title: Dark Adaptation at High Altitude: An Unexpected Pupillary Response to Chronic Hypoxia in Andean Highlanders.
abstract: Healy, Katherine, Alain B. Labrique, J. Jaime Miranda, Robert H. Gilman, David Danz, Victor G. Davila-Roman, Luis Huicho, Fabiola León-Velarde, and William Checkley. Dark adaptation at high altitude: an unexpected pupillary response to chronic hypoxia in Andean highlanders. High Alt Med Biol. 17:208-213, 2016.-Chronic mountain sickness is a maladaptive response to high altitude (>2500 m above sea level) and is characterized by excessive erythrocytosis and hypoxemia resulting from long-term hypobaric hypoxia. There is no known early predictor of chronic mountain sickness and the diagnosis is based on the presence of excessive erythrocytosis and clinical features. Impaired dark adaptation, or an inability to visually adjust from high- to low-light settings, occurs in response to mild hypoxia and may serve as an early predictor of hypoxemia and chronic mountain sickness. We aimed to evaluate the association between pupillary response assessed by dark adaptometry and daytime hypoxemia in resident Andean highlanders aged ≥35 years living in Puno, Peru. Oxyhemoglobin saturation (SpO2) was recorded using a handheld pulse oximeter. Dark adaptation was quantitatively assessed as the magnitude of pupillary contraction to light stimuli of varying intensities (-2.9 to 0.1 log-cd/m2) using a portable dark adaptometer. Individual- and stimulus-specific multilevel analyses were conducted using mixed-effect models to elicit the relationship between SpO2and pupillary responsiveness. Among 93 participants, mean age was 54.9 ± 11.0 years, 48% were male, 44% were night blind, and mean SpO2was 89.3% ± 3.4%. The magnitude of pupillary contraction was greater with lower SpO2(p < 0.01), and this dose relationship remained significant in multiple variable analyses (p = 0.047). Pupillary responsiveness to light stimuli under dark-adapted conditions was exaggerated with hypoxemia and may serve as an early predictor of chronic mountain sickness. This unexpected association is potentially explained as an excessive and unregulated sympathetic response to hypoxemia at altitude.
authors.affiliation: 1 Division of Pulmonary and Critical Care, School of Medicine, Johns Hopkins University , Baltimore, Maryland.|2 Program in Global Disease Epidemiology and Control, Department of International Health, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Katherine
authors.initials: K
authors.lastname: Healy
authors.affiliation: 2 Program in Global Disease Epidemiology and Control, Department of International Health, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Alain B
authors.initials: AB
authors.lastname: Labrique
authors.affiliation: 3 CRONICAS Center of Excellence in Chronic Diseases , Universidad Peruana Cayetano Heredia, Lima, Peru .
authors.forename: J Jaime
authors.initials: JJ
authors.lastname: Miranda
authors.affiliation: 2 Program in Global Disease Epidemiology and Control, Department of International Health, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Gilman
authors.affiliation: 4 Biomedical Research Unit , A.B. PRISMA, Lima, Peru .
authors.forename: David
authors.initials: D
authors.lastname: Danz
authors.affiliation: 5 Division of Cardiovascular, Cardiovascular Imaging and Clinical Research Core Laboratory, School of Medicine, Washington University , St. Louis, Missouri.
authors.forename: Victor G
authors.initials: VG
authors.lastname: Davila-Roman
authors.affiliation: 3 CRONICAS Center of Excellence in Chronic Diseases , Universidad Peruana Cayetano Heredia, Lima, Peru .|6 Centro de Investigación para el Desarrollo Integral y Sostenible and School of Medicine, Universidad Peruana Cayetano Heredia , Lima, Peru .
authors.forename: Luis
authors.initials: L
authors.lastname: Huicho
authors.affiliation: 7 Departamento de Ciencias Biológicas y Fisiológicas, Universidad Peruana Cayetano Heredia , Lima, Peru .
authors.forename: Fabiola
authors.initials: F
authors.lastname: León-Velarde
authors.affiliation: 1 Division of Pulmonary and Critical Care, School of Medicine, Johns Hopkins University , Baltimore, Maryland.|2 Program in Global Disease Epidemiology and Control, Department of International Health, Johns Hopkins Bloomberg School of Public Health , Baltimore, Maryland.
authors.forename: William
authors.initials: W
authors.lastname: Checkley
keywords: chronic mountain sickness; hypoxemia; impaired dark adaptation; oxyhemoglobin saturation; portable field dark adaptometer; pupillary contraction