Fig 1.
Labeling of Each Wave of ABR and Determination of Threshold.
A: ABR threshold is 20 dB SPL. B: ABR threshold is 40 dB SPL C: ABR threshold is 50 dB SPL. D: ABR threshold is 80 dB SPL.
Fig 2.
Changes in Auditory Brainstem Response (ABR) wave latencies in C57BL/6J mice exposed to a high-altitude hypobaric hypoxic environment.
A: Wave I latency: The 15-day group showed the most pronounced prolongation, whereas the 25-, 30-, and 35-day groups exhibited no significant difference compared with controls. B: Wave II latency: The 7-day group displayed the greatest prolongation, followed by the 10-day group. In contrast, the 35-day group showed a significantly shorter latency than the control group. C: Wave III latency: The 7-day group had the most significant prolongation, followed by the 10-day group. No significant differences were observed between the control, 15-day, and 20-day groups. The 35-day group showed a significantly shorter latency than controls. D: Wave IV latency: The 30-day group exhibited the greatest prolongation, followed by the 7-day group. No significant differences were found between the control, 3-day, 20-day, 25-day, and 35-day groups. E: Wave V latency: The 7-day and 10-day groups showed the most marked prolongation. No significant differences were observed between the control, 20-day, and 35-day groups, or among the 15- to 35-day groups. F: Click I–III interwave interval: The 5-day group exhibited the most pronounced prolongation, followed by the 3-day and 7-day groups. The 10- to 30-day groups showed no difference from controls, while the 35-day group displayed a shorter interval than controls.(ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 3.
Changes in Auditory Brainstem Response (ABR) wave amplitudes in C57BL/6J mice exposed to a high-altitude hypobaric hypoxic environment.
A: Wave II amplitude: Significant differences were observed among groups with different exposure durations. The 5-day group showed the greatest increase, followed by the 30-day group. The 10-day and 20-day groups exhibited decreased amplitudes, while the 7-day group showed no significant difference from the control group. B: Wave III amplitude: Marked group differences were observed. The 3-, 5-, 7-, 20-, and 30-day groups showed increased amplitudes, whereas the 25- and 35-day groups showed decreases. The 10- and 15-day groups did not differ significantly from the control group. C: Overall trend of Wave II amplitude across exposure durations. D: Overall trend of Wave III amplitude across exposure durations.(ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 4.
Shows the characteristics of the amplitude ratio between ABR Wave II and Wave III in each group.
As shown in the figure, the dominant wave type of ABR in each group can be clearly determined through this amplitude ratio: except for the 25-day group, all other groups take Wave III as the dominant wave; only the 25-day group takes Wave II as the dominant wave (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 5.
Distribution of Auditory Brainstem Response (ABR) wave latencies under 4000 Hz tone-burst stimulation in C57BL/6J mice exposed to a high-altitude hypobaric hypoxic environment.
A: Wave I latency: The 3-, 7-, and 30-day groups showed the most pronounced prolongation. The 5-, 10-, 20-, and 25-day groups showed no significant differences from controls, while the 15- and 35-day groups exhibited shorter latencies. B: Wave II latency: The 7-day group displayed the most significant prolongation, followed by the 30-day group. The 35-day group showed a significantly shorter latency than controls, while the 5- and 10-day groups showed no difference. C: Wave III latency: The 7-day group exhibited the greatest prolongation, followed by the 3- and 5-day groups. The 20- and 25-day groups showed no difference from controls, whereas the 35-day group had a significantly shorter latency. D: Wave IV latency: The 7-day group showed the most marked prolongation, followed by the 10-day group. The 25- and 35-day groups showed no significant difference from controls. E: Wave V latency: The 3- and 7-day groups showed evident prolongation, while the 10- and 35-day groups did not differ from controls. F: I–III interwave interval: All groups except the 35-day group exhibited prolonged intervals; the 7-day group showed the most significant prolongation (ns: P > 0.05; *: P ≤ 0.05; **: P < 0.01; ***: P < 0.001).
Fig 6.
Distribution of ABR Wave II and Wave III Amplitudes Under 4000 Hz Tone Burst Stimulation.
A: Distribution of ABR Wave II amplitude across groups. As shown in the figure, the Wave II amplitude of the 5-day group and 15-day group was significantly decreased compared with the control group; the 7-day group and 25-day group showed no statistical difference in Wave II amplitude from the control group; the 30-day group was the only group with a higher Wave II amplitude than the control group, and the difference was statistically significant. B: Distribution of ABR Wave III amplitude across groups. As seen with the control group as a reference: the 3-day group, 10-day group, and 35-day group all showed an increasing trend in Wave III amplitude; while the 15-day group and 25-day group had the lowest Wave III amplitude compared with all other groups, making them the two groups with the lowest Wave III amplitude levels among all groups. C: Figure of the overall change trend of ABR Wave II amplitude in each group. D: Figure of the overall change trend of ABR Wave III amplitude in each group (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 7.
Figure shows the distribution of the ABR Wave II/Wave III amplitude ratio in each group.
It can be seen that most experimental groups, like the control group, take Wave III as the dominant wave, while the 25-day group and 35-day group take Wave II as the dominant wave (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 8.
Distribution of Auditory Brainstem Response (ABR) wave latencies and interwave intervals under 8000 Hz tone-burst stimulation in C57BL/6J mice exposed to a high-altitude hypobaric hypoxic environment.
A: Wave I latency: All exposure groups showed prolonged latencies compared with controls (P < 0.05), with the 20- and 35-day groups exhibiting the greatest prolongation. B: Wave II latency: The 7-day and 20-day groups showed the most significant prolongation. No significant differences were found in the 10-day and 35-day groups (P > 0.05). C: Wave III latency: The 7-day group showed the most pronounced prolongation. The 10- and 15-day groups did not differ from controls (P > 0.05), while the 35-day group exhibited a significantly shorter latency (P < 0.01). D: Wave IV latency: The 7-day and 20-day groups showed marked prolongation. The 15- and 30-day groups showed no significant difference (P > 0.05), whereas the 35-day group exhibited shorter latency (P < 0.05). E: Wave V latency: The 7-day and 20-day groups showed the greatest prolongation. The 30-day group showed no difference from controls (P > 0.05). The 15- and 35-day groups exhibited significantly shorter latencies (P < 0.05). F: I-III interwave interval: The 5-day and 7-day groups showed the most significant prolongation, while the 10-day group showed no difference (P > 0.05). The 15-, 30-, and 35-day groups exhibited shorter intervals than controls (P < 0.05). G: I-V interwave interval: Prolongation was most prominent in the 7-day and 20-day groups. The 35-day group showed a shorter interval (P < 0.05), while the 15-, 25-, and 30-day groups did not differ significantly from controls (P > 0.05). H: III-V interwave interval: The 7-day and 20-day groups showed significant prolongation. The 15- and 35-day groups exhibited shorter intervals (P < 0.05), and the 5-day group showed no difference from controls (P > 0.05).(ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 9.
Changes in Amplitudes of ABR Wave Ⅱ and Wave Ⅲ under 8000 Hz Short Pure Tone Stimulation.
A: This panel shows the distribution of ABR Wave Ⅱ amplitudes in each group. Among them, the 15-day group had the highest Wave Ⅱ amplitude, the 10-day group had the lowest, and the 30-day group showed no significant statistical difference compared with the control group (P > 0.05). B: This panel shows the distribution of ABR Wave Ⅲ amplitudes in each group. Among them, the 10-day group had the highest Wave Ⅲ amplitude, the 20-day group had the lowest, and the 30-day group showed no significant statistical difference compared with the control group (P > 0.05) (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 10.
Figure depicts the distribution of ABR Wave Ⅱ/Ⅲ amplitude ratios in each group.
Notably, Wave Ⅱ was identified as the dominant wave across all groups. Specifically, the Wave Ⅱ/Ⅲ amplitude ratios of the 20-day, 25-day, and 35-day groups exhibited no statistically significant differences relative to the control group (P > 0.05) (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 11.
Shown in the figure is the distribution of the ratios of the latencies of each ABR wave to those of their respective control groups under different stimulus frequencies (click, 4000 Hz, and 8000 Hz).
Under the click stimulus condition, the latency prolongation ratios of Wave Ⅱ and Wave Ⅲ were the highest. Under the 4000 Hz stimulus condition, Wave Ⅱ exhibited the highest latency prolongation ratio. Whereas under the 8000 Hz stimulus condition, the latency prolongation ratios among all waves were negligible, with no significant differences observed (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 12.
Distribution of Auditory Brainstem Response (ABR) thresholds at different stimulus frequencies in C57BL/6J mice exposed to a high-altitude hypobaric hypoxic environment.
A: Click stimulation: The 15- and 25-day groups showed the most pronounced threshold elevation, whereas the 5- and 10-day groups showed no significant difference from controls (P > 0.05). B: 4000 Hz tone stimulation: All groups except the 10-day group exhibited elevated thresholds. Although the 35-day group showed a slight decline, its threshold remained significantly higher than that of the control group (P < 0.05). C: 8000 Hz tone stimulation: The 25- and 30-day groups showed the greatest threshold increase. The 10-day group showed no difference from controls (P > 0.05). The 35-day group showed a mild decline but remained significantly higher than the control group (P < 0.05). D: Summary: Within the first 10 days of exposure, hearing loss reached approximately 60 dB under click and 4000 Hz stimulation, and 40 dB under 8000 Hz stimulation. After 10 days, thresholds further increased-up to 70 dB for click, ~ 80 dB for 4000 Hz, and ~60 dB for 8000 Hz stimuli. (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 13.
Distribution of Electrocochleography (EcochG) negative summating potential (-SP) in C57BL/6J mice before and after exposure to a high-altitude hypobaric hypoxic (HBH) environment.
A: -SP latency across groups: The 15-day group showed no significant difference from controls (P > 0.05). All other groups exhibited prolonged -SP latencies, with the 7-, 25-, and 30-day groups showing the most pronounced prolongation. B: -SP latency before and after repressurization–reoxygenation (R-R): Following R-R, all groups showed a general decline in -SP latency compared with the HBH condition. C: Ratio of recovery in -SP latency (Δ-SP latency/pre-R–R latency): The 3-, 10-, 15-, and 20-day groups demonstrated better recovery after R–R, while the 7-, 25-, and 30-day groups exhibited the most pronounced prolongation under HBH and the poorest recovery following R-R. (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 14.
Distribution of Compound Action Potential (AP) Latency Under Exposure to the High-Altitude Hypobaric and Hypoxic Environment.
A: This panel displays the distribution of AP latency across each group. Compared with the control group, the AP latencies of the groups with 15-day and 35-day exposure to the hypobaric hypoxic environment showed no significant difference (P > 0.05); all other groups exhibited a significant prolongation in AP latency, with the 7-day group and 10-day group showing the most obvious prolongation effect. B: This panel presents the changes in AP latency of each group before and after repressurization-reoxygenation (R-R). C: This panel shows the relative change rate of each group before and after R-R (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 15.
A. This panel shows the overall trend of changes in the -SP/AP area ratio across each group.
B: This panel presents the specific comparison of -SP/AP area ratios across groups. It can be observed that the 7-day group had the highest -SP/AP area ratio, followed by the 25-day group and 30-day group, with the 7-day group having an -SP/AP area ratio > 2.0. In terms of group correlation, the groups with a significant increase in the -SP/AP area ratio were consistent with the previously observed group characteristics of “predominantly prolonged -SP latency”. C: This panel illustrates the annotation method for the areas of -SP and AP in electrocochleography (EcochG) (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 16.
Effects of different durations of high-altitude hypobaric hypoxia exposure on the -SP/AP amplitude ratio.
A: This panel shows the overall trend of changes in the -SP/AP amplitude ratio across each group under exposure to the high-altitude hypobaric and hypoxic environment. B: This panel clearly presents the distribution of -SP/AP amplitude ratios across each group. The -SP/AP amplitude ratio of the 35-day group showed no statistically significant difference from that of the normal control group (P > 0.05); the groups with an -SP/AP amplitude ratio > 0.4 were the 3-day, 5-day, 15-day, 20-day, 25-day, and 30-day groups; the groups with an -SP/AP amplitude ratio lower than that of the normal control group were the 7-day group and the 10-day group (P < 0.05) (ns: P > 0.05, *: P ≤ 0.05, **: P < 0.01, ***: P < 0.001).
Fig 17.
The Change Trends of EcochG Under Exposure to the High-Altitude Hypobaric and Hypoxic Environment.
A: This panel shows the EcochG of the right ear from a C57BL/6J mouse in the normal control group. B and C: These panels show an increase and elevation of -SP in the left ear. D: This panel shows elevation of -SP and widening of the waveform in the EcochG of the right ear. E: This panel shows a decrease in the amplitudes of -SP and AP, as well as widening of the waveform, in the EcochG of the right ear. F: This panel shows an increase in the amplitudes of -SP and AP at the late stage of exposure to the high-altitude hypobaric and hypoxic environment, while the waveform remains relatively wide.
Fig 18.
DPOAE (Distortion Product Otoacoustic Emissions) Test Results of C57BL/6J Mice Under Exposure to the High-Altitude Hypobaric and Hypoxic Environment.
A: This panel shows the DPOAE test result: “Passed”. B: This panel shows the DPOAE test result: “Failed”.