Raised Hematocrit at High Altitude: Its Relation to Sensorineural Hearing Loss

Abstract

Military troops deployed in high altitude areas (HAAs) may suffer from illnesses peculiar to the terrain which are usually due to hypoxia. The physiological dynamics at high altitude (HA) are different from those in the plains and hence environmental factors play an important role at HA. The effect, if any, of hemodynamic changes in terms of raised hemoglobin (Hb) levels in HA on otological disorders is not very well researched and needs to be explored further. This study was undertaken to study the clinical manifestations, if any, of the hemodynamic alterations in the inner ear and their correlation with the Hb levels after 1 year deployment at HA. A longitudinal descriptive study was conducted over 1 year duration at a Military Hospital located at HAA on 99 soldiers who were <40 years of age with no history of prior ear complaints/ear surgery and with normal pure tone audiometry (PTA) thresholds and Hb levels at initial evaluation. Each soldier underwent PTA and Hb estimation twice: initially, at the time of induction, and later after completion of 1 year deployment at HAA. Statistical analysis was done using simple paired t-test. On data analysis, no hearing loss was found in any participant of the study cohort at frequencies 500 Hz and 1 kHz in either ear on second evaluation. At 2 kHz, for left ear, the mean Hb level for the group with hearing thresholds greater than 25 dB was 17.07 g% with a standard deviation of 0.66, and for right ear, it was 16.95 g% with standard deviation of 0.64. At 4 kHz, the mean Hb level was 16.50 g% and 16.49 g% for hearing thresholds below and up to 25 dB for left and right ear, respectively. It was 16.99 g% and 16.96 g% for hearing thresholds above 25 dB. The results were statistically significant for both right and left ear at 4 kHz. A statistically significant deterioration of hearing thresholds for 4 kHz frequency with corresponding increase in Hb levels was observed in our study. Hb levels can therefore be used as a marker to ensure no further exposure to other risk factors like loud noise exposure, further deployment at higher altitudes to prevent deterioration, and progression of hearing loss.