Assessment of the Brainstem-Mediated Stapedius Muscle Reflex in Andean Children Living at High Altitudes

Evaluation of Middle Ear Function by Tympanometry and the Influence of Lower Barometric Pressure at High Altitude

Jiang, Tao, Liping Zhao, Yanbo Yin, Huiqian Yu, and Qingzhong Li. Evaluation of middle ear function by tympanometry and the influence of lower barometric pressure at high altitude. High Alt Med Biol. 22:70-76, 2021. Objective: To evaluate middle ear function in residents of high-altitude areas in comparison to sea-level participants. Design: Prospective observational study. Setting: All experiments were performed by experienced audiologists with a calibrated tympanometry machine. Participants: Young adults between the age of 17 and 23 were recruited. Seventy-five participants from Shanghai (altitude 4 m) and 133 participants from the Shigatse area (altitude 4,040 m) were recruited. Any participant with any otological disorder was excluded. Main Outcome Measure: Four indexes of the tympanogram were evaluated in the two groups from different altitudes. Results: Our results showed that the peak of static compliance for the participants in Shigatse was smaller, but the absolute compliance of tympanic membrane remained the same. Similarly, the ear canal volume (ECV) from tympanometry was also affected by the elevated altitude in Tibet. In addition, the tympanometric peak pressure was decreased in high-altitude residents, which suggests a slightly declined function of the Eustachian tube at lower barometric pressure. However, no difference was found in the tympanometric width (TW). Conclusion: Our results indicate that tympanograms were affected by decreased atmospheric pressure at high altitude. Therefore, other than pressure-related indexes, TW is better for evaluating the function of the middle ear in high-altitude regions.

Selection scan reveals three new loci related to high altitude adaptation in Native Andeans

The Andean Altiplano has been occupied continuously since the late Pleistocene, ~12,000 years ago, which places the Andean natives as one of the most ancient populations living at high altitudes. In the present study, we analyzed genomic data from Native Americans living a long-time at Andean high altitude and at Amazonia and Mesoamerica lowland areas. We have identified three new candidate genes - SP100, DUOX2 and CLC - with evidence of positive selection for altitude adaptation in Andeans. These genes are involved in the TP53 pathway and are related to physiological routes important for high-altitude hypoxia response, such as those linked to increased angiogenesis, skeletal muscle adaptations, and immune functions at the fetus-maternal interface. Our results, combined with other studies, showed that Andeans have adapted to the Altiplano in different ways and using distinct molecular strategies as compared to those of other natives living at high altitudes.

Middle Ear Function and Pathophysiology in Andean Children Living at High Altitudes

Counter, S. Allen, Leo H. Buchanan, Fernando Ortega, Anthony B. Jacobs, and Göran Laurell. Middle ear function and pathophysiology in Andean children living at high altitudes. High Alt Med Biol. 18:163-170, 2017.-The extent of altitude-related middle ear disorders in children native to high altitudes is unclear. This study examined middle ear pathophysiology in two groups of children living in high-altitude Ecuadorian Andean communities by investigating middle ear pressure (MEP), tympanic membrane compliance (TMC), and ear canal volume (ECV) using tympanometry, and by otological examination. Altitude I Group lived at 2850 m, and Altitude II Group resided at around 4000 m. The two high-altitude groups were compared with a reference group of children residing at sea level. Mean MEP was -3.6 daPa (SD: 39.2), 3.5 daPa (SD: 28.7), and 1.3 daPa (SD: 13.6) for Altitude I Group, Altitude II Group, and the Sea Level Group, respectively. The MEP was not significantly different among the three groups. Mean TMC was 0.63 cm³ (SD: 0.51), 0.60 cm³ (SD: 0.43), and 0.60 cm³ (SD: 0.24) for Altitude I Group, Altitude II Group, and the Sea Level Group, respectively. The TMC was not significantly different among the three groups. Mean ECV was 1.1 (SD: 0.26), 1.2 (SD: 0.26), and 1.0 (SD: 0.23) for Altitude I Group, Altitude II Group, and the Sea Level Group, respectively. The difference in ECV between Altitude I Group and Altitude II Group was significant (p = 0.043), as was the difference between Altitude II Group and the Sea Level Group (p = 0.001). ECV did not differ significantly between Altitude I Group and the Sea Level Group. Otological examination revealed a low incidence of ear canal and middle ear pathology. In conclusion, tympanometric and otological findings did not reveal a high incidence of middle ear pathophysiology in children living at altitudes as high as around 4000 m.