Blood pressure still high? Maybe it's stress
NEW YORK — Despite considerable advances in the treatment of hypertension, many patients fail to respond to standard drug therapy, which focuses on regulating blood volume, salt intake, and the body's renin-angiotensin system. These patients may have a frequently overlooked entity — neurogenic hypertension — that requires different medication, according to a report by a New York Weill Cornell Medical Center researcher.
The review, by Dr. Samuel J. Mann, Associate Professor of Clinical Medicine at Weill Cornell Medical College, helps explain why so many patients with high blood pressure do not respond to standard drug regimens. Hypertension, like fever, has many causes. Those causes may involve the nervous system and other so-called "stress" hormones besides those released by the kidneys.
Only one-third of all hypertensive patients are salt-sensitive (the number is higher for African-Americans and the elderly). This is where neurogenic hypertension comes in.
Hypertension may be caused by increased activity of another important regulatory system — the sympathoadrenal system (SAS) — which comprises the sympathetic nervous system and the adrenal gland. In this form of "neurogenic" hypertension, blood pressure elevation is caused by the increased production of stress hormones — epinephrine (adrenaline) and norepinephrine — that make the heart work harder and constrict systemic arteries. Epinephrine stimulates cardiac beta receptors, which increase heart rate, stroke volume, and cardiac output, while norepinephrine stimulates both cardiac beta receptors and the alpha receptors that stimulate constriction of the systemic arteries.
Beta and alpha blockers get good response
"Hypertension remains inadequately controlled in 40 percent of treated patients," Dr. Mann said. "We need to widen our scope of investigation and look at other mechanisms that may be causing the hypertension. Different causes require different drugs. The bottom line is that treatment really must be individualized. It's not simply a case of 'one size fits all."
Patients with neurogenic hypertension do not respond well to the recently recommended first-line therapy — diuretics — because their condition is not driven by blood volume and salt, said Dr. Mann. However, they do respond to other medications, such as beta blockers and alpha blockers.
Beta blockers lower blood pressure by reducing both renin secretion and cardiac output, while alpha blockers lower blood pressure by reducing peripheral resistance. Thus, identifying neurogenic forms of hypertension offers the potential to better understand what is causing hypertension in individual patients and which drugs to prescribe.
Clinical indicators, rather than biochemical ones, may give clues of possible neurogenic hypertension, Dr. Mann said. Many patients with hypertension have other conditions, such as stroke, sleep apnea, obesity, tachycardia (rapid heart rate), and alcohol abuse.
Other clinical factors also might serve as indicators of neurogenic hypertension, although this area has not been well studied. These include situations in which the onset or pattern of hypertension are atypical, such as sudden onset, or severe or labile blood pressure elevation. Psychological factors also may be involved in some patients, even in individuals who appear unaffected by severe stress.
"It is important to recognize that neurogenic hypertension does exist, and that we need more clinical trials designed to identify patients with neurogenic hypertension and their response to different regimens," Dr. Mann said.
Source: NewY ork Weill Cornell Medical Center