High blood pressure, or hypertension, is a common condition where the force of blood pushing against the artery walls is consistently too high. This chronic elevation forces the heart to work harder, which can lead to long-term damage to the arteries, heart, and other organs. Hypertension is a significant risk factor for serious events like heart attack and stroke, which become catastrophic underwater. Scuba diving with hypertension depends entirely on whether the condition is well-managed and if there is no evidence of associated organ damage. Clearance requires a careful medical assessment by a physician familiar with diving physiology.
Understanding Physiological Risks Underwater
The unique environment of scuba diving introduces several physiological stresses that can worsen pre-existing hypertension. Immersion in cold water causes blood vessels near the skin’s surface to narrow (peripheral vasoconstriction), shunting blood toward the body’s core. This shift significantly increases the central blood volume and can cause a temporary spike in blood pressure, adding strain to the cardiovascular system. The physical exertion of swimming, especially against a current or during an emergency, further elevates the heart rate and blood pressure, raising the risk of an underwater cardiac event.
The constant pressure changes and the cold environment also increase the risk of immersion pulmonary edema (IPE). IPE involves a rapid accumulation of fluid in the lungs, a rare but often fatal complication that is more likely to occur in individuals with hypertension. Hypertension is associated with endothelial dysfunction, which may make the blood vessels in the lungs more susceptible to the pressure changes and fluid shifts that trigger IPE. Divers with hypertension may also have an increased susceptibility to decompression illness (DCI).
Cold water immersion also triggers immersion diuresis, where the body perceives the increased central blood volume as a fluid overload and attempts to correct it by increasing urine production. This effect can lead to dehydration and an imbalance of electrolytes, which is particularly relevant for those with hypertension. Dehydration may increase the risk of DCI by reducing blood volume. The psychological stress often associated with diving also contributes to elevated blood pressure through the release of stress hormones.
Evaluating Antihypertensive Medications
Managing high blood pressure for diving involves ensuring the medication chosen is effective without introducing side effects that compromise safety underwater. The medication regimen must be stable and the blood pressure consistently controlled before a physician will consider clearance for diving.
Angiotensin-Converting Enzyme inhibitors (ACE inhibitors) and Angiotensin II Receptor Blockers (ARBs) are often considered the preferred first-line treatments for divers with hypertension. These classes of drugs are generally compatible with diving, though ACE inhibitors can sometimes cause a persistent dry cough, which might be problematic underwater.
Diuretics, which increase urination to lower blood pressure, are less preferred because they can exacerbate the immersion diuresis effect. This increased fluid loss raises the concern for dehydration and electrolyte disturbances, which may increase the risk of decompression sickness.
Beta-blockers pose challenges, as they slow the heart rate and reduce the force of contraction. This action can limit the diver’s maximum exercise tolerance and prevent the heart from responding adequately to the sudden, high exertion required during an emergency. Beta-blockers can also mask symptoms of other diving-related issues, such as hypoglycemia or severe decompression illness, by blunting the body’s natural stress response.
Calcium channel blockers relax blood vessels but carry a risk of orthostatic hypotension. This side effect causes a sudden drop in blood pressure when standing up, which is a safety concern when a diver is exiting the water and the central pooling effect of immersion is reversed. Physicians must confirm that the side effects are minimal and do not impair the diver’s performance or ability to manage an emergency.
Obtaining Medical Clearance for Diving Safety
A diver seeking clearance with a history of high blood pressure must undergo a thorough evaluation from a physician with expertise in diving medicine. This specialized consultation goes beyond a routine physical exam to assess how the body will respond to the specific physiological challenges of the underwater environment. The physician will require evidence that the hypertension is well-controlled, which is generally defined by a resting blood pressure reading below 140/90 mmHg, with some guidelines preferring a reading below 130/80 mmHg.
The medical assessment will often include baseline tests to check for any existing damage to organs that hypertension may have caused over time. These tests may involve an electrocardiogram (ECG) and potentially an exercise stress test, especially for divers over 40 or those with other cardiovascular risk factors. The stress test evaluates the heart’s capacity to handle the physical demands of diving, ensuring the diver can sustain the high exertion needed during an emergency. A detailed log of home blood pressure readings over several weeks is also typically required to demonstrate consistent control.
Diving is temporarily or permanently prohibited if the high blood pressure is uncontrolled, meaning readings are consistently above the acceptable threshold, or if there is evidence of significant associated health issues. Specific contraindications include malignant hypertension, recent stroke or heart event, or significant coronary artery disease. The physician’s final clearance confirms that the diver has sufficient cardiac reserve, a stable medication regimen, and no underlying complications that the stresses of diving could worsen.