cardiovascular

Module 10: Cardiovascular Pathophysiology

Chapter 16: Altered Perfusion

Definition of Perfusion

  • Perfusion: The process of forcing blood or other fluid to flow through a vessel and into the vascular bed of tissue to provide oxygen.

Requirements for Effective Perfusion

  • Adequate Ventilation and Diffusion
  • Intact Pulmonary Circulation
  • Adequate Blood Volume and Components
  • Adequate Cardiac Output
  • Intact Cardiac Control Center
  • Intact Receptors
  • Intact Parasympathetic and Sympathetic Nervous Systems
  • Intact Cardiac Circulation
  • Intact Coronary Circulation
  • Intact Systemic Circulation
  • Adequate Tissue Uptake of Oxygen

From Ventilation to Perfusion

  • Ventilation–Perfusion Ratio: Approximately 0.8 to 0.9.
  • Characteristics:
    • Rate of ventilation is less than perfusion.
    • In the lower lobes:
    • Ventilation is optimal due to reduced surface tension in alveoli, making them easier to inflate.
    • Perfusion is also optimal as blood pressure permits maximal blood flow.

Questions on Altered Perfusion

  • Question 1: Which of the following situations of altered perfusion could be triggered by Chronic Obstructive Pulmonary Disease (COPD)?
    a. Impaired cardiac output
    b. Impaired circulation
    c. Ventilation–perfusion mismatching
    d. Excessive cardiac demand

    • Answer: Ventilation-Perfusion Mismatching

  • Question 2: Which is not a requirement for effective perfusion?
    a. Absence of chronic disease
    b. Adequate blood volume
    c. Functional systemic circulation
    d. An open airway

    • Answer: Absence of Chronic Disease

Circulation Types

  • Pulmonary Circulation: Circulation through lungs that facilitates the transfer of oxygen from the atmosphere into the body.
  • Systemic Circulation: Blood flow to heart muscle that supports the pumping of oxygenated blood to the body.
  • Coronary Circulation: Supplies oxygen and nutrients to the heart muscle itself.

Movement of Blood Through the Circulation

  • Layers of the Heart:
    • Pericardium: Outer covering of the heart.
    • Myocardium: Thick muscular layer.
    • Endocardium: Inner lining of the heart.
  • Chambers of the Heart:
    • Right and left atria
    • Right and left ventricles

Cardiac Cycle

  • Processes:
    • Venous Blood Return:
    1. From head and arms via superior vena cava
    2. From trunk and legs via inferior vena cava
    • Blood enters right atrium.
    • Travels through tricuspid valve to right ventricle.
    • Moves through pulmonic valve to pulmonary artery and into lungs.
    • Oxygenation: Deoxygenated blood becomes oxygenated through the ventilation–perfusion exchange.
    • Blood returns to the heart via pulmonary vein into the left atrium.
    • Blood flows through bicuspid valve to left ventricle.
    • Finally, through the aortic valve into the aorta, entering systemic circulation.

Cardiac Cycle Phases

  • Systole: Contraction phase of the heart.
  • Diastole: Relaxation phase of the heart.

Sound of the Heart

  • Question: When you hear the “lub dub” sound from the heart, what does it signify? a. The sodium ions rapidly influxing into the cells b. The closure of the heart valves c. The contraction of the left ventricle d. Blood forcing its way through the aorta
    • Answer: The closure of the heart valves.

Conduction of Impulses in the Heart

  • Action Potentials: Stimulate cardiac contraction and relaxation occurring in slow and fast responses through distinct phases:
    1. Rapid depolarization
    2. Early repolarization
    3. Plateau
    4. Rapid repolarization
    5. Resting phase

Electrocardiogram Waveforms

  • P wave: Depolarization of atria via sinoatrial (SA) node.
  • P-Q Interval: Depolarization through atrioventricular (AV) node and bundle fibers.
  • QRS Complex: Depolarization of ventricles.
  • T wave: Repolarization of ventricles.
  • U wave: Repolarization of Purkinje fibers.

Heart Conduction System Components

  • Sinoatrial (SA) Node
  • Atrioventricular (AV) Node
  • Bundle of His
  • Right Bundle Branch
  • Left Bundle Branch
  • Purkinje Fibers

Cardiac Output (CO)

  • Definition: Measurement of the heart’s efficiency in pumping blood.
  • Components:
    • Stroke Volume (SV): Amount of blood pumped out of one ventricle of the heart in one beat.
    • Heart Rate (HR): Number of heartbeats per minute.
  • Formula:
    CO = SV imes HR

Blood Pressure (BP)

  • Definition: Pressure of blood in systemic arteries.
  • Components:
    • Systolic BP (pressure during ventricular contraction)
    • Diastolic BP (pressure during ventricular relaxation)
    • Pulse Pressure
    • Mean Arterial Pressure
  • Maintained by Factors:
    • Contraction of the left ventricle
    • Peripheral vascular resistance
    • Elasticity of arterial walls
    • Viscosity and volume of blood

Neuronal Control of Blood Pressure and Cardiovascular Adaptation

  • Components:
    • Neurons in the medulla and pons
    • Autonomic Nervous System (ANS)
    • Sympathetic Division (increases heart rate)
    • Parasympathetic Division (decreases heart rate)
  • Regulating Mechanisms:
    • Baroreceptors and chemoreceptors in arteries
    • Renin–angiotensin system
    • Kidneys

Altered Perfusion

  • Definition: The inability to adequately oxygenate tissues at the capillary level.
  • Factors that Could Alter Perfusion:
    • Ventilation–perfusion mismatching
    • Impaired circulation
    • Inadequate cardiac output
    • Excessive perfusion demands

Ventilation-Perfusion Mismatching

  • Characteristics:
    • Inadequate ventilation in well-perfused areas of the lungs.
    • Inadequate perfusion in well-ventilated areas of the lungs.

Impaired Circulation Factors

  • Causes of Impaired Circulation:
    • Injury to vessels
    • Hemorrhage
    • Obstruction (thrombosis)
    • Virchow’s Triad (factors leading to thrombosis)
    • Atherosclerosis
    • Bifurcations
    • Aneurysms
    • Venous Stasis
    • Hypercoagulability conditions (thrombocythemia, thromboembolus, embolus)
    • Infarction and infarct.

Inadequate Cardiac Output

  • Factors:
    • Changes in blood
    • Impaired ventricular pumping
    • Structural heart defects
    • Conduction defects
    • Changes in peripheral vascular resistance.

Excessive Perfusion Demands

  • Concept:
    • Excessive demands paired with poor perfusion supply can lead to altered perfusion.

General Manifestations of Altered Perfusion

  • Symptoms include:
    • Cyanosis
    • Pain
    • Pallor
    • Coolness
    • Edema
    • Shortness of breath
    • Impaired growth
    • Tachycardia
    • Tachypnea
    • Fatigue
    • Hypotension
    • Hypertension
    • Bleeding, bruising
    • Heart murmur.

Application of Concepts of Altered Perfusion

  • Clinical conditions relating to altered perfusion include:
    • Hypertension
    • Shock
    • Myocardial Infarction (MI)
    • Heart Failure
    • Stroke
    • Disseminated Intravascular Coagulation (DIC).

Hypertension

  • Pathophysiology:
    • A progressive cardiovascular syndrome characterized by elevated blood pressure and/or organ damage due to persistent blood pressure elevation.
    • Types: Primary versus secondary hypertension.
  • Risk Factors:
    • Family history
    • Aging
    • Black race
    • Decreased nephron count
    • Diabetes mellitus
    • Excessive dietary sodium intake
    • Obesity
    • Sedentary lifestyle
    • Nutrition
    • Excessive alcohol intake
    • Smoking.

Clinical Manifestations of Hypertension

  • Symptoms:
    • Often asymptomatic in early stages.
    • Advanced hypertension can cause CNS changes:
    • Headache
    • New-onset blurred vision
    • Nausea
    • Vomiting
    • Weakness
    • Fatigue
    • Confusion
    • Mental status changes.
    • Cardiovascular changes, pulmonary edema, heart failure, renal insufficiency characterized by:
    • Poor urinary output
    • Problems with urinary waste elimination
    • Hematuria
    • Proteinuria.

Shock

  • Pathophysiology:
    • Condition of circulatory failure and impaired perfusion of vital organs.
    • Sources of Impaired Perfusion:
    • Ineffective cardiac pumping (cardiogenic shock)
    • Decreased blood volume (hypovolemic shock)
    • Massive systemic vasodilation (septic shock)
    • Severe infection (septic shock)
    • Brain or spinal cord injury (neurogenic shock)
    • IgE-mediated allergic reaction (anaphylactic shock).
  • Clinical Manifestations:
    • Tachycardia, tachypnea
    • Cool, clammy extremities; peripheral pulses
    • Decreased arterial BP during decompensation
    • Cyanosis and/or pallor
    • Restlessness, apprehension, decreased mental function
    • Poor urinary output.

Myocardial Infarction (MI)

  • Pathophysiology:
    • Total occlusion of one or more coronary arteries resulting in ischemia and death of myocardial tissues.
    • Common Cause: Atherosclerosis.
  • Major Risk Factors:
    • Family history of coronary artery disease (CAD)
    • Hypertension and smoking
    • Blood cholesterol levels
    • Concurrent diabetes mellitus
    • High-sensitivity C-reactive protein (CRP)
    • Hyperhomocysteinemia.
  • Clinical Manifestations:
    • Gender variability in symptoms.
    • Symptoms to Note:
    • Chest pain or a crushing pressure, often radiating to the left arm, shoulder, or jaw
    • Fatigue, weakness, syncope, anxiety
    • Dizziness, shortness of breath
    • Sweating, pallor
    • Indigestion
    • Nausea, vomiting.

Question on Modifiable Risk Factors

  • Question: In evaluating modifiable cardiovascular risk factors for your patient, which one is NOT considered modifiable? a. Poorly controlled diabetes mellitus b. Hyperlipidemia c. Hypertension d. Female sex
    • Answer: Female sex.

Heart Failure

  • Pathophysiology:
    • Inadequacy of heart pumping leading to failure in maintaining blood circulation.
    • Causes:
    • Impaired cardiac functioning
    • Excessive workload demands
  • Types:
    • Left heart failure
    • Right heart failure.

Clinical Manifestations of Heart Failure

  • Right Heart Failure:
    • Congestion of peripheral tissues
    • Dependent edema and ascites
    • Liver congestion
    • GI tract congestion
    • Signs related to impaired liver function (anorexia, gastrointestinal distress, weight loss).
  • Left Heart Failure:
    • Pulmonary congestion
    • Activity intolerance and signs of decreased tissue perfusion
    • Impaired gas exchange (cyanosis, signs of hypoxia)
    • Pulmonary edema (cough with frothy sputum, orthopnea, paroxysmal nocturnal dyspnea).

Question on Right Heart Failure

  • Question: Your patient is experiencing peripheral edema, hepatomegaly, ascites, and splenomegaly. Which of the following conditions would be consistent with the patient’s findings? a. Endocarditis b. Myocardial infarction c. Right heart failure d. Left heart failure
    • Answer: Right-sided Heart Failure.

Stroke

  • Pathophysiology:
    • Any clinical event that leads to impairment of cerebral circulation.
    • Can be thrombotic, embolic, or hemorrhagic.
    • Involves inflammation, ischemia, and death of neurons.
  • Differentiation Between:
    • Cerebrovascular Accident (CVA)
    • Transient Ischemic Attack (TIA).

Clinical Manifestations of Stroke

  • Symptoms:
    • Focal brain injury
    • Abrupt onset of hemiparesis
    • Vision loss or field deficits
    • Dizziness, diplopia
    • Ataxia, aphasia
    • Sudden decrease in the level of consciousness.

References

  • Braun, J.N. C. (2022). Lippincott CoursePoint Enhanced for Nath’s Applied Pathophysiology (4th ed.). Wolters Kluwer Health.