PHARMACOLO NURS 251 MODULE 3

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. Table 3.1 Classification of Hypertension Classification Blood Pressure (mm/Hg) Normotensive 120/80 Prehypertensive 120-139/80-89 Hypertensive 140/90 Stage 1 140-159/90-99 Stage 2 160/100 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 · Centrally acting o Alpha Agonists · Peripherally acting Clonidine- centrally acting alpha agonist Doxazosin- peripheral acting alpha blocker Centrally acting: stimulate alpha2 adrenergic receptors in the brain causing a lack of norepinephrine production. It also reduced the Centrally acting- means their site of action is in the brain. o alpha blockers o beta blockers Metoprolol- beta blocker *Carvedilol and labetalol have both alpha and beta blocking action. (generally classified as Beta Blockers still) activity of renin which is responsible for the production of the potent vasoconstrictor angiotensin II Peripherally acting: 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. Peripherally acting means their site of action is in the heart and blood vessels. Angiotensin Converting Enzyme Inhibitors (ACE Inhibitors) Lisinopril (Prinivil) Prevent angiotensin I from being converted to angiotensin II. Angiotensin II is a potent vasoconstrictor. It also stimulates the reabsorption of water and sodium into the body. Both of these actions raise blood pressure. Therefore by blocking, blood pressure is reduced. First line Drug of choice for hypertensive patients with Heart Failure and Diabetes due to their cardioprotective effect and protective effects on the kidney. Angiotensin II Receptor Blockers (ARBs) Losartan (Cozzar) Block the binding of Angiotensin II to type 1 Angiotensin II receptors. 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. First line Calcium Channel Blockers Amlodipine (Norvasc) Blocks Calcium from binding to receptors which causes smooth muscles to relax, thereby preventing contraction. First line Diuretics *Thiazide Hydrochlorothiazide Work by decreasing plasma and extracellular fluid volumes- this decreases the preload, which leads to a decrease in cardiac output and total peripheral resistance. First line Vasodilators Hydralazine Directly cause peripheral vasodilation- this results in a reduced SVR. Side Effects Direct Renin Inhibitors Aliskiren (Tekturna) Inhibits renin and decreases the formation of angiotensin I and II. Not recommended for initial treatment