Exercise after SCUBA diving increases the incidence of arterial gas embolism

Address for reprint requests and other correspondence: M. Ljubkovic, Dept. of Physiology, Univ. of Split School of Medicine, Soltanska 2, 21 000 Split, Croatia (e-mail: [email protected] ).

Abstract

Arterialization of gas bubbles after decompression from scuba diving has traditionally been associated with pulmonary barotraumas or cardiac defects, such as the patent foramen ovale. Recent studies have demonstrated the right-to-left passage of bubbles through intrapulmonary arterial-venous anastamoses (IPAVA) that allow blood to bypass the pulmonary microcirculation. These passages open up during exercise, and the aim of this study is to see if exercise in a postdiving period increases the incidence of arterialization. After completing a dive to 18 m for 47 min, patent foramen ovale-negative subjects were monitored via transthoracic echocardiography, within 10 min after surfacing, for bubble score at rest. Subjects then completed an incremental cycle ergometry test to exhaustion under continuous transthoracic echocardiography observation. Exercise was suspended if arterialization was observed and resumed when the arterialization cleared. If arterialization was observed a second time, exercise was terminated, and oxygen was administered. Out of 23 subjects, 3 arterialized at rest, 12 arterialized with exercise, and 8 did not arterialize at all even during maximal exercise. The time for arterialization to clear with oxygen was significantly shorter than without. Exercise after diving increased the incidence of arterialization from 13% at rest to 52%. This study shows that individuals are capable of arterializing through IPAVA, and that the intensity at which these open varies by individual. Basic activities associated with SCUBA diving, such as surface swimming or walking with heavy equipment, may be enough to allow the passage of venous gas emboli through IPAVA.

venous gas emboli (vge) are a common occurrence during decompression from SCUBA diving and are normally trapped and eliminated by the pulmonary microcirculation. Arterialization of these emboli is usually associated with septal wall defects in the heart, such as a patent foramen ovale (PFO) (26), that allow the emboli to cross over from the right to the left side of the circulation. Arterialization may also occur in individuals who do not possess PFO, when the quantity of VGE overwhelms the ability of the pulmonary circuit to trap and eliminate these bubbles (4). Investigations of arterialization at rest show incidents rates to range from 13 to 26% (11, 16, 18). Recent studies have used contrast bubbles to investigate intrapulmonary arterial-venous anastamoses (IPAVA) that allow blood to bypass the pulmonary microcirculation (24). These vascular pathways allow the passage of contrast bubbles from the venous to arterial circulation in laboratory conditions during exercise (9, 13), and we hypothesize that these vascular pathways provide the path for arterialization of VGE in divers in the field.

Although the exact physiological role of IPAVA is not yet clear, recent studies have found that they open during physical activity and may serve to help regulate pulmonary arterial pressure (20, 24). The intensity of O2 uptake (V̇ o 2) consumption at which this occurs is variable, ranging from rest to maximal effort, with few subjects not showing any evidence of opening at all (9). IPAVA are larger in diameter than the surrounding pulmonary microcirculation and may allow the easier passage of bubbles that would normally be trapped and eliminated. Stickland et al. (24) and Eldridge et al. (9) were the first to use injected contrast bubbles during exercise in PFO negative subjects to demonstrate this passage. Further studies have shown that the use of supplemental oxygen during exercise can prevent the opening of these shunts (21). Supplemental oxygen is currently a recommended first aid treatment for divers experiencing symptoms of decompression sickness (DCS) (19). Any additional information on the relationship between arterialization, IPAVA, and oxygen supplementation may provide guidelines and protocol for prophylactic use of oxygen in certain scenarios.

Multiple diving studies have produced the arterialization of emboli without any reported incidence of DCS or other related acute symptoms. However, PFO and arterializations still remain linked to neurological symptoms of DCS (10, 23, 27, 28) and chronic cerebral microvascular damage (15). These relationships warrant the continued investigation of the physiological conditions that lead to arterialization.

Therefore, the purpose of this study is to explore the impact of exercise in a postdive period on potential VGE arterialization. Furthermore, the effect of oxygen administration in the subject exhibiting the VGE passage to systemic circulation was also investigated.

METHODS

This study received approval from the University of Split Medical School Ethics Committee, and each subject gave written, informed consent before participation. All studies were performed in accordance with the Declaration of Helsinki.

Subjects.

Twenty-three subjects (20 men and 3 women), age range of 23–65 yr, participated in the study. Diving experience of the subjects ranged from 2 to 41 yr (mean 19.25 ± 12.23 yr). Subjects selected have either been tested negative for PFO within the past 3 yr or were screened before participation in the study. PFO screening was conducted by an anesthesiologist using preestablished procedures (18). Twenty-five subjects volunteered for the study, 2 were excluded due to a positive PFO test, and 23 subjects completed the protocol. Pulmonary function, cycle ergometry, and anthropometric data are presented in Table 1. All subjects were apparently healthy and were cleared to dive at the time of the study, and there were no reports of illness during the duration of protocol.

Table 1. Anthropometric data for male and female divers

Values are means ± SD; n, no. of subjects. FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s; MVV, maximal voluntary ventilation; V̇ o 2max, maximum O2 uptake, determined through graded maximal cycle ergometry test. Power (in Watts) is of last completed stage of cycle ergometer test.

Pulmonary function and maximum V̇ o 2 testing.

Maximum V̇ o 2 (V̇ o 2max) and pulmonary function testing was performed by all divers at least 3 days before the diving experiment. Before testing, height, weight, and percent body fat for each subject were determined. Percent body fat was estimated by measurement of subcutaneous skin fold thickness with a caliper (Harpenden skinfold caliper, Baty International, West Sussex, UK) at the three sites, as dictated by the Jackson Pollock equations for male and female subjects. Pulmonary function assessment included forced vital capacity and maximal voluntary ventilation tests. The V̇ o 2max test was an incremental test conducted on a cycle ergometer (Marquette Hellige Medical Systems 900 ERG, Milwaukee, WI), beginning at 50 (for female subjects) or 80 W (male subjects) and increasing 15 W every minute until voluntary termination or until at least two of the three following requirements were met: 1) a plateau of V̇ o 2 (2) respiratory exchange ratio > 1.1; and 3) heart rate (HR) in excess of 90% of age predicted (220 − age) values. Once these criteria were met, the highest recorded V̇ o 2 was selected as the subject’s maximal value. The ergometer has been modified to stabilize the torso to aid in transthoracic contrast echocardiography (TTE) imaging and was used in the field data collection portion of the study. Performing the test on this equipment allowed the subjects to familiarize themselves with equipment that would be used in the future. Briefly, the modifications consisted of a backboard fixed to the base of the ergometer that would provide a surface for the subjects to brace their back against in a 90° upright position. The bicycle’s handlebars were lengthened to accommodate this new position and provide leverage for the cyclists to press their back into the board. This action, combined with straps, greatly reduced movement in the upper body during intense pedaling. Additionally, a support was made to hold the left arm in a 90° abducted and externally rotated position with a 90° bend at the elbow to open up the intercostal space for a better TTE window.

Diving protocol and location.

This study was performed at a military installation of the Croatian Navy Force. The dive site was located in the vicinity of the base, within a short (∼30 m) distance of the location where the experiments would take place. The site was chosen because of the minimal transit time between finishing the dive and beginning initial TTE analysis. All divers performed the dive at a depth of 18 m sea water (msw) with a 47-min bottom time. Decompression was performed at a rate of 9 msw/min, with direct ascent to the surface. Sea temperature at the bottom was ∼16°C, and the outside temperature was ∼26°C. Throughout the dive, divers performed swimming of moderate intensity.

Postdive exercise and echocardiography.

Within 8–15 min after surfacing, the divers were placed in the supine position where an ultrasonic probe connected to a Vivid q echographic scanner (GE, Milwaukee, WI) was used to obtain a clear apical four-chamber view of the heart. This position was monitored continuously until 30 min postsurfacing, and initial bubble images were recorded and scored on a scale of 0 to 5, with 4 being subdivided into 4A, 4B, and 4C, according to the method described by Eftedal and Brubakk (8), and later modified by Ljubkovic et al. (16). Next the subject was moved to a seating position where a bubble score was obtained again after approximately 2–3 min to observe the effect of the posture change on the bubble score. The subject then continued on with one of two potential procedures based on the observation at rest in the supine position. If arterialization was observed in the supine position, defined by an agreement on two trained observers of the appearance of bubbles in the left heart, the subject completed the supine oxygen protocol (O2) as described below. If the subjects displayed no arterialization, they advanced to the exercise protocol also described below.

O2 protocol.

In the supine position, the subject was continuously monitored in the apical four-chamber view via TTE by two experienced observers. O2 (99.5%) was administered through a mouthpiece, while the subject wore nose clips. With a continuously running timer, the time was marked when there was no longer any observed arterialization, as defined by 20 consecutive cardiac cycles with no bubbles in the left heart. At this time, the subject was switched from O2 to breathing room air. The next recorded time interval was when bubbles were again observed in the left heart, after being taken off of O2. The final time interval was recorded when no more arterializations were observed.

Exercise protocol.

After it was determined that a subject was not arterializing at rest, they were moved to an electronically braked cycle ergometer in an upright position. The torso was strapped into the support device as described above, and the left arm was moved into the abducted and externally rotated position. When a clear picture of the heart was obtained, the subject began the exercise procedure. The subjects completed a single incremental exercise test with a starting workload of 60 W and a 30-W increases every 2 min. After beginning exercise, on the first appearance of bubbles in the left heart (in divers in whom the arterialization was observed), the exercise was immediately suspended while TTE observation of the heart continued. The time was noted both when the bubbles first appeared in the left heart and when the left heart was clear of bubbles. The criterion for clearance of the bubbles was 20 consecutive cardiac cycles without appearance of bubbles in the left heart. This observation was used as an estimation of when, and at what workload, pulmonary shunting had occurred. Once the left heart was clear of bubbles, exercise was resumed at the same intensity from which it was suspended when the shunting occurred. The subjects continued with the protocol until bubbles were again observed in the left heart. At this second occurrence of arterialization, exercise was terminated, and oxygen at a concentration of 99.5% O2 was immediately given. The time interval of the appearance and clearing of the bubbles was again recorded as before: the only difference was the use of O2. For individuals who did not arterialize, the protocol was terminated when subjects could no longer maintain consistent power output. Expired gasses and HR were monitored and recorded during the initial V̇ o 2max test and during the exercise protocols after diving via a portable metabolic system (Cosmed K4 B 2 , Rome, Italy).

Oxygen subgroup.

On a separate occasion, an additional subgroup of six divers, selected from the group of those who arterialized during exercise, completed a second dive. The goal of this dive was to see how, and on what schedule, VGE react to the administration of oxygen at rest after diving. After completing a dive of the same profile (18 msw, 47 min bottom time), divers preceded directly to the field laboratory for imaging. In the supine position, divers were given oxygen 30 min after surfacing, to match both the timing of the procedure, as well as peak bubble production, while under continuous TTE observation. Oxygen was given at 12 l/min for 20 min, and bubble score was recorded at 2-min intervals.

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Statistical analysis.

An independent samples t-test was used to compare the time of exercise after surfacing in the group that arterialized during exercise with the group that did not. A paired samples t-test was used to compare the time for arterialization to stop while breathing room air and while breathing oxygen in the exercise group. The supine and upright bubble score at rest of those two groups, as well as the oxygen subgroup was compared with a Mann-Whitney test.

RESULTS

Data obtained after the dive, exercise, and oxygen protocols are presented in Table 2. All subjects completed the dive as planned without showing any signs or symptoms of DCS or any other adverse effects. In subjects 1–3, we detected gas bubbles in both the right and left sides of the heart at rest. These divers then completed the oxygen protocol. Subjects 4–23 displayed a range of emboli (bubble score 0–4B) in the right heart at rest, but without apparent arterialization, and advanced to the exercise protocol. Subjects 4–15 displayed arterialization at some point during exercise to V̇ o 2max (Table 3), while in subjects 16–23 we did not observe arterialization at any point during the study (Table 4).

Table 2. Subjects who arterialized at rest

M, male; R, right cardiac chambers; L, left cardiac chambers.

* No bubbles observed in L cardiac chambers.

Table 3. Conditions in which subjects arterialized during exercise

Subject number from prior study, Ljubkovic et al. (18), is shown in Table 2, under same dive profile. Times are in min:s. BS, bubble score; F, female; art, arterialization; ex, exercise.

* Subjects did not display arterialization during the second bout of exercise.

† Initial BS is of subjects at rest during previous study (18).

‡ Time to clear is time when arterialization of gas bubbles was no longer observed breathing room air. §Time to clear with O2 is time when arterialization of gas bubbles was no longer observed breathing oxygen.

Table 4. Subjects who did not arterialize during rest or exercise

Subject number from prior study, Ljubkovic et al. (18), is shown in Table 2.

Oxygen protocol.

Subjects who displayed arterialization at rest were given oxygen while under continuous observation via TTE in the supine position. The time between the first observation of arterialization and the application of O2 ranged between 2 and 7 min. This includes the time to monitor the heart in the upright position, and the relatively wide range of time is the result of the extra time associated with obtaining a new cardiac window with the TTE probe, which varied in difficulty from subject to subject. When oxygen was applied, arterialization was no longer observed in any of the divers, with the mean time of 55 ± 22 s. After the left heart was clear of bubbles, and the subjects were switched back to room air, the arterialization resumed in all divers, within 96 ± 75 s. After arterialization was confirmed, the mean time for emboli in the left heart to clear, while breathing room air, was 1,397 ± 614 s.

Exercise protocol.

The exercise intensity, as %V̇ o 2max, at which arterialization was first observed in subjects 4–23 is displayed in Fig. 1. Once arterialization was observed and exercise suspended, the mean time until the left heart was clear of emboli was 88 ± 41 s. Exercise was then resumed at the same intensity at which it was suspended. During the second round of exercise, supplemental O2 (99.5%) was given once arterialization was observed and exercise was suspended. The %V̇ o 2max that elicited arterialization in the second round was variable within individuals. However, the workload in Watts at the time of the observed arterializations was equal in 9 of 10 subjects who arterialized in both rounds of exercise. The mean time until the left heart was clear of emboli was 46 ± 15 s. Subjects 4 and 6 did not produce any observable emboli in the left heart during the second round of exercise.

Fig. 1.

Fig. 1.Percentage of maximum O2 uptake (V̇ o 2max) during observed arterializations. Histograms represent the distribution of intensity, as a percentage of V̇ o 2max at which arterialization was observed during exercise. art., Arterialization.

Oxygen subgroup.

Oxygen administration at rest reduced VGE over 20 min. Immediately after the application, there was no change in VGE (2 min P = 0.634, 6 min P = 0.567). The reduction was not significant until 16 min into the protocol (P = 0.026). Additional details are displayed in Table 5.

Table 5. Bubble score of all subjects during oxygen subgroup

Determinants of arterialization.

There was no difference in the time to starting exercise in the group that arterialized (subjects 4–15) and the group that did not (subjects 16–23) (P = 0.58). However, in subjects who arterialized with exercise, both the supine and upright resting bubble scores were significantly higher than in the subjects who did not exhibit exercise arterialization (P = 0.001 and 0.0009 for supine and upright position, respectively) There was a significant difference in the time for arterialization to stop after exercise when oxygen was used (P = 0.035).

DISCUSSION

The purpose of this study was to investigate the possibility that exercise may increase the incidence of arterial gas embolism after SCUBA diving, presumably via opening of IPAVA. Our results show that 12 subjects who were not arterializing at rest after SCUBA diving experienced arterialization during exercise on a cycle ergometer. Although the subjects were seated in an upright position during exercise, it is unlikely that the posture change alone was responsible for arterialization, since subjects were observed in both the seated and supine positions at rest. A recent study by Ljubkovic et al. (18) has detailed the conditions necessary to provoke arterialization of VGE after diving at rest. One of these conditions was a bubble score of at least 4B in the right heart. We have shown that, with postdive exercise, divers can arterialize with a bubble score as low as 3. For subjects 16–23, who we did not observe any arterialization, bubble score during exercise at V̇ o 2max ranged from 0 to 3. It is possible that the IPAVA were open, providing a potential path to arterialization, yet there was a lack of adequate or even any observable VGE to pass through them. Of these eight subjects who did not arterialize, only one produced a bubble score of 3, while the rest produced peak scores of 0 or 1 throughout the duration of the study.

In subjects who were exposed to the exercise protocol, the timing of exercise after diving may impact arterialization, since divers typically reach peak bubble production 30–60 min after surfacing. It is thus possible that timing of exercise could be the difference between arterialization or not. However, in this study, there was no significant difference in the exercise start time between those who did and those who did not arterialize (subjects 4–15 and 16–23). Rather, there was a significant difference in the initial bubble score, both supine and seated, which may contribute to arterialization during exercise. It is possible that there is still a minimal bubble score required to arterialize, even if open IPAVA during exercise provide a pathway. For the subjects who arterialized at rest (subjects 1–3), two of them fit the requirements for arterialization at rest, as described before (18), while one was just below the threshold. It is possible that IPAVA could be the pathway if the activity between surfacing and arriving to the testing site was enough to open them, or it may be that the higher bubble score was enough on its own to overwhelm the pulmonary clearing capacity.

It has been proposed by Eldridge et al. (9) that exercise opens up normally closed arteriovenous intrapulmonary shunts in healthy humans. In their study, with incremental cycle ergometer exercise, 21 out of 23 PFO negative subjects demonstrated the passage of contrast bubbles from the right to left heart, as viewed in a four-chamber echocardiogram. This occurrence of shunting was again demonstrated by Lovering et al. (20, 21) and Stickland et al. (24) when eight of nine, seven of seven, and seven of eight subjects, respectively, shunted during exercise. Although Dujic et al. (7) reported previously that shunting did not occur with exercise after diving, in a case study presented by that same group in 2007 (22), in the current experimental setting, divers displayed a high level of VGE and shunting with exercise following a dive. There are at least four possible explanations for the discrepancies between our present findings and previous studies. 1) We continuously monitored the subjects rather than only during select time points, so it is less likely that arterialization could have occurred during a period of time that we were not monitoring. 2) This study has a higher number of subjects than previous studies with divers. 3) As imaging technology improves, the investigators have decreased chances to miss the passage of emboli due to a lack of resolution. 4) The subjects in this study exercised until voluntary termination rather than toward a predetermined HR or workload, so it is unlikely that those who did not arterialize failed to do so as a result of not exercising at a high enough intensity.

Asymptomatic venous bubbles are common after a dive and vary in size from 19 to 700 μm (12). The diameter of capillaries at the site of gas exchange ranges from 6 to 15 μm and does not allow easy passage of these bubbles from the venous to the arterial circulation. The trapped bubbles are commonly eliminated during gas exchange and ventilation. However, this system of clearing bubbles from the blood may be overwhelmed by a high bubble load in the circulation, greater than the pulmonary circuit is capable of clearing, allowing VGE to cross over to the arterial circulation, either through IPAVA, through distention of pulmonary capillaries, or through deformation of bubbles into cylindrical shapes (1). Under the theoretical, ideal conditions, larger bubbles may deform into a cylindrical shape to pass through smaller diameter vessels (3). Alternatively, as bubbles outpace the pulmonary circuit’s ability to eliminate them through gas exchange, pulmonary arterial pressure may increase as a result of the stack of bubbles blocking local circulation (6, 17). This increase in pulmonary arterial pressure may then open the IPAVA and allow bubbles to pass, as previously suggested by Stickland et al. (24). In our laboratory’s previous studies, it has been shown that a bubble score of 4B is likely a prerequisite for arterialization at rest (18). These studies excluded divers with PFO, so VGE may not cross over through defects in the septal wall. This may explain why during PFO testing, when large quantities of bubbles are injected in subjects who are found to be PFO negative, bubbles appear in the left heart in lower quantities after 10 or more cardiac cycles.

In this study, administration of oxygen upon detection of gas bubbles in the left heart, both resting and immediately after exercise, caused rapid cessation of arterialization in all tested individuals. Furthermore, the use of oxygen terminated arterialization quite rapidly compared with breathing room air. We hypothesize that this is related to the mechanism of closing IPAVA with the application of oxygen. One alternative to this proposal is that a decrease in arterialization is related to an increased rate of nitrogen elimination, seen as a reduction of bubble load in the right heart. Oxygen prebreathing is used in high-altitude flights and astronaut extravehicular activity to eliminate nitrogen from the blood via an increased concentration gradient, and this principle has also been applied to SCUBA diving (2). This denucleation protocol can last between 1 and 4 h for high-altitude excursions (30). Exercise can speed this process up by increasing cardiac output and blood flow though the pulmonary circuit, although even the shortened protocols studied last at least 15 min (29). Due to the rapid cessation of arterialization (46 s mean) and the relatively low duration of oxygen administration, the time frame matches up more closely with other exercise and IPAVA studies rather than nitrogen washout. Additionally, our subgroup of six divers breathing oxygen shows that, while oxygen did reduce VGE in divers at rest, this reduction was not significant until 16 min into the administration procedure. However, we cannot completely rule out the possibility that breathing 100% O2, leading to an increased gradient for nitrogen elimination at the alveolocapillary membrane, may still reduce the amount of bubbles in the pulmonary microcirculation.

To our knowledge, this is the first study that demonstrates the use of supplemental O2 can stop arterialization after SCUBA diving. The use of oxygen significantly decreased the time for arterialization to stop, compared with breathing room air, in exercise (subjects 4–15, P = 0.035). With only three subjects arterializing at rest, statistical conclusions are of little use; however, in this study, the difference in the time to stop arterializing with oxygen vs. room air is noticeable. In the case of both rest and exercise, once the subject was taken off the oxygen, arterialization resumed after a relatively short amount of time. Without the use of supplemental oxygen, the half-life of the bubble scores and arterialization at rest followed closely with previously observed results with similar dive profiles (25). The mean time for the reduction of the bubble score to zero in the left heart occurred at 45:05 min after surfacing, accompanied by a concurrent decrease in VGE in the right cardiac chambers. For the subjects who shunted with exercise, while oxygen did decrease the time to clear emboli from the left heart, for practical purposes, removing the exercise stimulus also stopped arterialization within a few minutes.

Study limitations.

There are other possible explanations for VGE to appear in the left heart other than IPAVA. Bubbles will decrease in diameter as time passes and may become small enough to pass through the pulmonary microcirculation, although bubbles of this size would be much more difficult to visualize via TTE and less likely to survive until they reach the left side of the heart. Larger gas emboli may also deform into a cylindrical shape with a small enough diameters to pass through the pulmonary circulation to be visualized in the left heart. Regardless of these limitations, 65% of divers arterialized (exercise and rest) in the postdive period of our study. This proportion is much greater than is found in studies that examine these parameters for divers at rest, which range between 0 and 39% (16, 18). Another study by Gerriets et al. (11) observed arterialization in 7 of 13 dives where VGE were present; however, five of these incidences were associated with PFO. One of the primary drawbacks to using VGE resulting from decompression as a visualization agent is the relatively small load compared with a bolus injection. For optimal echo imaging conditions, exercise was initiated 30–40 min after surfacing, so that observations would be made during the postdive time period in which divers tend to produce their peak bubble scores (5). It is possible that subjects could have arterialized with or without this exercise, even if they were not during the initial 30-min TTE evaluation. However, three subjects arterialized with a bubble score of 3, and six subjects with a score of 4A. These are lower scores than typical arterializations at rest.

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Conclusions.

The safety of exercise after diving has been debated for some time. We have shown that exercise may directly contribute to arterialization. It may be concluded that exercise directly increases vulnerability to arterialization of VGE after diving. In some individuals, specifically those who have a low workload threshold for opening of IPAVA, it is possible that even relatively mild physical exertion associated with surface swimming at the end of a dive, climbing onto a boat, or walking with heavy gear on would be enough to provoke arterialization. These could all be considered regular activities that occur within 0 to 90 min after surfacing. This study also demonstrates the possibility that divers without PFO under certain circumstances may arterialize much more than it was previously thought. Divers who shunt at rest or at very low levels of exercise may be at similar risk levels as those with PFO. Conservative diving has been shown to decrease the risk of DCS in divers with a PFO (14), a similar tactic may be useful for individuals with VGE at low exercise intensities. Although many studies have shown that divers can arterialize with no DCS symptoms, there still remains a correlation between neurological DCS and the presence of arterial bubbles. Finally, subclinical levels of damage related to microemboli in the brain should not be ignored, especially in career divers.

GRANTS

This work was supported by FP7-PEOPLE-2010-ITN (264816 PHYPODE) and Croatian Ministry of Science, Education and Sports (Grant No. 216-2160133-0130 to Z. Dujic).

How Dangerous Is Scuba Diving: Top 7 Risks You Should Know!

There is no doubt that scuba diving is one of the most exciting aquatic sports globally. It is accessible for both adults and children. By exploring the magnificent underwater world, divers can get incredible experiences that they will hardly forget for the rest of their life.

Nevertheless, like any other outdoor activity, scuba diving comes with various potential dangers, some of which even lead to fatal accidents. These hazards are mainly generated as a result of high water pressure, toxic sea life, and equipment failure.

My article is written with its key aim to give an overview of the inherent risks of scuba diving. The practical information here can help you maximize your safety when participating in this adventurous sport.

Besides, I have also attached numerous valuable tips that you should strictly follow to avoid unexpected incidents.

Table of Contents

The 7 Risks of Scuba Diving

Scuba diving is exciting but extremely risky as well. It forces you to enter a foreign environment where you must use some extra gear for breathing underwater. This results in a wide range of dangers that pose a common cause of diving-related deaths.

Below is a list of hazards you may confront during a dive. However, you do not need to worry because most of them can be eliminated thanks to proper training and thorough preparation.

1. Drowning

Drowning occurs in the highest frequency for scuba diving, and most of that case leads to death. This fatal accident is mainly caused by a feeling of panic or a severe non-diving-related health problem that scuba divers can encounter regardless of their ages.

To be more specific, if your scuba tank suddenly runs out of air while you are still below the surface, you will be prone to overreact. Therefore, you may lose your temper quickly and make poor decisions, resulting in lower chances of survival.

In addition, you should not attend a dive if the physical condition of your body does not support it. A diver who has an illness relating to cardiac or respiratory must report in his or her medical checklist and receive special consultation from a professional instructor.

Divers of all levels should not ignore the importance of health conditions. They will not imagine how dangerous a mild heart attack can become while diving. It is likely that you lose your scuba regulator as a result of unconsciousness.

How to Avoid Drowning

  • Never dive without a buddy to prevent drowning.
  • Be appropriately trained to scuba dive as well as effectively deal with challenging situations.
  • Frequently check your pressure gauge and remaining breathable air.
  • Learn how to survive in an out-of-air case.
  • Swimming is required for scuba divers. See the reasons here: Do You Need to Know How to Swim to Scuba Dive!

Your diving buddy system will reduce the risk of drowning

2. Decompression Sickness

Decompression Sickness is one of the most prevalent dangers for scuba diving. It happens when you ascend too quickly from a high-pressure environment to a lower-pressure one. The compressed air used to breathe during a dive has been absorbed exceedingly to your body tissues.

Hence, if you do not decompress properly, the nitrogen in that mixture will form bubbles that block your blood flow. In addition to this primary cause, Decompression Sickness is also the result of many factors, including dehydration, alcohol plus other drug use, lack of sleep, and stress.

Decompression Sickness is detrimental to divers’ health, and thereby, it must be cured as soon as possible. Some typical symptoms are joint pain, headache, dizziness, and nausea.

If you delay treatment, your body may suffer permanent injuries such as bladder dysfunction and muscular weakness. Nerve and spinal cord damage and even death are also involved.

How to Avoid Decompression Sickness

  • Buy an affordable dive computer to track vital dive statistics. Learn How to Use a Dive Computer to calculate your bottom time here!
  • Ascend slowly at no faster than 30 feet per minute, conduct standard safety stop, and perform surface intervals between dives.
  • Always dive within your limit. To know How Deep Can You Scuba Dive, read this article!
  • Have a good lifestyle to stay healthy.
  • When you realize that your body has a few symptoms of Decompression Sickness, get treatment immediately.
  • Ensure that you will not stay underwater too long by planning before any dive.
  • Keep in mind that deep diving is always shorter than shallow diving.

allow yourself short safety stops during a dive to avoid Decompression Sickness

3. Arterial Air Embolism

In addition to causing Decompression Sickness, that your body ascends to the surface too rapidly also leads to Arterial Air Embolism due to pulmonary barotrauma.

The main reason for this risk is differences in pressure between your lungs and the underwater environment. During an ascending process, the more the water pressure is reduced, the more air in the body expands, making your lungs swell and generating fatal damages.

Additionally, scuba diving requires compressed air to breathe underwater, which means that nitrogen bubbles are produced while ascending. This creates blockages that prevent your bloodstream from freely flowing.

How to Avoid Arterial Air Embolism

  • Ascend to the surface at a slow rate.
  • Never hold your breath while ascending.
  • Make sure that you always breathe while diving, even through your nose or your mouth.

4. Nitrogen Narcosis

As I said above, nitrogen contributes to causing many fatal accidents for scuba divers, and Nitrogen Narcosis is no exception. This risk occurs when your body absorbs too much nitrogen, and its narcotic effect makes you feel like being drunk; thus, it is also known as Martini Effect.

Although Nitrogen Narcosis seems not to damage directly to your body, its potential consequences are unexpected. This danger impairs your judgment, leading to risky behaviors through creating a sense of overconfidence.

Nitrogen Narcosis often happens when you dive beyond 80 feet with some common symptoms such as dizziness, euphoria, and anxiety.

How to Avoid Nitrogen Narcosis

  • Dive with a professional instructor if you want to take a deep dive. He or she is experienced enough to recognize in case you encounter Nitrogen Narcosis.
  • Ascend slightly to mitigate the nitrogen’s narcotic effect.
  • Do not dive deeper than 100 feet since Nitrogen Narcosis mostly appears at this depth.
  • Use nitrox as your breathing air mixture because it helps reduce the percentage of nitrogen.
  • Go deeper gradually. This facilitates your adaptability to increasing nitrogen in the body.

The amount of breathing gas you consume directly affects how much nitrogen your body absorbs. Let’s check the Youtube video below to learn some helpful tips about decreasing air consumption while scuba diving.

5. Malfunctioning Equipment

Most amateur people rent equipment at dive shops. However, this is extremely risky since the quality of these rental tools is not always guaranteed. For example, a poor-quality dive computer will offer wrong calculations, resulting in a higher risk of decompression sickness.

Another dangerous case, an inaccurate pressure gauge, may lead to sudden out-of-air situations, which makes you panic as well as increases drowning. In addition, your buoyancy control ability will be affected when a broken scuba BCD significantly alters the amount of air pumped into it.

How to Avoid Malfunctioning Equipment

  • Carefully check rental dive gear.
  • Ask for a new piece of scuba diving equipment if you suspect the quality of the current one.
  • Have your equipment serviced at least once a year.
  • Check and make necessary setup prior to any dive.
  • Always dive with a buddy to get emergency support.

Ensure that your pressure gauge is always checked carefully prior to any dive

6. Oxygen Toxicity

Oxygen Toxicity is only a problem for deep diving. A standard scuba tank usually provides you with a mixture of breathing gas, including 21% oxygen. That percentage of oxygen is usual for recreational and shallow diving, but it will become poisonous beyond 135 feet.

Besides, oxygen can also become toxic if your body absorbs too much under a high water pressure environment. Consider some early symptoms like nausea and twitching to avoid falling into unconsciousness or tunnel vision.

How to Avoid Oxygen Toxicity

  • Do not go beyond your diving limit.
  • Only dive with nitrox or gas mixture if you want to dip deeper than 135 feet and you are an advanced diver.
  • Never dive with 100% oxygen.

7. Marine Life Hazards

Most sea creatures are not aggressive unless you deliberately confront or provoke them. Although deaths associated with marine animals are rare, they can even occur when scuba divers are unaware of dangerous critters.

These life-threatening creatures include Barracuda, Scorpionfish, Fire Coral, Stonefish, Box Jellyfish, Blue-ringed Octopus, Pufferfish, and more. Sharks are one of the scariest predators in the blue ocean as well.

How to Avoid Marine Life Hazards

  • Keep a safe distance.
  • Never touch as well as provoke sea creatures, corals, and wrecks.
  • When you attend a shark dive, remember to dive with experienced instructors, carefully listen to their guidelines, and follow the rules.

scorpionfish

Frequently Asked Questions

Are you still confused about environmental dangers while scuba diving? You might want to check my answers to some of the frequently asked questions in the section below.

What Are the Odds of Dying While Scuba Diving?

The mortality rate for scuba divers is relatively low, with only 0.5 to 1.2 cases per 100,000 dives. This means that scuba diving is less dangerous than most outdoor activities such as base jumping, kite surfing, and skydiving.

Is Scuba Diving an Extreme Sport?

Scuba diving is regarded as an extreme sport for two fundamental reasons. The first one is that it requires you to use additional gear for breathing. And the second one is when your equipment fails to help you breathe underwater, you will need emergency support from your dive buddy.

Is Scuba Diving Dangerous at 30 Feet?

An arterial air embolism is the most outstanding risk you may encounter when diving at 30 feet. When you ascend to the surface from the depth of 30 feet, your lungs literally swell like a balloon if you hold your breath. This causes severe damage and creates blockages in the blood flow.

Besides, 30 feet below the surface is home to a few hazardous sea life such as scorpionfish or stonefish.

What Is the Most Common Injury in Scuba Diving?

Ear barotrauma is the most frequent injury for scuba divers to encounter. This danger happens when your middle ear space fails to equalize pressure changes during the descending process.

Does Diving Damage the Brain?

Scuba diving requires divers to use compressed air for breathing as well as the breath-hold ability for deep adventures. However, this increases the risk of decompression illness. If these divers delay immediate treatment, they can suffer from Acute decompression illness.

Cerebral decompression illness is a severe complication of Acute decompression illness since it can leave long-term damage to the brain of a diver.

Conclusion

The potential hazards of scuba diving are life-threatening and unforeseen. Thus, divers must be equipped with specialized knowledge as well as careful training before every dive. This helps them keep their scuba diving safe, whether they are inexperienced or seasoned.

Read Post  Reasons to Become a Scuba Diver

To sum up, drowning has the highest fatality rate, while decompression sickness is the most common risk for scuba divers. Hence, you should take practical tips such as diving with a buddy and using a pressure gauge to avoid both dangers.

Is there any problem related to this subject that is not captured in the discussion? Do you have suggestions and comments? Kindly forward them to me via the comment box below. And do not forget to share this article with your friends and family members if you find it helpful.

  • SSI vs. PADI: Which Is Better?
  • NAUI vs. PADI: Which Training Agencies Are Better?
  • What Does BCD Stand For in Scuba Diving?
  • How Old Do You Have to Be to Scuba Dive?
  • 5 Useful Scuba Diving Exercises You Must Know Before Diving Into the Water
  • Snorkeling vs. Scuba Diving – Which One Is Suitable for You?

About Scott Maldonado

Hi, I am Scott Maldonado, the founder of diveaeris.com. You are welcome to this website. Diving is so much fun, and I’ve got a flair for it. With many diving sessions under my belt, I have transformed from just an experienced diver to a professional instructor.
I will love to contribute to your development as a diver. Therefore, I will be engaging my years of experience by discussing anything related to diving on this website.
Read more about me.

How Dangerous Is Scuba Diving: Top 7 Risks You Should Know!

There is no doubt that scuba diving is one of the most exciting aquatic sports globally. It is accessible for both adults and children. By exploring the magnificent underwater world, divers can get incredible experiences that they will hardly forget for the rest of their life.

Nevertheless, like any other outdoor activity, scuba diving comes with various potential dangers, some of which even lead to fatal accidents. These hazards are mainly generated as a result of high water pressure, toxic sea life, and equipment failure.

My article is written with its key aim to give an overview of the inherent risks of scuba diving. The practical information here can help you maximize your safety when participating in this adventurous sport.

Besides, I have also attached numerous valuable tips that you should strictly follow to avoid unexpected incidents.

Table of Contents

The 7 Risks of Scuba Diving

Scuba diving is exciting but extremely risky as well. It forces you to enter a foreign environment where you must use some extra gear for breathing underwater. This results in a wide range of dangers that pose a common cause of diving-related deaths.

Below is a list of hazards you may confront during a dive. However, you do not need to worry because most of them can be eliminated thanks to proper training and thorough preparation.

1. Drowning

Drowning occurs in the highest frequency for scuba diving, and most of that case leads to death. This fatal accident is mainly caused by a feeling of panic or a severe non-diving-related health problem that scuba divers can encounter regardless of their ages.

To be more specific, if your scuba tank suddenly runs out of air while you are still below the surface, you will be prone to overreact. Therefore, you may lose your temper quickly and make poor decisions, resulting in lower chances of survival.

In addition, you should not attend a dive if the physical condition of your body does not support it. A diver who has an illness relating to cardiac or respiratory must report in his or her medical checklist and receive special consultation from a professional instructor.

Divers of all levels should not ignore the importance of health conditions. They will not imagine how dangerous a mild heart attack can become while diving. It is likely that you lose your scuba regulator as a result of unconsciousness.

How to Avoid Drowning

  • Never dive without a buddy to prevent drowning.
  • Be appropriately trained to scuba dive as well as effectively deal with challenging situations.
  • Frequently check your pressure gauge and remaining breathable air.
  • Learn how to survive in an out-of-air case.
  • Swimming is required for scuba divers. See the reasons here: Do You Need to Know How to Swim to Scuba Dive!

Your diving buddy system will reduce the risk of drowning

2. Decompression Sickness

Decompression Sickness is one of the most prevalent dangers for scuba diving. It happens when you ascend too quickly from a high-pressure environment to a lower-pressure one. The compressed air used to breathe during a dive has been absorbed exceedingly to your body tissues.

Hence, if you do not decompress properly, the nitrogen in that mixture will form bubbles that block your blood flow. In addition to this primary cause, Decompression Sickness is also the result of many factors, including dehydration, alcohol plus other drug use, lack of sleep, and stress.

Decompression Sickness is detrimental to divers’ health, and thereby, it must be cured as soon as possible. Some typical symptoms are joint pain, headache, dizziness, and nausea.

If you delay treatment, your body may suffer permanent injuries such as bladder dysfunction and muscular weakness. Nerve and spinal cord damage and even death are also involved.

How to Avoid Decompression Sickness

  • Buy an affordable dive computer to track vital dive statistics. Learn How to Use a Dive Computer to calculate your bottom time here!
  • Ascend slowly at no faster than 30 feet per minute, conduct standard safety stop, and perform surface intervals between dives.
  • Always dive within your limit. To know How Deep Can You Scuba Dive, read this article!
  • Have a good lifestyle to stay healthy.
  • When you realize that your body has a few symptoms of Decompression Sickness, get treatment immediately.
  • Ensure that you will not stay underwater too long by planning before any dive.
  • Keep in mind that deep diving is always shorter than shallow diving.

allow yourself short safety stops during a dive to avoid Decompression Sickness

3. Arterial Air Embolism

In addition to causing Decompression Sickness, that your body ascends to the surface too rapidly also leads to Arterial Air Embolism due to pulmonary barotrauma.

The main reason for this risk is differences in pressure between your lungs and the underwater environment. During an ascending process, the more the water pressure is reduced, the more air in the body expands, making your lungs swell and generating fatal damages.

Additionally, scuba diving requires compressed air to breathe underwater, which means that nitrogen bubbles are produced while ascending. This creates blockages that prevent your bloodstream from freely flowing.

How to Avoid Arterial Air Embolism

  • Ascend to the surface at a slow rate.
  • Never hold your breath while ascending.
  • Make sure that you always breathe while diving, even through your nose or your mouth.

4. Nitrogen Narcosis

As I said above, nitrogen contributes to causing many fatal accidents for scuba divers, and Nitrogen Narcosis is no exception. This risk occurs when your body absorbs too much nitrogen, and its narcotic effect makes you feel like being drunk; thus, it is also known as Martini Effect.

Although Nitrogen Narcosis seems not to damage directly to your body, its potential consequences are unexpected. This danger impairs your judgment, leading to risky behaviors through creating a sense of overconfidence.

Nitrogen Narcosis often happens when you dive beyond 80 feet with some common symptoms such as dizziness, euphoria, and anxiety.

How to Avoid Nitrogen Narcosis

  • Dive with a professional instructor if you want to take a deep dive. He or she is experienced enough to recognize in case you encounter Nitrogen Narcosis.
  • Ascend slightly to mitigate the nitrogen’s narcotic effect.
  • Do not dive deeper than 100 feet since Nitrogen Narcosis mostly appears at this depth.
  • Use nitrox as your breathing air mixture because it helps reduce the percentage of nitrogen.
  • Go deeper gradually. This facilitates your adaptability to increasing nitrogen in the body.

The amount of breathing gas you consume directly affects how much nitrogen your body absorbs. Let’s check the Youtube video below to learn some helpful tips about decreasing air consumption while scuba diving.

5. Malfunctioning Equipment

Most amateur people rent equipment at dive shops. However, this is extremely risky since the quality of these rental tools is not always guaranteed. For example, a poor-quality dive computer will offer wrong calculations, resulting in a higher risk of decompression sickness.

Another dangerous case, an inaccurate pressure gauge, may lead to sudden out-of-air situations, which makes you panic as well as increases drowning. In addition, your buoyancy control ability will be affected when a broken scuba BCD significantly alters the amount of air pumped into it.

How to Avoid Malfunctioning Equipment

  • Carefully check rental dive gear.
  • Ask for a new piece of scuba diving equipment if you suspect the quality of the current one.
  • Have your equipment serviced at least once a year.
  • Check and make necessary setup prior to any dive.
  • Always dive with a buddy to get emergency support.

Ensure that your pressure gauge is always checked carefully prior to any dive

6. Oxygen Toxicity

Oxygen Toxicity is only a problem for deep diving. A standard scuba tank usually provides you with a mixture of breathing gas, including 21% oxygen. That percentage of oxygen is usual for recreational and shallow diving, but it will become poisonous beyond 135 feet.

Besides, oxygen can also become toxic if your body absorbs too much under a high water pressure environment. Consider some early symptoms like nausea and twitching to avoid falling into unconsciousness or tunnel vision.

How to Avoid Oxygen Toxicity

  • Do not go beyond your diving limit.
  • Only dive with nitrox or gas mixture if you want to dip deeper than 135 feet and you are an advanced diver.
  • Never dive with 100% oxygen.

7. Marine Life Hazards

Most sea creatures are not aggressive unless you deliberately confront or provoke them. Although deaths associated with marine animals are rare, they can even occur when scuba divers are unaware of dangerous critters.

These life-threatening creatures include Barracuda, Scorpionfish, Fire Coral, Stonefish, Box Jellyfish, Blue-ringed Octopus, Pufferfish, and more. Sharks are one of the scariest predators in the blue ocean as well.

How to Avoid Marine Life Hazards

  • Keep a safe distance.
  • Never touch as well as provoke sea creatures, corals, and wrecks.
  • When you attend a shark dive, remember to dive with experienced instructors, carefully listen to their guidelines, and follow the rules.

scorpionfish

Frequently Asked Questions

Are you still confused about environmental dangers while scuba diving? You might want to check my answers to some of the frequently asked questions in the section below.

What Are the Odds of Dying While Scuba Diving?

The mortality rate for scuba divers is relatively low, with only 0.5 to 1.2 cases per 100,000 dives. This means that scuba diving is less dangerous than most outdoor activities such as base jumping, kite surfing, and skydiving.

Is Scuba Diving an Extreme Sport?

Scuba diving is regarded as an extreme sport for two fundamental reasons. The first one is that it requires you to use additional gear for breathing. And the second one is when your equipment fails to help you breathe underwater, you will need emergency support from your dive buddy.

Is Scuba Diving Dangerous at 30 Feet?

An arterial air embolism is the most outstanding risk you may encounter when diving at 30 feet. When you ascend to the surface from the depth of 30 feet, your lungs literally swell like a balloon if you hold your breath. This causes severe damage and creates blockages in the blood flow.

Besides, 30 feet below the surface is home to a few hazardous sea life such as scorpionfish or stonefish.

What Is the Most Common Injury in Scuba Diving?

Ear barotrauma is the most frequent injury for scuba divers to encounter. This danger happens when your middle ear space fails to equalize pressure changes during the descending process.

Does Diving Damage the Brain?

Scuba diving requires divers to use compressed air for breathing as well as the breath-hold ability for deep adventures. However, this increases the risk of decompression illness. If these divers delay immediate treatment, they can suffer from Acute decompression illness.

Cerebral decompression illness is a severe complication of Acute decompression illness since it can leave long-term damage to the brain of a diver.

Conclusion

The potential hazards of scuba diving are life-threatening and unforeseen. Thus, divers must be equipped with specialized knowledge as well as careful training before every dive. This helps them keep their scuba diving safe, whether they are inexperienced or seasoned.

To sum up, drowning has the highest fatality rate, while decompression sickness is the most common risk for scuba divers. Hence, you should take practical tips such as diving with a buddy and using a pressure gauge to avoid both dangers.

Is there any problem related to this subject that is not captured in the discussion? Do you have suggestions and comments? Kindly forward them to me via the comment box below. And do not forget to share this article with your friends and family members if you find it helpful.

  • SSI vs. PADI: Which Is Better?
  • NAUI vs. PADI: Which Training Agencies Are Better?
  • What Does BCD Stand For in Scuba Diving?
  • How Old Do You Have to Be to Scuba Dive?
  • 5 Useful Scuba Diving Exercises You Must Know Before Diving Into the Water
  • Snorkeling vs. Scuba Diving – Which One Is Suitable for You?

About Scott Maldonado

Hi, I am Scott Maldonado, the founder of diveaeris.com. You are welcome to this website. Diving is so much fun, and I’ve got a flair for it. With many diving sessions under my belt, I have transformed from just an experienced diver to a professional instructor.
I will love to contribute to your development as a diver. Therefore, I will be engaging my years of experience by discussing anything related to diving on this website.
Read more about me.

Source https://journals.physiology.org/doi/full/10.1152/japplphysiol.00029.2013

Source https://www.diveaeris.com/how-dangerous-is-scuba-diving-top-7-risks-you-should-know/#:~:text=How%20to%20Avoid%20Arterial%20Air%20Embolism%20Ascend%20to,diving,%20even%20through%20your%20nose%20or%20your%20mouth.

Source https://www.diveaeris.com/how-dangerous-is-scuba-diving-top-7-risks-you-should-know/

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