Breath-hold Divers Research Articles

Occurrence and resolution of freediving-induced pulmonary syndrome in breath-hold divers: an online survey of lung squeeze incidents.

Breath-hold divers occasionally surface with signs of fluid accumulation and/or bleeding in air-filled spaces. This constellation of symptoms, recently termed 'freediving induced pulmonary syndrome', is thought to come from immersion pulmonary oedema and/or barotrauma of descent and is colloquially termed a 'squeeze'. There is limited understanding of the causes, diagnosis, management, and return to diving recommendations after a squeeze. We developed an online survey that queried breath-hold divers on the circumstances and management of individual squeeze events. A total of 132 (94 M, 38 F) breath-hold divers filled out the survey. Most were recreational or competitive freedivers with mean age of 37 years old and nine years of experience. Of those, 129 (98%) held a certification in freediving from an accredited training agency. A total of 103 individuals reported 140 squeeze events from 2008-2023. The average depth at which a squeeze occurred was 43 m. The top contributors to lung squeezes were described as movement at depth, contractions, and inadequate warm-up. The most common symptoms of a squeeze were cough, sputum production, and fatigue. Divers were instructed to wait an average of two months before returning to diving after a squeeze. On average, divers were able to achieve the same depth of their squeeze event three months after the incident. Inadequate warm-up, contractions, and abnormal movement at depth are the most reported causes for a squeeze. Most divers do not seek medical treatment after a lung squeeze event and can return to the same depth within three months.

Respiratory muscle strength pre- and post-maximal apneas in a world champion breath-hold diver.

Maximal static dry, i.e., on land, apneas (breath-holds) result in severe hypoxemia and hypercapnia and have easy-going and struggle phases. During the struggle phase, the respiratory muscles involuntarily contract against the closed glottis in increasing frequency and magnitude, i.e., involuntary breathing movements (IBMs). IBMs during a maximal static apnea have been suggested to fatigue respiratory muscles, but this has yet to be measured. Thus, the purpose of this study was to quantify respiratory muscle strength pre- and post-apneas in an elite, world champion, world record holding apneist. To do so, maximal inspiratory and expiratory pressure maneuvers (MIP and MEP, respectively) were performed pre- and post-apnea protocol which included 3 preparatory apneas with 2.5 min rest. All preparatory apneas were ended after the participant reported 7-10 IBMs. Next, he performed 3 maximal static dry apneas with 5 min rest in between. The participant had maximal apneas lasting 363, 408, and 460 seconds. Including preparatory apneas, the participant's total apnea duration was 33.4 min in 57.0 min. Following the apnea protocol, i.e., pre vs. post, there was no change in MIP (-124.2 vs. -123.6 cmH2O) or MEP (259.4 vs. 262.5 cmH2O). These data, albeit in a single individual, suggest that respiratory muscle strength is not impacted by maximal static breath-holds. This could be the result of training and/or be a feature of this individual that allows him to excel in this sport.

Adverse Events in Competitive Freediving – Clinical Presentation, Management, and Prevention

Freediving (synonyms: breath-hold diving, apnea diving) has become a popular leisure activity and continues to gain popularity and recognition as both a competitive and recreational sport. Formal freediving competitions are sanctioned by the international Confédération Mondiale des Activités Subaquatiques (CMAS) or the Association Internationale pour le Développement de l’Apnée (AIDA). Both organizations have set up rules and guidelines for competitive pool disciplines where athletes compete for maximum submerged breath-hold time or underwater swimming distance with or without fins. In freshwater disciplines athletes strive for maximum depth using different freediving techniques. These aquatic breath-holding activities carry unique medical risks that are related to environmental factors eliciting extreme physiological challenges. Pool disciplines carry an increased risk of hypoxemia and, consequently, loss of consciousness, particularly in untrained individuals. Hypoxic complications are reported to occur in up to 10% of dives during freediving competitions. Shallow water blackout following hyperventilation to extend breath-hold capability is a serious risk applying to all aquatic breath-hold activities, however, is more common during recreational freediving. Deep freediving poses the athlete to further risks such as barotrauma of ear drums or lungs, immersion pulmonary edema, nitrogen narcosis, and decompression sickness when reaching great depths. While serious complications in competitive freediving are rare, however, the risk clearly rises with increasing depth. Special breathing techniques to increase lung volumes such as glossopharyngeal insufflation carry additional risks. This article reviews possible complications and injury that may occur in competitive freedivers and discusses strategies for management and prevention of possible injury.

Taravana syndrome and posterior reversible encephalopathy syndrome: a microbubble hypothesis for neurological accidents in breath-hold divers.

Breath-hold diving is a challenging activity that can lead to serious and dangerous complications, such as the "Taravana" syndrome. This syndrome is characterized by the onset of neurological symptoms after deep or repeated dives. The main clinical manifestations are cerebral, including stroke and cognitive impairment. The pathophysiology of Taravana syndrome is still widely debated, but the most accepted theory is that it is a specific form of decompression sickness. We have reviewed the main theories explaining the onset of Taravana syndrome and, through the description of a particularly illustrative case of a freediver using an underwater scooter, we have formulated a hypothesis according to which micro-bubbles formed directly in cerebral structures would be at the origin of this syndrome. MRI showed diffuse encephalopathy with vasogenic edema. Analysis of the radiological sequences did not suggest an ischemic or embolic mechanism. This finding is likely to be associated with the diagnosis of posterior reversible encephalopathy syndrome. The rapid ascent speeds associated with underwater scooter use could potentially result in the formation of nitrogen micro-bubbles in the capillaries of brain tissue. The emergence of scooters in freediving can be a hazard because of their ability to facilitate very rapid ascents. It is therefore essential to take preventive measures to ensure the safety of users of these devices.

Higher proportion of prematurely born adults in elite breath-hold divers

Higher proportion of prematurely born adults in elite breath-hold divers

Lung Ultrasound as an Adjunct to Pulse Oximetry and Respiratory Symptoms in the Diagnosis of Freediving-Induced Pulmonary Syndrome.

B-lines on lung ultrasound have been found in asymptomatic competitive breath-hold divers, but their significance and time to resolution are not well understood. We sought to investigate the relationship between B-lines, oxygen saturation, and respiratory symptoms after competitive dives to diagnose pulmonary injury. We performed lung ultrasounds before (predive), immediately after (postdive), and within 1 h (follow-up) of a competitive dive. B-lines were counted in each intercostal space in the anterior, lateral, and posterior lung fields, and the highest number of B-lines within a space was recorded for each lung region. At follow-up, each diver's oxygen saturation and respiratory symptoms were recorded. Statistical analysis included the Kruskal-Wallis test, Spearman's correlation, and sensitivity and specificity calculations. Forty-four divers completed 143 individual dives of four different disciplines. The median number of B-lines was 0 (IQR inclusive=0) predive, 1 (IQR=3) postdive, and 0 (IQR=1) at follow-up. There was a significant difference in total B-lines between measurement times (p<0.001). Sensitivity and specificity of hypoxemia, clinically significant B-lines, and both measures in tandem in detecting respiratory symptomatology were 52% and 76%, 24% and 92%, and 24% and 95%, respectively. B-lines are a common phenomenon in competitive breath-hold divers on surfacing and decrease within 1 h, suggesting a physiologic fluid shift. B-lines are negatively correlated with oxygen saturation, indicating that extravascular fluid impairs gas exchange in the lung. Neither hypoxemia nor clinically significant B-lines were found to be reliable indicators for respiratory symptomatology, suggesting that there may be multiple phenotypes of freediving-induced pulmonary syndrome.

Cardiovascular and hematological responses to a dry dynamic apnea in breath hold divers.

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea. However, the dive reflex to a single, maximal, dry, dynamic apnea (DYN) and how it compares to a time-matched exercise control trial (EX) or dry static apnea (SA) has not been studied. We examined the hypotheses that, compared with EX and SA, the magnitude of the 1) cardiovascular response and 2) hematological response to DYN would be greater. Cardiovascular parameters [heart rate (HR), systolic (SBP), diastolic (DBP), and mean arterial (MAP) blood pressure] were continuously collected in 23 (F = 6 females) moderate and elite freedivers, first during a maximal DYN, then during a time-matched SA and EX on a swimming ergometer in randomized order. Venous blood draws were made before and following each trial. The change in calculated oxygen saturation (DYN: -17 ± 13%, EX: -2 ± 1%, ΔSA: -2 ± 1%; P < 0.05, all comparisons) was greater during DYN compared with EX and SA. During DYN, ΔSBP (DYN: 104 ± 31 mmHg; EX: 38 ± 23 mmHg; and SA: 20 ± 11 mmHg), ΔDBP (DYN: 45 ± 12 mmHg; EX: 14 ± 10 mmHg; and SA: 15 ± 8 mmHg), and ΔMAP (DYN: 65 ± 17 mmHg; EX: 22 ± 13 mmHg; and SA: 16 ± 9 mmHg) were increased compared with EX and SA, while ΔHR was greater during EX (DYN: -24 ± 23 beats/min; EX: 33 ± 13 beats/min; and SA: -1 ± 10 beats/min) than either DYN or SA (P < 0.0001, all comparisons). Females had a greater pressor response to EX (ΔSBP: 59 ± 30 mmHg; ΔDBP: 24 ± 14 mmHg; and ΔMAP: 35 ± 8 mmHg) than males (ΔSBP: 31 ± 15 mmHg; ΔDBP: 11 ± 6 mmHg; and ΔMAP: 18 ± 8 mmHg; P < 0.01, all comparisons). Together, these data indicate that DYN elicits a distinct, exaggerated cardiovascular response compared with EX or SA alone.NEW & NOTEWORTHY This study performed a dry dynamic apnea with sport-specific equipment to closely mimic the physiological demands of competition diving. We found the cardiovascular and hematological responses to dynamic apnea were more robust compared with time-matched exercise and dry static apnea control trials.

Pulmonary vascular adaptations to hypoxia in elite breath-hold divers.

Elite breath-hold divers (BHD) possess several oxygen conserving adaptations to endure long dives similar to diving mammals. During dives, Bottlenose Dolphins may increase the alveolar ventilation (VA) to perfusion (Q) ratio to increase alveolar oxygen delivery. We hypothesized that BHD possess similar adaptive mechanisms during apnea. Pulmonary blood volume (PBV) was determined by echocardiography, 15O-H2O PET/CT, and cardiac MRi, (n = 6) during and after maximum apneas. Pulmonary function was determined by body box spirometry and compared to matched controls. After 2min of apnea, the PBV determined by echocardiography and 15O-H2O-PET/CT decreased by 26% and 41%, respectively. After 4min of apnea, the PBV assessed by echocardiography and cardiac MRi decreased by 48% and 67%, respectively (n = 6). Fractional saturation (F)O2Hb determined by arterial blood-gas-analyses collected after warm-up and a 5-minute pool-apnea (n = 9) decreased by 43%. Compared to matched controls (n = 8), spirometry revealed a higher total and alveolar-lung-capacity in BHD (n = 9), but a lower diffusion-constant. Our results contrast with previous studies, that demonstrated similar lung gas transfer in BHD and matched controls. We conclude that elite BHD 1) have a lower diffusion constant than matched controls, and 2) gradually decrease PBV during apnea and in turn increase VA/Q to increase alveolar oxygen delivery during maximum apnea. We suggest that BHD possess pulmonary adaptations similar to diving mammals to tolerate decreasing tissue oxygenation. This manuscript addresses novel knowledge on tolerance to hypoxia during diving, which is shared by elite breath-hold divers and adult diving mammals: Our study indicates that elite breath-hold divers gradually decrease pulmonary blood volume and in turn increase VA/Q, to increase alveolar oxygen delivery during maximum apnea to tolerate decreasing oxygen levels similar to the Bottlenose Dolphin.

Mucosal Petechiae and Hemorrhage in Pulmonary Barotrauma in Breath-Hold Diving: Direct Observation of a Suspected Pathophysiologic Mechanism.

Mucosal Petechiae and Hemorrhage in Pulmonary Barotrauma in Breath-Hold Diving: Direct Observation of a Suspected Pathophysiologic Mechanism.

Monitoring the Breath-Hold Training Load during an Ecological Session: A Pilot Study.

This study aimed to create a training load index to measure physiological stress during breath-hold (BH) training and examine its relationship with memory performance. Eighteen well-trained BH divers (Age: 35.8±6.6 years, BH training practice: 5.3±4.5 years) participated in this study. During a standard 1.5-hour BH training in the pool, perceived exertion, heart rate, distance, and duration were measured. The training load index was modelled on the basis of a TRIMP (TRaining IMPulse) with four different equations and was used to measure the stress induced by this BH training. A reference value, based on the ratio between the average heart rate during all BHs and the lowest heart rate during BH training, was used for comparing training load index. Memory assessment was conducted both before and after this training. Of the four equations proposed, equation no. 4, named aTRIMP for "apnoea," showed the strongest correlation with our reference value (r=0.652, p<0.01). No difference was found between any of the memory tests before and after the BH training. The aTRIMP was a new representative index for monitoring habitual training of well-trained BH divers. Furthermore, this training had no negative impact on memory performance.

The Cardio-Respiratory Mechanisms Involved in the Diving Response Adaptation and Breath-Hold Training Effects in Freedivers

This review aims to explore the cardiovascular and respiratory mechanisms involved in the training effects of the diving response adaptation and to determine the adaptive changes during apnoea and breath-hold training in breath-hold divers. A sounder theoretical knowledge of these critical aspects is necessary to be able to understand the oxygen-conserving mechanism of the diving response, and the apnoea-induced cardiorespiratory adjustments involved in enriching the science of respiratory physiology and the development of breath-hold training and ability. These insights may contribute to understanding the pathophysiology of respiratory abnormalities and dysfunctional breathing in humans. Furthermore, it may facilitate the development of efficacious interventions to increase breath-holding ability, and sports performance, as well as assist with the management and treatment of various physiological and psychological conditions. This review will be presented in four separate sections. Section one will describe the diving response and its physiology. Section two will explore the cardio-respiratory mechanisms of the diving response. Section three will discuss the adaptive changes associated with breath-hold training and/or apnoea training, as well as the associated cardio-respiratory adaptions. Section four will explore the clinical applications and implications of the diving response.

Risk profiles of elite breath-hold divers

ABSTRACT This study aimed to determine a typical profile of elite breath-hold divers (BHDs), in relation to loss of consciousness (LOC) and episodic memory. Forty-four BHDs were evaluated during a world championship with anthropometric and physiological measurements, psychosociological factors and memory assessment. Seventy-five percent of the BHDs had at least one LOC with the predominance being men (p < 0.05). Thirty six percent of BHDs presented a low-risk profile and 64% a high-risk profile with no particular psychological pattern. Stepwise multiple linear regression showed that body fat, years of BH practice, age and forced vital capacity explained a significant amount of the variance of LOC for all BHDs (F(4,39) = 16.03, p < 0.001, R2 = 0.622, R2 Adjusted = 0.583). No correlation was found between resting physiological parameters and their training or depth performances. In conclusion, anthropometric data, pulmonary factors and breath-holding experience were predictive of LOC in elite BHDs, with men taking more risks. BHDs episodic memory was not impaired.

Low hunting costs in an expensive marine mammal predator.

Many large terrestrial mammalian predators use energy-intensive, high-risk, high-gain strategies to pursue large, high-quality prey. However, similar-sized marine mammal predators with even higher field metabolic rates (FMRs) consistently target prey three to six orders of magnitude smaller than themselves. Here, we address the question of how these active and expensive marine mammal predators can gain sufficient energy from consistently targeting small prey during breath-hold dives. Using harbor porpoises as model organisms, we show that hunting small aquatic prey is energetically cheap (<20% increase in FMR) for these marine predators, but it requires them to spend a large proportion (>60%) of time foraging. We conclude that this grazing foraging strategy on small prey is viable for marine mammal predators despite their high FMR because they can hunt near continuously at low marginal expense. Consequently, cessation of foraging due to human disturbance comes at a high cost, as porpoises must maintain their high thermoregulation costs with a reduced energy intake.

Cardiovascular and Hematological Responses to Simulated Dynamic Apnea in Breath Hold Divers

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea or facial submersion in water. However, the dive reflex to a single, maximal effort dynamic apnea (DYN), and how it compares to a time-matched exercise control trial (EX), has not been studied. We examined the hypotheses that, when compared to EX, (a) the magnitude of the cardiovascular response, including reduced heart rate (HR), increased systolic-, diastolic-, and mean arterial- pressure (SBP, DBP, and MAP, respectively) would be greater during DYN, and; (b) red blood cells (RBCs), hemoglobin (Hb), and hematocrit (Hct) would also all be elevated following DYN. Twenty-three (F=6) apnea divers performed a maximal DYN and time-matched EX on a swimming ergometer without facial submersion. For the DYN protocol, participants were instructed to exercise maximally while holding their breath which the EX trial was then time and distance matched. Trial duration was similar between DYN (126±7s [mean±SE]) and EX (126±7s;P&gt;0.3), however the change in venous lactate (DYN 1.8±0.3mmol/l, EX: 0.2±0.2mmol/l) and peripheral oxygen saturation (DYN: -15±3%, EX: -1.8±0.5%;p&lt;0.05, both comparisons) were greater during DYN compared to EX. During DYN ΔSBP (DYN: 107±6mmHg, EX: 45±6 mmHg), ΔDBP (DYN: 46±3mmHg, EX: 17±3mmHg) and ΔMAP (DYN: 66±3mmHg EX: 26±3mmHg) were increased compared to EX, while ΔHR was greater during EX (DYN: -24±5bpm, EX: 36±5bpm;p&lt;0.0001, all comparisons). Similarly, the change in estimated stroke volume was further reduced in DYN (DYN: -15.2±3.3mL, EX: -1.0±3.3m;p&lt;0.005) while Δcardiac output was reduced during DYN (-2.9±0.4l/min) and elevated during EX (2.9±0.4l/min;p&lt;0.0001). The change in RBCs (DYN: 0.20±0.04x106 cells/μL, EX: 0.06±0.04x106 cells/μL) and Hct (DYN:1.7±0.3%, EX:0.5±0.3%) were greater during DYN than EX (p&lt;0.02, both comparisons), whereas ΔHb (DYN: 4.0±0.9g/dL, EX: 1.9±0.8g/dL) and spleen volume (DYN: -9.1±7.4cm3, EX:-8.3±6.4cm3;P&gt;0.1, both comparisons) was comparable between the two trials. There was a main effect of sex for ΔDBP (Female: 36±3mmHg, Male: 27±2mmHg), and ΔMAP (Female: 52±5mmHg, Male: 40±3mmHg) indicating that females overall had a greater blood pressure response to both DYN and EX (p&lt;0.05, both comparisons). Together, these data indicate that DYN elicits a greater cardiovascular and hematological response than EX alone, likely due to the combined activation of the metabo- and chemo-reflex during DYN. The mechanism(s) that may elicit greater changes in blood pressure response to DYN and EX in females when compared to males warrant future investigation. NSERC, University Research Chair. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Breath-Hold Diving Injuries - A Primer for Medical Providers.

Breath-hold divers, also known as freedivers, are at risk of specific injuries that are unique from those of surface swimmers and compressed air divers. Using peer-reviewed scientific research and expert opinion, we created a guide for medical providers managing breath-hold diving injuries in the field. Hypoxia induced by prolonged apnea and increased oxygen uptake can result in an impaired mental state that can manifest as involuntary movements or full loss of consciousness. Negative pressure barotrauma secondary to airspace collapse can lead to edema and/or hemorrhage. Positive pressure barotrauma secondary to overexpansion of airspaces can result in gas embolism or air entry into tissues and organs. Inert gas loading into tissues from prolonged deep dives or repetitive shallow dives with short surface intervals can lead to decompression sickness. Inert gas narcosis at depth is commonly described as an altered state similar to that experienced by compressed air divers. Asymptomatic cardiac arrhythmias are common during apnea, normally reversing shortly after normal ventilation resumes. The methods of glossopharyngeal breathing (insufflation and exsufflation) can add to the risk of pulmonary overinflation barotrauma or loss of consciousness from decreased cardiac preload. This guide also includes information for medical providers who are tasked with providing medical support at an organized breath-hold diving event with a list of suggested equipment to facilitate diagnosis and treatment outside of the hospital setting.

Evolution of the peroxiredoxin gene family: an antioxidant enzyme in the context of hypoxia-induced by aquatic mammals dives

Peroxiredoxins are a group of antioxidant enzymes that play a crucial role in eliminating hydrogen peroxide (H2O2) produced during cellular metabolism. In conditions such as tissue ischemia/reperfusion, H2O2 production is heightened. This scenario is recurrent in aquatic mammals, such as cetaceans and pinnipeds, when they perform breath-hold dives that lead to depletion of oxygen stores and cell hypoxia due to prolonged submersion. In such circumstances, peroxiredoxins are essential for regulating metabolism and preventing oxidative damage. Thus, our objective was to investigate evolutionary patterns of the peroxiredoxin gene family among aquatic mammalian species. Accordingly, we identified the number of ortholog and paralog genes among mammals, examining events of gene duplication, patterns of chromosomal distribution, and adaptive selection. We found that most subtypes of peroxiredoxins are characterized by single-copy genes with minimal missing data, with PRDX1, the most highly expressed subtype found in both the nucleus and cytoplasm, exhibiting an increase in gene copies in aquatic mammals, particularly in pinnipeds. The distribution of the copies was dispersed along the genome and the majority were retrocopies of the main coding sequence with little divergence among them. We also found evidence of positive selection in the PRDX3 gene, especially in a convergent mutation among two deepest-diving species, cuvier’s beaked whale and southern elephant seal in which the amino acid had radical physical-chemical property change, possibly affecting the protein function. These results suggest that the peroxiredoxin gene family has a role in the evolution of aquatic mammals by reducing oxidative damage intrinsic to diving behavior in these species. FAPESP - São Paulo Research Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hypoxia Exposure Fine-Tunes Mitochondrial Function in Primary Dermal Fibroblasts Derived from Loggerhead Sea Turtles

Sea turtles are constantly exposed to changes in oxygen tension derived from extended breath-hold diving, but the cellular-level response to such changes is not completely understood. Most studies in hypoxia-tolerant reptiles have focused on the freshwater turtle Trachemys scripta, which responds to anoxia by inducing metabolic rewiring and preserving mitochondrial integrity, facilitating effcient mitochondrial respiration during reoxygenation. Here, we derived primary dermal fibroblasts from loggerhead sea turtles and western fence lizards to study the bioenergetic cellular response to hypoxia exposure in diving and non-diving reptiles. Cells from both species stained positive for the fibroblast markers vimentin and PDGFRb and responded to hypoxia exposure (0.1% O2) by accumulating HIF-1α. We measured oxygen consumption rates (OCR) in intact cells using Seahorse technology. We found that basal, maximal, and spare respiratory capacity was lower in lizard than in loggerhead cells at 26oC under normoxic (room air) conditions (p &lt; 0.0001). Exposure to short (1h) and long-term hypoxia (24h) altered mitochondrial function in both species. Maximal and spare respiratory capacity were lower in loggerhead than in lizard cells (p &lt; 0.01) after 1h hypoxia followed by 1h reoxygenation. In contrast, basal and maximal respiratory capacity was higher in loggerhead compared to lizard cells after 24h hypoxia (p &lt; 0.04). Nonetheless, the overall OCR after 24h hypoxia in both species was lower than that observed after 1h hypoxia. Overall, there was a significant reduction in cellular respiration in both species from short-term to long-term hypoxia exposure. In lizard cells, basal OCR decreased by a factor of three while maximal OCR decreased by a factor of 4.5. In loggerhead cells, both the basal and maximal OCR decreased by a factor of two. Our results demonstrate species-specific regulation of cellular respiration after hypoxia exposure. Remarkably, loggerhead cells show a steady downregulation of cellular respiration in response to hypoxia exposure and faster recovery after extended hypoxia (24h) than lizard cells, aligning with the remarkable hypoxic tolerance exhibited by sea turtles, which can endure up to 7 hours of breath-holding underwater. Understanding the cellular mechanisms that drive hypoxic tolerance in diving animals can provide insights for treating human conditions characterized by hypoxia signaling. Ford Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Fasting Metabolic Profiles are Cell-Autonomous in Elephant Seal Primary Muscle Cells

Northern elephant seals ( Mirounga angustirostris) undergo prolonged terrestrial fasts during energetically intensive life stages including breeding, molting, and postnatal development. Fasting-tolerant vertebrates generally extend the second phase of fasting, during which body mass declines but homeostasis is preserved through reliance on lipid fuel sources and sparing of body protein stores. In elephant seals, the postnatal fast coincides with development of the extensive body oxygen stores required to support extended breath-hold diving, as well as an increased capacity for apnea-related metabolic suppression. Studies in grizzly bears, another large-bodied fasting-tolerant mammal, have identified both serum-derived and intrinsic cellular regulation of the adipocyte metabolic phenotype. However, it is unknown whether these mechanisms extend across species, tissue, or fasting type (active vs inactive). Thus, we derived proliferative primary skeletal muscle cells (myoblasts) from weaned elephant seal pups; biopsies that yielded cells were collected at both early (~1 week) and late (~8 weeks) points in the postnatal fast. We found that total ATP production rate was greater in myoblasts collected from animals late in the fast (27% increase over early, p=0.08). Throughout the fast, myoblasts relied predominantly on glycolytic rather than oxidative ATP production (p&lt;0.001), and this reliance increased as the fast progressed (p&lt;0.014). Together, these data suggest that metabolic reliance is at least partially cell-autonomous in elephant seal myoblasts. KNA is supported by an NSF Graduate Research Fellowship (DGE 1752814 &amp; 2146752) and a UC Berkeley Fellowship. JPV-M is supported by a NIH/NIGMS grant (R35GM146951). Research was funded by UC Berkeley startup funds and the Winkler Family Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers.

Elite breath-hold divers (BHD) enduring apneas of more than 5min are characterized by tolerance to arterial blood oxygen levels of 4.3kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD. After 4min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6min), lower extremity volume assessed by DXA-scan revealed a ∼268mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations. Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.

Dive Hazards: Barotrauma, Flora, Fauna, Equipment, and Free Diving.

Present-day diving comes in various forms, from utilizing sophisticated diving equipment to relying solely on one's ability to hold their breath. The diver and physician must be aware of the many common medical conditions and environmental considerations of this unique activity. While barotrauma remains the most common dive-related injury, injuries and accidents also are related to diving equipment-related accidents and exposure to marine flora and fauna. In addition, breath-hold diving, which includes free diving, snorkeling, and tasks, is an activity humans have done for thousands of years for recreation or survival. This article will update the dangers of diving and methods to prevent or treat injuries.