Sports-related lung injury during breath-hold diving

Respiratory system responses to a maximal apnoea

A maximal apnoea provides significant challenges to one's physiological systems, including significantly altered arterial blood gases, and requires a highly integrative response from multiple systems, that is, changes in blood pressure, maintenance of cerebral blood flow, etc. Previous work and reviews have focused on the cardiovascular responses to a maximal apnoea, but very little work has focused upon the responses of the respiratory muscles and respiratory mechanics. This is important because of the changes to arterial blood gases leading to an increased drive to breath and the appearance of involuntary respiratory muscle contractions. This review outlines what is known about how the respiratory system responds to a maximal apnoea. We put forth the hypothesis that the respiratory muscles may become fatigued following a maximal apnoea and that the respiratory muscles of elite divers may be more fatigue-resistant, which could be an important feature of these individuals which allows them to be successful in this sport. Finally, we provide direction for future work to explore the long-term health of apnoea diving.

Respiratory anatomy and physiology in diving penguins

The anatomy and function of the respiratory systems of penguins are reviewed in relation to gas exchange and minimization of the risks of pulmonary barotrauma, decompression sickness and nitrogen narcosis during dives. Topics include available lung morphology and morphometry, respiratory air volumes determined with different techniques, review of possible physiological and biomechanical mechanisms of baroprotection, calculations of baroprotection limits and review of air sac and arterial partial pressure of oxygen (PO2) profiles in relation to movement of air during breathing and during dives. Limits for baroprotection to 200, 400 and 600 m in Adélie, king and emperor penguins, respectively, would require complete transfer of air sac air and reductions in the combined tracheobronchial tree-parabronchial volume of 24% in Adélie, 53% in king penguins and 76% in emperor penguins. Air sac and arterial PO2 profiles at rest and during surface activity were consistent with unidirectional air flow through the lungs. During dives, PO2 profiles were more complex, but were consistent with compression of air sac air into the parabronchi and air capillaries with or without additional air mixing induced by potential differential air sac pressures generated by wing movements.This article is part of the theme issue 'The biology of the avian respiratory system'.

Trends in competitive freediving accidents

Introduction

Understanding safety issues in competitive freediving is necessary for taking preventive actions and to minimise the risk for the athletes.

Methods

We analysed occurrence of loss of consciousness (LOC) and pulmonary barotrauma (PBt) in various freediving disciplines in 988 competitions over five years (from 2019 to 2023 inclusive), with 38,789 officially registered performances (starts): 26,403 in pool disciplines and 12,386 in depth disciplines.

Results

Average incident rate in competitive freediving (all cases: LOCs plus PBt, 2019-2023) was 3.43% (1,329 incidents / 38,789 starts). The average incident rate of LOC and PBt within five years were 3.31% and 0.38% respectively for all disciplines. Two disciplines present higher risk for LOC: dynamic without fins (DNF) (mean risk ratio (RR) = 1.48, 95% CI, 1.13 to 1.96, P < 0.01) and constant weight without fins (CNF) (mean RR = 2.02, 95% CI, 1.39 to 2.94, P < 0.001). The RR for PBt was not higher in any discipline. The overall risk of all types of incidents (LOC plus PBt) was also higher for DNF (mean RR = 1.55, 95% CI, 1.18 to 2.04, P < 0.01) and CNF (mean RR = 2.80, 95% CI, 1.70 to 5.04, P < 0.001).

Conclusions

The disciplines without fins in the pool (DNF) and at depth (CNF) appear to be the most dangerous in terms of LOC. We may recommend that organisers and safety teams should pay a special attention to no-fin disciplines as most risky for possible LOC.

Breath-Hold Diving Injuries - A Primer for Medical Providers

ABSTRACT

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.

Unlocking the depths: multiple factors contribute to risk for hypoxic blackout during deep freediving

PURPOSE

To examine the effect of freediving depth on risk for hypoxic blackout by recording arterial oxygen saturation (SpO2) and heart rate (HR) during deep and shallow dives in the sea.

METHODS

Fourteen competitive freedivers conducted open-water training dives wearing a water-/pressure proof pulse oximeter continuously recording HR and SpO2. Dives were divided into deep (> 35 m) and shallow (10-25 m) post-hoc and data from one deep and one shallow dive from 10 divers were compared.

RESULTS

Mean ± SD depth was 53 ± 14 m for deep and 17 ± 4 m for shallow dives. Respective dive durations (120 ± 18 s and 116 ± 43 s) did not differ. Deep dives resulted in lower minimum SpO2 (58 ± 17%) compared with shallow dives (74 ± 17%; P = 0.029). Overall diving HR was 7 bpm higher in deep dives (P = 0.002) although minimum HR was similar in both types of dives (39 bpm). Three divers desaturated early at depth, of which two exhibited severe hypoxia (SpO2 ≤ 65%) upon resurfacing. Additionally, four divers developed severe hypoxia after dives.

CONCLUSIONS

Despite similar dive durations, oxygen desaturation was greater during deep dives, confirming increased risk of hypoxic blackout with increased depth. In addition to the rapid drop in alveolar pressure and oxygen uptake during ascent, several other risk factors associated with deep freediving were identified, including higher swimming effort and oxygen consumption, a compromised diving response, an autonomic conflict possibly causing arrhythmias, and compromised oxygen uptake at depth by lung compression possibly leading to atelectasis or pulmonary edema in some individuals. Individuals with elevated risk could likely be identified using wearable technology.

Serum Amino Acid Profile Changes After Repetitive Breath-Hold Dives: A Preliminary Study

Background

The aim of this work was to investigate the serum amino acid (AA) changes after a breath-hold diving (BH-diving) training session under several aspects including energy need, fatigue tolerance, nitric oxide (NO) production, antioxidant synthesis and hypoxia adaptation. Twelve trained BH-divers were investigated during an open sea training session and sampled for blood 30 min before the training session, 30 min and 4 h after the training session. Serum samples were assayed for AA changes related to energy request (alanine, histidine, isoleucine, leucine, lysine, methionine, proline threonine, valine), fatigue tolerance (ornithine, phenylalanine, tyrosine), nitric oxide production (citrulline), antioxidant synthesis (cystine, glutamate, glycine) and hypoxia adaptation (serine, taurine).

Main results

Concerning the AA used as an energy support during physical effort, we found statistically significant decreases for all the investigated AA at T1 and a gradual return to the basal value at T2 even if alanine, proline and theonine still showed a slight significant reduction at this time. Also, the changes related to the AA involved in tolerance to physical effort showed a statistically significant decrease only at T1 respect to pre-diving value and a returned to normal value at T2. Citrulline, involved in NO production, showed a clear significant reduction both at T1 and T2. Concerning AA involved in endogenous antioxidant synthesis, the behaviour of the three AA investigated is different: we found a statistically significant increase in cystine both at T1 and T2, while glycine showed a statistically significant reduction (T1 and T2). Glutamate did not show any statistical difference. Finally, we found a statistically significant decrease in the AA investigated in other hypoxia conditions serine and taurine (T1 and T2).

Conclusions

Our data seem to indicate that the energetic metabolic request is in large part supported by AA used as substrate for fuel metabolism and that also fatigue tolerance, NO production and antioxidant synthesis are supported by AA. Finally, there are interesting data related to the hypoxia stimulus that indirectly may confirm that the muscle apparatus works under strong exposure conditions notwithstanding the very short/low intensity of exercise, due to the intermittent hypoxia caused by repetitive diving.

Blunted hypoxic pulmonary vasoconstriction in apnoea divers

NEW FINDINGS

What is new and noteworthy? What is the central question of this study? Does the hyperbaric, hypercapnic, acidotic, hypoxic stress of apnoea diving lead to greater pulmonary vasoreactivity and increased right-heart work in apnoea divers? What is the main finding and its importance? Compared to sex- and age-matched controls, Divers had a significantly lower change in total pulmonary resistance in response to short duration isocapnic hypoxia. With oral sildenafil (50 mg), there were no differences in total pulmonary resistance between groups, suggesting Divers can maintain normal pulmonary artery tone in hypoxic conditions. Blunted hypoxic pulmonary vasoconstriction may be beneficial during apnoea diving.

ABSTRACT

Competitive apnoea divers repetitively dive to depths beyond 50 m. During the final portions of ascent, Divers experience significant hypoxaemia. Additionally, hyperbaria during diving increases thoracic blood volume while simultaneously reducing lung volume, increasing pulmonary artery pressure. We hypothesized that Divers would have exaggerated hypoxic pulmonary vasoconstriction leading to increased right-heart work due to their repetitive hypoxaemia and hyperbaria, and that the administration of sildenafil would have a greater effect in reducing pulmonary resistance in Divers. We recruited 16 Divers and 16 age and sex matched non-diving controls (Controls). Using a double-blinded, placebo-controlled, cross-over design, participants were evaluated for normal cardiac and lung function, then their cardiopulmonary responses to 20-30 minutes of isocapnic hypoxia (end-tidal PO₂  = 50 mm Hg) were measured one hour following ingestion of 50 mg sildenafil or placebo. Cardiac structure and cardiopulmonary function were similar at baseline. With placebo, Divers had a significantly smaller increase in total pulmonary resistance than controls after 20-30 minutes isocapnic hypoxia (Δ -3.85 ± 72.85 vs 73.74 ± 91.06 dynes/sec/cm^-5 , p = .0222). With sildenafil, Divers and Controls had similarly blunted increases in total pulmonary resistance after 20-30 minutes of hypoxia. Divers also had a significantly lower systemic vascular resistance following sildenafil in normoxia. These data indicate that repetitive apnoea diving leads to a blunted hypoxic pulmonary vasoconstriction. We suggest this is a beneficial adaption allowing for increased cardiac output with reduced right heart work and thus reducing cardiac oxygen utilization under hypoxemic conditions. This article is protected by copyright. All rights reserved.

Breath-Hold Diving - The Physiology of Diving Deep and Returning

Breath-hold diving involves highly integrative physiology and extreme responses to both exercise and asphyxia during progressive elevations in hydrostatic pressure. With astonishing depth records exceeding 100 m, and up to 214 m on a single breath, the human capacity for deep breath-hold diving continues to refute expectations. The physiological challenges and responses occurring during a deep dive highlight the coordinated interplay of oxygen conservation, exercise economy, and hyperbaric management. In this review, the physiology of deep diving is portrayed as it occurs across the phases of a dive: the first 20 m; passive descent; maximal depth; ascent; last 10 m, and surfacing. The acute risks of diving (i.e., pulmonary barotrauma, nitrogen narcosis, and decompression sickness) and the potential long-term medical consequences to breath-hold diving are summarized, and an emphasis on future areas of research of this unique field of physiological adaptation are provided.

Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Temporal changes in pulmonary gas exchange efficiency when breath-hold diving below residual volume

NEW FINDINGS

What is the central question of this study? How does deep breath-hold diving impact cardiopulmonary function, both acutely and over the subsequent 2.5 hours post-dive? What is the main finding and its importance? Breath-hold diving, to depths below residual volume, is associated with acute impairments in pulmonary gas exchange, which typically resolve within 2.5 hours. These data provide new insight into the behaviour of the lungs and pulmonary vasculature following deep diving.

ABSTRACT

Breath-hold diving involves highly integrative and extreme physiological responses to both exercise and asphyxia during progressive elevations in hydrostatic pressure. Over two diving training camps (Study 1 and 2), 25 breath-hold divers (recreational to world-champion) performed 66 dives to 57 ± 20 m (range: 18-117 m). Using the deepest dive from each diver, temporal changes in cardiopulmonary function were assessed using non-invasive pulmonary gas exchange (indexed via the O₂ deficit), ultrasound B-line scores, lung compliance and pulmonary haemodynamics at baseline and following the dive. Hydrostatically induced lung compression was quantified in Study 2, using spirometry and lung volume measurement, enabling each dive to be categorized by its residual volume (RV)-equivalent depth. From both studies, pulmonary gas exchange inefficiency - defined as an increase in O₂ deficit - was related to the depth of the dive (r²  = 0.345; P < 0.001), with dives associated with lung squeeze symptoms exhibiting the greatest deficits. In Study 1, although B-lines doubled from baseline (P = 0.027), cardiac output and pulmonary artery systolic pressure were unchanged post-dive. In Study 2, dives with lung compression to ≤RV had higher O₂ deficits at 9 min, compared to dives that did not exceed RV (24 ± 25 vs. 5 ± 8 mmHg; P = 0.021). The physiological significance of a small increase in estimated lung compliance post-dive (via decreased and increased/unaltered airway resistance and reactance, respectively) remains equivocal. Following deep dives, the current study highlights an integrated link between hydrostatically induced lung compression and transient impairments in pulmonary gas exchange efficiency.

Changes in Lung Diffusing Capacity of Elite Artistic Swimmers During Training

Artistic swimmers (AS) are exposed to repeated apnoeas in the aquatic environment during high intensity exercise provoking specific physiological responses to training, apnoea, and immersion. This study aimed to evaluate the changes in lung diffusing capacity in AS pre-, mid- and post-training in a combined session of apnoeic swimming, figures and choreography. Eleven elite female AS from the Spanish national team were the study's participants. The single-breath method was used to measure lung diffusing capacity for carbon monoxide (DL_CO) and one-way repeated measures ANOVA was utilized to evaluate the statistical analysis. Basal values of DL_CO were higher than normal for their age and height (33.6±4.9 mL·min^-1·mmHg^-1; 139±19%) and there were a significant interaction between DL_CO and AS training (ŋ² _p=0.547). After the apnoeic swimming (mid-training) there was an increase in DL_CO from basal to 36.7±7.3 mL·min^-1·mmHg^-1 (p=0.021), and after the figures and choreography (post-training) there was a decrease compared to mid-training (32.3±4.6 mL·min^-1·mmHg^-1, p=0.013). Lung diffusing capacity changes occur during AS training, including a large increase after apnoeic swimming. There were no differences in lung diffusing capacity from pre- to post-training, although large inter-individual variability was observed.

Lung Diffusion in a 14-Day Swimming Altitude Training Camp at 1850 Meters

Swimming exercise at sea level causes a transient decrease in lung diffusing capacity for carbon monoxide (DL_CO). The exposure to hypobaric hypoxia can affect lung gas exchange, and hypoxic pulmonary vasoconstriction may elicit pulmonary oedema. The purpose of this study is to evaluate whether there are changes in DL_CO during a 14-day altitude training camp (1850 m) in elite swimmers and the acute effects of a combined training session of swimming in moderate hypoxia and 44-min cycling in acute normobaric severe hypoxia (3000 m). Participants were eight international level swimmers (5 females and 3 males; 17–24 years old; 173.5 ± 5.5 cm; 64.4 ± 5.3 kg) with a training volume of 80 km per week. The single-breath method was used to measure the changes in DL_CO and functional gas exchange parameters. No changes in DL_CO after a 14-day altitude training camp at 1850 m were detected but a decrease in alveolar volume (VA; 7.13 ± 1.61 vs. 6.50 ± 1.59 L; p = 0.005; d = 0.396) and an increase in the transfer coefficient of the lung for carbon monoxide (K_CO; 6.23 ± 1.03 vs. 6.83 ± 1.31 mL·min⁻¹·mmHg⁻¹·L⁻¹; p = 0.038; d = 0.509) after the altitude camp were observed. During the acute hypoxia combined session, there were no changes in DL_CO after swimming training at 1850 m, but there was a decrease in DL_CO after cycling at a simulated altitude of 3000 m (40.6 ± 10.8 vs. 36.8 ± 11.2 mL·min⁻¹·mmHg⁻¹; p = 0.044; d = 0.341). A training camp at moderate altitude did not alter pulmonary diffusing capacity in elite swimmers, although a cycling session at a higher simulated altitude caused a certain degree of impairment of the alveolar–capillary gas exchange.

Physiology of static breath holding in elite apneists

NEW FINDINGS

What is the topic of this review? This review provides an up-to-date assessment of the physiology involved with extreme static dry-land breath holding in trained apneists. What advances does it highlight? We specifically highlight the recent findings involved with the cardiovascular, cerebrovascular and metabolic function during a maximal breath hold in elite apneists.

ABSTRACT

Breath-hold-related activities have been performed for centuries, but only recently, within the last ∼30 years, has it emerged as an increasingly popular competitive sport. In apnoea sport, competition relates to underwater distances or simply maximal breath-hold duration, with the current (oxygen-unsupplemented) static breath-hold record at 11 min 35 s. Remarkably, many ultra-elite apneists are able to suppress respiratory urges to the point where consciousness fundamentally limits a breath-hold duration. Here, arterial oxygen saturations as low as ∼50% have been reported. In such cases, oxygen conservation to maintain cerebral functioning is critical, where responses ascribed to the mammalian dive reflex, e.g. sympathetically mediated peripheral vasoconstriction and vagally mediated bradycardia, are central. In defence of maintaining global cerebral oxygen delivery during prolonged breath holds, the cerebral blood flow may increase by ∼100% from resting values. Interestingly, near the termination of prolonged dry static breath holds, recent studies also indicate that reductions in the cerebral oxidative metabolism can occur, probably attributable to the extreme hypercapnia and irrespective of the hypoxaemia. In this review, we highlight and discuss the recent data on the cardiovascular, metabolic and, particularly, cerebrovascular function in competitive apneists performing maximal static breath holds. The physiological adaptation and maladaptation with regular breath-hold training are also summarized, and future research areas in this unique physiological field are highlighted; particularly, the need to determine the potential long-term health impacts of extreme breath holding.

Effects of Breath-Hold Deep Diving on the Pulmonary System

This short review focuses on pulmonary injury in breath-hold (BH) divers. When practicing their extreme leisure sport, they are exposed to increased pressure on pulmonary gas volumes, hypoxia, and increased partial gas pressures. Increasing ambient pressures do present a serious problem to BH deep divers, because the semi-rigid thorax prevents the deformation required by the Boyle-Mariotte law. As a result, a negative-pressure barotrauma (lung squeeze) with acute hemoptysis is not uncommon. Respiratory maneuvers such as glossopharyngeal insufflation (GI) and glossopharyngeal exsufflation (GE) are practiced to prevent lung squeeze and to permit equalizing the paranasal sinuses and the middle ear. GI not only impairs venous return, thereby provoking hypotension and even fainting, but also produces intrathoracic pressures likely to induce pulmonary barotrauma that is speculated to induce long-term injury. GE, in turn, further increases the already negative intrapulmonary pressure, thereby favoring alveolar collapse (atelectasis). Finally, hypoxia seemingly not only induces brain injury but initiates the opening of intrapulmonary shunts. These pathways are large enough to permit transpulmonary passage of venous N2 bubbles, making stroke-like phenomena in deep BH divers possible.

Environmental Physiology and Diving Medicine

Man's experience and exploration of the underwater environment has been recorded from ancient times and today encompasses large sections of the population for sport enjoyment, recreational and commercial purpose, as well as military strategic goals. Knowledge, respect and maintenance of the underwater world is an essential development for our future and the knowledge acquired over the last few dozen years will change rapidly in the near future with plans to establish secure habitats with specific long-term goals of exploration, maintenance and survival. This summary will illustrate briefly the physiological changes induced by immersion, swimming, breath-hold diving and exploring while using special equipment in the water. Cardiac, circulatory and pulmonary vascular adaptation and the pathophysiology of novel syndromes have been demonstrated, which will allow selection of individual characteristics in order to succeed in various environments. Training and treatment for these new microenvironments will be suggested with description of successful pioneers in this field. This is a summary of the physiology and the present status of pathology and therapy for the field.