Hypertension and Diving

By Fred Bove, M.D., Ph.D.

Hypertension (high blood pressure) affects more than 12 million Americans, and when untreated causes serious illness and shortens life. Questions often arise about diving with hypertension while taking medication.

The Nature of Blood Pressure
Blood pressure is the pressure that is present in the arteries of the body. The pressure is generated by the heart, and it is the driving force that delivers blood to the tissues and organs of the body. Blood pressure is usually given as two numbers. The upper number, systolic blood pressure, is the pressure at the height of the pulse. The lower number, diastolic pressure, is the pressure inside the arteries during the resting phase of the heartbeat. Normal blood pressure in an adult is around 120/80 mm of mercury.

Sustained elevation of blood pressure exceeding 140/90 is considered to be hypertension. Most people with hypertension have no identifiable cause for it, and many are unaware of their elevated pressure. In a few patients, however, hypertension has an identifiable cause such as abnormal function of the thyroid or the adrenal glands, narrowing of the central artery of the body, kidney problems or hormonal imbalances. In addition, the frequent use of alcohol causes hypertension, and it is thought by some that cigarette smoking also elevates blood pressure.

Hypertension causes damage to the heart and kidneys, and to blood vessels feeding the brain, the heart and the limbs. It is the damage to blood vessels that causes an increased risk for strokes and heart attacks. Elevated blood pressure reduces exercise tolerance by causing an excess load on the heart during exercise.

Treatment of Hypertension
Often mild hypertension can be treated with exercise and reductions of salt intake, weight, alcohol and smoking. If blood pressure is severely elevated, or if these initial efforts are unsuccessful, then treatment must include medication. While a single daily dose of one medication may be all that is needed, often combinations of two or more medicines are more effective.

If you are being treated with a medication for hypertension, you should know the name of the medication, the dose and the side effects of the drug. Different blood pressure medications cause different reactions to both exercise and diving. Knowledge of your medication will help to avoid problems while diving.

Interaction of Blood Pressure Drugs with Diving
Anti-hypertensive medication can affect mental status, resistance to cold, ability to exercise, fluid balance, fatigue and the ability to maintain normal blood pressure during changes in position. Some medications cause mild sedation and might interact with nitrogen to exaggerate the effects of nitrogen narcosis.

Beta blocker medications block the effects of adrenaline on the circulation and the heart. Some divers taking these medications experience cold hands and feet due to blood vessel constriction during cold water diving. Beta blockers also reduce exercise tolerance, but in the doses used for hypertension they rarely will cause significant reductions in ability to exercise while diving.

Some blood pressure medications are diuretics, drugs that cause the body to lose sodium and water. Diuretics can interact with a hot, dry environment to exaggerate dehydration. If you are taking a diuretic, it is advisable to take the medication after diving, and to drink adequate fluids to avoid dehydration.

Another class of anti-hypertensive medication is the Calcium Channel Blocker. Since muscle cells rely on calcium to contract, these medications lower blood pressure by blocking calcium entry into the cells, thereby relaxing the muscle cells in the arterial walls and allowing the arteries to dilate.

Whenever blood pressure medications are being used, you should be careful to avoid sudden changes from lying to standing or sitting to standing. Dizziness may indicate that the medication is excessive.