CIRCULATION NOTES

• Heart disease is the 2nd leading cause of death

  
• The Aging HEART


  • Thickening blood vessel walls
  • Narrowing lumen
  • Less elastic vessels

  
• As the heart ages

  • Pulmonary vascular tension increases
  • Risk of orthostatic hypotension increases
  • Systolic BP increases
  • Peripheral Circulation decreases
  • Cardiac Output decreases
  • Heart Muscle Fibers decrease
  • Baroreceptor sensitivity decreases
  • Venous valve efficiency decreases
  • SBP (systolic BP) increases
  • Heart valve efficiency decreases

  
• Heart


  Approximately the size of your fist and positioned in the left side of your heart
• Heart - Apex (bottom)


  • 5th ICS ~7-9cm midsternal line
• Epicardium


  • The outermost layer of the heart wall, consisting of a thin layer of connective tissue and adipose (fat) tissue
  • Protective covering for the heart and helps anchor the coronary blood vessels that supply oxygen and nutrients to the myocardium
  • Secretes a small amount of serous fluid, which lubricates the outer surface of the heart and reduces friction as the heart beats within the pericardial cavity

  
• Myocardium


  • The middle layer of the heart wall, composed of cardiac muscle tissue (cardiomyocytes) arranged in an interwoven network
  • Responsible for the contractile activity of the heart, generating the force necessary to pump blood throughout the body
  • Contains specialized muscle fibers that allow for coordinated and efficient contraction of the heart chambers during the cardiac cycle

  
• Endocardium


  • The innermost layer of the heart wall, consisting of a thin layer of endothelial cells and connective tissue
  • Provides a smooth lining for the chambers of the heart and the valves, allowing for smooth blood flow
  • Helps prevent blood clots from forming within the heart chambers

  
• Blood components


  • RBC - carries O2 with hemoglobin (120 days)
  • WBC - fights infection (12-20 days)
  • Platelets - clotting (6 days)
• Blood volume


  5 liters or 10 units make up about 10% of body weight
• Cardiomegaly


  Enlarged heart which can occur from underlying factors, including physiological adaptations, pathological conditions, or external influences

  
• Decrease in blood components

  • Erythropenia - decrease in RBCs
  • Thrombocytopenia - decrease in platelets
  • Leukopenia - decrease in WBCs
• Increase in blood components

  • Erythrocytosis (polycythemia) - increase in RBCs
  • Thrombocytosis - increase in platelets
  • Leukocytosis - increase in WBCs

  
• Blood production processes


  • Erythropoiesis - RBC production
  • Thrombopoiesis - platelet production
  • Leukopoiesis - WBC production

  
• Cardiovascular System Function


  • Myocardial pump - Heart acts as a pump that contracts rhythmically to generate force to propel blood (120/80 = BP)
  • Myocardial blood flow - Flow of blood through coronary arteries to supply oxygen and nutrients to the myocardium
  • Coronary artery circulation - Network of arteries that supply blood to the heart muscle
  • Systemic circulation - Circulation of blood throughout the entire body, excluding the lungs
  • Blood flow regulation - Mechanisms that regulate blood flow to meet metabolic demands

  
• Baroreceptors


  Found in carotid sinus and aortic arch, detect changes in blood pressure

  
• Low blood pressure (hypotension)


  Baroreceptors detect, physiological response is tachycardia, vasoconstriction, increase of peripheral resistance and raises blood pressure

  
• High blood pressure (hypertension)


  Baroreceptors detect, physiological response is bradycardia, vasodilation, decreases peripheral resistance and lowers blood pressure

  
• Heart Valves


  • Ensure blood flows in the correct direction through the heart and prevents backflow or regurgitation
  • AV valves (S1 is AV closure) at end of diastole - Tricuspid and mitral valve
  • Semilunar valves (S2 is SV closure) at end of systole - Pulmonic and aortic

  
• The two valves most commonly need replacement or repair are the mitral valve and aortic valve
• Blood in the heart does not directly supply O2 and nutrients to the myocardium

  
• Heart is perfused during diastole (rest) via the coronary artery

  
• Systemic Circulation


  Arteries > arterioles > capillaries > oxygenated to deoxygenated > capillaries > venule > vein
• Arteries


  • Carry blood away from the heart
  • All arteries carry oxygenated blood except for the pulmonary arteries
  • High pressure system

  
• Veins


  • Carry blood towards the heart
  • All veins carry deoxygenated blood except for the pulmonary veins
  • Low pressure system which relies on valves and muscles

  
• Cardiac output


  • Volume of blood pumped by the heart during 1 minute
  • Stroke volume X Heart rate

  
• Stroke volume


  Volume of blood ejected from the heart's left ventricle with each contraction

  
• Heart rate


  Number of times the heart beats per unit of time
• Preload


  Ventricular stretch at the end of diastole (rest), end diastole volume
• Heart failure


  Volume overload or high pressure in preload

  
• Hypovolemia


  Low volume or decreased venous return
• Preload can increase myocardial O2 demand
• Afterload


  • Resistance the heart overcomes to eject blood from the ventricles
  • 3 Vs: vessel diameter, valves, viscosity

  
• Hypertension (HTN) or aortic stenosis


  Increased resistance from left ventricle

  
• Distributive shock (sepsis, anaphylaxis)


  Decreased resistance from left ventricle
• Afterload can increase myocardial O2 demand
• Preload and afterload can affect cardiac output and stroke volume
• Mean Arterial Pressure (MAP)

  Represents the average pressure in the arteries throughout the cardiac cycle

  MAP = (Diastolic BP + Systolic BP - Diastolic BP) / 3
• Contractility


  • Ability of the heart to contract and the force at which it contracts
  • Increased contractility = SNS, meds
  • Decreased contractility = HF, MI, hypoxemia, meds
• Cardiac Conduction


  SA nodes (pacemaker) form an impulse > conduction system > mechanical: myocardial contraction