The question of whether an individual with high blood pressure (hypertension) can safely participate in scuba diving is serious, as the activity places significant demands on the cardiovascular system. Diving involves exposure to cold, increased ambient pressure, and physical exertion, all of which dramatically affect blood pressure regulation. Hypertension is a major risk factor for heart-related events, and the underwater environment can magnify these risks if the condition is not well-managed. Given the potential for sudden incapacitation, which is especially dangerous underwater, medical clearance is required for anyone with a history of hypertension who wishes to dive. Fitness to dive is conditional and depends almost entirely on the stability of the condition and the absence of associated organ damage.
Controlled Versus Uncontrolled High Blood Pressure
Diving medical organizations generally suggest that a diver’s blood pressure should be below 140/90 mmHg, though some sources accept 145/90 mmHg for a stable patient. The most important factor is the absence of damage to organs such as the heart, kidneys, or eyes that results from long-term, unmanaged high blood pressure.
Uncontrolled hypertension is a contraindication for diving because it significantly increases the risk of a cardiovascular event. A blood pressure reading consistently above 160/100 mmHg typically prevents diving until the pressure is successfully lowered and stabilized with treatment. All divers with hypertension must undergo a thorough medical evaluation by a physician familiar with diving medicine to confirm control and assess overall cardiovascular fitness. This evaluation ensures the heart can handle the extra work imposed by the underwater environment.
How Immersion Affects the Cardiovascular System
Immersion in water, particularly cold water, triggers physiological responses that increase the workload on the heart and raise central blood pressure. Peripheral vasoconstriction occurs when blood vessels near the skin constrict to conserve body heat. This constriction increases the resistance the heart must pump against (systemic vascular resistance), driving blood pressure upward.
Simultaneously, the hydrostatic pressure of the water causes a central fluid shift, pushing blood from the extremities back toward the chest cavity and central circulation. This pooling increases the volume of blood returning to the heart, elevating the heart’s preload. A hypertensive heart must work harder to pump this increased central blood volume against the elevated resistance caused by cold-induced vasoconstriction.
This combination of increased preload and afterload places strain on the heart. The dense compressed gas breathed at depth and the physical exertion required for swimming also add to the heart’s workload. For divers with uncontrolled hypertension, this magnified strain can lead to acute incidents like heart failure or immersion pulmonary edema (IPO), where fluid leaks into the lungs.
Navigating Antihypertensive Medications Underwater
Most divers with controlled high blood pressure use medication, and the primary goal is that the drug effectively controls blood pressure without causing side effects that compromise safety underwater.
Beta-Blockers and Diuretics
Beta-blockers slow the heart rate and reduce maximum output, potentially lowering a diver’s exercise tolerance. Physicians may require a stress test to confirm that a diver taking a beta-blocker can still achieve sufficient exercise capacity. Diuretics increase urine production to reduce blood volume, but this effect carries the risk of dehydration. Divers on diuretics must be diligent about maintaining proper hydration and electrolyte balance.
ACE Inhibitors and ARBs
Angiotensin-converting enzyme (ACE) inhibitors and Angiotensin II Receptor Blockers (ARBs) are often preferred because they are generally well-tolerated and less likely to impair exercise capacity. However, all antihypertensive medications can cause orthostatic hypotension, a sudden drop in blood pressure upon standing. This could cause dizziness or fainting when exiting the water or standing up quickly on a boat.
Increased Risk of Diving-Related Medical Incidents
Hypertension significantly elevates the risk of severe medical incidents underwater. The increased cardiac workload and elevated central blood pressure during a dive can precipitate a myocardial infarction (heart attack) or a stroke, especially during maximal exertion like fighting a strong current. These events are often fatal underwater, where immediate medical intervention is impossible.
Hypertension is also linked to an increased susceptibility to Decompression Illness (DCI). Long-term high blood pressure can compromise the health of the blood vessel lining (endothelium). This impaired vascular function may interfere with the body’s ability to efficiently off-gas inert nitrogen, potentially increasing the risk of bubble formation and DCI.
Another specific danger is the increased risk of Immersion Pulmonary Edema (IPO). Individuals with hypertension are more prone to IPO, as their cardiovascular systems are less resilient to the cold-induced peripheral vasoconstriction and central fluid shift. Divers with this condition must use conservative safety margins, often meaning shorter or shallower dives than standard no-decompression limits.