Volume 4 Supplement 1

15th International Conference on Environmental Ergonomics (ICEE XV)

Open Access

An eye on hydration: efficacy of intraocular pressure to measure body water deficit

Extreme Physiology & Medicine20154(Suppl 1):A139

https://doi.org/10.1186/2046-7648-4-S1-A139

Published: 14 September 2015

Introduction

Current best-practice hydration assessment include techniques involving isotope dilution to estimate total body water; osmolality of blood, saliva, or urine; specific gravity or colour of urine; and changes in body mass. These techniques are either prohibitively expensive, invasive, require clinical laboratory equipment, rely on a non-dehydrated baseline criterion, or on body fluids that are compromised in a dehydrated individual. In this study we report on the capability of intraocular pressure (the pressure within the eye; IOP), to assess dehydration. IOP can be measured quickly and accurately using a handheld device (tonometer), therefore offering portability, and sterility, and can be used by anyone following minimal training [1].

Methods

Twelve healthy males (mean (SD): age 24 (2.3) yr, height 178 (6.1) cm, weight 75 (6.6) kg, VO2max 56 (4.4) mL.kg-1.min-1, sum of eight skinfolds 75 (29) mm) completed two trials each comprising 150 minutes of treadmill walking (5 km,h-1 and 1 % grade), in a hot and dry environment (40 °C and 20 % relative humidity). One trial was undertaken with fluid (water) replacement to minimise body mass changes (EUH) and one without fluid to maximise dehydration (DEH). The order of the trials was randomized and the trial days were separated by a minimum of seven days. At baseline and at 30 minute intervals participants were removed from the hot and humid environment into a temperate air-conditioned laboratory to have IOP, nude body mass and serum osmolality assessed.

Discussion

IOP was progressively reduced during a period of exercise causing dehydration, but remained relatively stable if hydration was maintained. The large within and between individual variation in IOP meant that an absolute IOP value could not be identified to provide a criterion cut-off to represent a dehydrated condition. However utilising a change from a euhydrated baseline, delta IOP was significantly different between the conditions at increasing levels of body mass loss and serum osmolality.

Conclusion

The evidence suggests that IOP is influenced by hydration status, likely due to the effect of a rise in blood osmolality on the rate of formation of aqueous humour.

Table 1

 

Baseline

30

60

90

120

150

IOP (mmHg)

      

EUH

14.4 (4.1)

15.5 (3.9)

14.7 (3.9)

14.1 (4.0)

14.5 (3.5)

14.2 (4.0)

DEH

15.6 (3.5)

14.2 (3.5)*

14.8 (4.1)

13.3 (3.3)

13.2 (3.6)*

13.0 (3.0)

IOP delta (mmHg)

      

EUH

 

1.0 (1.7)

0.3 (2.7)

-0.3 (1.7)

0.0 (1.7)

-0.3 (2.4)

DEH

 

-1.5 (1.8)*

-0.8 (1.2)

-2.4 (1.7)*

-2.5 (1.6)*

-2.7 (1.9)*

Body Mass delta (%)

      

EUH

 

0.0 (0.1)

-0.1 (0.1)

-0.1 (0.1)

-0.1 (0.2)

-0.2 (0.2)

DEH

 

-0.5 (0.1)*

-1.0 (0.1)*

-1.5 (0.1)*

-2.0 (0.2)*

-2.5 (0.2)*

Serum Osmolality (mOsmol.kg -1 )

     

EUH

291 (4.9)

291 (3.7)

291 (3.6)

291 (3.0)

292 (3.6)

292 (3.4)

DEH

292 (3.4)

293 (3.0)*

294 (2.7)*

297 (4.0)*

298 (4.5)*

299 (4.9)*

EUH, euhydrated trial; DEH, dehydrated trial. *Significantly different to EUH at same time point, p < 0.05.

Authors’ Affiliations

(1)
School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology
(2)
Extreme Environments Laboratory, Department of Sport and Exercise Science, University of Portsmouth

References

  1. Hunt A, Feigl B, Stewart I: The intraocular pressure response to dehydration: a pilot study. Eur J Appl Physiol. 2012, 112 (5): 1963-1966. 10.1007/s00421-011-2143-5.View ArticlePubMedGoogle Scholar

Copyright

© Stewart et al.; 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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