Send Orders for Reprints to reprints@benthamscience.net 16 The Open Sports Medicine Journal, 2014, 8, 16-22 1874-3870/14 2014 Bentham Open Open Access Hypercapnic Ventilatory Response: A Comparison Between Elite and Novice Skin Divers Dimitrios I. Bourdas, Theodoros S. Tsakiris, Athanasios I. Konstantopoulos, Despoina V. Triantafillou and Nickos D. Geladas * Department of Sports Medicine & Biology of Exercise, Faculty of Physical Education and Sport Science, University of Athens, 17237 Daphne, Greece Abstract: This study tested whether hypercapnic ventilatory response (HCVR) is affected by experience in apnoea and explored the possible underlying mechanisms of this phenomenon, with reference to maximum breath hold time (BHT). Elite apnoea divers (EBH=11) and novice subjects (NBH=10) performed a HCVR test (BM), which was repeated by the latter group on another day (PRE) after subjects executed five repeated maximum apnoeas. Subsequently, after a two week period of daily apnoea training, NBH subjects repeated HCVR test (POST). Diaphragmatic activity was recorded to determine apnoea easy going phase. Baseline HCVR of EBH was not lower than that of NBH. After execution of five apnoeas, HCVR in EBH decreased (P≤0.05) whereas it was not different among BM, PRE, and POST conditions in the NBH. Higher BHT and easy going phase values ensued from apnoea maneuvers in EBH than in NBH (PRE and POST), and in NBH POST compared to PRE condition (P≤0.05). HCVR was highly correlated (P≤0.05) with the cumulative easy going phase in EBH, PRE condition but nothing-similar observed in NBH, neither in PRE nor in POST conditions. These results indicate that at rest HCVR is not lower in experienced, than novice, skin divers; this response becomes dull after five repeated maximum apnoeas only in EBH. In the NBH group, two weeks of apnoea training are not adequate to affect HCVR despite an increase of BHT. It appears that after a repeated maximum apnoeas maneuver experienced skin divers improve BHT by extending easy going phase whereas NBH by other means. Keywords: Breath hold, CO 2 sensitivity, easy going apnoea phase, repeated breath hold efforts. INTRODUCTION Breath responsiveness to a high concentration of carbon dioxide (CO 2 ) in arterial blood is referred as hypercapnic ventilatory response (ΗCVR). It is estimated by the slope (α) of the relation between ventilation (  VE) and partial pressure of end tidal CO 2 (α =  VE/PETCO2) and manifests the adaptability, health and welfare of pulmonary respiration [1]. Experienced skin divers because of familiarization and training seem to develop long term low chemosensitivity to CO 2 [2-5], leading probably to a reduced need for ventilation and consequently in increased duration of breath hold time (ΒΗΤ) [6]. Repeating breath hold efforts with a short time interval of 4 min between them, increases, temporarily though, CO 2 retention [7]. Similarly, after five repeating breath hold efforts with face immersion in cold water at 12 ο C with an interval of 2 min between each effort, induce significant retention of CO 2 which lasts at least 60 min in both experienced and novice divers [8]. It was speculated that repeated breath hold efforts through retention of CO 2 resets in both novice and experienced divers, the sensitivity *Address correspondence to this author at the Department of Sports Medicine & Biology of Exercise, Faculty of Physical Education and Sport Science, University of Athens, 17237 Daphne, E. Antistassis 41, Greece; Tel: +306977997102; E-mail: geladas@phed.uoa.gr threshold of central chemoreceptors [8] like apnoea training probably does and consequently both short apnoea repetition and training may reduce the need for breathing [9]. This phenomenon has been speculated to gradually lead in increased BHT in protocols of five repeated breath holds with an interval of 2-8 min [10-15]. However, all these assumptions were recently questioned since five repeated breath holds did not change HCVR in novice subjects and therefore recorded gradual BHT enhancement could not be attributed to HCVR alterations [16]. Collectively, dullness of hypercapnic ventilatory res- ponse is not observed indiscriminately in all skin divers and the influence of short and mid term training on it, remains entirely controversial. The scope of the present study was to explore the effect of short (five consecutive breath hold efforts) and mid term (two weeks of daily sessions) training on the development of low chemosensitivity in experienced and novice divers. It was assumed that hypercapnic venti- latory response is a trait, which befits to only experienced skin divers and short term training would not be effective in improving it. MATERIALS AND METHODS Subjects were grouped according to their experience in breath holding activities; the group of elite breath hold divers were members of apnoea national team (EBH, n = 11) with