transparently.