Abstract
PurposeSerum erythropoietin (EPO) concentration is increased following static apnoea-induced hypoxia. However, the acute erythropoietic responses to a series of dynamic apnoeas in non-divers (ND) or elite breath-hold divers (EBHD) are unknown.MethodsParticipants were stratified into EBHD (n = 8), ND (n = 10) and control (n = 8) groups. On two separate occasions, EBHD and ND performed a series of five maximal dynamic apnoeas (DYN) or two sets of five maximal static apnoeas (STA). Control performed a static eupnoeic (STE) protocol to control against any effects of water immersion and diurnal variation on EPO. Peripheral oxygen saturation (SpO2) levels were monitored up to 30 s post each maximal effort. Blood samples were collected at 30, 90, and 180 min after each protocol for EPO, haemoglobin and haematocrit concentrations.ResultsNo between group differences were observed at baseline (p > 0.05). For EBHD and ND, mean end-apnoea SpO2 was lower in DYN (EBHD, 62 ± 10%, p = 0.024; ND, 85 ± 6%; p = 0.020) than STA (EBHD, 76 ± 7%; ND, 96 ± 1%) and control (98 ± 1%) protocols. EBHD attained lower end-apnoeic SpO2 during DYN and STA than ND (p < 0.001). Serum EPO increased from baseline following the DYN protocol in EBHD only (EBHD, p < 0.001; ND, p = 0.622). EBHD EPO increased from baseline (6.85 ± 0.9mlU/mL) by 60% at 30 min (10.82 ± 2.5mlU/mL, p = 0.017) and 63% at 180 min (10.87 ± 2.1mlU/mL, p = 0.024). Serum EPO did not change after the STA (EBHD, p = 0.534; ND, p = 0.850) and STE (p = 0.056) protocols. There was a significant negative correlation (r = − 0.49, p = 0.003) between end-apnoeic SpO2 and peak post-apnoeic serum EPO concentrations.ConclusionsThe novel findings demonstrate that circulating EPO is only increased after DYN in EBHD. This may relate to the greater hypoxemia achieved by EBHD during the DYN.
Highlights
Hypoxia is a condition of reduced oxygen concentration in breathable air or blood
Data are presented as mean ± SD A Static apnoea, B Dynamic apnoea, EBHD elite breath-hold divers, ND non-divers p = 0.122) or red cell volume (r = − 0.048, p = 0.643) (Fig. 3). This is the first study to make a novel distinction between the acute effects of static and dynamic apnoeas on erythropoietic responses in ND and EBHD
The primary findings were that: (1) dynamic apnoeas induced a more pronounced oxygen desaturation rate compared with static apnoeas, (2) which led into a significant increase in circulating EPO in EBHD only, (3) with no effect of static or eupnoea protocols on EPO
Summary
Hypoxia is a condition of reduced oxygen concentration in breathable air or blood. Elite breath-hold divers (EBHD) regularly endure periods of acute hypoxemia (oxygen saturation levels < 90%) during their training sessions, interspaced by periods of normal breathing (1–2 min). (apnoea) triggers a series of physiological modifications known as the diving reflex which collectively lower oxygen utilisation and in turn, prolong apnoeic durations. The diving reflex is characterised by an initial parasympatheticallyinduced bradycardial response (Schagatay and Holm 1996), followed by a sympathetically-induced peripheral vasoconstriction of non-vital organs and extremities (Campbell et al 1969), with oxygenated blood preferentially redistributed to the vital organs (Sterba and Lundgren 1988). Systemic hypoxemia is induced in renal vascular beds (Bron et al 1966). This stimulates the release of the glycoprotein hormone erythropoietin (EPO) from the renal peritubular fibroblasts into the circulation (Elliott 2008; Jelkmann 2011). The magnitude of EPO release is directly proportional to the level of hypoxia (Eckardt et al 1989; Knaupp et al 1992), and the transcription of EPO is controlled, at the cellular level, by hypoxia-inducible
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