Hypertension

Hypertension (high blood pressure) is a common medical condition among the general population and divers.

Blood pressure is a measure of the force with which blood pushes outward on the arterial walls. A blood pressure reading is a ratio. The first number (systolic pressure) is measured when your heart is beating. The second is the diastolic pressure, taken when your heart is resting between beats. Blood pressure numbers are in millimetres of mercury (mmHg). A typical reading is 120/80 mmHg (“120 over 80”). What constitutes hypertension varies slightly from country to country and from reference to reference.

Epidemiology

• About one-third of U.S. adults have hypertension.
• 69% of those who have a first heart attack, 77% of those who have a first stroke and 74% of those with chronic heart failure have hypertension. It is also a risk factor for kidney disease.
• 348,000 deaths in the U.S. in 2009 had hypertension as either a primary or contributing cause.
• Only 47% of people with hypertension have the condition under control.
• 30% of American adults have prehypertension.

Sources: U.S. Centers for Disease Control and Prevention; and American Heart Association

Symptoms

Most people don’t have obvious symptoms and therefore don’t know they have hypertension. Some know they have it but don’t manage it because they feel fine.

Symptomatic people commonly have headaches, particularly at the back of the head. Headaches are common enough that people can underestimate them as a symptom. Spontaneous nosebleeds and shortness of breath are more concerning but don’t tend to occur until blood pressure has reached life-threatening levels.

Management

Mild hypertension can often be controlled with diet and exercise. In some cases medication may be necessary to keep blood pressure within acceptable limits. Many classes of drugs are used to treat hypertension, and they have varying side effects. Some individuals change medications after one is (or becomes) ineffective. Others might need more than one drug at a time to keep their blood pressure under control.

• Antihypertensive drugs, known as beta-blockers, may cause a decrease in maximum exercise tolerance and have some effect on the airways. These side effects typically pose no problem for the average diver.
• Another class of antihypertensives, known as angiotensin-converting enzyme (ACE) inhibitors, may be preferred for divers. A persistent dry cough is a possible side effect of ACE inhibitors.
• Calcium channel blockers are another choice. A potential side effect of these drugs is becoming lightheaded when standing up.
• Diuretics (drugs that promote the production of urine) are frequently used to treat hypertension. Their use requires careful attention to maintaining adequate hydration and monitoring electrolyte levels in the blood.

Complications

High blood pressure can affect your health in several ways. A person with hypertension faces short- and long-term complications. One of the main reasons why doctors pay so much attention to hypertension is because it is a silent killer.

• Short-term complications generally result from extremely high blood pressure. The most significant is the risk of a stroke due to the rupture of a blood vessel in the brain.
• Long-term detrimental effects are more common, including:
  • Coronary artery disease (angina)
  • Congestive heart failure
  • Atrial fibrillation
  • Chronic kidney disease
  • Stroke
  • Loss of vision

Implications in Diving

For The Diver

• With controlled blood pressure and no evidence of damage to major organs, the main concerns regarding fitness to dive are the side effects of the medication(s) used. Most antihypertensive drugs are compatible with diving as long as side effects are minimal and your performance in the water is not significantly compromised.
• If you have a history of hypertension, have a doctor monitor possible associated damage to the heart and kidneys.
• Have regular physical examinations, including screening for long-term consequences of hypertension such as coronary artery disease.

For The Dive Operator

• Controlled hypertension is not a contraindication for diving but is one of several cardiovascular risk factors.
• Medications for blood pressure control may have side effects such as dehydration, dizziness, chronic cough or decreased exercise capacity. These side effects can be a contraindication to diving and need to be addressed by a physician.
• Divers with hypertension should be under a physician’s care and be able to tell you their condition is under control and without complications.
• Older, obese or clearly out of shape divers are at increased risk of cardiovascular emergencies and may need further medical evaluation before diving.

For The Physician

• Ensure that divers with hypertension can tolerate high exertion for at least five to 10 minutes should it be required. Environmental conditions may change, or an emergency may arise in which the diver needs to exert themself to avoid a life-threatening risk.
• Elevated levels of catecholamines may cause additional stress on a heart that is already undergoing an increased preload and afterload due to immersion. A more conservative criterion for further testing is justified for divers.
• Cardiac arrest in the water has even worse outcomes than out-of-hospital events, so closer screening and evaluation for unacceptable risks are justified.
• When adding or changing a medication regimen, allow several weeks to monitor side effects. Do not have patients discontinue antihypertensive medication before diving.