Hypertension Blog

To determine if a patient has hypertension, of course, you’ll measure his blood pressure. From his blood pressure measurements, you can determine his pulse pressure and mean arterial pressure (MAP). These measurements, in turn, can help you detect related disorders and understand the effects of certain hemodynamic factors on your patient’s blood pressure.

Arterial System

Arteries, the vessels through which blood travels away from the heart, all carry oxygenated blood, except for the pulmonary arteries, which carry oxygen-depleted blood from the heart to the lungs. The arterial system is made up of vessels of various sizes:

• large, usually elastic arteries, such as the aorta and the pulmonary trunk
• medium-sized arteries, which make up most of the arterial vasculature
• large and small arterioles.

Arteries have nerves bundled along their outer walls. Primarily derived from the sympathetic nervous system, these nerves cause the arteries to contract and relax, thus regulating the flow of blood to various parts of the body.

Arterial Walls

All arteries have three distinct layers. The outer layer (tunica adventitia or externa) is made of strong connective tissue with abundant elastic fibers. The middle layer (tunica media) consists of more elastic fibers than smooth-muscle fibers. The inner layer (tunica intima) is a transparent and highly elastic structure that has direct contact with the circulating blood.

The thickness of each of these layers varies depending on the location of the artery. For instance, large arteries like the aorta or pulmonary arteries typically have a thick tunica media with more elastic fiber than smooth muscle, enabling them to stretch as blood is ejected from the heart during systole and to recoil during diastole. However, arteries located farther away from the heart have less elastic tissue and more smooth muscle. These small-sized to medium-sized vessels are muscular arteries. Together, all arteries help to maintain blood pressure throughout the high-pressure, high-resistance, low-volume arterial system.

Arteries become arterioles when the diameter of the vessel is less than 0.5 mm. The thick smooth-muscle layer of the arterioles enables them to control the flow of blood through the systemic circulatory system by means of vasodilation and vasoconstriction and push the blood through finer arterial structures, the capillaries.

You can derive two measurements from a patient’s systolic and diastolic blood pressures. These measurements can help in detecting conditions related to a patient’s high blood pressure and in understanding the hemodynamic factors that affect blood pressure. One such measurement, pulse pressure, is the difference between the systolic and diastolic pressures. For instance, if a patient’s blood pressure is 120/80 mm Hg, his pulse pressure is 40 mm Hg. Normally, a patient’s pulse pressure is 30 to 40 mm Hg.

Pulse pressure reflects stroke volume (SV), ejection velocity, systemic vascular resistance, and CO. An increased or widened pulse pressure, such as in a patient with a blood pressure of 160/40 mm Hg, signifies increased SV, which could result from the following conditions:

• high blood pressure
• sinus bradycardia
• complete heart block
• aortic regurgitation
• anxiety
• exercise
• catecholamine production
• arteriosclerosis of the large arteries and aorta.

Increases in pulse pressure reduce a patient’s systemic vascular resistance and may appear when a patient has a fever, is in a hot environment, or has been exercising.

A decreased pulse pressure can be caused by factors such as:

• heart failure, which causes reduced ejection velocity
• hypovolemia
• shock.

A patient’s MAP is the average pressure in the arteries throughout the cardiac cycle as influenced by CO and vascular resistance. This pressure varies in different parts of the body, from about 100 mm Hg in the aorta and large arteries to about 0 mm Hg at the end of the vena caval system.

To calculate a patient’s MAP, use the following formula:

MAP = diastolic pressure + Y3 pulse pressure Using this equation, a patient whose blood pressure is 120/80 mm Hg and pulse pressure is 40 mm Hg would have a MAP of 93.2 mm Hg.

Normally, a patient’s MAP ranges from 70 to 100 mm Hg. An increased MAP occurs with primary hypertension, arterial disease, and epinephrine release, and a decreased MAP can indicate decreased vascular resistance, cardiac failure, or hypovolemia.

Normally, hypertensive patients have a systolic blood pressure of 140 mm Hg or higher or a diastolic pressure of 90 mm Hg or higher on at least two separate occasions. However, even in healthy people, blood pressure fluctuates depending on the time of day and the activities they’ve been performing, so assessing hypertension requires several blood pressure measurements.Obtain at least one reading in both arms with the patient sitting, lying, and standing. A difference of 5 to 10 mm Hg between the arms is normal, but if the difference is more than 10 mm Hg, the patient may have arterial compression or obstruction on the side with the lower pressure.

If a hypertensive patient’s diastolic pressure increases when he stands up from a supine position, he may have primary hypertension. However, if his diastolic pressure decreases when he stands (and he’s not taking an antihypertensive drug), he may have secondary hypertension.

Take at least two measurements separated by at least 2 minutes. If the readings from the same arm vary by more than 5 mm Hg, recheck your technique and take additional readings until you obtain two that are similar. In particular, confirm a high reading with at least two subsequent readings. This helps to rule out white-coat syndrome­elevated blood pressure in response to the stress of having a health care professional take the reading. White-coat syndrome occurs about 20% of the time. Several other factors also can influence the accuracy of blood pressure readings.

Placing the cuff improperly or using a wrong­sized cuff may result in inaccurate readings. For example, using a regular adult cuff on an obese patient may give an incorrectly high reading .

You can use either a mercury or aneroid manometer. But remember that aneroid manometers require monthly calibration to ensure their accuracy.

Patient Preparation

To prepare the patient for blood pressure measurement, make sure you have him remain seated quietly, in a comfortable environment, for at least 5 minutes. Free his arm from clothing by either roIling up the sleeve or having him remove his long-sleeved shirt and offering him a patient gown, if necessary. Then place the arm in a comfortable position. Make sure his arm doesn’t have an AV fistula for dialysis, scarring from brachial artery cut­downs, or lymphedema, which may follow axillary node dissection and radiation therapy.

Palpate for the brachial pulse to make sure it’s present. Before applying the cuff, make sure the brachial artery, located at the crease of the antecubital fossa, is positioned at heart level. If the patient is sitting, a table that reaches just above his waist is usually sufficient. If the patient is standing, support his arm at midchest level. The reading can be falsely elevated if he expends effort keeping his arm up.

Nursing Considerations

If using a mercury manometer, position the gauge vertically with the meniscus at eye level. If using a calibrated aneroid manometer, turn the gauge so that it faces you. Place the cuff on the patient’s arm by centering the inflatable bladder over the brachial artery. Securely fasten the lower border of the cuff about 2.5 cm above the antecubital crease.

Falsely low blood pressure readings commonly occur when the cuff isn’t inflated high enough. To prevent this, first estimate the patient’s systolic blood pressure. Then add 30 mm Hg to this estimated pressure. This number will be the target for subsequent inflations; using it should prevent errors caused by an auscultatory gap. After obtaining the target number, deflate the cuff completely and wait a few minutes before taking an actual measurement .

To obtain the patient’s blood pressure measurement, place the bell of the stethoscope lightly over his brachial artery. The full rim should be in contact with his arm to create an air seal. Remember, the bell of the stethoscope will allow you to hear low-pitched Korotkoff sounds better than the diaphragm will.

Inflate the bladder quickly to the target level. Then deflate it at a rate of 3 mm Hg per second. As the pressure decreases, note the patient’s systolic pressure as the level at which you hear the sounds of at least two consecutive beats.

While continuing to release the pressure in the bladder, listen for the Korotkoff sounds to become muffled and then disappear. Note this level as the patient’s diastolic pressure. Usually, the points where the sounds are muffled and where the sounds disappear differ by only a few mm Hg. However, if the difference is more than 10 mm Hg, record both numbers along with the systolic pressure-for example, you might record a patient’s blood pressure as 160/90/72.

After the sounds have disappeared, continue listening while the pressure decreases another 10 to 20 mm Hg. Then rapidly deflate the cuff to zero.

If the sounds are difficult to hear, have your patient raise his arm and then open and close his hand five to ten times. Quickly inflate the cuff with his arm raised, then lower it and take a reading. This maneuver should help intensify the Korotkoff sounds.

You may also measure blood pressure in a patient’s leg, particularly if you’re trying to detec coarctation of the aorta. Wrap a thigh cuff around his thigh and place the stethoscope bell in the popliteal space. Then obtain the blood pressure measurement just as you would in the arm. If the systolic pressure in the leg is more than 20 mm Hg lower than the brachial systolic pressure, the patient probably has an arterial occlusion.

Another simple technique-the cold pressor test-can be used to enhance blood pressure measurement and help identify the severity of hypertension.

Recognizing Korotkoff Sounds

To accurately assess your patient’s systolic and diastolic blood pressure readings, you need to recognize the variations in the sounds you hear. After you inflate the blood pressure cuff and begin releasing air from it, you’ll hear the first of the five Korotkoff sounds described below. In this example, the blood pressure reading is 140/90 mm Hg.

Phase 1 (systolic blood pressure) A sharp thump, and then tapping.

Phase 2 A murmuring or swishing sound

Phase 3 The murmuring disappears, and sounds increase in intensity and clarity.

Phase 4 (first diastolic blood pressure) A softer blowing sound that fades.

Phase 5 (second diastolic blood pressure) The sounds disappear

You can measure a patient’s blood pressure directly or indirectly. To measure it directly, you’ll need an arterial catheter attached to a pressure measuring monitor. To measure it indirectly, you’ll need a blood pressure cuff, a stethoscope, and a sphygmomanometer, such as a mercury gravity or aneroid type.When performed correctly, indirect measurements are within 5 mm Hg of direct measurements. To measure blood pressure indirectly, first place an appropriate-sized blood pressure cuff on the patient’s arm. Then, place the bell of the stethoscope over the artery distal to the cuff. Next, inflate the cuff 30 mm Hg beyond the patient’s systolic pressure, at which point blood flow in the artery stops. Then, lower the cuff pressure and auscultate for Korotkoff sounds.

Korotkoff sounds

During auscultation, you’ll hear five Korotkoff sounds or phases. Phase 1 is characterized by a faint, clear, rhythmic tapping gradually increasing in intensity. The first sharp thump you hear is the systolic blood pressure, and this sound is produced by blood rushing into the collapsed artery as the pressure in the cuff decreases. The force of the blood determines the intensity of the sound.

Phase 2 begins when murmuring or swishing sounds are produced by blood flowing through the narrowed artery under the pressure cuff and into a wider artery distal to it. The difference in artery widths creates currents that cause the blood and vessel walls to vibrate. These sounds may temporarily disappear, particularly in hypertensive patients, and this silence is called the auscultatory gap. If you don’t detect the auscultatory gap, you may underestimate the patient’s systolic blood pressure or overestimate his diastolic pressure.

Phase 3 begins when the murmur of phase 2 disappears and the sounds begin to increase in intensity and clarity. In phase 3, the compressed vessel opens during systole but closes during diastole.

Phase 4 occurs when the sounds become muffled and less intense. This phase is referred to as the first diastolic pressure.

Finally, the sounds disappear completely in phase 5, also called the second diastolic pressure. During this phase, the vessel is completely open, and blood flows freely through the artery. At this point, you can palpate a strong radial pulse

Capillaries

Capillaries are the smallest and most numerous vessels in the arterial circulatory system. The walls of the capillaries consist of a fine, transparent, endothelial layer of tissue similar to the inner layer of the arteries. Capillaries have no elastic or muscular tissues, so nutrients and metabolic end products can pass through their thin walls.

Capillaries are interposed between arterioles and venules, creating networks. These networks permeate all tissues, supplying blood and nutrients. The more active the function of an organ or tissue, the greater the network of capillaries with­in it. These networks are typically large in bones and ligaments, smaller in glands and mucous membranes, and nearly absent in tendons.

Capillary networks contain specialized channels called metarterioles and rings of smooth muscle called precapillary sphincters. These sphincters contract and relax, regulating the flow of blood through the capillaries. Blood enters the capillary network as arterial blood, and after the exchange of nutrients and metabolic end products takes place, it exits as venous blood returning to the heart through the venous system .