Blood Flow & Blood Pressure

Blood Flow Through the Heart

• Blood flow through the heart is as follows: 1. Right atrium, 2. Right ventricle, 3. Pulmonary artery, 4. Left atrium, 5. Left Ventricle, 6. Aorta

Mechanical System

• Systole involves contraction of the myocardium
• Diastole involves relaxation of the myocardium
• Cardiac output refers to the amount of blood pumped by each ventricle in one minute
• CO (cardiac output) is the product of SV (stroke volume) and HR (heart rate)

Factors Influencing Blood Pressure

• Blood pressure equals cardiac output multiplied by systemic vascular resistance
• Systemic Vascular Resistance dilation of blood vessels and the amount of blood pumping through the heart

Evidence-Based Guidelines for Blood Pressure Management

• Blood pressure measurements are categorized into four stages: Normal, Elevated, Stage 1, Stage 2, and Hypertensive Crisis
• Studies show elevated SBP is strongly associated with heart failure, stroke, and renal failure
• "Prehypertensive" blood pressures are no longer considered "high normal” needing only lifestyle modification to prevent CV (cardiovascular) Disease
• Thiazide-type diuretics are considered the initial drug therapy for most patients with hypertension, reducing the volume of blood being pumped

Etiology of Hypertension

• Primary hypertension occurs without an identified cause, and is 90-95% of all cases
• Contributing factors include increased sodium-retaining hormones and vasoconstrictors, diabetes mellitus, greater than ideal body weight, increased sodium intake, and excessive alcohol intake
• Secondary hypertension is defined as elevated blood pressure with a specific cause in 5–10% of adult cases
• Contributing factors of secondary hypertension: Coarctation of the aorta, renal disease, endocrine disorders, neurologic disorders, cirrhosis, and sleep apnea

Risk Factors for Primary Hypertension

• Risk factors include age, where vessels become more rigid, alcohol, cigarette smoking, diabetes mellitus, elevated serum lipids, excess dietary sodium, as well as gender, family history, obesity, ethnicity, sedentary lifestyle, socioeconomic status, and stress

Pathophysiology of Primary Hypertension

• Genetic factors have little contribution to blood pressure levels in the general population
• Stress and increased sympathetic nervous system (SNS) activity produces vasoconstriction, increases heart rate, and increases renin release
• Water and sodium retention indicate a high sodium intake may activate mechanisms resulting in water retention
• High insulin concentration stimulates SNS activity and nitric oxide-mediated vasodilation, resulting in elevated blood pressure
• Certain demographics are associated with "salt sensitivity," including obesity, increasing age, and African American ethnicity

Hypertension: Clinical Manifestations

• Development is very insidious because patients are frequently asymptomatic until target organ disease occurs
• Symptoms are often secondary to target organ disease and can include fatigue, reduced activity tolerance, dizziness, palpitations, angina, and dyspnea

Hypertension: Complications

• Target organ diseases occur most frequently in the heart, brain, peripheral vasculature, kidney, and eyes

Hypertension Complications

• Hypertensive heart disease can result in coronary artery disease, left ventricular hypertrophy, and heart failure

Hypertension Collaborative Care

• Overall Goals include control blood pressure
• Reduce CVD (Cardiovascular Disease) risk factors
• Drug therapy's primary mechanism: Reduce SVR (systemic vascular resistance)
• Reduce volume of circulating blood

Antihypertensive Drugs

• Categories: Diuretics, adrenergic drugs, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), calcium channel blockers (CCBs), direct renin inhibitors, and vasodilators

Diuretics

• Decreases plasma and extracellular fluid volumes
• Results include decreased preload, decreased cardiac output, and decreased total peripheral resistance
• Overall effect: Decreased workload of the heart and decreased blood pressure

Thiazide Diuretics

• Prototype is Hydrochlorothiazide, which is the first-line treatment for hypertension
• Thiazide Diuretics have a site of action in a distal convoluted tubule of kidney
• Thiazide Diuretics inhibit the reabsorption of sodium, potassium, and chloride, and are associated with osmotic water loss
• These diuretics directly relax the small blood vessels, which reduces peripheral vascular resistance (afterload)
• Indications for use include heart failure, hypertension, edema, hypercalciuria, and diabetes insipidus
• Contraindications include drug allergy, anuria, and renal failure

Thiazide Diuretics Adverse Effects

• Dizziness, headache, blurred vision, paresthesia are adverse effects in the CNS
• Anorexia, nausea, vomiting, diarrhea, pancreatitis, and cholecystitis are adverse effects in the GI body system
• Decreased libido and impotence (Sexual activity) is an adverse effect in the GU body system
• Jaundice, leukopenia, purpura, thrombocytopenia are hematologic adverse effects
• Urticaria and photosensitivity are integumentary adverse effects
• Hypokalemia, glycosuria, hyperglycemia, and hyperuricemia are metabolic adverse effects
• Toxicity can occur with overdose of medications can result in severe hypokalemia with symptoms such as lethargy, muscle weakness, confusion and severe hypotension

Adrenergic Drugs 'Sympathomimetics'

• These drugs bind to adrenergic receptors and inhibit (block stimulation) of the sympathetic nervous system (SNS)
• Classified by the type of adrenergic receptor blocked: Alpha1 and alpha2 receptors and Beta1 and beta2 receptors
• Multiple sub-groups can cause drowsiness or sedation
• Types include Alpha-blockers and beta-blockers, Centrally acting alpha2 agonists, and Peripherally acting alpha adrenergic blockers
• Alpha1- adrenoceptors cause vasoconstriction and Increased peripheral resistance
• Alpha2 - adrenoceptors Inhibit norepinephrine release and Inhibit acetylcholine - inhibits vasodilation
• Beta1 - adrenoceptors cause tachycardia and Increases lipolysis
• Beta2 - adrenoceptors cause Vasodilation and Slightly decreased peripheral resistance

Adrenergic Drugs: Centrally Acting alpha2 agonists

• Prototype: clonidine (Catapres)
• Other Medications: methyldopa (Aldomet) and Stimulate alpha2-adrenergic receptors in the brain
• Mechanism of action: decrease sympathetic outflow from the CNS, decrease norepinephrine production, and stimulate alpha2-adrenergic receptors. This reduces renin activity in the kidneys
• Results in decreased blood pressure
• Indications: Hypertension
• Clonidine is useful in the management of withdrawal symptoms in opioid- or nicotine-dependent persons
• Can be used for hypertension in pregnancy (Methyldopa)

Adrenergic Drugs: Centrally Acting alpha2 agonists

• Contraindications: Use cautiously in patients who have had stroke, recent MI, major depressive disorder, and chronic renal failure
• Adverse Effects/Side Effects:
  • Drowsiness and drowsiness
  • Sedation
  • Dry Mouth
  • Rebound Hypertension
• Nursing Adminstration:
  • Administered by oral, transdermal, and epidural routes
  • Medication is usually administered twice daily and instructing patients to take larger dose at bedtime
  • Transdermal patches are applied every seven days

Adrenergic Drugs Peripherally Acting Alpha₁ Blocker

• Doxazosin mesylate (Cardura)
• Terazosin (Hytrin)
• Mechanism of action: block alpha1 adrenergic receptors that cause vasoconstriction
• Cause both arterial and venous dilation, reducing peripheral vascular resistance and BP
• Results in decreased blood pressure
• Used to treat hypertension
• Tamulosin (Flomax) has an effect on receptor on prostate gland and bladder and decreases resistance to urinary outflow, thus reducing urinary obstruction and relieving effects of BPH
• Contraindications: Hypotension, angina, and renal insufficiency
• Nursing Administration
  • First dose often at night, teach safety measures

Alpha-Blockers: Adverse Effects

• Cardiovascular: Palpitations, orthostatic hypotension, chest pain, tachycardia, edema, dysrhythmias, hypotension, or bradycardia
• CNS: Dizziness, headache, drowsiness, anxiety, depression, vertigo, weakness, numbness, fatigue
• Gastrointestinal: Nausea, vomiting, diarrhea, constipation, abdominal pain
• Other: Incontinence, nosebleeds, tinnitus, dry mouth, pharyngitis, rhinitis

Adrenergic Drugs Beta-Blockers

• Nonselective beta-blockers block both beta₁ and beta2 receptors
• Beta₁ adrenoceptors cause tachycardia and Increases lipolysis
• Beta₂ adrenoceptors cause vasodilation and Slightly decreased peripheral resistance
• Blocks stimulation of beta receptors in the SNS
• Compete with norepinephrine and epinephrine and can be selective or nonselective

Beta Receptors

• Beta1 receptors are located primarily on the heart
• Beta-blockers selective for these receptors are called cardioselective beta-blockers
• Beta2 receptors are located primarily on smooth muscle of bronchioles and blood vessels

Mechanism of Action of Beta-Blockers

• Reduce BP by reducing heart rate through beta1-blockade
• Cause reduced secretion of renin
• Long-term use reduces peripheral vascular resistance
• Result: Decreased blood pressure

Adrenergic Drugs: Beta Blockers

• Selective Beta 1
  • Reduce SNS stimulation of the heart
  • Decrease heart rate and prolong SA node recovery
  • Slow conduction rate through the AV node
  • Decrease myocardial contractility resulting in reduced myocardial oxygen demand
• Non-Selective Beta 1 and 2
  • Can result in same effects on the heart as cardio selective beta-blockers
  • Can constrict bronchioles which can result in narrowing of airways and shortness of breath
  • Can produce vasoconstriction of blood vessels through smooth muscle
  • Reduce heart rate owing to B1-blockade

Beta-Blockers: Indications

• Indicated for Angina, decreasing the myocardial oxygen demand
• Cardioselective Beta-Blockers are cardioprotective as they inhibits stimulation from circulating catecholamines
• Reduce risk of post-MI cardiac arrest
• Dysrhythmias, Migraine headaches, Antihypertensive, Heart failure, and Glaucoma (topical use) are further uses for Beta-Blockers

Beta-Blockers: Examples

• Carvedilol (Coreg), Labetalol (Normodyne), metoprolol (Lopressor), atenolol (Tenormin), esmolol (Brevibloc) and propranolol (Inderal) are all example of Beta-Blockers

Adverse Effects: Beta-Blockers

• Thrombocytopenia reported
• Bradycardia, AV heart block and heart failure is possible adverse effects
• Peripheral Vascular Insufficiency is indicated adverse effect
• Dizziness, mental depression lethargy, hallucinations, unusual dreams
• Nausea, dry mouth, vomiting, diarrhea, cramps and ischemic colitis
• Impotence, rash, alopecia and bronchospasm

Beta-Blocking Drugs

• Rebound hypertension or chest pain may occur if this medication is discontinued abruptly
• Nursing implications: Instruct patients to notify their physician if they become ill and unable to take medication
• Inform patients that they may notice a decrease in tolerance for exercise, and have patients notify the physician if these problems occur
• Inform patients due to fluid shifts, of increased weight again, of over 2 pounds a day/ 5 pound a week
• Symptoms of edemas of the feet and ankles, as well as shortness of breath or excessive fatigue may indicate an issue
• Syncope dizziness may occur

Adrenergic Drugs: Summary of Adverse Effects

• Adrenergic Drugs can results in High incidence of orthostatic hypotension and is the most common sign can Drowsiness, sedation, or constipation
• Adverse affects are Headaches, Sleep disturbances, and Nausea, as Rash or other cardiac disturbances (palpitations) may occur

Adrenergic-Blocking Drugs: Nursing Implications

• Assess for allergies and history of COPD, hypotension, cardiac dysrhythmias, bradycardia, or heart failure
• Alpha-blockers may precipitate hypotension and Beta-blockers may precipitate - Bradycardia, Hypotension, and Heart block
• Heart failure or Bronchoconstriction are also possible

Adrenergic-Blocking Drugs: Nursing Implications for Drugs

• A patient should avoid over-the-counter medications of a possible drug interaction
• Possible interactions include: Antacids, Antimuscarinics, Diuretics, Neuromuscular blocking drugs, and Oral hypoglycemic drugs
• Many drugs trigger sympathetic system

Nursing Implications

• Teach patients to change positions slowly to prevent slow postural hypotension
• Instruct patients to avoid caffeine stimulation excessive irritability
• Instruct patients to avoid alcohol ingestion and hazardous activities until blood levels become stable
• Instruct patients to notify their physician if palpitations, dyspnea, nausea, or vomiting occurs
• Monitor for adverse effects and for therapeutic effects by monitoring for BP and HR control