scuba diving

A Look at Crowdsourcing for Research Funding

financial

Crowdsourcing is a means to raise funds through public contributions in a manner which allows a large number of small contributions to make a difference. Originally started in technology areas where considerable upfront capital was required to make the project viable, SciFund and Experiment.com have taken this into the research arena to allow small research projects to gain support. As those in research know, it is notoriously difficult to raise funds for small research projects and crowdsourcing provides that opportunity. As an example of how well it can work, Experiment has raised $600,000 over the last 4 years.

(more…)

Medicinal nicotine and diving

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Smoking has been recognized as a major health problem, which decreases physical fitness and increases risk of serious illness and premature death.  The surgeon general’s “Smoking and Health” report released in 1964  launched the anti-smoking campaign in United States. Back then, 42 percent of adult population smoked in comparison to today’s 18 percent. The government set the goal to reduce this to about 12 percent of the adult population by 2020. While the public awareness is there, individuals still struggle with the habit mostly due to the addictive nature of nicotine. Smoking is less prevalent among divers, but it is still a problem because its acute and chronic effects may contribute to scuba diving fatalities.

(Learn more about the current state of smoking in America, with this PBS NewsHour Interview with Acting Surgeon General Boris Lushniak)

Acute effects of  smoking

Nicotine affects the body in many ways. It increases blood pressure and heart rate frequency. The mechanism of blood pressure and heart rate elevation by nicotine occurs via activation of the sympathetic nervous system with release of norepinephrine and epinephrine (adrenaline).  Cigarette smoking results in sympathetic neural arousal that lasts for 24 hours. This is reflected in a loss of natural heart rate variability and an increased risk of arrhythmia. Narrowing of blood vessels requires the heart to work harder and use more oxygen, while the simultaneous narrowing of the coronary arteries diminishes the blood and oxygen supply to the heart muscle, which can contribute to myocardial infarction. Carbon monoxide reduces availability of oxygen in blood and may exaggerate hypoxia of heart muscles. Nicotine also induces endothelial dysfunction and increased tendency to clotting. Besides that, cigarette smoke contains many toxins other than nicotine (for example, carbon monoxide and oxidant gases) that might contribute to cardiovascular toxicity. Chronic smoking contributes to development of atherosclerosis, heart disease, cancer and premature death.

Major health damage related to smoking is caused by various components of the smoke, but nicotine has its own adverse effects. In an attempt to reduce risks while satisfying the cravings for nicotine, several products that deliver nicotine without smoke have been brought to the market. They are in form of skin patches, nasal spray, chewing gums and inhalers. The most recent, the e-cigarette,  is generating a lot of public discussion. It is important to note that while administering nicotine without smoke may reduce health damage caused by smoke components, it does not reduce effects of nicotine.

Divers are encouraged to cease smoking. Any effective help is welcomed. Medicinal nicotine may be the way to go for those who have failed in their previous attempts, but medical supervision is advised. Some means of delivery of medicinal nicotine, like chewing gums, nasal sprays, dermal patches and inhalers have been approved or tolerated by FDA which summarizes mainstream medical judgement. However some methods raise concerns about propagating the addiction, such as the more elaborate deliveries like the e-cigarette. Divers on a cessation program using medicinal nicotine must be aware of the side effects of nicotine use, nicotine overdose and nicotine withdrawal symptoms.

Side effects

Adverse effects of medicinal nicotine depend on dose and method of administration. Using nicotine inhalers  may cause local irritation in mouth and throat, coughing and rhinitis, change of taste, pain in jaw and neck, tooth disorders and sinusitis. Lozenge and chewing gums may cause dyspepsia. Other adverse events occurring in greater than 3% of patients on active drug include nausea, headache, influenza-like symptoms, pain, back pain, allergy, paresthesia, flatulence and fever.

Nicotine overdose

The overdose of nicotine among adult smokers is not very likely; however, a person can overdose on nicotine through a combination of nicotine patches, nicotine gum, nicotine inhaler cartridges and/or tobacco smoking at the same time. Intoxications with nicotine have been reported and causes include ingestion of nicotine pharmaceuticals, tobacco products, and prolonged skin contacts with nicotine containing plants or accidental ingestion of pesticides containing nicotine. The initial symptoms are caused by stimulatory effects and include nausea and vomiting, excessive salivation, abdominal pain, pallor, sweating, hypertension, tachycardia, ataxia, tremor, headache, dizziness, muscle twitching, and seizures. This may be later followed by depressor effects including low blood pressure and slow heart rate, central nervous system depression, coma, muscular weakness and/or paralysis, with difficulty breathing or respiratory failure.

Withdrawal

Symptoms of withdrawal may occur early on in the smoking cessation process and while on medicinal nicotine. Common withdrawal symptoms include dizziness, anxiety, sleep disorder, depression, drug dependence, fatigue and myalgia.

Diving and medicinal nicotine

Divers are encouraged to quit smoking using any possible help they need with due medical supervision. However, use of medicinal nicotine as a convenient replacement or addition to smoking may be unsafe and is not advised. While on a cessation program, divers must be aware of potential adverse effects which may be confused for dive related symptoms. As with all  medical interventions, it is wise to abstain from diving for a while to weather out possible adverse events and their interaction with dive safety.

Post written by: Petar Denoble, MD, D.Sc.

Cardiovascular Disease as a Disabling Condition in Breath-Hold and Scuba Fatalities

snorkelIn a recent report on diving fatalities in Australia during 2009, Lippmann and colleagues identified 12 cases among breath-hold (BH) and 9 cases among scuba divers (SD). Cardiovascular disease was the apparent disabling condition in 3 BH and 3 SD fatalities, and possibly in 4 more BH and 3 SD fatality cases.

In comparison to the period 1977 – 2005 when 18% of deaths were caused by apparent cardiovascular diseases, the proportion in 2009 is much higher and more in-line with what DAN America reported for the period 1992-2003. Authors assume that this is probably due to the increased participation of older divers, which makes the current population of divers in Australia closer in age to the population of recreational divers in the United States. In this series, the age range of the victims who likely died of cardiac cause was 50 to 63 years. Seven out of 12 BH fatalities and four out of nine SC were older than 50 years.

Other causes of disabling conditions in BH were apneic hypoxia (3) and aspiration (2), while in SC fatalities there were two cases of seizures and two of probable cerebral arterial gas embolism (CAGE). Being over-weighted and failure to establish positive buoyancy needed to surface contributed to three deaths.

Besides the cardiac disease that may not be diagnosed previously, many victims may not have been physically fit for diving. Many were overweight and in one case the victim was extremely obese. A medical statement is not mandatory for snorkeling; however, this snorkel operator required a medical statement, but the extremely obese victim failed to declare various medical conditions (asthma, hypertension, arrhythmia and depression) and the medications she was taking. She died quietly, at the surface, a few meters from the boat. The autopsy did not document any apparent cause. While the authors justifiably suggest that in the case of an unfit customer who insists on snorkeling she could be assigned a personal guide, in this particular case even that may not have prevented the fatal outcome.

In some cases victims knew that they had conditions which may turn fatal in diving (seizures, poor physical fitness) but failed to report them. However, most victims who died of cardiac causes in this series were apparently healthy. Age itself is not a disease, but it is associated with increasing incidence of coronary artery disease, which may remain asymptomatic for a long time. The discussion of who should undergo additional medical testing and how often is ongoing with no satisfactory answer in sight.

This paper provides detailed accounts of each accident with an extensive expert comment and thus it makes a worthy read for all divers.

Source:

Lippmann J, Lawrence C, Fock Andrew, Wodal T, Jamieson S. Provisional report on diving-related fatalities in Australian waters 2009. Diving and Hyperbaric Medicine. 2013. December; 43(4):194-217.

Post written by: Petar Denoble, MD, D.Sc.

Effects of a single dive on small airway functions in divers with asthma

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Diving with asthma is still a bit of a controversial issue due to insufficient research of how divers with asthma respond to dive conditions and lack of data on their dive safety. A recent study conducted by a group of researchers associated with DAN Europe contributes to current knowledge how diving may affect small airways function in divers with asthma. They conducted pulmonary function tests in 22 divers with asthma and 15 healthy control divers, before and after a single pool dive to 15 feet (5 meters).  A single pool scuba dive to a depth of 15 feet may impair small airways function in divers with asthma. Among the subjects, no one experienced any symptoms, but the effect on small airways varied significantly among divers with asthma. Most showed a minimal reduction of function (3 – 10%) not seen in healthy divers, while one diver exhibited a reduction of 22-26% in FVC, FEV1 and PEF of the predive values. The latter change was significant enough to advise the diver against further diving.

It is important to notice that all divers with asthma participating in this study were previously cleared for diving and have been diving for an average of four years. They did not report any incident of asthma attack or difficulty breathing while diving although they recorded between 10 and 220 dives in the past.

Asthma manifests in various forms; provocative factors, frequency and severity of symptoms and fitness to dive should be evaluated on an individual basis. Obviously, not all people with asthma would qualify for diving. The individuals included in this study are those that passed medical evaluation. It appears that they and their physicians made a reasonable decision. The only diver who had significant changes in small airway functions somehow bypassed physical evaluation by a physician prior to diving and made his choice without a physician’s opinion.

The article is a good read for any diver or would-be diver with asthma as well as for diving physicians. It gives an overview of available literature on the topic and provides extensive discussion of factors that should be considered in the fitness evaluation process.

Ivkovic D, Markovic M, Todorovic BS, Balestra C, Marroni A , Zarkovic M. Effect of a single pool dive on pulmonary function in asthmatic and non-asthmatic divers. Diving and Hyperbaric Medicine 2012; 42(2): 72-77 

Post written by: Petar Denoble, MD, D.Sc.

Scuba diving and Pregnancy: Is Another Study Justified?

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The possible effects of scuba diving on pregnancy have been a concern since the sport began. The main concern is that decompression may cause occurrence of free gas that could hurt the fetus. Indeed, it was shown in sheep that circulating bubbles do occur in maternal and fetal circulation, even when the mother does not display signs of decompression sickness. As such, the general advisement issued is not to dive while pregnant.

Unfortunately, most women become aware of their condition weeks or months after conception and some after they have already dived. This raises concerns about possible damage to their fetus and women often seek counseling after the fact. In an era of evidence-based medicine, it does not suffice to offer good wishes. However, the evidence about safety of diving while pregnant or damaging effects on outcome of pregnancy is not available.

In the past  several survey-based studies queried about exposure and outcome, but most came up short of conclusions, because, wisely, most women stop diving when they learn they are pregnant. Thus, there are few reported cases of pregnancy exposed to diving and the exposures are limited to a small number of dives. This further limits the ability to detect a possible small increase in frequency of adverse outcomes above the baseline rates. Thus, it seems that another survey is justified if it could provide a sufficient sample size to achieve reliable conclusions.

Dr. David Baud, MD, PhD, specialist in obstetrics, gynecology and materno-fetal medicine from Lausanne, Switzerland, proposed an international survey that could reach enough women who had inadvertently dived in pregnancy to yield sufficient data to detect even small increases in rates of possible adverse events.  The study is supported by International DAN organizations: DAN Europe, DAN America, DAN Southern Africa and hopefully by others. Researchers from these organizations are co-investigators on the study, but most the important support will be that of female divers from all over the world.

If you are a female diver, regardless if you are currently pregnant or not, please click and complete the survey. The survey is available in English and in several other languages. It is anonymous and it takes up to 10 minutes to complete it.

For more information about pregnancy and diving read:

Scuba diving and pregnancy: Can we determine safe limits?

The Risks of Diving While Pregnant

Post written by: Petar Denoble, MD, D.Sc.

Swimming induced pulmonary edema (SIPE)

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SIPE, which is also known as Immersion Pulmonary Edema, has been occasionally reported during the last two decades. It may affect scuba divers, breath-hold divers and swimmers. The incidence of SIPE is probably underestimated, because mild cases may resolve on their own and the most severe cases may be mistaken for drowning or cardiac-related death. Two recent papers present three documented and unusual cases of SIPE.

Case 1

A 33-year-old healthy military diver was immersed for 10 minutes in 50 F (10 C) while wearing a 5 mm neoprene wetsuit. After two breath-hold dives to 18 ft (6 m) for 0.5-1 min duration with a surface interval of 1 min, he noted wheezing and coughed pink, frothy sputum. At admission to a hospital, he had already improved but imaging of his lungs showed obvious signs of SIPE. This was an unusually short exposure, shallow dive and quick onset of symptoms.1

Case 2

A 46-year-old man was spearfishing in 5 m of water in a 5 mm neoprene wetsuit. He did not report feeling cold, although the water was 57.2 F (14 C).While swimming back to shore against strong current for only two minutes, he suddenly felt such respiratory distress that he could not call for help or swim. His wife brought him back to shore; he was unconscious. He recovered in a few hours and was discharged from the hospital after three days.2

Case 3

A 48-year-old man was performing an 800-m swim test. The day before, during the same exercise he reported becoming severely breathless, but recovered within a short period of time. On his next attempt, he had to swim 500 m with a snorkel while wearing his complete scuba equipment. After 250 m his buddy discovered he was unconscious and sinking. An emergency medical team responded quickly and properly, but he was in a coma when admitted to a hospital where he was kept in artificially induced protective hypothermia (the initial diagnosis was cardio-circulatory arrest and drowning).2

In all three cases, the victims recover – some sooner, others later. Medical causes, except hypertension in the first case, could not be identified; all victims appeared to be in normal health, except for the findings of lung edema.

The lesson learned is that SIPE may occur suddenly and be very severe. It can be life threatening while in water and it may require intensive care to recover. The apparently low incidence of SIPE may be due to misidentification of some fatalities as a cardiac-related death instead of SIPE.

Authors suggest two major points to prevent SIPE and fatal outcome in case of it:

  •  Do not struggle against a strong current; maintaining a good respiration is better than increasing the swimming effort.
  • Always have diving or swimming buddy.

To learn more, read “Immersion Pulmonary Edema.”

Studies referenced in this post:

  1.  Gempp E. et al. Pulmonary oedema in breath-hold diving: an unusual presentation and computed tomography findings. Diving Hyperb Med 2013; 43:162-163.
  2. Cochard G. et al. Swimming-induced immersion pulmonary edema while snorkeling can be rapidly life-threatening: Case reports. UHM 2013; 40(5): 411-415

Post written by: Petar Denoble, MD, D.Sc.

Effects of scuba diving on heart function

Recently, a group of Italian researchers conducted an underwater Doppler echocardiography study of 18 healthy scuba divers titled “Cardiovascular changes during SCUBA diving: an underwater Doppler echocardiographic study.” The rationale for the study was a concern that body immersion, which induces redistribution of blood from the periphery to the chest, may adversely affect subjects with previous heart disease. The aim of the study was to evaluate cardiovascular changes during immersion using underwater Doppler echocardiography. They found that the left ventricle is enlarged during immersion, an effect that is expected because there is more blood moving into the chest area. In addition, there were some changes in the velocity of the ventricle filling measured, but the significance of this is not clear. These changes were still noticeable when the Doppler echocardiography was repeated immediately after a dive; however, some older studies reported that most changes disappeared within one hour after the dive.

Please note, although the motivating concerns for the study were about divers with pre-existing cardiovascular conditions like hypertension and coronary heart disease, the study involved 18 healthy subjects. While there are quite a few papers that report temporary changes in cardiovascular functions in healthy divers, there are no studies exploring how these temporary changes may acutely affect divers with pre-existing conditions or how long these changes may persist in such divers.

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DAN is conducting a study that aims to provide more answers. Cardiac function is evaluated by echocardiography after multiple days of diving. Possible arrhythmias are monitored with a continuous underwater electrocardiogram (ECG) using a specially adapted mini Holter recorder.

We just conducted our first field study involving 25 volunteers and plan to do five more trips to study up to 120 divers by the end of 2014.

Learn More

“Matters of the Heart.”

“Underwater Scan Finds Significant Heart Changes in Divers”

“Cardiovascular changes during SCUBA diving: an underwater Doppler echocardiographic study” 

Photography and post by: Petar Denoble, MD, D.Sc.

Trip Report: Left ventricular hypertrophy and risk of cardiac death in divers

We’ve just recently returned from the first field trip for the left ventricular hypertrophy and risk of cardiac death in divers study in Bonaire (August  31-September 7). For the first time, we field tested the study logistics and the protocol. The dive trip was organized by Down Under Surf & Scuba in Raleigh, N.C. Out of 36 subjects in the group, 25 were qualified participants over 40 years of age and actively participated in the study. Most of the baseline testing was completed prior to the trip in four sessions: two at DAN Headquarters and two at the dive shop. Five new subjects joined us from other parts of the country and were pre-screened upon arrival to Bonaire.

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The Buddy Dive Resort was our central study location. They were very accommodating and allowed us to use their main classroom as a lab. The classroom was at the waterfront where most divers enter and exit water or board the boat for the boat dives.

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 The plan was to get every participant scanned by echo twice after a full day of diving and once in the morning after a night’s rest. We took take a resting electrocardiogram (ECG) to monitor heart rate variability after a full day of diving on select dive days. All divers carried the Holter Monitor during at least one dive and were asked to record the depth and time of all their dives.

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The compliance was nearly perfect. In fact, the only delays were related to travel time back from some remote dive sites. We completed a total of:

  • 100 echo scans
  • 50 resting ECGs
  • 24 underwater Holters
  • Nearly 500 recorded dives

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The research team included cardiologist Dr. Douglas Ebersole, two professional echo cardiographers Brandy Emory of Lakeland Clinic and Lisa Caudill of Duke and myself. They did an excellent job maintaining the tight schedule and were well received by all of the participants. They even had time to join participants on some dives.

Scott Powell, the manager of Down Under Surf & Scuba and Rochelle Wright, a DAN Member Services specialist, managed all of the logistical challenges so we were able to complete our study. We’re very thankful for their support as well as the overwhelming support from the participants. We appreciate your participation and thank you for helping us to work toward improving diver safety.

Photography and Post by: Petar Denoble, MD, D.Sc.

What is the practical significance of arterialization of gas bubbles after diving?

Decompression sickness (DCS) is a condition that may result from quick decompression, which may occur when diving or flying. One mechanism involved in DCS is the passage of venous gas emboli (VGE or “bubbles”) to the arterial side of circulation; this is known as arterialization.

Until recently, arterialization was considered a rare event except when there is a passage in the heart wall because of a patent foramen ovale, (PFO), atrial septal defect or ventricular septal defect. In people with normal hearts it was previously thought that when venous gas passed through the narrow pulmonary capillaries, the potential for VGE was eliminated. It is known that some pathways allow up to five percent of venous blood to bypass pulmonary capillary filters, but the caliber of these bypasses was considered too small to allow VGE to pass through. Occasionally, some bubbles would arterialize, but it was considered a rare event. Recently, however, several authors have reported postdive VGE arterialization, but the true incidence of this phenomenon was not known.

Our colleagues of University Split, Ljubkovic M., et al. studied VGE arterialization and published two papers. The first, “Determinants of arterial gas embolism after scuba diving” (http://jap.physiology.org/content/112/1/91.long), reports results of laboratory testing and postdive findings. They tested 34 subjects by injecting saline with air bubbles in an arm vein and used echocardiography to monitor for bubble passage to the left side of the heart. In 23 out of 34 subjects, the transpulmonary passage of bubbles was observed at rest or after mild exercise. Nine subjects with confirmed arterialization in lab conditions also experienced arterialization after a field dive. All nine had large amounts of VGE in their right heart (VGE grade of 4B or greater). In subjects with no arterialization in lab conditions, there was no arterialization postdive either despite five of them having VGE grade 4B.

Authors concluded that “Postdive VGE arterialization occurs in subjects that meet two criteria: 1) transpulmonary shunting of contrast bubbles at rest or at mild/moderate exercise and 2) VGE generation after a dive reaches the threshold grade.”

It is important to notice that none of the nine divers with echocardiographically detected arterialization had any symptoms or signs of DCS or cerebral arterial gas embolization (CAGE). There is also no clear evidence concerning long-term consequences of chronic embolization in divers without history of manifested DCS or CAGE. Read the Alert Diver article, “Effects of diving on the brain” to learn more.

The significance of these findings is dubious. In the first place, it is now clear that a certain level of arterialization occurs more often than previously assumed and proven. One of the reasons may be in increased resolution of new generations of echocardiography machines, which enables us to detect smaller VGE than before. Second, it is reasonable to assume that occurrence of DCS in cases of VGE arterialization depends on the size and quantity of VGE, but the threshold values are not known. Third, a loose relationship between the presence of PFO and DCS may be due to not accounting for transpulmonary bubble passage.

Thus, we are looking forward to results of a prospective study conducted by Germonpre, P. and colleagues, which relates to the presence of VGE in carotid artery (accounting for PFO and transpulmonary passage) to DCI.

Additional Readings:

PFO Research Foundation

“PFO and decompression illness in recreational divers”

“Effects of diving on the brain”

Post written by: Petar Denoble, MD, D.Sc.

When to refer a diver for PFO screening?

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Postdive occurrence of bubbles in divers venous blood (venous gas emboli or VGE) is quite common. VGE are usually filtered out of circulation by the pulmonary capillary filter. However, in the case of PFO, transpulmonary passage of venous blood or other rare causes of right-to-left shunt (RLS), VGE may pass to the arterial circulation and cause damage of vital tissues manifesting decompression illness (DCI). Note that DCI includes both decompression sickness and cerebral arterial gas embolism. Because of high prevalence of RLS, mainly as a result of PFO, and low incidence of DCI, there is a general agreement that screening for RLS should not be done routinely on all divers. While in some cases screening may be useful, there is no consensus about when the screening is justified. In a recent paper by Oliver Sykes and James E. Clark titled, “Patent foramen ovale and scuba diving: a practical guide for physicians on when to refer for screening,” the authors detail clear guidelines for physicians as well as their definitions of safe diving practices, provocative dive profiles and factors suggestive of PFO. Their recommendations are very useful. Do not miss this paper. It is available for free from the above link.

Their recommendations are summarized in Figure 8 of Sykes and Clark’s paper:

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Figure 1. Flow chart on when to refer for screening by a cardiologist with an interest in diving. Courtesy of London Hyperbaric Medicine.

The findings in DAN’s PFO study coincide with most of the recommendations above. Retrospectively established incidence of various DCI manifestations in divers with PFO participating in our study is shown in following table:

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Multiorgan DCI manifestations were a frequent finding and we suggest adding it to the indications for RLS screening. In this context, multiorgan means coincidental occurrence of symptoms from two or more of the following symptom groups: skin, neurological (brain, spinal cord, ocular or inner ear), pulmonary and constitutional.

Learn more: Read about the dive and DCS history in divers who tested positive for PFO and pursue closure. http://www.alertdiver.com/Study_Update_PFO

Post written by: Petar Denoble, MD, D.Sc.