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CHAPTER 16ALTERATIONS IN BLOOD

PRESSURE

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ARTERIAL BLOOD PRESSURE

• It is the pressure differences between the left and right sides of the heart that produce the gradient allowing systemic movement of blood

• Arterial blood pressure is produced by the force of left ventricular contraction overcoming the resistance of the aorta to open the aortic valve

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ARTERIAL BLOOD PRESSURE (CONT.)

Determinants of Systemic Blood Pressure• Cardiac output and the resistance to the ejection

of blood from the heart• CO = SV (stroke volume) x HR (heart rate)• End-diastolic volume is the preload• Systemic vascular resistance (afterload) is

determined by the radius of arteries and degree of vessel compliance

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ARTERIAL BLOOD PRESSURE (CONT.)

Measurement of Blood Pressure• Components of blood pressure measurement

• Systolic blood pressure—peak pressure during cardiac systole

• Diastolic blood pressure—lowest pressure during cardiac diastole

• SV is the primary factor influencing systolic pressure• SVR is the major determinant of diastolic pressure

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ARTERIAL BLOOD PRESSURE (CONT.)

• Components of blood pressure measurement• Mean arterial pressure is the calculated average pressure

within the circulatory system throughout the cardiac cycle

• MAP = (2 x diastolic pressure) + systolic pressure 3

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ARTERIAL BLOOD PRESSURE (CONT.)

Direct Measurement of Blood Pressure• Requires intraarterial catheter to transduce

arterial fluid pulsations into electrical signals (waveforms)

• Catheter commonly placed in radial artery• Most accurate method of measuring blood

pressure

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ARTERIAL BLOOD PRESSURE (CONT.)

Indirect Measurement of Blood Pressure• Commonly measured indirectly via the brachial

artery using a stethoscope and sphygmomanometer or automated oscillometric system

• Requires careful technique to ensure accuracy• Auscultation of Korotkoff sounds

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MECHANISMS OF BLOOD PRESSURE REGULATION

• Affected by neural, humoral, and renal factors• Blood pressure fluctuates over 24 hours due to

physiologic changes associated with circadian rhythm

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MECHANISMS OF BLOOD PRESSURE REGULATION (CONT.)

Short-Term Regulation of Systemic BloodPressure• Changes in BP are mediated through activation of

the sympathetic nervous system• Results in release of neurotransmitters

epinephrine and norepinephrine• Vasomotor center indirectly activated via

baroreceptors• Activates α1 receptors in smooth muscle of arterioles• Activates β1 receptors of the heart

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SHORT-TERM REGULATION OF SYSTEMIC BLOOD PRESSURE

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MECHANISMS OF BLOOD PRESSURE REGULATION

Long-Term Regulation of Systemic BloodPressure• Increase in extracellular fluid volume = increased

CO and SVR = elevated BP• Increased serum sodium level = increased

osmolality = increased ADH secretion• Renin–angiotensin–aldosterone system (RAAS)

important regulator of BP

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LONG-TERM REGULATION OF SYSTEMIC BLOOD PRESSURE

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MECHANISMS OF BLOOD PRESSURE REGULATION

Long-Term Regulation of Systemic BloodPressure• Angiotensin II produces an increase in SVR• Atrial natriuretic peptides cause kidneys to

increase sodium and water excretion by increasing the glomerular filtration rate

• Intrarenal arteriolar constriction leads to increased tubular reabsorption of sodium and water

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LONG-TERM REGULATION OF SYSTEMIC BLOOD PRESSURE

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MECHANISMS OF BLOOD PRESSURE REGULATION

Normal Fluctuations in Systemic BloodPressure• Suprachiasmatic nuclei in the brain govern daily

variations in bodily functions• Neural and hormonal regulation influences BP• Lifestyle influences can affect BP

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HYPERTENSION

• Most common primary diagnosis in the United States

• Increases morbidity and mortality associated with heart disease, kidney disease, peripheral vascular disease, and stroke

• Responsible for an annual worldwide death rate of 7 million

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HYPERTENSION (CONT.)

Definition and Classification• Determined by the Joint National Committee on

Prevention, Detection, Evaluation, and Treatment of High Blood Pressure

• Prehypertension is a range of pressures between normal and stage 1 hypertension in an effort to initiate interventions early enough to prevent or deter progression of the disease process

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

Primary Hypertension• Idiopathic disorder• Most common form of hypertension• Rare prior to the age of 10

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HYPERTENSION (CONT.)

Primary Hypertension • Subtypes

• Isolated systolic hypertension• Isolated diastolic hypertension• Combined systolic and diastolic hypertension• SBP is a major risk factor for subsequent cardiovascular

disease

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HYPERTENSION (CONT.)

Primary Hypertension • Risk factors

• Nonmodifiable• Family history• Age

• Modifiable• Dietary factors• Sedentary lifestyle• Obesity• Metabolic syndrome

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HYPERTENSION (CONT.)

Primary Hypertension• Outcomes

• End-organ damage• Increased myocardial work results in heart failure• Glomerular damage results in kidney failure• Affects microcirculation of the eyes• Increased pressure in cerebral vasculature can result in

hemorrhage

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

Primary Hypertension• Treatment interventions

• Lifestyle modifications are first and most important prevention and treatment strategy

• Drug therapy for hypertension address heart rate, SVR, and stroke volume

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

Secondary Hypertension• Hypertension attributed to a specific identifiable

pathology or condition• Most common form in children <10 years of age• May be related to:

• Renal disease• Coarctation of the heart• Pregnancy• Obesity/obstructive sleep apnea• Endocrine disorders

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HYPERTENSION (CONT.)

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HYPERTENSION (CONT.)

Hypertensive Emergencies and Urgency• Hypertensive emergency: sudden increase in

either or both systolic or diastolic blood pressure with evidence of end-organ damage• Rapid but controlled reduction of blood pressure using

parenteral antihypertensive agents under close monitoring (typically in ICU setting)

• Hypertensive urgency: similar blood pressure elevation without evidence of end-organ damage• Oral medications to bring blood pressure under control

over 24-48 hours

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LOW BLOOD PRESSURE

• Orthostatic (postural) hypotension is a decrease in systolic blood pressure (>20 mm Hg or >10 mm Hg within 3 minutes) when moving to an upright position

• Excessive increase in heart rate (by 20-30 beats/minute) may also be diagnostic

• May be a result of:• Problem with vasomotor or baroreceptor response• Adverse effect of drug therapy• Arterial stiffness• Volume depletion• Secondary disease process

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LOW BLOOD PRESSURE (CONT.)

Treatment• Review medication history• Slow positional changes• Avoid hot environments• Avoid large or carbohydrate-heavy meals• When symptoms begin, squatting/bending

forward or crossing legs may reduce effects