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Abstract Background The respiratory rate (RR) is a critical vital sign controlled by not only metabolic factors but behavior while awake. The prevalence of obstructive sleep apnea (OSA) is remarkably high. Therefore, a non-constraining and non-contact respiratory monitor to measure the RR both while awake and asleep is preferable. Methods A millimeter wave radar (MWR) device was used for RR monitoring of participants suspected of OSA while awake (supine before and after polysomnography PSG, sitting, and positioned on both sides) and asleep. Apnea and hypopnea during 1 hour of sleep (AHI) by PSG was compared with 1 hour of respiratory events (REI) judged by MWR. Portable monitoring (PM) and percutaneous arterial O 2 (SpO 2 ) monitoring were done simultaneously. Results Correlations between the RR by MWR and respiratory inductance plethysmography at PSG while awake in every measured position including the supine position before and after PSG were very high (r=0.92∼0.99) (n=60). The REI by MWR were significantly correlated with AHI determined by PSG, PM, or SpO 2 monitoring (p<0.001). Brand-Altman plot showed that the MWR for AHI monitoring was acceptable. Predicted AHI by MWR relative to PSG was almost the same as with PM or SpO 2 monitoring. Conclusions The developed MWR respiratory monitor was useful during wakefulness and sleep, including detection of apnea and hypopnea. This system can be useful in multiple medical settings such as critical care with and without sleep apnea, pandemic infection, elder care at home, etc. Trial registration number: UMIN000045833 ( http://www.umin/ac.jp )
Chin et al. (Tue,) studied this question.