Module 3
3.1: Introduction to Cardiology
Taking a Blood Pressure
Blood pressure is the pressure exerted against the walls of blood vessels as blood circulates through the body. Blood
pressure is measured using an instrument called a sphygmomanometer, perhaps more commonly known as the blood
...
module 3 31 introduction to cardiology taking a blood pressure blood pressure is the pressure exerted against the walls of blood vessels as blood circulates through the body blood pressure is meas
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Module 3
3.1: Introduction to Cardiology
Taking a Blood Pressure
Blood pressure is the pressure exerted against the walls of blood vessels as blood circulates through the body. Blood
pressure is measured using an instrument called a sphygmomanometer, perhaps more commonly known as the blood
pressure cuff. The pressures associated are measured in units of millimeters of mercury (mm/Hg). The health care
provider inflates a blood pressure cuff in order to cut off the blood flow from the brachial artery. As they release the
pressure in the cuff, they are listening with a stethoscope, for the first sound, called the Korotkoff sound, meaning there
is no longer enough pressure to keep all the blood from flowing. The Korotkoff sound corresponds to a numerical gauge
on the sphygmomanometer and is called the systolic value (top number) of the patient’s blood pressure. The provider
continues to let air out of the cuff and eventually the sounds disappear, representing that the brachial artery is now
completely open. When this occurs, the numerical value on the sphygmomanometer is known as the diastolic value
(bottom number) in a patient’s blood pressure.
Hypertension is defined as the persistent systolic blood pressure of greater than 150mm/Hg and/or a diastolic blood
pressure greater than 90mm/Hg in patients 60 years of age and older. For patients younger than 60 or those with kidney
disease or diabetes, it is defined as a systolic reading greater than 140mm/Hg and diastolic greater than 90mmHg.
Hypertension is often an asymptomatic disease and is also considered the most common disease state worldwide. Table
3.1 below breaks down different classifications of hypertension.
Essential hypertension, also known as primary hypertension, is when the cause of the increased blood pressure is
unknown.
Secondary hypertension is when a patient’s elevated blood pressure is caused by another disease.
Orthostatic hypotension, which is when a patient experiences a sudden drop in blood pressure when they change
positions (i.e. when going from a seated position to standing).
Physiologic Factors that Determine Blood Pressure
Blood Pressure is determined by cardiac output, the amount of blood ejected from the heart’s left ventricle multiplied by
the Systemic Vascular Resistance (SVR), the resistance to blood flow.
Cardiac output is determined by two factors: heart rate (beats per minute) and stroke volume (volume of blood pumped
per minute).
SVR is determined by the diameter of the blood vessel as well as the musculature nature of the blood vessel.
An increase in any of the above factors: heart rate, stroke volume or SVR will result in a rise in blood pressure.
There are also several factors commonly associated with high blood pressure even though they alone do not cause high
blood pressure. Associated factors of blood pressure include: sodium intake, maintaining a healthy weight, avoiding
,smoking, proper exercise, and minimizing stress. If these contributing factors can be carefully regulated, then the blood
pressure can be reduced. Figure 3.1 below shows the factors that regulate blood pressure within the body and where
certain antihypertensive medications work.
Figure 3.1. Normal Regulation of Blood Pressure and corresponding medications. Blue boxes represent align with Cardiac Output.
Yellow boxed align with Systemic Vascular Resistance.
The kidney’s role will be discussed in more detail later in this module, but it is important to mention that with high blood
pressure there is an increased peripheral resistance which in turn decreases the blood supply to the kidney. Peripheral
resistance is the resistance generated by the flow of blood through the arteries. When this happens, the kidney releases
an enzyme called renin. Ultimately, renin leads to further vasoconstriction, water and sodium retention, and an increase
in blood pressure.
3.2: Antihypertensives
The goal of antihypertensive therapy is the reduction of cardiovascular and renal morbidity and mortality. According to
guidelines, drug therapy should be started in patients over the age of 60 if their blood pressure is greater than
150/90mm/Hg. In younger patients or those with chronic kidney disease or diabetes, it should be started when the blood
pressure is greater than 140/90mm/Hg.
Fortunately, we are now living in a time where there are many drug therapy options available for patients and often their
treatment needs to be individualized to meet their specific needs. There are essentially seven main classes of
antihypertensives that can be used or more commonly are used in combination with one another in order to get the
patient’s blood pressure to goal. Table 3.2 summarizes the different drug classes available to treat high blood pressure
and highlights how they work to reduce blood pressure. Refer to Figure 3.2 to place where in the body each of these
major drug classes is exerting their effect.
Table 3.2 Antihypertensive Drug Classes and Mechanism of actions.
Class Example Mechanism of Action Special Considerations
Adrenergic Agents Clonidine- centrally Centrally acting: stimulate alpha2 Centrally acting- means
· Centrally acting acting alpha agonist adrenergic receptors in the brain their site of action is in the
o Alpha Agonists Doxazosin- peripheral causing a lack of norepinephrine brain.
· Peripherally acting acting alpha blocker production. It also reduced the
, o alpha blockers Metoprolol- beta blocker activity of renin which is responsible Peripherally acting means
o beta blockers *Carvedilol and labetalol for the production of the potent their site of action is in the
have both alpha and beta vasoconstrictor angiotensin II heart and blood vessels.
blocking action.
(generally classified as Peripherally acting:
Beta Blockers still) Alpha-block norepinephrine’s effect
on alpha1 adrenergic receptors.
Primarily this dilates arteries and
veins reducing SVR and blood
pressure.
Beta- Block beta receptors causing a
reduction in heart rate. They also
reduce the secretion of renin. Long
term use also reduced SVR.
Angiotensin Lisinopril (Prinivil) Prevent angiotensin I from being First line
Converting Enzyme converted to angiotensin II. Drug of choice for
Inhibitors (ACE Angiotensin II is a potent hypertensive patients with
Inhibitors) vasoconstrictor. It also stimulates Heart Failure and Diabetes
the reabsorption of water and due to their
sodium into the body. Both of these cardioprotective effect and
actions raise blood pressure. protective effects on the
Therefore by blocking, blood kidney.
pressure is reduced.
Angiotensin II Losartan (Cozzar) Block the binding of Angiotensin II First line
Receptor Blockers to type 1 Angiotensin II receptors.
(ARBs) This blocks vasoconstriction and the
secretion of aldosterone.
Aldosterone causes sodium and
water to be reabsorbed into the
body, which can raise BP. Therefore,
by blocking, blood pressure is
reduced.
Calcium Channel Amlodipine (Norvasc) Blocks Calcium from binding to First line
Blockers receptors which causes smooth
muscles to relax, thereby preventing
contraction.
Diuretics Hydrochlorothiazide Work by decreasing plasma and First line
*Thiazide extracellular fluid volumes- this
decreases the preload, which leads
to a decrease in cardiac output and
total peripheral resistance.
Vasodilators Hydralazine Directly cause peripheral Side Effects
vasodilation- this results in a
reduced SVR.
Direct Renin Aliskiren (Tekturna) Inhibits renin and decreases the Not recommended for
Inhibitors formation of angiotensin I and II. initial treatment
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