According to the American Heart Association, resistant hypertension is a condition in which a person's blood pressure remains elevated despite treatment with three blood pressure-lowering medications or in which a person's blood pressure has been stabilized using at least four medications. Resistant hypertension increases the risk of heart disease, blood clots and strokes.
Renal Artery Stenosis
Renal arteries are arteries that branch out from the main artery of the heart, which is called the aorta. Renal arteries transport 25 percent of the blood that comes from the heart to the kidneys, which then filter the blood. Renal artery stenosis is a narrowing of the renal arteries. Constricted renal arteries to both kidneys often result in renal, or kidney, failure, whereas a constricted renal artery to one kidney can result in high blood pressure, also known as "renovascular hypertension," report Susan Begelman and Jeffrey Olin, contributors to the book "Endovascular Therapy for Atherosclerotic Renal Artery Stenosis." Renovascular hypertension normally resists treatment with blood pressure-lowering medications.
Renal Parenchymal Disease
Renal parenchymal disease is an umbrella term for diseases of the kidneys. It commonly involves an impairment of the mechanism that controls sodium levels, resulting in water retention, reports Michael Moore, M.D., contributor to "Hypertension Primer: The Essentials of High Blood Pressure." Renal parenchymal disease can be a cause or a consequence of resistant hypertension. Patients with renal parenchymal disease tend not to respond to blood pressure-lowering medications, and in many cases, the only life-preserving treatment is dialysis or a kidney transplant.
Overactive Adrenal Glands
Adrenal grands produce androgenic steroid hormones such as testosterone and stress hormones such as cortisol and adrenaline. Overactive adrenal glands secrete too much of one or more of these hormones, according to Dimitrios Linos and Jonathan Van Heerden, editors of "Adrenal Glands: Diagnostic Aspects and Surgical Therapy." Too much testosterone can give rise to excessive male features, including a deepening of the voice, body and facial hair growth, baldness, and increased muscle volume. An excess secretion of aldosterone can result in resistant high blood pressure and low potassium levels. An excess amount of stress hormones, or corticosteroids, can result in resistant high blood pressure, weakened muscles and anxiety. The complications of the excess production of corticosteroids is also referred to as Cushing's syndrome.
Obstructive Sleep Apnea
In obstructive sleep apnea, breathing is obstructed several times during sleep after a period of heavy snoring. People with severe obstructive sleep apnea are 58 percent more likely to develop heart failure caused by resistant hypertension compared to controls, reports a Boston research team in the July 2010 issue of "Circulation: Journal of the American Heart Association." Sleep apnea results in oxygen depletion that lasts at least 10 seconds. Oxygen depletion causes blood oxygen levels to lower significantly. The body then compensates for this by secreting large amounts of adrenaline from the adrenal gland, which can cause hypertension or directly attack the heart, the researchers note.
Lifestyle Factors
According to the American Heart Association, heavy alcohol consumption and obesity commonly lead to resistant hypertension. Excess fat can cause the body to retain more sodium and hence more fluid, which normally leads to high blood pressure, reports a Georgia research team in the June 2010 issue of "American Journal of Physiology--Regulatory, Integrative and Comprehensive Physiology." Excess fat generates fat inflammatory molecules, including interleukin-6, or IL-6, which triggers a series of events that lead to salt reabsorption, the researchers explain. Cholesterol-lowering medications can control the condition to some extent, but in many cases, the resultant hypertension is resistant and potentially deadly.
References
- "Endovascular Therapy for Atherosclerotic Renal Artery Stenosis"; Michael R. Jaff, ed.; 2001
- "Hypertension Primer: The Essentials of High Blood Pressure"; Joseph L. Izzo, Henry Richard Black, Council for High Blood Pressure Research (American Heart Association); 2003
- "Adrenal Glands: Diagnostic Aspects and Surgical Therapy"; Dimitrios A. Linos and Jonathan A. Van Heerden; 2005
- "Circulation"; Prospective Study of Obstructive Sleep Apnea and Incident Coronary Heart Disease and Heart Failure: The Sleep Heart Health Study; Daniel Gottlieb et al.; July 2010
- "American Journal of Physiology: Regulatory, Integrative and Comparative Physiology"; Interleukin-6 Stimulates Epithelial Sodium Channels in Mouse Cortical Collecting Duct Cells; Ke Li et al.; August 2010
