Are beta-blockers compatible with underwater activity (scuba diving or freediving) ?

By seriniti , on 31 May 2022 - 8 minutes to read


A beta blocker is a drug indicated for the treatment of high blood pressure, coronary artery disease (angina), certain rhythm disorders and heart failure. It is also prescribed in cases of obstructive cardiomyopathy, essential tremors (without a known cause), and thyrotoxicosis (a set of symptoms related to hyperthyroidism, among which is a significant tachycardia). This list is not exhaustive. Some beta-blockers can be proposed for the treatment of migraine and sometimes be prescribed “blow for blow” to calm stress and anxiety.

It should be noted from the outset that certain pathologies constitute a formal and definitive contraindication to diving (scuba or apnea). These include obstructive cardiomyopathy, heart failure due to the risk of acute pulmonary edema, certain specific ventricular rhythm disorders, all pathologies with a risk of syncope and long QT syndromes (read our article on the subject here).

Beta blockers act by blocking the place of adrenergic mediators (noradrenaline/adrenaline) on beta receptors without triggering any reaction (this is why they are called competitive antagonists of these receptors).

There are two kinds of adrenergic receptors in the body :

  • The beta 1 receptors, located in the heart muscle and on the kidney ;
  • Beta 2 receptors, located mainly in the smooth muscle fibers of the lung and in the coronary vessels.

Therapeutic effects of beta blockers

Therapeutic effects in relation to their binding to beta1 receptors :

  • Decreased force of cardiac contraction (inotropic effect),
  • Decrease in heart rate (chronotropic effect),
  • Decrease in atrioventricular conduction velocity,
  • Decreased ventricular excitability,
  • Increased renin secretion (which raises blood pressure).

These effects result in :

  • A decrease in cardiac output,
  • A decrease in blood pressure,
  • A decrease in the O2 consumption of myocytes (muscle cells responsible for muscle contractions),
  • An increase in coronary perfusion.

Therapeutic effects after binding to beta2 receptors :

  • Vasoconstriction of the vessels by contraction of the muscle cells of their wall,
  • Constriction of the bronchi and bronchioles making the gas exchanges less efficient.

It is therefore immediately clear that, in this large family of drugs (17 present), a beta blocker with a selective affinity for beta1 receptors should be chosen for diving, giving it a cardio selective character. The beta2 receptors have unfavorable effects (bronchoconstriction, vasoconstriction) but it should be remembered that, whatever the treatment chosen, each molecule acts, in variable proportions, on both receptors.

Side effects related to the use of beta blockers

Some side effects are very frequent but not very serious, such as gastrointestinal problems like diarrhea, nausea, vomiting, sleep disorders, sometimes with nightmares, and, potentially more seriously, excessive bradycardia or cold extremities, which may necessitate stopping the treatment, which should always be done gradually. They occur at the beginning of treatment and generally subside in the weeks following the intake. More rarely, there may be a decrease in physical performance during exercise (related to the negative inotropic and chronotropic effect). A significant drop in blood pressure may cause fatigue and dizziness. Decreasing the dosage may be sufficient to solve the problem.

Use of beta blockers in diving

The undesirable effects of these drugs require a perfect tolerance with a controlled and well-balanced treatment. In no case should diving be formally contraindicated in a patient treated with a beta blocker except, as we have seen, if the treatment is indicated for a pathology that excludes the practice of diving because of the risks inherent to this pathology.

Neither should a diver’s beta blocker treatment be modified for another treatment, especially if the tolerance is good and the dosage is adapted.

Conduct of the federal physician (or the sports physician) for the Certificate of Absence of Contraindication (CACI) in a patient seen for the first time for a CACI or for a renewal of CACI :

  • Patient seen in consultation, treated with beta blocker and under 40 years old :

We will put aside from the outset the cases of certificates for professional diving which are outside the scope of recreational diving. In recreational diving, the use of beta blockers was formally discouraged until recently. However, things have changed. Currently, the recommendations adopted are those of Bove, who admits that beta blockers are not contraindicated provided that they are perfectly tolerated and, above all, that physical capacities are verified by an effort test under treatment. Diving will not be contraindicated if the peak VO2 max (maximum flow of O2 that the body will be able to absorb to meet its needs) is greater than 40 ml/min/kg.

  • Patients over 40 years old :

The course of action is the same if tolerance is excellent, but as a precaution, an electrocardiogram will be added every year.

  • Patient seen for the first time, treated with beta blocker and wishing to dive :

In no way should the treatment be changed for this sole wish. Apart from the absolute contraindications already mentioned, the indications compatible with diving remain the following :

  • Arterial hypertension, migraines, essential tremors, stabilized hyperthyroidism and sinus tachycardia. The assessment remains the same ;
  • Coronary artery disease will require a case-by-case evaluation before any decision is made to issue a certificate, as will supraventricular rhythm disorders, which need to be well tolerated and well stabilized by treatment.

In all cases, it is essential to look for signs of breathlessness (sometimes ignored by the patient) which are quite frequent with beta blockers, especially those that act significantly on beta2 receptors. This shortness of breath may herald a bronchospasm during diving, which will reveal asthma that may be very serious. If asthma is confirmed after a pneumological assessment, it is imperative that the use of beta blockers be contraindicated. In addition, the authorization to dive with asthma will refer to the decision tree adopted by the FFESSM. Shortness of breath under beta blockers can also reveal a moderate chronic bronchopneumopathy (pneumo assessment necessary with realization of a maximum expiratory volume second). If the indication of beta blockers cannot be avoided in this case, selective beta1 molecules should be used. The pneumological control will be repeated before making the decision to authorize the dive.

In conclusion :

Medical treatments with beta blockers are anything but harmless. It is a drug which, in the majority of cases, remains very well tolerated, in particular the selective beta1 molecules. Its medical indications are very strict and regular monitoring is necessary.

Special mention should be made of the treatment of stress by beta blockers. It is curious that such a treatment is proposed for a discomfort, sometimes important, which does not constitute an affection. However, it is understandable to use such a drug knowing that any organism subjected to stress naturally produces adrenaline and noradrenaline, which are responsible for muscular tension, sometimes tremors and an increase in heart rate. In addition, the beta blocker, unlike anxiolytics, has no sedative effect. It appears then that beta blocker is the miracle treatment before any examination. But in addition to these effects, beta blockers decrease the O2 consumption of myocytes and they also increase coronary perfusion. These are all very interesting factors during competitions for apneists who, for some, certainly think in good faith that by doing so, they are only reducing the understandable stress before an exam..

And yet !

In addition to the ever-present risk of bronchospasm, which is particularly possible and serious in apneists at the end of exercise, the bradycardia naturally induced by the drug will be further aggravated in these swimmers by a reflex bradycardia of immersion leading to a very low heart rate which is added to a decrease in the force of cardiac contraction. The progressive decrease during apnea exercise of the O2 concentration in the blood will progressively decrease the cerebral perfusion in O2 with a greater risk of syncope in these individuals.

The ethics of any sportsman, worthy of the name, obviously goes against such practices and any “facilitating” treatment to say the least. This sport, perhaps more than any other, is an inner journey, a fight against oneself and against the stopping of ventilation. It imposes a surpassing of oneself at every moment and no search for personal success justifies such behavior and such risk-taking.

Article written by Dr. Jean Jacques HUBINOIS, ENT, federal doctor, hyperbaric doctor and diving doctor.

Source : National and Medical Prevention Commission

Photo of the article : Alex Voyer©

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