A. Introduction • Hypertension (HT) is defined as a sustained elevation of systemic arterial blood pressure.
Systolic pressure: ventricles contract and eject blood, creating pressure in the arteries
Diastolic pressure: ventricles relax, heart temporarily stops ejecting blood, pressure in arteries falls
One in three adults in the U.S. have been diagnosed with HT, making this the most common of the cardiovascular diseases.
HT is usually found incidentally by healthcare professionals, and it is estimated that up to 30% of people with HT do not know they have it.
B. Factors affecting blood pressure • There are 3 major factors which affect blood pressure • 1. directions from vasomotor center, based on input from baroreceptors • 2. emotions • 3. hormonal/enzyme factors
1. Vasomotor center • Vasomotor center: this is a cluster of neurons in the medulla oblongata which regulates blood pressure on a minute to minute basis
Nerves travel from the medulla oblongata to the arteries and direct smooth muscle to constrict (↑ blood pressure) or relax (↓ blood pressure)
Baroreceptorsare clusters of neurons in the aorta and carotid artery that have the ability to sense blood pressure within these vessels and then provide the vasomotor center with this information
2. Emotions • Emotions can affect an individual’s blood pressure
Anger and stress may cause an increase in blood pressure, and if present for a long time may contribute to chronic hypertension.
a. Renin-angiotensin-aldosterone(RAA) pathway • This is the primary homeostatic mechanism controlling blood pressure and fluid balance
When there is a ↓ in blood pressure or blood volume (due to hemorrhage, dehydration, etc) the enzyme renin is released by the kidneys
Renin acts on angiotensinogen (produced by liver) converting it to angiotensinI (inactive)
In the lung capillaries, angiotensin converting enzyme (ACE) modifies angiotensin I to angiotensin II (active)
Angiotensin II then: • a. stimulates secretion of aldosterone which causes Na1+ retention and H2O reabsorption at kidneys
b. stimulates the secretion of ADH (vasopressin) which is synthesized in the hypothalamus and stored in the posterior pituitary, leading to H2O reabsorption
b. atrial natriuretic peptide(ANP) • An ↑ in blood pressure or blood volume leads to a stretching of the cardiac muscle fibers in the walls of the atria
They release ANP, whose 3 effects are the opposite of angiotensin II: • a. ANP enhances the secretion of Na1+ and H2O at kidneys
b. ANP inhibits the secretion of aldosterone and ADH • c. ANP suppresses thirst
Category Systolic Diastolic • Normal < 120 <80 • Pre HT 120-139 80-89 • Stage 1 HT 140-159 90-99 • Stage 2 HT ≥ 160 ≥ 100
Optimal blood pressure is associated with the lowest cardiovascular risk.
Those who fall into the pre HT category are at risk for developing HT unless life-style modification is instituted.
Stages 1 and 2 are associated with increased risk for target organ disease events: • MI • kidney disease • stroke
Therefore, both Stage 1 and Stage 2 HT need effective long-term therapy.
D. Primary versus Secondary HT • HT may also be classified as either primary or secondary.
1. Primary hypertension • Primary HT is also known as idiopathic HT and accounts for 90-95% of cases.
A combination of genetic and environmental factors is thought to be responsible for the development of primary HT including:
c. gender/ethnicity • Caucasian: 30.6% of males, 31.0% of females; • Hispanic Americans: 27.8% of males, 28.7% of females; • African Americans: 41.8% of males, 45.4% of females; • (derived from the American Heart Association 2006).
f. heavy alcohol consumption • This is considered to be more than 3 drinks per day, but moderate drinkers (2-4 drinks per week) appear to have lower blood pressure than either abstainers or heavy drinkers
g. obesity • As you gain weight, the amount of blood circulating through your body increases, resulting in added pressure on your artery walls.
In addition, excess weight often is associated with an increase in heart rate and a reduction in the capacity of your blood vessels to transport blood. All of these factors can increase blood pressure.
2. Secondary hypertension • Secondary HT is caused by altered hemodynamics associated with a primary disease, such as renal disease
Although many diseases can cause secondary HT, this form accounts for only 5-8% of all cases of HT.
Known causes for secondary HT include: • a. diabetic nephropathy (the most common type of kidney failure)
b. Polycystic kidney disease, an inherited condition, where cysts in the kidneys disrupt normal function and raise blood pressure.