Abstract
What is the central question of this study? Splenic contractions occur in response to apnoea-induced hypoxia with and without face immersion in water. However, the splenic responses to a series of static or dynamic apnoeas with whole-body water immersion in non-divers and elite breath-hold divers are unknown. What is the main finding and its importance? Static and dynamic apnoeas were equally effective in stimulating splenic contractions across non-divers and elite breath-hold divers. These findings demonstrate that the magnitude of the splenic response is largely dictated by the degree of the hypoxemic stress encountered during voluntary apnoeic epochs. Splenic contractions occur in response to apnoea-induced hypoxia with and without facial water immersion. However, the splenic responses to a series of static (STA) or dynamic (DYN) apnoeas with whole-body water immersion in non-divers (NDs) and elite breath-hold divers (EBHDs) are unknown. EBHD (n=8), ND (n=10) and control participants (n=8) were recruited. EBHD and ND performed a series of five maximal DYN or STA on separate occasions. Control performed a static eupnoeic (STE) protocol to control against any effects of water immersion and diurnal variation on splenic volume and haematology. Heart rate (HR) and peripheral oxygen saturation (SpO2 ) were monitored for 30s after each apnoea. Pre- and post-apnoeic splenic volumes were quantified ultrasonically, and blood samples were drawn for haematology. For EBHD and ND end-apnoeic HR was higher (P<0.001) and SpO2 was lower in DYN (P=0.024) versus STA. EBHD attained lower end-apnoeic SpO2 during DYN and STA than NDs (P<0.001). Splenic contractions occurred following DYN (EBHD, -47±6%; ND, -37±4%; P<0.001) and STA (EBHD, -26±4%; ND, -26±8%; P<0.01). DYN-associated splenic contractions were greater than STA in EBHD only (P=0.042). Haemoglobin concentrations were higher following DYN only (EBHD, +5±8g/L, +4±2%; ND, +8±3g/L, +4.9±3%; P=0.019). Haematocrit remained unchanged after each protocol. There were no between group differences in post-apnoeic splenic volume or haematology. In both groups, splenic contractions occurred in response to STA and DYN when combined with whole-body immersion. DYN apnoeas, were effective at increasing haemoglobin concentrations but not STA apnoeas. Thus, the magnitude of the splenic response relates to the hypoxemic stress encountered during apnoeic epochs.
Highlights
The diving reflex is an oxygen conserving mechanism that is activated during the state of apnoea (Gooden, 1994)
This study made the first investigations into the splenic responses to a series of repeated maximal static and dynamic apnoeas with wholebody water immersion in elite breath-hold divers (EBHDs) and ND
These findings demonstrate that the magnitude of the splenic response is largely dictated by the magnitude of the hypoxemic stress encountered during apnoeic epochs
Summary
The diving reflex is an oxygen conserving mechanism that is activated during the state of apnoea (Gooden, 1994). Static and dynamic apnoeas were effective in stimulating splenic contractions across nondivers and elite breath-hold divers These findings demonstrate that the magnitude of the splenic response is largely dictated by the degree of the hypoxemic stress encountered during voluntary apnoeic epochs. Apnoea-induced physiological responses (e.g. the magnitude of the bradycardial response, erythropoietin release) vary across trained and untrained populations (Elia et al, 2019a; Joulia, Steinberg, Wolff, Gavarry, & Jammes, 2002; Lemaitre et al, 2005; Lemaitre, Buchheit, Joulia, Fontanari, & TournyChollet, 2008) Evidence suggests that these differences across diving and non-diving populations are, at least in part, the result of a traininginduced stimulus (Joulia et al, 2003; Richardson et al, 2005; Schagatay, van Kampen, Emanuelsson, & Holm, 2000). Stronger hypoxemic stress compared with static apnoeas and that this will stimulate a greater splenic and systemic haematological response
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