Last Word on Point: Counterpoint: Hypobaric hypoxia induces different

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TO THE EDITOR: We thank the authors of the comments (see Ref. 1) who contributed ... the comments are in line with our view that hypobaric hypoxia induces ...
J Appl Physiol 112: 1795, 2012; doi:10.1152/japplphysiol.00338.2012.

Letter To The Editor

Last Word on Point: Counterpoint: Hypobaric hypoxia induces different responses from normobaric hypoxia Grégoire P. Millet,1 Raphael Faiss,1 and Vincent Pialoux2 1

ISSUL Institute of Sport Sciences-Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland; and 2Centre de Recherche et d’Innovation sur le Sport, Université Claude Bernard, Lyon, France TO THE EDITOR: We thank the authors of the comments (see Ref. 1) who contributed their thoughts to this debate (3, 5). Many additional interesting arguments were provided, and most of the comments are in line with our view that hypobaric hypoxia induces different physiological responses from normobaric hypoxia but also that the underlying mechanisms and clinical/ practical relevance have not yet been investigated enough. Regarding the mechanisms, we concur with Verges et al. (see Ref. 1) that motor cortex excitability might be affected differently between HH and NH (4). We also agree with Laymon et al. (see Ref. 1) and Verges et al. (see Ref. 1) that the cost of breathing is likely different between HH and NH. Several authors (Conkin; Guenette and Koehle; Loeppky; Taylor et al.; Vagula and Nelatury; see Ref. 1) supported the view that pressure change associated with hypobaria plays a role in pulmonary fluid flux differences between HH and NH (2). However, because “there is no direct comparison...in HH vs NH...on AMS severity” as noted in our Point (3), the question of the clinical relevance for AMS remains unanswered (Loeppky vs. Schommer and Bartsch; see Ref. 1). Finally, the comments of Conkin and Wessel (see Ref. 1) or Koehle et al. (see Ref. 1) on the inaccuracy of defining correct hypoxic levels, those of Chapman and Levine (see Ref. 1) on the differences in intermittent exposure between NH and HH or those of Girard (see Ref. 1) on the impact on air resistance during repeated sprints support that, from a practical point of

Address for reprint requests and other correspondence: G. P. Millet, ISSUL Institute of Sport Sciences-Dept. of Physiology, Faculty of Biology and Medicine, Univ. of Lausanne, Batiment Vidy, CH-1015, Lausanne, Switzerland (e-mail: [email protected]).

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view, training in NH is different by nature from training in HH. To conclude, we would like to borrow the statement of Pun (see Ref. 1): Hypobaric hypoxia has complex and multitude of stimuli compared with normobaric hypoxia. DISCLOSURES No conflicts of interest, financial or otherwise, are declared by the authors. AUTHOR CONTRIBUTIONS Author contributions: G.P.M. drafted manuscript; G.P.M. and V.P. edited and revised manuscript; G.P.M., R.F., and V.P. approved final version of manuscript. REFERENCES 1. Girard O, Koehle MS, MacInnis MH, Richard N, Guenette JA, Koehle MS, Verges S, Rupp T, Jubeau M, Perrey S, Millet GY, Chapman RF, Levine BD, Conkin J, Wessell JH III, Nespoulet H, Wuyam B, Tamisier R, Verges S, Levy P, Casey DP, Taylor BJ, Snyder EM, Johnson BD, Laymon AS, Stickford JL, Weavil JC, Leoppky JA, Pun M, Schommer K, Bartsch P, Vagula MC, Nelatury CF. Comments on Point:Counterpoint: Hypobaric hypoxia induces/does not induce different responses from normobaric hypoxia. J Appl Physiol; doi:10.1152/japplphysiol.00356.2012. 2. Hirai K, Kobayashi T, Kubo K, Shibamoto T. Effects of hypobaria on lung fluid balance in awake sheep. J Appl Physiol 64: 243–248, 1988. 3. Millet GP, Faiss R, Pialoux V. Point: Hypobaric hypoxia induces different physiological responses from normobaric hypoxia. J Appl Physiol; doi: 10.1152/japplphysiol.00067.2012. 4. Miscio G, Milano E, Aguilar J, Savia G, Foffani G, Mauro A, MordilloMateos L, Romero-Ganuza J, Oliviero A. Functional involvement of central nervous system at high altitude. Exp Brain Res 194: 157–162, 2009. 5. Mounier R, Brugniaux JV. Counterpoint: Hypobaric hypoxia does not induce different physiological responses from normobaric hypoxia. J Appl Physiol; doi:10.1152/japplphysiol.00067.2012a.

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