title: Changes in labial capillary density on ascent to and descent from high altitude.
abstract: Present knowledge of how the microcirculation is altered by prolonged exposure to hypoxia at high altitude is incomplete and modification of existing analytical techniques may improve our knowledge considerably. We set out to use a novel simplified method of measuringin vivocapillary density during an expedition to high altitude using a CytoCam incident dark field imaging video-microscope. The simplified method of data capture involved recording one-second images of the mucosal surface of the inner lip to reveal data about microvasculature density in ten individuals. This was done on ascent to, and descent from, high altitude. Analysis was conducted offline by two independent investigators blinded to the participant identity, testing conditions and the imaging site.  Additionally we monitored haemoglobin concentration and haematocrit data to see if we could support or refute mechanisms of altered density relating to vessel recruitment. Repeated sets of paired values were compared using Kruskall Wallis Analysis of Variance tests, whilst comparisons of values between sites was by related samples Wilcoxon Signed Rank Test. Correlation between different variables was performed using Spearman's rank correlation coefficient, and concordance between analysing investigators using intra-class correlation coefficient. There was a significant increase in capillary density from London on ascent to high altitude; median capillaries per field of view area increased from 22.8 to 25.3 (p=0.021). There was a further increase in vessel density during the six weeks spent at altitude (25.3 to 32.5, p=0.017). Moreover, vessel density remained high on descent to Kathmandu (31.0 capillaries per field of view area), despite a significant decrease in haemoglobin concentration and haematocrit. Using a simplified technique, we have demonstrated an increase in capillary density on early and sustained exposure to hypobaric hypoxia at thigh altitude, and that this remains elevated on descent to normoxia. The technique is simple, reliable and reproducible.
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Gilbert-Kawai
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, UK.
authors.forename: Jonny
authors.initials: J
authors.lastname: Coppel
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, UK.
authors.forename: Hennis
authors.initials: H
authors.lastname: Phillip
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, UK; Integrative Physiology and Critical Illness Group, Clinical and Experimental Sciences, Mailpoint 810, Sir Henry Wellcome Laboratories, Faculty of Medicine, University of Southampton, University Hospital Southampton NHS Foundation Trust, Southhampton, UK; Anaesthesia and Critical Care Research Unit, University Hospital Southampton NHS Foundation Trust, Southhampton, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Grocott
authors.affiliation: Department of Intensive Care, Erasmus MC University Hospital Rotterdam, Rotterdam, Netherlands.
authors.forename: Can
authors.initials: C
authors.lastname: Ince
authors.affiliation: University College London Centre for Altitude Space and Extreme Environment Medicine, UCLH NIHR Biomedical Research Centre, Institute of Sport and Exercise Health, London, UK; University College London, Division of Surgery and Interventional Science, Royal Free Hospital, London, UK; Erasmus MC-Sophia Children's Hospital, Rotterdam, Netherlands.
authors.forename: Daniel
authors.initials: D
authors.lastname: Martin
keywords: Altitude; Capillaries; Microcirculation; Microscopy; Oxygen