Cardiovascular Mechanisms of Extravascular Lung Water Accumulation in Divers

Static Immersion and Negative Static Lung Load-Induced Right Ventricle Systolic Function Adaptation: A Risk Factor for Immersion Pulmonary Edema

BACKGROUND

Immersion pulmonary edema (IPE) is a form of hemodynamic edema likely involving individual susceptibility.

RESEARCH QUESTION

Can assessing right ventricle (RV) systolic adaptation during immersion be a marker for IPE susceptibility?

STUDY DESIGN AND METHODS

Twenty-eight divers participated: 15 study participants with a history of IPE (IPE group; mean ± SD age, 40.2 ± 8.2 years; two women) and 13 control participants (no IPE group; mean ± SD age, 43.1 ± 8.5 years; two women) underwent three transthoracic echocardiography studies under three different conditions: dry (participants were in the supine position on an examination table without immersion), surface immersion (participants were floating prone on the water's surface and breathing through a snorkel), and immersion and negative static lung load (divers were submerged 20 cm below the water's surface in the prone position using a specific snorkel connected to the surface for breathing). Echocardiographic measurements included tricuspid annular plane systolic excursion (TAPSE), tissue S' wave, and right ventricle global strain (RVGLS).

RESULTS

For all divers, immersion increased RV preload. In the no IPE group, the increase in RV preload induced by immersion was accompanied by an improvement in the contractility of the RV, as evidenced by increases in TAPSE (17.08 ± 1.15 mm vs 20.89 ± 1.32 mm), S' wave (14.58 ± 2.91 cm/s vs. 16.26 ± 2.77 cm/s), and RVGLS (25.37 ± 2.79 % vs. 27.09 ± 2.89 %). Negative SLL amplified these RV adaptations. In contrast, among divers with IPE, the increase in RV preload did not coincide with an improvement in RV contractility, indicating altered adaptive responses. In the IPE group, the TAPSE values changed from 17.19 ± 1.28 mm to 21.69 ± 1.67 mm and then to 23.55 ± 0.78 mm, respectively, in the dry, surface immersion, and immersion and negative SLL conditions. The S' wave values changed from 13.42 ± 2.94 cm/s to 13.26 ± 2.96 cm/s and then to 12.49 ± 0.77 cm/s, respectively, and the RVGLS values changed from -24.09% ± 2.91% to -23.99% ± 3.38% and then to -21.96% ± 0.55%, respectively.

INTERPRETATION

Changes in RV systolic function induced by immersion (especially with the addition of negative static lung load) vary among divers based on the history of IPE. Analyzing ventricular contractility during immersion, particularly RVGLS, could help to identify individual susceptibility in divers. These findings provide insights for the development of preventive strategies.

TRIAL REGISTRY

Comité de Protection des Personnes; No.: 21.05.05.35821; Recherche Impliquant la Personne Humaine de type 1 (RIPH1) HPS; No.: 2021-A01225-36.

Cardiovascular considerations on recreational scuba diving. SEC-Clinical Cardiology Association/SEC-Working Group on Sports Cardiology consensus document

The practice of recreational scuba diving has increased worldwide, with millions of people taking part each year. The aquatic environment is a hostile setting that requires human physiology to adapt by undergoing a series of changes that stress the body. Therefore, physical fitness and control of cardiovascular risk factors are essential for practicing this sport. Medical assessment is not mandatory before participating in this sport and is only required when recommended by a health questionnaire designed for this purpose. However, due to the significance of cardiovascular disease, cardiology consultations are becoming more frequent. The aim of the present consensus document is to describe the cardiovascular physiological changes that occur during diving, focusing on related cardiovascular diseases, their management, and follow-up recommendations. The assessment and follow-up of individuals who practice diving with previous cardiovascular disease are also discussed. This document, endorsed by the Clinical Cardiology Association of the Spanish Society of Cardiology (SEC) and the SEC Working Group on Sports Cardiology of the Association of Preventive Cardiology, aims to assist both cardiologists in evaluating patients, as well as other specialists responsible for assessing individuals' fitness for diving practice.

The effect of a single closed-circuit rebreather decompression dive in extremely cold water to cardiac function

PURPOSE

Dive-induced cardiac and hemodynamic changes are caused by various mechanisms, and they are aggravated by cold water. Therefore, aging divers with pre-existing cardiovascular conditions may be at risk of acute myocardial infarction, heart failure, or arrhythmias while diving. The aim of this study was to assess the effect of a single decompression CCR dive in arctic cold water on cardiac function in Finnish technical divers.

METHODS

Thirty-nine divers performed one identical 45 mfw CCR dive in 2-4 °C water. Hydration and cardiac functions were assessed before and after the dive. Detection of venous gas embolization was performed within 120 min after the dive.

RESULTS

The divers were affected by both cold-water-induced hemodynamic changes and immersion-related fluid loss. Both systolic and diastolic functions were impaired after the dive although the changes in cardiac functions were subtle. Venous inert gas bubbles were detected in all divers except for one. Venous gas embolism did not affect systolic or diastolic function.

CONCLUSION

A single trimix CCR dive in arctic cold water seemed to debilitate both systolic and diastolic function. Although the changes were subtle, they appeared parallel over several parameters. This indicates a real post-dive deterioration in cardiac function instead of only volume-dependent changes. These changes are without a clinical significance in healthy divers. However, in a population with pre-existing or underlying heart problems, such changes may provoke symptomatic problems during or after the dive.

Characterizing Immersion Pulmonary Edema (IPE): A Comparative Study of Military and Recreational Divers

BACKGROUND

Immersion Pulmonary Edema (IPE) is a common and potentially serious diving accident that can have significant respiratory and cardiac consequences and, in some cases, be fatal. Our objective was to characterize cases of IPE among military trainees and recreational divers and to associate their occurrence with exposure and individual background factors such as age and comorbidity. We conducted a retrospective analysis on the medical records and diving parameters of all patients who were treated for IPE at the Hyperbaric Medicine Department of Sainte-Anne Military Hospital in Toulon, France, between January 2017 and August 2019. In total, 57 subjects were included in this study, with ages ranging from 20 to 62 years. These subjects were divided into two distinct groups based on exposure categories: (1) underwater/surface military training and (2) recreational scuba diving. The first group consisted of 14 individuals (25%) with a mean age of 26.5 ± 2.6 years; while, the second group comprised 43 individuals (75%) with a mean age of 51.2 ± 7.5 years. All divers under the age of 40 were military divers.

RESULTS

In 40% of cases, IPE occurred following intense physical exercise. However, this association was observed in only 26% of recreational divers, compared to 86% of military divers. Among civilian recreational divers, no cases of IPE were observed in subjects under the age of 40. The intensity of symptoms was similar between the two groups, but the duration of hospitalization was significantly longer for the recreational subjects.

CONCLUSION

It seems that the occurrence of IPE in young and healthy individuals requires their engagement in vigorous physical activity. Additionally, exposure to significant ventilatory constraints is a contributing factor, with the intensity of these conditions seemingly exclusive to military diving environments. In contrast, among civilian recreational divers, IPE tends to occur in subjects with an average age twice that of military divers. Moreover, these individuals exhibit more prominent comorbidity factors, and the average level of environmental stressors is comparatively lower.

Pulmonary Physiology and Medicine of Diving

Pulmonary physiology is significantly altered during underwater exposure, as immersion of the body and increased ambient pressure elicit profound effects on both the cardiovascular and respiratory systems. Thoracic blood pooling, increased breathing gas pressures, and variations in gas volumes alongside ambient pressure changes put the heart and lungs under stress. Normal physiologic function and fitness of the cardiovascular and respiratory systems are prerequisites to safely cope with the challenges of the underwater environment when freediving, or diving with underwater breathing apparatus. Few physicians are trained to understand the physiology and medicine of diving and how to recognize or manage diving injuries. This article provides an overview of the physiologic challenges to the respiratory system during diving, with or without breathing apparatus, and outlines possible health risks and hazards unique to the underwater environment. The underlying pathologic mechanisms of dive-related injuries are reviewed, with an emphasis on pulmonary physiology and pathophysiology.

Individual Changes in Respiratory Compliance Upon Immersion May Predict Susceptibility to Immersion Pulmonary Edema

BACKGROUND

Immersion pulmonary edema (IPE) is a frequent diving accident, and it is the primary cause of hospitalization for young military divers during training. The objective of this study was to identify immersion-induced parameters predicting individual susceptibility to IPE.

METHODS

Eighteen experienced male divers having completed at least 100 dives were recruited. Eight divers had previously been hospitalized for IPE (IPE), and the other ten had never developed IPE (non-IPE). The two groups were matched for age, BMI, and number of dives performed. Ventilatory function and overall compliance of the respiratory system (Crs) were measured on land and during head-out-of-water immersion. Subjects also performed 30 min of fin swimming in a channel at 33 m min^-1. Following this exercise, the presence of extravascular lung water, revealed by ultrasound lung comets (ULC), was assessed.

RESULTS

In the whole group, the decrease in Crs upon immersion correlated with the immersion-induced alterations to expiratory reserve volume, ERV (r² = 0.91; p < 0.001), inspiratory reserve volume, IRV (r² = 0.94; p < 0.001), and tidal volume, Vt, changes (r² = 0.43; p < 0.003). The number of ULC correlated strongly with immersion-induced changes in ventilatory function (r² = 0.818; p < 0.001 for ERV, r² = 0.849; p < 0.001 for IRV, r² = 0.304; p = 0.0164 for Vt) and reduced Crs (r² = 0.19; p < 0.001). The variations of ERV, IRV, and Crs at rest induced by head-out-of-water immersion and the number of ULC measured after swimming for 30 min were significantly greater in IPE subjects.

CONCLUSION

In the face of similar immersion stresses, the extent of alterations to ventilatory function and the number of ULCs were very different between individuals but remained statistically correlated. These parameters were significantly greater in divers with a history of IPE. Alterations to pulmonary function and, in particular, to pulmonary compliance induced by head-out-of-water immersion, through their effects on work of breathing appear to allow the identification of divers with a greater susceptibility to developing IPE. Measurement of these parameters could therefore be proposed as a predictive test for the risk of developing IPE.

Oxygen uptake ( V ˙ O2) and pulmonary ventilation ( V ˙ E) during military surface fin swimming in a swimming flume: Effects of surface immersion

Introduction: During military fin swimming, we suspected that oxygen uptake (V ˙ O2) and pulmonary ventilation (V ˙ E) might be much higher than expected. In this framework, we compared these variables in the responses of trained military divers during land cycling and snorkeling exercises. Methods: Eighteen male military divers (32.3 ± 4.2 years; 178.0 ± 5.0 cm; 76.4 ± 3.4 kg; 24.1 ± 2.1 kg m-2) participated in this study. They performed two test exercises on two separate days: a maximal incremental cycle test (land condition), and an incremental fin swimming (fin condition) in a motorized swimming flume. Results: The respective fin and landV ˙ O2max were 3,701 ± 39 mL min-1 and 4,029 ± 63 mL min-1 (p = 0.07), these values were strongly correlated (r 2 = 0.78 p < 0.01). Differences inV ˙ O2max between conditions increased relative to l;V ˙ O2max (r 2 = 0.4 p = 0.01). FinV ˙ E max values were significantly lower than landV ˙ E max values (p = 0.01). This result was related to both the significantly lower fin Vt and f (p < 0.01 and <0.04, respectively). Consequently, the finV ˙ E max /V ˙ O2max ratios were significantly lower than the corresponding ratios for land values (p < 0.01), and the fin and landV ˙ E max were not correlated. Other parameters measured at exhaustion-PaO2, PaCO2, and SO2 - were similar in fin and land conditions. Furthermore, no significant differences between land and fin conditions were observed for peak values for heart rate, blood lactate concentration, and respiratory exchange ratio R. Conclusion: Surface immersion did not significantly reduce theV ˙ O2max in trained divers relative to land conditions. As long asV ˙ O2 remained belowV ˙ O2max , theV ˙ E values were identical in the two conditions. Only atV ˙ O2max wasV ˙ E higher on land. Although reduced by immersion,V ˙ E max provided adequate pulmonary gas exchange during maximal fin swimming.

Thermal response of human body with immersion suit in cold environment

Hypothermia caused by cold water immersion is one of the main causes of death in marine accidents. Immersion suit is a kind of protective clothing when implementing flying tasks over the sea in cold seasons, with the main function to slow down the loss of human heat in water and prolong the survival time. In this study, the thermal properties and wearing types of immersion suit and underwear were analyzed. The subjects with internal- and external-wear immersion suit exposed to the experimental environments for 2 h in five working conditions. The core temperature, weighted average skin temperature, and average body temperature were measured and calculated. Both internal- and external-wear immersion suits could fulfil the cold protection requirements under the experimental conditions. The results of clothing parameter tests and physiological experiments both exhibit that the external-wear immersion suit has better thermal insulation effect. And the tolerance time in low-temperature water was predicted, which is crucial for effective and efficient rescue during shipwreck in adverse thermal scenarios. In future research, a comprehensive evaluation and analysis of the thermal insulation performance of immersion suit could be completed in combination with the water ingress of the clothing, the subjects' thermal comfort, and flexibility of the clothing.

Pulmonary Effects of One Week of Repeated Recreational Closed-Circuit Rebreather Dives in Cold Water

Background and Objectives: The use of closed-circuit rebreathers (CCRs) in recreational diving is gaining interest. However, data regarding its physiological effects are still scarce. Immersion, cold water, hyperoxia, exercise or the equipment itself could challenge the cardiopulmonary system. The purpose of this study was to examine the impact of CCR diving on lung function and autonomous cardiac activity after a series of CCR dives in cold water. Materials and Methods: Eight CCR divers performed a diving trip (one week) in the Baltic Sea. Spirometry parameters, SpO₂, and the lung ultrasonography score (LUS) associated with hydration monitoring by bioelectrical impedance were assessed at the end of the week. Heart rate variability (HRV) was recorded during the dives. Results: No diver declared pulmonary symptoms. The LUS increased after dives combined with a slight non-pathological decrease in SpO₂. Spirometry was not altered, and all body water compartments were increased. Global HRV decreased during diving with a predominant increase in sympathetic tone while the parasympathetic tone decreased. All parameters returned to baseline 24 h after the last dive. Conclusions: The lung aeration disorders observed seem to be transient and not associated with functional spirometry alteration. The HRV dynamics highlighted physiological constraints during the dive as well as environmental-stress-related stimulation that may influence pulmonary changes. The impact of these impairments is unknown but should be taken into account, especially when considering long and repetitive CCR dives.

Swimming-Induced Pulmonary Edema: Evaluation of Prehospital Treatment With CPAP or Positive Expiratory Pressure Device

BACKGROUND

Swimming-induced pulmonary edema (SIPE) occasionally occurs during swimming in cold open water. Although optimal treatment for SIPE is unknown, non-invasive positive pressure ventilation (NPPV) is an option for prehospital treatment.

RESEARCH QUESTION

Is NPPV a feasible and safe prehospital treatment for SIPE, and which outcome measures reflect recovery after treatment?

STUDY DESIGN AND METHODS

A prospective observational study was conducted at Vansbrosimningen, Sweden's largest open water swimming event, from 2017 through 2019. Swimmers with a diagnosis of SIPE and with peripheral oxygen saturation (Spo2) of ≤ 95%, persistent respiratory symptoms, or both were eligible for the study. NPPV was administered on site as CPAP by facial mask or as positive expiratory pressure (PEP) by a PEP device. Discharge criteria were Spo2 of > 95% and clinical recovery. Four outcome measures were evaluated: Spo2, crackles on pulmonary auscultation, pulmonary edema on lung ultrasound (LUS), and patient-reported respiratory symptoms.

RESULTS

Of 119 treated individuals, 94 received CPAP, 24 received treatment with a PEP device, and one required tracheal intubation. In total, 108 individuals (91%) were discharged after NPPV for a median of 10 to 20 min and 11 individuals (9%) required hospital transfer. NPPV resulted in increased Spo2 from a median of 91% to 97% (P < .0001) together with improvement of six patient-reported respiratory symptoms (median numerical rating scales, 1-7 to 0-1; P < .0001). No significant decrease in auscultation of crackles (93% vs 87%; P = .508) or pulmonary edema on LUS (100% vs 97%; P = .500) was seen during NPPV treatment.

INTERPRETATION

NPPV administered as CPAP or via a PEP device proved feasible and safe as prehospital treatment for SIPE with a vast majority of patients discharged on site. Spo2 and patient-reported respiratory symptoms reflected recovery after treatment, whereas pulmonary auscultation or LUS findings did not.

Fatal diving: could it be an immersion pulmonary edema? Case report

Immersion pulmonary edema is a rare, underrecognized, and potentially lethal pathology developing during scuba diving and other immersion-related activities (swimming or apnoea). Physiopathology is complex and not fully understood, but its mechanisms involve an alteration of the alveolo-capillary barrier caused by transcapillary pressure elevation during immersion, leading to an accumulation of fluid and blood in the alveolar space. Diagnosis remains a challenge for clinicians and forensic practionner. The symptoms begin during ascent, with cough, frothy sputum, and hemoptysis. Auscultation reveals signs of pulmonary edema. Pulmonary CT scan, which is the radiological exam of choice, shows ground glass opacities and interlobular thickening, eventually demonstrating a patterned distribution, likely in the anterior segments of both lungs. Apart from the support of vital functions, there is no specific treatment and hyperbaric oxygen therapy is not systematically recommended. We present a case of fatal IPE occurring in a recreational diver who unfortunately died shortly after his last dive. Diagnosis was made after complete forensic investigations including post-mortem-computed tomography, complete forensic autopsy, histological examination, and toxicological analysis.

Physiological effects of mixed-gas deep sea dives using a closed-circuit rebreather: a field pilot study

PURPOSE

Deep diving using mixed gas with closed-circuit rebreathers (CCRs) is increasingly common. However, data regarding the effects of these dives are still scarce. This preliminary field study aimed at evaluating the acute effects of deep (90-120 msw) mixed-gas CCR bounce dives on lung function in relation with other physiological parameters.

METHODS

Seven divers performed a total of sixteen open-sea CCR dives breathing gas mixture of helium, nitrogen and oxygen (trimix) within four days at 2 depths (90 and 120 msw). Spirometric parameters, SpO₂, body mass, hematocrit, short term heart rate variability (HRV) and critical flicker fusion frequency (CFFF) were measured at rest 60 min before the dive and 120 min after surfacing.

RESULTS

The median [1st-3rd quartile] of the forced vital capacity was lower (84% [76-93] vs 91% [74-107] of predicted values; p = 0.029), whereas FEV1/FVC was higher (98% [95-99] vs 95% [89-99]; p = 0.019) after than before the dives. The other spirometry values and SpO₂ were unchanged. Body mass decreased from 73.5 kg (72.0-89.6) before the dives to 70.0 kg (69.2-85.8) after surfacing (p = 0.001), with no change of hematocrit or CFFT. HRV was increased as indicated by the higher SDNN, RMSSD and pNN50 after than before dives.

CONCLUSION

The present observation represents the first original data regarding the effects of deep repeated CCR dives. The body mass loss and decrease of FVC after bounce dives at depth of about 100 msw may possibly impose an important physiological stress for the divers.

Broad individual immersion-scattering of respiratory compliance likely substantiates dissimilar breathing mechanics

Head-out water immersion alters respiratory compliance which underpins defining pressure at a “Lung centroid” and the breathing “Static Lung Load”. In diving medicine as in designing dive-breathing devices a single value of lung centroid pressure is presumed as everyone’s standard. On the contrary, we considered that immersed respiratory compliance is disparate among a homogenous adult group (young, healthy, sporty). We wanted to substantiate this ample scattering for two reasons: (i) it may question the European standard used in designing dive-breathing devices; (ii) it may contribute to understand the diverse individual figures of immersed work of breathing. Resting spirometric measurements of lung volumes and the pressure–volume curve of the respiratory system were assessed for 18 subjects in two body positions (upright Up, and supine Sup). Measurements were taken in air (Air) and with subjects immersed up to the sternal notch (Imm). Compliance of the respiratory system (Crs) was calculated from pressure–volume curves for each condition. A median 60.45% reduction in Crs was recorded between Up-Air and Up-Imm (1.68 vs 0.66 L/kPa), with individual reductions ranging from 16.8 to 82.7%. We hypothesize that the previously disregarded scattering of immersion-reduced respiratory compliance might participate to substantial differences in immersed work of breathing.

Epidemiological, clinical, and echocardiographic features of twenty 'Takotsubo-like' reversible myocardial dysfunction cases with normal coronarography following immersion pulmonary oedema

BACKGROUND

Pulmonary immersion oedema is a frequent diving accident. Although its outcome is generally favourable within 72 h, it can nonetheless lead to heart failure or sudden death. Cases of transient myocardial dysfunction have been reported in the literature. This phenomenon is similar to Takotsubo syndrome in many ways. It is characterised by transient myocardial hypokinesia, without associated coronary lesions.

METHODS

We report on 20 cases of patients who showed transient alteration of left ventricular kinetics with normal coronary angiography over the course of an immersion pulmonary oedema.

RESULTS

The echocardiographic localisation of the myocardial damage was generally focal and not centred on the apex with an average left ventricular ejection fraction of 45%. The main anomalies in the electrocardiographic repolarisation were T wave inversion with corrected QT interval prolongation. We also observed a moderate increase in troponin levels, with discordance between the enzymatic peak and the severity of the left ventricle segmental dysfunction.

CONCLUSION

These cases suggest the incidence of a clinical entity strongly reminiscent of Takotsubo phenomenon of atypical topography as a consequence of diving accidents.

Diving Accident Evacuations by Helicopter and Immersion Pulmonary Edema

BACKGROUND: Scuba diving activities expose divers to serious accidents, which can require early hospitalization. Helicopters are used for early evacuation. On the French Mediterranean coast, rescue is made offshore mainly by a French Navy Dauphin or at a landing zone by an emergency unit EC 135 helicopter.METHODS: We retrospectively analyzed diving accidents evacuated by helicopter on the French Mediterranean coast from 1 September 2014 to 31 August 2016. We gathered data at the Center for Hyperbaric Medicine and Diving Expertise (SMHEP) of the Sainte-Anne Military Hospital (Toulon, France), the 35 F squadron at Hyres (France) Naval Air Station, and the SAMU 83 emergency unit (Toulon, France).RESULTS: A total of 23 diving accidents were evacuated offshore by Dauphin helicopter and 23 at a landing zone on the coast by EC 135 helicopter without hoist. Immersion pulmonary edema (IPE) accounted for one-third of the total diving accidents evacuated by helicopter with identified causes. It was responsible for at least half of the deaths at the dive place. A quarter of the rescued IPE victims died because of early cardiac arrest.DISCUSSION: Helicopter evacuation is indicated when vital prognosis (IPE and pulmonary overpressure in particular) or neurological functional prognosis (decompression sickness) is of concern. IPE is the primary etiology in patients with serious dive injuries that are life-threatening and who will benefit from helicopter evacuation. A non-invasive ventilation device with inspiratory support and positive expiratory pressure must be used, in particular for IPE.Corgie L, Huiban N, Pontier J-M, Brocq F-X, Boulard J-F, Monteil M. Diving accident evacuations by helicopter and immersion pulmonary edema. Aerosp Med Hum Perform. 2020; 91(10):806811.

Is a 12-h Nitrox dive hazardous for pulmonary function?

PURPOSE

Prolonged exposure to a high partial pressure of oxygen leads to inflammation of pulmonary tissue [pulmonary oxygen toxicity (POT)], which is associated with tracheobronchial irritation, retrosternal pain and coughing, and decreases in vital capacity (V_C). The nitric oxide (NO) concentration in exhaled gas (FeNO) has been used as an indicator of POT, but the effect of SCUBA diving on FeNO has rarely been studied. The study presented here aimed to assess alterations to pulmonary function and FeNO following a 12-h dive using breathing apparatus with a relatively high partial pressure of oxygen.

METHODS

Six healthy, male, non-smoking military SCUBA divers were recruited (age 31.8 ± 2.7 years, height 179 ± 0.09 cm, and body weight 84.6 ± 14 kg). Each diver completed a 12-h dive using a demand-controlled semi-closed-circuit rebreather. During the 12 h of immersion, divers were subjected to 672 oxygen toxicity units (OTU). A complete pulmonary function test (PFT) was completed the day before and immediately after immersion. FeNO was measured using a Nobreath™ Quark (COSMED™, Rome, Italy), three times for each diver. The first datapoint was collected before the dive to establish the "basal state", a second was collected immediately after divers emerged from the water, and the final measurement was taken 24 h after the dive.

RESULT

Despite prolonged inhalation of a hyperoxic hyperbaric gas mixture, no clinical pulmonary symptoms were observed, and no major changes in pulmonary function were detected. However, a major decrease in FeNO values was observed immediately after emersion [0-12 ppb (median, 3.8 ppb)], with a return to baseline [2-60 ppb (median, 26 ppb) 24 h later (3-73 ppb (median, 24.7 ppb)].

CONCLUSION

These results suggest that if the OTU remain below the recommended limit values, but does alter FeNO, this type of dive does not persistently impair lung function.

A literature review of immersion pulmonary edema

IMPORTANCE

Immersion pulmonary edema (IPE) is a rare but important complication associated with surface swimming and underwater diving. It tends to reoccur and can be fatal. It is not very well-known to clinicians involved in the care of individuals participating in aquatic activities. We performed a systematic review of immersion pulmonary edema to describe the condition and provide guidelines for its management.

EVIDENCE REVIEW

We searched PubMed to identify case reports and studies using the MeSH terms "immersion," "pulmonary edema," "cold-induced," "exercise," "hemodynamics," "water immersion,'' "cardiovascular response," alone and in combinations. We identified 121 relevant articles including 54 case reports. We reviewed in detail 24 studies and all 54 case reports.

FINDINGS

The incidence of IPE is estimated to be around 1.1- 1.8%. The risk factors for IPE include age >50 years, female sex, overhydration before exercise, tight wetsuits, cold water exposure and physically trained individuals such as endurance athletes. Individuals with pre-existing heart disease are at increased risk, however, IPE is seen even in healthy individuals. Symptoms such as cough, sputum production, hemoptysis and shortness of breath can occur immediately after immersion. Combination of water immersion, cold exposure, and exercise lead to an increase in pulmonary capillary pressures and eventual pulmonary capillary stress failure that leads to the flooding of alveolar spaces and edema. Conclusion and relevance: Clinicians should be aware of IPE to avoid overestimating the severity of coronary or valvular conditions sometimes coincidentally present in IPE victims. Management is usually supportive. Functional and clinical recovery usually happens spontaneously within 24 h to 2 days, with or without diuretic therapy and a beta-adrenergic agonist. IPE can be recurrent and fatal, hence subjects with a history of IPE should undergo extensive cardiopulmonary investigation and should avoid cold water and physically demanding swimming events or avoid immersion activities.

The end of the unique myocardial band: Part II. Clinical and functional considerations

Two of the leading concepts of mural ventricular architecture are the unique myocardial band and the myocardial mesh model. We have described, in an accompanying article published in this journal, how the anatomical, histological and high-resolution computed tomographic studies strongly favour the latter concept. We now extend the argument to describe the linkage between mural architecture and ventricular function in both health and disease. We show that clinical imaging by echocardiography and magnetic resonance imaging, and electrophysiological studies, all support the myocardial mesh model. We also provide evidence that the unique myocardial band model is not compatible with much of scientific research.

Immersion pulmonary oedema in a healthy diver not exposed to cold or strenuous exercise

In healthy divers, the occurrence of immersion pulmonary oedema (IPE) is commonly caused by contributory factors including strenuous exercise, cold water and negative-pressure breathing. Contrary to this established paradigm, this case reports on a 26-year-old, well-trained combat swimmer who succumbed to acute IPE during static immersion in temperate (21°C) water, while using a front-mounted counterlung rebreather. The incident occurred during repeated depth-controlled ascent practice at the French military diving school. It was discovered that the diver had attempted to stop any gas leakage into the system by over-tightening the automatic diluent valve (ADV) (25th notch of 27) during the dive, thus causing a high resistance to inspiratory flow. The ventilatory constraints imposed by this ADV setting were assessed as a 3.2 Joules·L⁻¹ inspiratory work of breathing and -5 kPa (-50 mbar) transpulmonary pressure. This report confirms the key role of negative pressure breathing in the development of interstitial pulmonary oedema. Such a breathing pattern can cause a lowering of thoracic, airway and interstitial lung pressure, leading to high capillary pressure during each inspiration. Repetition of the diving drills resulted in an accumulation of interstitial lung water extravasation, causing pathological decompensation and proven symptoms.

The Key Roles of Negative Pressure Breathing and Exercise in the Development of Interstitial Pulmonary Edema in Professional Male SCUBA Divers

Background

Immersion pulmonary edema is potentially a catastrophic condition; however, the pathophysiological mechanisms are ill-defined. This study assessed the individual and combined effects of exertion and negative pressure breathing on the cardiovascular system during the development of pulmonary edema in SCUBA divers.

Methods

Sixteen male professional SCUBA divers performed four SCUBA dives in a freshwater pool at 1 m depth while breathing air at either a positive or negative pressure both at rest or with exercise. Echocardiography and lung ultrasound were used to assess the cardiovascular changes and lung comet score (a measure of interstitial pulmonary edema).

Results

The ultrasound lung comet score was 0 following both the dives at rest regardless of breathing pressure. Following exercise, the mean comet score rose to 4.2 with positive pressure breathing and increased to 15.1 with negative pressure breathing. The development of interstitial pulmonary edema was significantly related to inferior vena cava diameter, right atrial area, tricuspid annular plane systolic excursion, right ventricular fractional area change, and pulmonary artery pressure. Exercise combined with negative pressure breathing induced the greatest changes in these cardiovascular indices and lung comet score.

Conclusions

A diver using negative pressure breathing while exercising is at greatest risk of developing interstitial pulmonary edema. The development of immersion pulmonary edema is closely related to hemodynamic changes in the right but not the left ventricle. Our findings have important implications for divers and understanding the mechanisms of pulmonary edema in other clinical settings.

[Diving Accidents in Lakes - a Retrospective Study of a Level-1 Emergency Centre in Switzerland]

Diving Accidents in Lakes - a Retrospective Study of a Level-1 Emergency Centre in Switzerland Abstract. Switzerland is a country in the middle of Europe without access to an open sea. Here one does not assume a noteworthy number of diving accidents. However, this study shows a large number and attempts to explore the main risks of diving accidents. The data from 2001 to 2016 of patients had been collected und retrospectively evaluated using the electronic database of the emergency center of the university hospital in Bern, Switzerland. Barotrauma of the ear (69.0 %), decompression accidents (20.7 %) as well as cardiovascular complications (13.8 %) appeared quite frequently during scuba diving in Switzerland. In contrast, otitis occurred only at a very low percentage (3.5 %). The risk of diving accidents is clearly underestimated. Preventative measures should include more emphasis on the vertical diving profile with increasing diving depths and on the hazards of cardiovascular diseases with increasing age.

Observational study of potential risk factors of immersion pulmonary edema in healthy divers: exercise intensity is the main contributor

BACKGROUND

The risk factors of pulmonary edema induced by diving in healthy subjects are not well known. The aim of the present study was to assess the parameters contributing to the increase in extravascular lung water after diving.

METHODS

This study was carried out in a professional diving institute. All divers participating in the teaching program from June 2012 to June 2014 were included in the study. Extravascular lung water was assessed using the detection of ultrasound lung comets (ULC) by chest ultrasonography. Clinical parameters and dive profiles were recorded using a questionnaire and a dive computer.

RESULTS

One-hundred six divers were investigated after 263 dives. They used an open-circuit umbilical supplying compressed gas diving apparatus in 202 cases and a self-contained underwater breathing apparatus in 61 cases. A generalized linear mixed model analysis was performed which demonstrated that the dive induced a significant increase in ULC score (incidence rate ratio: 3.16). It also identified that the predictive variable of increased extravascular lung water after the dive was the exercise intensity at depth (z = 3.99, p < 0.0001). The other parameters studied such as the water temperature, dive profile, hyperoxic exposure, or anthropometric data were not associated with the increase in extravascular lung water after the dive.

CONCLUSIONS

In this study, the exercise intensity was the main contributor to the increase in extravascular lung water in healthy divers. To improve the prevention of immersion pulmonary edema, the exercise intensity experienced during the dive should thus be adapted to the aerobic fitness level of the divers.