Characteristics of the study population
A total of 90 participants were included in this study. The mean age was 61.1 ± 12.6 years (range, 22–86 years), and 72 were male. According to the criteria, patients were categorized as mild (n=9), moderate (n=30), or severe OSA (n=51). The average ages were 54.7 ± 10.1, 64.5 ± 11.9, and 60.3 ± 13.0 years for the mild, moderate, and severe groups, respectively. Notably, the highest average age was observed in the moderate group; however, no statistically significant differences were found among the groups. Similarly, sex ratios were comparable among the groups. BMI, NC, AC, and HC exhibited higher values with higher severity, and these differences were statistically significant.
As the severity of OSA increased, the AHI and respiratory disturbance index (RDI) values increased, and the lowest oxygen saturation decreased with significance (p<0.001, both). Apnea maximum length increased with severity (20.9 ± 18.0, 29.9 ± 17.5, and 41.0 ± 25.0), approaching statistical significance (p=0.051). However, no significant differences were found in hypopnea or total maximum length between the groups.
Hearing thresholds showed elevated values across all frequencies and mean values, including PTA and HF PTA, in the order of the mild, severe, and moderate groups. Statistically significant differences were noted between the three groups only at 0.25 and 1 kHz (p=0.038 and 0.040). Subsequent post-hoc tests demonstrated significant differences between the mild and moderate groups at 0.25 and 1 kHz (p=0.008 and 0.012). However, no significant differences in hearing thresholds were found across all frequencies when comparing the moderate and severe groups (Table 1, Figure 1).
Table 1. Characteristics of the study population according to the severity of obstructive sleep apnea.
Hearing level according to the presence of OSA
We compared hearing levels between the OSA and non-OSA groups and those categorized as low-risk for OSA using the SBQ from the KNHANES data.
The OSA group showed significantly worse hearing levels compared to the non-OSA group across all frequencies. Statistical significances were observed at frequencies of 0.5, 1, 2, and 8 kHz (p=0.031, 0.003, 0.008, and 0.011, respectively), except for 4 kHz. Consequently, PTA and HF PTA also showed worse values in the OSA group, which were 28.0 ± 15.8 dB and 42.3 ± 20.2 dB, compared to the non-OSA group, which were 22.8 ± 12.6 dB (p=0.018) and 35.7 ± 17.4 dB (p=0.024) (Table 2, Figure 2).
The OSA group showed significantly worse hearing levels compared to the non-OSA group across all frequencies except at 4 kHz.
The factors contributing to hearing loss in OSA
After establishing the impact of OSA on hearing, we attempted to identify specific factors of OSA contributing to HL. The OSA group was further classified into HL and non-HL groups based on 40 dB, and PSG parameters were compared. PTA and HF PTA were used as standards. (Table 3).
When the OSA group was categorized into two groups based on PTA values, 69 patients were classified into the HL group. Comparisons of PSG parameters revealed a significantly longer apnea maximum length in the HL group (44.8 s) compared to the non-HL group (32.7 s) (p=0.038). Although tendencies towards longer hypopnea and total maximum length were observed in the HL group, these differences did not reach statistical significance. Additionally, despite higher AHI and RDI values in the HL group than in the non-HL group, these differences were not statistically significant.
Similarly, after dividing the OSA group into HFHL and non-HFHL groups, 48 patients were classified into the HFHL group. The HFHL group also showed a significantly longer apnea maximum length than the non-HFHL group (p=0.006). Additionally, the HFHL group showed higher values of hypopnea, total maximum length, AHI, and RDI than the non-HFHL group; however, these differences were not statistically significant.
Although apnea maximum length showed a significant difference between the HL and non-HL groups, additional analyses were performed to determine the factors associated with HL in patients with OSA. We tried to investigate the specific impact of these factors while controlling for other influential factors. Besides age and sex, which are well-known factors affecting both OSA and hearing, every accessible variable, such as BMI, NC, AC, and HC, as well as PSG parameters including AHI, lowest oxygen saturation, apnea maximum length, and hypopnea maximum length, were considered. This analysis was performed for both the PTA and HF PTA samples.
A stepwise multiple linear regression demonstrated that age was the most significant influencing factor on HL (ß=0.584 for PTA and ß=0.602 for HF PTA). Apnea maximum length appeared as the second most influencing factor (ß=0.404 for PTA, and ß=0.425 for HF PTA), followed by lowest oxygen saturation (ß=0.296 for PTA, and ß=0.273 for HF PTA). The other variables had no significant effect on HL (Table 4).