Cardiovascular Fitness To Dive


Article Author:
Francis Matuszak


Article Editor:
Jeffrey Cooper


Editors In Chief:
Jeffrey Cooper


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes


Updated:
1/19/2019 5:57:42 PM

Introduction

All major diving organizations require medical screening before a person may participate in SCUBA (self-contained underwater breathing apparatus) diving. The screening intervals vary depending on the country and the purpose of the diving (recreational versus commercial). In 2017, there were 67 SCUBA diving fatalities reported to the Diver’s Alert Network (DAN), and for the cases with cause reported, 15% were related to an underlying cardiac disease.[1] Thus, all SCUBA divers should be assessed for cardiovascular comorbidities that could affect their fitness to dive.

Function

Several physiologic changes occur within the body during diving that can predispose a patient to cardiac events. Most evident, SCUBA diving causes an increase in metabolic oxygen consumption from the muscular contraction required to swim while carrying the necessary gear.[2] It is estimated that swimming in a 1-knot current corresponds to about 8 METs (metabolic equivalents).[3] Decreased heart rate is also common during diving due to the increase in vagal tone associated with the mammalian diving reflex and from the increased partial pressure of hyperbaric oxygen inhaled from the SCUBA tank.[2] Immersion in water also exerts increased pressure on the vasculature relative to air, causing an increase in intrathoracic blood volume.[4] This increase in blood volume is associated with an increase in central venous pressure as well as cardiac output.[4]

The other primary concern when assessing fitness to dive is the risk for decompression sickness (DCS). While resurfacing from diving, the ambient pressure exerted on the gases inhaled while underwater decreases. Consequently, the inert gasses (primarily nitrogen) can expand and form micro-bubbles in the blood. Typically, these bubbles can be exhaled through gas exchange at the lungs. However, if ascent is too rapid, the micro-bubbles can form in the other tissues of the body. There are two recognized forms: minor and major. The minor type which affects primarily the musculoskeletal system and is characterized by joint pain, itching, and skin changes. The major type is typified by neurological symptoms such as altered mental status, vertigo, confusions, and vision abnormalities.[3] The primary method for preventing DCS is to make appropriate safety stops to allow the gas to safely diffuse from the body; however, several cardiovascular factors may increase the risks of DCS while diving, and these will be discussed in this article.

In general, it has been shown that the most effective tool for assessing cardiovascular risk is a well-designed questionnaire as physical examination is unlikely to identify abnormalities that preclude diving.[5] Divers should be queried on their past medical history as well as for risk factors of cardiovascular disease including obesity, hypertension, diabetes, smoking status, and hyperlipidemia.

Issues of Concern

Coronary Artery Disease and Congestive Heart Failure[6]

As mentioned, SCUBA is a physically taxing sport that can increase myocardial oxygen demand and induce ischemia in patients with heart disease. Ninety percent of deaths while diving occur in the 50+ age range, and consequently, Diver Alert Network recommends that all patients above the age of 40 be evaluated for coronary artery disease through an inventory of risk factors and electrocardiography.[3] In patients with findings concerning for myocardial ischemia, exercise stress testing is indicated. Iideally, prospective divers should be able to tolerate 13 METs without ischemic findings during testing.[3]

In patients with a known history of myocardial infarction or therapeutic catheterization, it is recommended that divers abstain from SCUBA for at least 6 to 12 months. Beyond this observational period, fitness to dive should again be based on the patient’s exercise tolerance.[3]

Reduced ejection fraction is a relative, but not an absolute contraindication to diving. Due to the hemodynamic changes from submersion, patients should be aware that diving can precipitate acute pulmonary edema. Consequently, it is recommended that patients with a history of congestive heart failure exacerbations refrain from diving. Of note, due to these hemodynamic changes, pulmonary edema has been reported in otherwise healthy divers; however, this finding does warrant further evaluation for heart failure with echocardiography.[4]

Diabetes Mellitus

In addition to being a cardiac risk factor, diabetes mellitus carries its own considerations for diving. As it would be difficult to manage neurological symptoms from blood glucose extremes underwater, current guidelines recommend that divers should not have had any episodes of hypoglycemia or hyperglycemia in the past 12 months. For patients dependent on insulin, their regimen should be stable before diving. Additionally, current guidelines recommend divers maintain a hemoglobin A1c below 9%.[7]

Patent Foramen Ovale and Septal Wall Defects

Patent foramen ovale (PFO), atrial, and ventricular septal defects create a right-to-left shunt in the heart. Thus, these findings theoretically increase the risk for DCS by creating a pathway for nitrogen bubbles to enter the systemic circulation while bypassing the lungs. In practice, epidemiological studies find the association to be somewhat rare. As a result, it is generally recommended not to screen specifically for PFO in the general diving population. In patients with a history of major decompression symptoms without provoking factors, transesophageal echocardiography may be performed to assess for the presence of a PFO or septal defect.[8][9][3] Patients with known PFO or septal defects may dive if these patients can otherwise tolerate exercise without symptoms. Currently, it is recommended that patients with known defects try to restrict their dives to 10 meters in maximum depth to reduce the extent to which nitrogen microbubbles form. Commercial divers with PFO should be offered surgical closure as there is some evidence that the procedure decreases DCS symptoms.[8][4]

Valvulopathy

Valvular disease is a relative contraindication; however, individuals with normal hemodynamics and asymptomatic exercise tolerance may be fit to dive. Despite this, patients with aortic or mitral stenosis and a valve opening < 1.5 cm2 should not dive.[6]

Cardiac Dysrhythmias and Pacing Devices

As in diabetes, the relative contraindication of cardiac dysrhythmias with diving stems from the difficulty in managing an incapacitated patient in the water. Patients with pre-excitation disorders, such as Wolf-Parkinson-White, may be permitted to dive if they have never experienced symptoms or cardiac arrhythmias stemming from their pre-excitation. Patients who have experienced paroxysmal supraventricular tachycardia are absolutely contraindicated in diving.[10] Chronic atrial fibrillation is another relative contraindication that may be permitted if the patient has been able to maintain good exercise tolerance.[10] And, as mentioned, diving can stimulate increased vagal tone which may incite symptomatic bradycardia in susceptible individuals.[9]

Patients with pacing devices may be able to dive depending on the model; however, it is essential to check the barometric rating for the device.[10] It is recommended that patients with AICDs refrain from diving as it is possible for the device to trigger while underwater which could incapacitate the diver or otherwise provoke anxiety. Patients who have received AICD placement prophylactically for genetic susceptibility to dysrhythmia may be permitted to dive as long as they remain within the depth specifications provided by the manufacturer.[4]

Obesity

In addition to being a risk factor for coronary artery disease, obesity has been found to be associated with higher grades of nitrogen microbubbles in tissues as nitrogen has a higher solubility in fat.[6] Thus, there is theoretically a higher chance of DCS in obese patients; however, this has not yet been demonstrated in epidemiologic studies.

Hypertension and Medication Management

While breath-holding is discouraged, it may occur at times while diving and is associated with an increase in blood pressure. Current guidelines recommend that blood pressure be controlled for at least 3 months before clearance for diving. It should be noted that some agents should be avoided in divers, particularly beta-adrenergic blockers, as these can induce bradycardia when combined with the increase in vagal tone from the diving reflex.

Clinical Significance

SCUBA is a physiologically taxing exercise. Despite the many considerations, the most important tools in determining cardiovascular fitness to dive are the risk factor screening questionnaires and the patient’s exercise tolerance. While there are many relative contraindications, the absolute contraindications remain those that are symptomatic and likely to incapacitate a diver as explained above.

Other Issues

Other considerations must be accounted for when considering fitness to dive. In particular, respiratory history and otolaryngeal anomalies may cause difficulties with diving. These topics are discussed elsewhere and should be reviewed during the initial screening for clearance to dive.


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Cardiovascular Fitness To Dive - Questions

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What is the minimum Mets required for someone with a history of coronary artery disease to be cleared for recreational diving?



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Which of the following factors is least likely to place divers at risk for dysrhythmia?



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At what age should a potential scuba diver with no known cardiovascular history be screened with an electrocardiogram?



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Which of the following is an absolute contraindication to diving?



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A 23-year-old female presents to your clinic for evaluation as she would like to enroll in scuba diving classes at the community college. She has a past medical history of diabetes mellitus. Which of the following is an absolute contraindication to diving?



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Cardiovascular Fitness To Dive - References

References

[Scuba diving and the heart. Cardiac aspects of sport scuba diving]., Muth CM,Tetzlaff K,, Herz, 2004 Jun     [PubMed]
null. 2017     [PubMed]
Doubt TJ, Cardiovascular and thermal responses to SCUBA diving. Medicine and science in sports and exercise. 1996 May     [PubMed]
Lynch JH,Bove AA, Diving medicine: a review of current evidence. Journal of the American Board of Family Medicine : JABFM. 2009 Jul-Aug     [PubMed]
Bove AA, Diving medicine. American journal of respiratory and critical care medicine. 2014 Jun 15     [PubMed]
Glen S,White S,Douglas J, Medical supervision of sport diving in Scotland: reassessing the need for routine medical examinations. British journal of sports medicine. 2000 Oct     [PubMed]
Korzeniewski K,Krzyżak J, Travel medicine for divers. International maritime health. 2017     [PubMed]
Sykes O,Clark JE, Patent foramen ovale and scuba diving: a practical guide for physicians on when to refer for screening. Extreme physiology     [PubMed]
Schwerzmann M,Seiler C, Recreational scuba diving, patent foramen ovale and their associated risks. Swiss medical weekly. 2001 Jun 30     [PubMed]
Eichhorn L,Leyk D, Diving medicine in clinical practice. Deutsches Arzteblatt international. 2015 Feb 27     [PubMed]

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