Comparison of Newer Hand-Held Ultrasound Devices for Post-Dive Venous gas Emboli Quantification to Standard Echocardiography.

Decompression sickness (DCS) can result from the growth of bubbles in tissues and blood during or after a reduction in ambient pressure, for example in scuba divers, compressed air workers or astronauts. In scuba diving research, post-dive bubbles are detectable in the venous circulation using ultrasound. These venous gas emboli (VGE) are a marker of decompression stress, and larger amounts of VGE are associated with an increased probability of DCS. VGE are often observed for hours post-dive and differences in their evolution over time have been reported between individuals, but also for the same individual, undergoing a same controlled exposure. Thus, there is a need for small, portable devices with long battery lives to obtain more ultrasonic data in the field to better assess this inter- and intra-subject variability. We compared two new handheld ultrasound devices against a standard device that is currently used to monitor post-dive VGE in the field. We conclude that neither device is currently an adequate replacement for research studies where precise VGE grading is necessary.

Evaluation of the Helicopter Emergency Breathing Apparatus on Egress Performance.

BACKGROUND: Emergency helicopter landing at sea is dangerous. Specialized training, known as helicopter underwater escape training (HUET), prepares occupants to quickly exit the helicopter, which often inverts and sinks. In most jurisdictions, helicopter occupants are equipped with a helicopter underwater egress breathing apparatus (HUEBA) to provide sufficient air for escape. HUET trainees report that the HUEBA is easy to use, but it is well known that learners are often overconfident in their judgement of learning. To better understand how the HUEBA affects HUET sequence performance, we investigated whether using the HUEBA influences the sequence movement time and number of errors.METHODS: Twelve participants (7 men and 5 women, mean age 25.33 9.57 SD) with no prior experience with HUET performed consecutive trials of the HUET sequence, 5 with the HUEBA and 5 without the HUEBA. Video of each trial recorded the total movement time and enabled movement time analyses of each component of the sequence: crossing arms, tucking the head, pushing the window, inserting the regulator, and releasing the seatbelt. These recordings were also used to score performance errors according to a checklist.RESULTS: Analyses revealed that using a HUEBA increased the total movement time and time to release the seatbelt by 0.36 and 0.39 s, respectively, in comparison to without the HUEBA.DISCUSSION: Our study illustrates that using the HUEBA during the HUET sequence increases total movement time and time to release the seatbelt. However, this difference is marginal and unlikely to have practical significance during underwater escape.King M, Sanli E, Mugford K, Martina S, Brown R, Carnahan H. Evaluation of the helicopter emergency breathing apparatus on egress performance. Aerosp Med Hum Perform. 2020; 91(12):962965.

Venous Gas Emboli and Ambulation at 4.3 psia.

INTRODUCTION: Ambulation during extravehicular activity on Mars may increase the risk of decompression sickness through enhanced bubble formation in the lower body. HYPOTHESES: walking effort (ambulation) before an exercise-enhanced denitrogenation (prebreathe) protocol at 14.7 psia does not increase the incidence of venous gas emboli (VGE) at 4.3 psia, but does increase incidence if performed after tissues become supersaturated with nitrogen at 4.3 psia. METHODS: VGE results from 45 control subjects who performed exercise prebreathe without ambulation before or during a 4-h exposure to 4.3 psia were compared to 21 subjects who performed the same prebreathe but ambulated before and during the hypobaric exposure (Group I) and to 41 subjects who only ambulated before the hypobaric exposure (Group II). Monitoring for VGE in the pulmonary artery was for 4 min at about 12-min intervals using precordial Doppler ultrasound (2.5 mHz). Detected VGE were assigned a categorical grade from I to IV. The detection of Grade III or IV was classified as "high VGE grade." RESULTS: The incidence of high VGE grade for Group I (57%) was greater than the control (17%) and Group II (15%). The incidence of pain-only decompression sickness was greater for Group I (20%) than the control (0%) and Group II (5%). CONCLUSIONS: High-grade VGE are increased by mild ambulation conducted under a supersaturated state (Group I vs. II); however, no increase was observed with mild ambulation during the saturated state alone (control vs. Group II).Conkin J, Pollock NW, Natoli MJ, Martina SD, Wessell JH III, Gernhardt ML. Venous gas emboli and ambulation at 4.3 psia. Aerosp Med Hum Perform. 2017; 88(4):370-376.

Sildenafil: Possible Prophylaxis against Swimming-induced Pulmonary Edema.

Swimming-induced pulmonary edema (SIPE) occurs during swimming and scuba diving, usually in cold water, in susceptible healthy individuals, especially military recruits and triathletes. We have previously demonstrated that pulmonary artery (PA) pressure and PA wedge pressure are higher during immersed exercise in SIPE-susceptible individuals versus controls, confirming that SIPE is a form of hemodynamic pulmonary edema. Oral sildenafil 50 mg 1 h before immersed exercise reduced PA pressure and PA wedge pressure, suggesting that sildenafil may prevent SIPE. We present a case of a 46-yr-old female ultratriathlete with a history of at least five SIPE episodes. During a study of an exercise submerged in 20°C water, physiological parameters before and after sildenafil 50 mg orally were as follows: O2 consumption 1.75, 1.76 L·min; HR 129, 135 bpm; arterial pressure 189/88 (mean 121.5), 172/85 (mean 114.3) mm Hg; mean PA pressure 35.3, 28.8 mm Hg; and PA wedge pressure 25.3, 19.7 mm Hg. She has had no recurrences during 20 subsequent triathlons while taking 50 mg sildenafil before each swim. This case supports sildenafil as an effective prophylactic agent against SIPE during competitive surface swimming.

Deaths in triathletes: immersion pulmonary oedema as a possible cause.

BACKGROUND/AIM: To address the question as to whether immersion pulmonary oedema (IPO) may be a common cause of death in triathlons, markers of swimming-induced pulmonary oedema (SIPO) susceptibility were sought in triathletes' postmortem examinations. METHODS: Deaths while training for or during triathlon events in the USA and Canada from October 2008 to November 2015 were identified, and postmortem reports requested. We assessed obvious causes of death; the prevalence of left ventricular hypertrophy (LVH); comparison with healthy triathletes. RESULTS: We identified 58 deaths during the time period of the review, 42 (72.4%) of which occurred during a swim. Of these, 23 postmortem reports were obtained. Five individuals had significant (≥70%) coronary artery narrowing; one each had coronary stents; retroperitoneal haemorrhage; or aortic dissection. 9 of 20 (45%) with reported heart mass exceeded 95th centile values. LV free wall and septal thickness were reported in 14 and 9 cases, respectively; of these, 6 (42.9%) and 4 (44.4%) cases exceeded normal values. 6 of 15 individuals (40%) without an obvious cause of death had excessive heart mass. The proportion of individuals with LVH exceeded the prevalence in the general triathlete population. CONCLUSIONS: LVH-a marker of SIPO susceptibility-was present in a greater than the expected proportion of triathletes who died during the swim portion. We propose that IPO may be a significant aetiology of death during the swimming phase in triathletes. The importance of testing for LVH in triathletes as a predictor of adverse outcomes should be explored further.

Swimming-Induced Pulmonary Edema: Pathophysiology and Risk Reduction With Sildenafil.

BACKGROUND: Swimming-induced pulmonary edema (SIPE) occurs during swimming or scuba diving, often in young individuals with no predisposing conditions, and its pathophysiology is poorly understood. This study tested the hypothesis that pulmonary artery and pulmonary artery wedge pressures are higher in SIPE-susceptible individuals during submerged exercise than in the general population and are reduced by sildenafil. METHODS AND RESULTS: Ten study subjects with a history of SIPE (mean age, 41.6 years) and 20 control subjects (mean age, 36.2 years) were instrumented with radial artery and pulmonary artery catheters and performed moderate cycle ergometer exercise for 6 to 7 minutes while submersed in 20°C water. SIPE-susceptible subjects repeated the exercise 150 minutes after oral administration of 50 mg sildenafil. Work rate and mean arterial pressure during exercise were similar in controls and SIPE-susceptible subjects. Average o2 and cardiac output in controls and SIPE-susceptible subjects were: o2 2.42 L·min(-1) versus 1.95 L·min(-1), P=0.2; and cardiac output 17.9 L·min(-1) versus 13.8 L·min(-1), P=0.01. Accounting for differences in cardiac output between groups, mean pulmonary artery pressure at cardiac output=13.8 L·min(-1) was 22.5 mm Hg in controls versus 34.0 mm Hg in SIPE-susceptible subjects (P=0.004), and the corresponding pulmonary artery wedge pressure was 11.0 mm Hg versus 18.8 mm Hg (P=0.028). After sildenafil, there were no statistically significant differences in mean pulmonary artery pressure or pulmonary artery wedge pressure between SIPE-susceptible subjects and controls. CONCLUSIONS: These observations confirm that SIPE is a form of hemodynamic pulmonary edema. The reduction in pulmonary vascular pressures after sildenafil with no adverse effect on exercise hemodynamics suggests that it may be useful in SIPE prevention. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00815646.

Immersion pulmonary edema and comorbidities: case series and updated review.

PURPOSE: Immersion pulmonary edema (IPE) occurs in swimmers (especially triathletes) and scuba divers. Its pathophysiology and risk factors are incompletely understood. This study was designed to establish the prevalence of preexisting comorbidities in individuals who experience IPE. METHODS: From 2008 to May 2010, individuals who had experienced IPE were identified via recruitment for a physiological study. Past medical history and subject characteristics were compared with those available in the current body of literature. RESULTS: At Duke University Medical Center, Durham, NC, 36 subjects were identified (mean age = 50.11 ± 10.8 yr), of whom 72.2% had one or more significant medical conditions at the time of IPE incident (e.g., hypertension, cardiac dysrhythmias or structural abnormality or dysfunction, asthma, diabetes mellitus, overweight or obesity, obstructive sleep apnea, hypothyroidism). Forty-five articles were included, containing 292 cases of IPE, of which 24.0% had identifiable cardiopulmonary risk factors. Within the recreational population, cases with identifiable risk factors comprised 44.9%. Mean age was 47.8 ± 11.3 yr in recreational divers/swimmers and 23.3 ± 6.4 yr in military divers/swimmers. CONCLUSIONS: Cardiopulmonary disease may be a common predisposing factor in IPE in the recreational swimming/diving population, whereas pulmonary hypertension due to extreme exertion may be more important in military cases. Individuals with past history of IPE in our case series had a greater proportion of comorbidities compared to published cases. The role of underlying cardiopulmonary dysfunction may be underestimated, especially in older swimmers and divers. We conclude that an episode of IPE should prompt the evaluation of cardiac and pulmonary function.