Female predominance in nocturnal hypoxemia among elderly OSAS patients: hemoglobin mediates sex-specific hypoxic burden in Chinese cohorts

To explore the clinical characteristics and sex differences in relevant indicators of obstructive sleep apnea syndrome (OSAS) in elderly patients. A total of 1290 elderly patients diagnosed with OSAS by polysomnography (PSG) from 2015 to 2017 were consecutively collected from multiple medical institutions. Detailed demographic data, laboratory indicators, and sleep breathing parameters were recorded for each patient. All subjects were grouped according to sex, and the differences in each index between groups were statistically analyzed. Furthermore, analyses of the interaction between the influencing factors of nocturnal hypoxia were performed. The male to female ratio was 1.62:1 in all subjects. There was no significant difference in age between groups (65 years vs. 66 years). The men had a higher BMI than the women (26.7 kg/m2 vs. 25.8 kg/m2), but the women had a slightly higher ratio of waistline to height (0.56 vs. 0.53). Hemoglobin, creatinine, and uric acid levels were higher in male patients (all P < 0.001). The prevalence of hypertension was higher in both sexes, but it was greater in men (60.4% vs. 67.4%, P = 0.011). Male patients had a greater apnea-hypopnea index (AHI) (25.5 events/h vs. 30.9 events/h) and a longer apnea time (44 s vs. 56 s); nonetheless, the percent of total time with an oxygen saturation lower than 90% during sleep (T90) showed no significant difference between the two groups (3.9% vs. 3.6%, P > 0.05). Furthermore, in men, hemoglobin attenuated the effect of apnea duration on the risk of more pronounced nocturnal hypoxemia (Pinteraction=0.037). In the subgroup of patients ≥ 70 years, the AHI was consistent in both groups, but T90 was longer in women than in men (7.4% vs. 3.8%, P = 0.001). The proportion of severe OSAS in elderly patients was high. It was more severe in men than in women, but women tended to have more pronounced nighttime hypoxia. Therefore, clinical attention should be paid to sex differences in the effects of hypoxia on health in patients with OSAS. 1. Male patients are found to have more severe OSAS and a higher prevalence of hypertension than female patients of the elderly. 2. Although the severity of OSAS is the same across genders, the degree of nighttime hypoxia in older female may be more severe and pronounced. Hemoglobin levels play a role in this gender difference. 3. In the process of clinical individualized prevention and treatment, attention should be paid to the gender differences in the health effects of hypoxia on patients with OSAS.