Hypertension

rterial hypertension Greek hyper = over + Latin tensus = stretch is a very common condition of elevated blood pressure in the arterial circulation.  Commonly, the arterial tension or Blood Pressure (BP) is measured with a blood pressure cuff (sphygmomanometer) in the brachial artery of the left arm with the subject seated at rest for two minutes.  A stethoscope is placed over the brachial artery below the cuff.  The cuff is inflated to a level of pressure which completely compresses the artery, stopping pulsatile blood flow.  The cuff is gradually deflated until Korotkoff sounds (pulsing noises created by turbulent blood flow emerging from the partially compressed brachial artery) are heard via the stethoscope-the pressure reading on the sphygmomanometer at the point where the Korotkoff sounds are first heard is recorded and represents the systolic pressure.  Listening to the Korotkoff sounds continues until they stop-this reading is the diastolic pressure.

A standard arterial blood pressure reading is made up of two numbers XXX/YY, where XXX represents the systolic blood pressure, and YY equals the diastolic blood pressure.  The Systolic Blood Pressure (SBP) is the higher number, related to the Total Peripheral Resistance (TPR) determined by the degree of constriction of muscles in arteriolar walls, and the Cardiac Output (CO) of the heart = the amount of blood pumped into the arterial circulation with each beat of the heart.  The Diastolic Blood Pressure reflects the resting (diastolic) tension in the circulatory tree.  The pulse pressure equals the systolic minus the diastolic blood pressure.  In summary:

Arterial Blood Pressure = TPR x CO

Pulse Pressure (PP) = SBP - DBP

Normal BP is < 120/80 mmHg.¹ 

Early or prehypertension is a persistent BP of 120-139/80-89.

Hypertension (HTN), stage 1, is a BP of 140-159/90-99.

HTN stage 2 is a BP > 160/>100.

When taking the BP of some people, the Korotkoff sounds may persist, all the way down to zero-the diastolic BP is taken as the point at which the Korotkoff sounds suddenly become softer.

People over the age of 65 may develop systolic HTN with a widened PP, from stiffening (hardening) of their arteries due to atherosclerosis and calcification. 

Purpose

Why does the body elevate its arterial tension, when to do so over time increases the risk of heart attack, heart failure, strokes, dementia, kidney failure, and more?

When exposed to a life-threatening situation, the Fight or Flight response leaps into motion.                                 Maximal activation of the sympathetic nervous system, with the primitive brain (medulla oblongata) orchestrating the response.  Catecholamines (epinephrine and norepinephrine) are released (dumped) from the adrenal glands and sympathetic chains, constricting arterioles and increasing the heart rate and contractility, therefore  ^TPR x ^CO = ^BP, shunting blood flow to organs (brain, heart, lungs, kidneys, and skeletal muscle) critical in Fighting or Fleeing.  At the same time blood flow to the skin is decreased (to decrease blood loss if lacerated), and the gut (you're not going to feel like eating at a time like this).  In modern times, stress often comes from job pressures and the battles of daily living (smog and traffic, etc.).  The same Fight or Flight responses often operate under these conditions, pushing up the BP.

Hypervigilance or persistent sympathetic activation may be seen in some individuals working in stressful environments.  HTN may result from persistent ^TPR x ^CO, and tension-reducing food- and alcohol-seeking behavior may increase the BMI, with ^TPR x ^CO.  Other "escapes" from stressor angst may come via peripherals, such as the Internet, Television, Cinema, etc., with attendant mindless eating and soda drinking adding calories, but burning little.

Example Clinical Vignette

A fictitious person goes to a fictitious Primary Care Physician's (PCP's) office for chest pain off and on for 2 weeks.  A family history of obesity and HTN in the mother and MI in the father at age 43 was found.  The patient was a nonsmoker who was drinking 2 beers per night.  The height was 69 inches, weight  220 lbs., and BMI = 32.5 kg/m².  The BP was 216/106 mmHg.  Abdominal obesity was found.  A treadmill exercise stress test revealed low exercise tolerance at 7 METs but no evidence of ischemia by Electrocardiogram ECG = EKG).  Fasting laboratory tests were within normal limits, except for a Total Cholesterol (TC) of 303 mg/dL and LDL-cholesterol of 253 mg/dL, with HDL-C of 30 mg/dL and Triglycerides of 100 mg/dL.

The PCP makes diagnoses of HTN, stage 2; obesity, and hypercholesterolemia.  Nonpharmacologic interventions include a weight loss, lipid-lowering diet, with 2-3 gram/day sodium restriction (the US average daily sodium intake is 7-8 gm.-2-3 gm is pretty much the lower tolerated limit).  Stress reduction is recommended via yoga and daily walking, with target up to 2 miles in 30 minutes 5 days/wk.  A diuretic (hydrochlorothiazide) and ACE inhibitor  (lisinopril) are prescribed for the HTN, and a statin (atorvastatin) for the hypercholesterolemia.  Home blood pressure monitoring and recording are ordered, with cessation of alcohol use.  Follow up in 3 days for BP check.

Over 6 months of treatment, the patient quit alcohol, followed the diet, lost 25 lbs., with BP consistently at 120/70.  The weight is 170 lb. ( BMI = 26.0).  The TC is now 160, with LDL-C at 100, HDL-C at 45, and Triglycerides at 75.  Exercise now includes walkathons for various community groups.

Pathophysiology

HTN most frequently is said to be "essential" because no definite cause is found.  Contributing factors include emotional, financial and physical stress, obesity, genetic predisposition, alcohol use and other drug use, and lack of regular aerobic exercise (deconditioning). 

Many parts of the human body are involved in the regulation of BP: the brain, heart, kidneys, sympathetic nervous system, adrenal glands, the lining of the muscular walls of arterial-arteriolar systems, carotid bulbs (bodies), and more.  A problem with any of these organs or tissues can produce HTN.  An example: a rare type of tumor growing in an adrenal gland dumps large amounts of norepinephrine and epinephrine into the blood stream, increasing TPR and CO, causing severe BP elevations (^TPR x ^CO).

Complications

LaPlace's law says that the tension in the wall of a tube or balloon increases as the radius of the balloon increases.  The increased tension seen in the walls of arteries in the presence of HTN leads to: increased atherosclerosis (hardening of the arteries), increased proclivity for strokes, heart attacks, LVH (Left Ventricular Hypertrophy-enlargement of the pumping chamber exposed directly to HTN forces), heart failure, kidney failure, formation of aneurysms-bulges in arterial walls, such as an abdominal aortic aneurysm, most commonly seen in 65+ yr old men who smoke or have previously smoked for several years, often have HTN-use ultrasound for screening.  Larger aneurysms are prone to rupture as predicted by LaPlace's law.

Treatment

Nonpharmcological treatment includes diet, exercise, weight loss, relaxation methods, guided imagery, yoga, meditation and avoidance of contributing substance use-alcohol, tobacco, other drugs, such as ephedrine, pseudoephedrine and many OTC cold/allergy/sinus remedies.

Pharmacological intervention includes meds targeting alpha receptors of the brain, such as clonidine, doxazosin; meds slowing the heart rate and force of muscular contraction (decreased CO), such as beta blockers-metoprolol, inderal, etc. and drugs decreasing blood volume (decreased CO), such as diuretics-hydrochlorothiazide, etc. 

The kidneys are very important in the regulation of BP, so many agents for treatment of HTN act on their regulatory features-diuretics have already been mentioned, others include drugs which act on the renin-angiotensin system, such as ACE (Angiotensin Coverting Enzyme) inhibitors, ARBs (Angiotensin Receptor Blockers), and spironolactone, a drug which blocks the effect of an adrenal gland hormone called aldosterone, preventing the hormone's excretion of potassium in the renal tubule in exchange for sodium-this drug is used in treating heart failure, and Conn's syndrome-a condition which causes HTN because an adrenal gland tumor is secreting elevated amounts of aldosterone. 

Calcium channel blockers, such as amlodipine or nifedipine, block the flow of calcium in smooth muscle cells of the artery walls and affect the heart in such a way that TPR is decreased and CO is decreased (v TPR x v CO = v BP).

Many other agents are useful in the treatment of HTN, and more are on the way-with new applications, such as finding that sildenafil is helpful in the treatment of pulmonary hypertension.²

Summary

Hypertension is a highly treatable condition-it has no early symptoms or warning signals, therefore it must be sought out by screening BP checks, PCP physical exams, automatic blood pressure testing at pharmacies, health fairs, or a friend's or relative's cuff or a neighbor who happens to be a nurse.  Although most cases of HTN have no definite cause, BP remains highly controllable with nonpharmacologic and pharmacologic interventions.  Applying the above course of action = good prognosis.

Resources:

1.      Washington Manual of Medical Therapeutics LWW 2007; page 102

2.      Physician's Drug Handbook  LWW 2008; pp. 1076-1078