A simple, non-invasive medical procedure holds the exciting prospect of permanently reducing high blood pressure in patients whose blood pressure is not adequately reduced by medication, or who cannot tolerate the medication. The procedure, known as renal denervation, targets the renin-angiotensin system, a chemical process within the body in which the kidneys contribute to elevated blood pressure.
Within the kidneys, specialized cells manufacture the enzyme renin, which is crucial to the regulation of blood pressure in the body. Renin combines with other enzymes from the liver and lung capillaries to form angiotensin II, a stimulant that causes the smooth wall muscles of the vascular system to contract, increasing blood pressure. The kidneys produce renin mainly to maintain blood pressure at a level necessary for their blood filtration process to function properly. If blood pressure falls, for example, due to some sort of trauma, the kidneys will increase renin production in an effort to counteract the drop in pressure.
Another stimulator of renin production in the kidneys is the sympathetic nervous system, the part of the nervous system responsible for the unconscious flight-or-fight response of the body under stress. Under actual trauma, blood vessel constriction resulting from renin production helps the body endure wounds by reducing blood loss. However, for some people, hyperactivity of the sympathetic nervous system serving the kidneys may exist even under normal conditions, leading to chronic overproduction of renin, and thus, chronic high blood pressure.
The sympathetic nervous system pathway to renin production is the target of renal denervation. The treatment consists of a one-time procedure in which a catheter is inserted into a leg artery and routed to the renal artery. A line with a specialized RF emitting tip is inserted through the catheter, to the vicinity of the target nerves, where approximately six two-minute bursts of high frequency radio waves are applied. The radio bursts weaken the problematic sympathetic nerves without damaging the renal artery.
The procedure has not been shown to have any adverse effects on kidney function.
Blood pressure medications that target specific enzymes of the renin-angiotensin system, either by inhibiting their production or by blocking their actions, have been available for a number of years. Some patients require several of these medications in combination to achieve the desired reduction in blood pressure.
But in many cases, despite taking numerous medications, a patient’s blood pressure may remain stubbornly high. These patients are likely to be the first to benefit from renal denervation.
The results of trials with renal denervation showed a lasting reduction of blood pressure, averaging 27-32 mmHg systolic (upper reading) and 10-17 mmHg diastolic (lower reading). These benefits persisted, even at 12 months post-treatment. There have been some questions as to whether nerve regeneration will eventually occur after the procedure, resulting in a gradual reduction in benefits over time, but that remains to be determined by long-term studies.
If future renal denervation trials confirm the safety and effectiveness of the treatment that has been observed so far, then medical science will have yet another tool in its arsenal to combat the major public health issue of uncontrollable high blood pressure.
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Krum, H., et. al. Catheter-Based Renal Sympathetic Denervation in the Management of Resistant Hypertension. http://www.ardian.com/pdfs/ACC%20-%20FIM%2050%20Final%20for%20PDF.pdf. Retrieved 18 Dec. 2010.