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Progressive changes of oxygenation, diving response, and involuntary breathing movements during repeated apneas
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences (HOV).ORCID iD: 0000-0002-6916-4121
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences (HOV).ORCID iD: 0000-0003-1957-1527
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences (HOV). (Swedish Winter Sports Research Centre)ORCID iD: 0000-0001-5477-9265
2025 (English)In: Respiratory Physiology & Neurobiology, ISSN 1569-9048, E-ISSN 1878-1519, Vol. 336, article id 104455Article in journal (Refereed) Published
Abstract [en]

Purpose: This study investigated whether trained freedivers can sustain a 1:1 apnea-to-recovery ratio without progressive arterial or cerebral oxygen desaturation. Methods: 21 trained freedivers (6 females) performed 7 static apneas of fixed 2-min duration, each followed by 2-min of rest, in a supine laboratory setting. Arterial oxygen saturation (SpO₂) and heart rate (HR) were measured continuously. Near-infrared spectroscopy (NIRS) assessed cerebral and peripheral muscle oxygenation. A chest force sensor recorded involuntary breathing movements (IBM). End-tidal CO₂ (EtCO₂) was measured pre- and post apnea. Results: SpO₂ declined most during the first apnea (94 ± 3 %) but stabilized thereafter (p < 0.005). Lowest HR increased from 61 ± 15 to 65 ±13 bpm across the series (p = 0.02), and the intial apnea tachycardia declined by 10 bpm (p = 0.012). Cerebral oxygenation increased above baseline only during the first apnea (1.0 ± 2.3 %); in subsequent apneas it remained stable, although slightly below baseline. Muscle oxygenation declined during all apneas but was more pronounced in the first (-6.7 ± 3.1 %). IBM onset was progressively delayed; 63 % of participants showed no IBM during the final apnea. EtCO₂ increased after each apnea by ≈ 1.0kPa (p < 0.001) but did not change progressively across the series. Conclusion: A 1:1 apnea-to-recovery ratio was physiologically sustainable in trained freedivers at rest, without inducing progressive oxygen desaturation. The initial apnea elicited the strongest oxygen-conserving responses, which progressively attenuated across the series, suggesting that physiological regulation during repeated submaximal apneas is adaptable to meet situation-specific demands. The progressive IBM delay despite stable CO2 levels suggests additional mechanisms beyond chemoreflex-driven stimulation of breathing may contribute to ventilatory drive. 

Place, publisher, year, edition, pages
Elsevier BV , 2025. Vol. 336, article id 104455
Keywords [en]
Blackout, Breath-holding, Cardiovascular, Cerebrovascular, Diving safety, Freediving
National Category
Physiology and Anatomy
Identifiers
URN: urn:nbn:se:miun:diva-54754DOI: 10.1016/j.resp.2025.104455ISI: 001517546300001PubMedID: 40482793Scopus ID: 2-s2.0-105007685621OAI: oai:DiVA.org:miun-54754DiVA, id: diva2:1976085
Available from: 2025-06-24 Created: 2025-06-24 Last updated: 2025-09-25

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Mulder, Eric R.Holmström, Pontus K.Schagatay, Erika K.

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Mulder, Eric R.Holmström, Pontus K.Schagatay, Erika K.
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