The prevalence of obstructive sleep apnea (OSA) has been increasing year by year, but the current diagnostic criteria of apnea-hypopnea index (AHI) >5 times/h commonly used for OSA has gradually revealed drawbacks in the diagnosis, severity evaluation, treatment effect and long-term complications prediction of the disease. This study proposed that there is a need for more information about the duration of apnea-hypopnea for assessing OSA in addition to AHI.

To investigate the significance of duration of respiratory events in nocturnal hypoxemia in adults with OSA.

A total of 296 patients with suspected OSA who were admitted to the sleep monitoring room of the First Hospital of Shanxi Medical University from October 2021 to March 2022 were selected as the study subjects. Before PSG, the subjects underwent a physical examination in terms of height, body mass, neck circumference, and were asked about their sleep history, as well as history of hypertension and diabetes. The subjects were divided into three groups according to AHI of 5 times/h≤AHI<15 times/h as the mild OSA group (n=56), 15 times/h≤AHI<30 times/h as the moderate OSA group (n=62), AHI≥30 times/h as the severe OSA group (n=178). The three groups were compared for blood oxygen indexes[lowest oxygen saturation (LSpO₂), mean oxygen saturation (MSpO₂), baseline oxygen saturation (BSpO₂), oxygen desaturation index (ODI), oxygen saturation (SpO₂) below 90% in total sleep time (T90) ]and duration parameters of respiratory events [mean total apnea duration (MTAD), mean hypopnea duration (MHD), mean apnea-hypopnea duration (MAD), the longest apnea duration (LTAD), the longest hypopnea duration (LHD), the longest apnea-hypopnea duration (LAD), total apnea-hypopnea duration (TAD), AHI, percentage of apnea/hypopnea time from total sleep time (AHT%) ]. Spearman rank correlation analysis was used to investigate the correlation between respiratory event duration parameters and blood oxygen indexes. The OSA patients were divided into the short event group (short TAD subgroup, short AHT% subgroup, n=74) and long event group (long TAD subgroup, long AHT% subgroup, n=222) according to the median of TAD and AHT% (69.78 min and 14.33%, respectively), and the correlation of TAD, AHT% and AHI with blood oxygen indexes in each group was further analyzed.

There were significant differences in gender, age, BMI, neck circumference, daytime sleepiness, history of hypertension and diabetes among the mild, moderate and severe OSA groups (P<0.05). ODI and T90 in the severe OSA group were higher than those in the mild and moderate OSA groups, and LSpO₂ and MSpO₂ were lower than those in the mild and moderate OSA groups (P<0.05) ; LSpO₂ in the moderate OSA group was lower than that in the mild OSA group, ODI and T90 were higher than that in the mild OSA group (P<0.05). MTAD, LTAD, TAD, AHT% in the severe OSA group were higher than those in the mild and moderate OSA groups, and MHD was lower than that in the mild and moderate OSA groups (P<0.05) ; LHD in the severe OSA group was lower than that in the moderate OSA group, LAD was higher than that in the mild OSA group. MTAD, LTAD, TAD and AHT% in the moderate OSA group were higher than those in the low OSA group (P<0.05). The scatter plot and loess fitting curve showed that the values of MTAD, MHD, MAD, LTAD, LHD and LAD all increased first and then decreased with AHI. TAD and AHT% were prolonged with increasing AHI. Spearman rank correlation analysis showed that AHI, MTAD, LTAD, TAD, AHT% were negatively correlated with LSpO₂ and MSpO₂, but positively correlated with ODI and T90 in OSA patients (P<0.05) ; MHD and LHD were positively correlated with LSpO₂ and MSpO₂, and negatively correlated with ODI and T90 (P<0.05) ; MAD was negatively correlated with ODI (P<0.05) ; LAD was negatively correlated with LSpO₂ (P<0.05). Further subgroup Spearman rank correlation analysis showed that TAD, AHT% and AHI were negatively correlated with LSpO₂ and positively correlated with ODI in short TAD subgroup, short AHT% subgroup, long TAD subgroup and long AHT% subgroup (P<0.05), and had no correlation with BSpO₂ (P>0.05) ; TAD, AHT%, and AHI were all negatively correlated with MSpO₂ and positively correlated with T90 in the long event group (P<0.05) .

Duration of respiratory events plays an important role in the evaluation of nocturnal hypoxemia in OSA patients, and can be used as a supplement to the existing diagnostic and evaluation index AHI, and indexes such as TAD and AHT% are even more representative than AHI in some cases. The combination of AHI and LSpO₂ with the duration of respiratory events can more objectively assess the severity of OSA patients.