Relevance Between Reduction of SpO2 and Parasympathetic Nervous Activity During Sleep

Sleep apnea syndrome (SAS) is associated with cardiopulmonary and dental nasopharyngeal diseases. The blood oxygen saturation (SpO2) detected using pulse oximetry is a diagnostic screening method for SAS. SAS severity is assessed using the oxygen desaturation index (ODI), which measures the number of times the SpO2 decreases by more than 3% for longer than 10 s. This study investigated the association between reduced SpO2 and parasympathetic nervous system activity (PSNA) during night sleep in young adults (n = 63; aged 20–32 years). Changes in PSNA were measured every minute for 24 h during a free-moving day using an ActiveTracer accelerometer. Pulse oximetry was performed simultaneously during sleep. All participants had significantly lower PSNA when the SpO2 decreased by 3% or more than when it did not. There were no significant differences in PSNA when an ODI cutoff of 5 events/h was used. However, participants with an ODI >5 events/h had significantly lower PSNA during normal SpO2 than those with an ODI <5 events/h, suggesting an association between SpO2 desaturation and PSNA decline during sleep. A high ODI may indicate reduced PSNA levels during sleep, affecting sleep efficiency. Treatment aimed at reducing the ODI may improve sleep quality, even in young adults.