The Author's Reply - Letter to the Editor

We acknowledge that the serum sodium values for Subjects 4 and 6 are probably a typographical error which occurred during data collection and this anomaly should have been noticed before submission. The serum osmolality seems to confirm that the actual value was much closer to those of the other subjects which are all values compatible with life and consistent with exercise induced dehydration.

There is no evidence that there is any flaw in our measurement of brain volumes nor does the study cited confound our results. Flux of fluids and osmolytes between compartments in the cranium is complex and is likely to occur at different times in different individuals. Our study is a small pilot but nevertheless it is the first to show changes in intra cranial compartment volumes in humans as a result of dehydration. We would welcome a larger systematic study to clarify the implications of our data.