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. 2014 Apr 21;13:46. doi: 10.1186/1475-925X-13-46

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Copyright © 2014 Chang et al.; licensee 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 credited. 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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The illustration of end-tidal CO₂(EtCO₂) concentration and corresponding FFT spectrum within 1 minute in one subject for example. The physiologic challenges of EtCO₂ include (a) baseline, (b) breathing with 6 cycles per minute, (c) breathing with 30 cycles per minute, (d) head-up tilt (HUT) and corresponding FFT spectrum during (e) baseline, (f) breathing with 6 cycles per minute, (g) breathing with 30 cycles per minute, (h) HUT.