Hemodynamics 1 and 2 Flashcards Preview

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Flashcards in Hemodynamics 1 and 2 Deck (37):

Role of the Cardiovascular System (9)

• Move oxygen from the lungs to all body cells
• Move nutrients and water from the gastrointestinal system to all body cells
• Move metabolic wastes from all body cells to kidney for excretion
• Move heat from cells to skin for dissipation
• Move carbon dioxide from body cells to lungs for elimination
• Move particular toxic substances from some cells to liver for processing
• Move hormones from endocrine cells to their targets
• Move stored nutrients from liver and adipose tissue to all cells
• Carries immune cells, antibodies, and clotting proteins to wherever they are needed


Pulmonary vs. Systemic Circulation

  • Pulmonary
    • Right heart --> lungs
    • Permit gas exchange (oxygenation of the blood and removal of CO2)
  • Systemic
    • Left heart --> body (except lungs)
    • Perfuses all the cells of the body


Anatomy of the Cardiovascular System

  • Superior and inferior vena cava
    • Blood is blue b/c carries less oxygen than blood in systemic circulation
  • Right atrium
  • Tricuspid valve
    • Assures unidirectional blood flow
  • Right ventricle
  • Pulmonary semilunar valve
  • Pulmonary arteries
  • Lungs
    • Blood is oxygenated
  • Pulmonary veins
  • Left atrium
  • Bicuspid (mitral) valve
  • Left ventricle
  • Aortic semilunar valve
  • Aorta
    • Distributes oxygenated blood throughout body


What heart is enclosed in and mainly comprised of

  • Heart is enclosed in a tough membranous sac: pericardium
  • Heart is mainly comprised of cardiac muscle: myocardium


Matching of Pulmonary and Systemic Blood Flow

  • Volume of blood leaving left and right heart per unit time must be matched
    • Otherwise, fluid would accumulate in one system
  • Ex. Severely damaged left ventricle (congestive heart failure)
    • Blood would accumualte in pulmonary circulation
    • --> impairment of gas exchange in the lungs



  • Liquid medium: plasma
    • 50-55% blood volume
    • Contains plasma proteins (albumin, globulin), electrolytes, hormones, enzymes, and blood gases
  • Formed elements
    • Red cells (erythrocytes)
      • 40-45% total blood volume
      • Centrifuged: settle to bottom
      • Hematocrit: volume of RBCs in blood
      • Contain hemoglobin: bind w/ & transport oxygen
    • White cells (leukocytes)
      • 5% total blood volume
      • Centrifuged: settle on top of red cells
      • For immune processes & bodily defense
    • Platelets
      • Little blood volume
      • For blood coagulation


Fluid Flow & Pressure

  • Fluid moves form regions of higher pressure to regions of loewr pressure
  • Contraction of ventricles imparts pressure
  • Friction is lost as blood flows through blood vessels


Ohm's Law

  • ( Q = ΔP/R ) or ( ΔP = Q * R ) or ( R = ΔP/Q )
    • ΔP = change in pressure on two ends of a vessel (not within the vessel itself)
    • Q = blood flow
    • R = resistance
  • Flow through a vessel will be directly proportional to pressure and inversely proportional to resistance
    • Ex. if you increase the length of a vessel, you increase resitance and decrease flow


Poiseuille's Law

  • Q = πΔPr4/ 8ηl
    R = 8ηl / πr4
    • Q = flow
    • π/8 is a constant
    • ΔP = the pressure driving force
    • r = radius of the vessel
    • η = viscosity of the fluid
    • l = length of the vessel
  • Explains the flow of fluid through tubes of different sizes
  • A change in radius has a huge effect on blood flow
    • If halve the radius, you decrease blood flow by 16x
  • Only valid under conditoins of laminar flow


Laminar vs. Turbulence / Tubulent Flow

  • Laminar flow
    • Fluid on the inside moves faster than the fluid on the outside of a vessel
    • Large vessel: fluid flows faster
    • Small vessel: fluid flows slower
    • Ex. normal blood flow
  • Turbulence
    • As flow velocity increases, eventually a criticla velocity is reached at which the concentric layers break down 
    • --> side-to-side motion of fluid
    • Increased turbulence --> increased viscosity --> decreased flow
  • Turbulent Flow
    • Frictional resistance is increased
    • The bigger the vessel (increased diameter) and the quicker the blood flow (increased velocity), the more likely turbulent flow will occur
    • Sounds which emanate from the circulatory system (murmurs) are the result of localized turbulence


Reynold's Number (Re)

  • Re = dvD/η
    • d = fluid density
    • v = velocity
    • D = tube diameter
    • η = viscosity
  • Critical Re = 1000
  • Re < 1000 --> laminar flow
    • Smaller vessels
    • Decreased velocity
  • Re > 1000 --> turbulen flow
    • Larger vessels
    • Increased velocity


Poiseuille's Law and Vasodilation/Vasoconstriction

  • Can affect blood flow by altering blood vessel size via vasodilation/vasoconstriction
  • Vasodilation --> decreased resistance --> increased blood flow
  • Vasoconstriction --> increased resistance --> decreased blood flow


Poiseuille's Law and Hematocrit

  • Increased hematocrit --> increased viscosity --> increased resistance --> decreased blood flow
  • Anemia: low hematocrit, increased blood flow
  • Polycythemia: high hematocrit, decreased blood flow


Blood Pressure: Systole, Diastole, Pulse, Pulse Pressure

  • Systole: cardiac muscle contracts
  • Diastole: cardiac muscle relaxes
    • Lasts 2x as long as systole
    • If heart rate = 67
      • Cardiac cycle = 900 ms
      • Diastole = 600 ms
      • Systole = 300 ms
  • Pulse: wave transmitted when the left ventricle contracts
  • Pulse pressure: amplitude of pulse wave
    • Depends on the volume of blood ejected and the compliance of the arteries


Blood Pressure: Potential vs. Kinetic Energy

  • Arteries contain fibrous and elastic connective tissue
  • When high-pressure blood contacts arterial walls, potential energy is absorbed when the artery becomes stretched
  • Energy is released as kinetic energy through elastic recoil
  • Process limits the drop in arterial pressure during diastole
    • Flow of blood from arteries to capillaries is continuous even though the flow from ventricle to aorta is pulsatile



  • Tendency of a hollow organ to resist recoil toward its original dimensions
    • Ability of an artery to absorb energy during systole and resorb it during diastole
    • Ability of the arterial tree to store potential energy depends on compliance
  • C = ΔV/ΔP or ΔP = ΔV/C
    • ΔV = stroke volume
    • ΔP = pulse pressure
  • C = 0 --> completely rigid vessels
    • --> all energy of contraction would be kinetic energy
    • --> pressure would fluctuate: high during systole, low during diastole


Mean Arterial Pressure (MAP)

  • Driving force for fluid entering arterial circulation
  • Determined by measuring blood pressure continuously and determining the mean level
    • Estimated from rmeasurements of systolic and diastolic BP
    • Diastole lasts twice as long as systole
  • MAP = 2/3 (diastolic P) + 1/3 (systolic P)
    • Innacurate when HR becomes high b/c time spent in diastole decreases
  • MAP = CO * TPR
    • Based on ΔP = Q * R
    • MAP = ΔP when pressure in the vena cava is assumed to be 0
    • CO = Q = SV * contractions/time = SV * HR
    • TPR = total peripheral resistance (sum of resistances provided by every arterial bed)
      • R = total resistance in the cardiovascular system


Clinical Manifestations of Alterations in Vessel Properties

  • Effects of smooth muscle vasoconstriction
  • Nutrient delivery
  • Myogenic autoregulation
  • Advantages of increasing BP
  • Compliance during aging

  • Smooth muscle vasoconstriction --> increased BP --> decreased blood flow to downstream capillaries
    • Deprives oxygen and nutrients from downstream tissues
  • Nutrient delivery depends on blood flow through the capillary bed perfusing tissue
  • Myogenic autoregulation: nromalizes blood flow as pressure changes so only large changes in pressure --> changes in tissue perfusion
  • Advantages of increasing BP
    • Push blood against gravity
    • Push fluid out of capillaries into interstitial space (esp in brain arterioles)
    • Assure blood can reach the head when standing
  • Compliance during aging decreases
    • Pulse pressure amplifes w/ aging due to large artery stiffness


Effect of Gravity on CV Control

  • Overcoming gravity: greatest challenge that the CV system faces
  • Normal MAP = 100mmHg = column of blood 4.5 ft high
  • BP changes
    • BP decreases as blood is propelled upward
    • BP increases as blood moves down w/ gravity
  • When standing
    • Arterial pressure at head = 70mmHg
    • Arterial pressure at feet = 170mmHg


Pressure Waves in Arteries

  • Pressure wave: generated from ejection of blood from the left ventricle
    • Felt via palpitation as the periphreal pulse
    • Speed of propagation increases w/ increased SV and with decreased arterial compliance
  • When pressure wave reaches small peripheral bifurcations, it's reflected back in the reverse direction
    • Distorts arterial wave form to look like greater systolic & pulse pressure in peripheral parteries than in larger proximal arteries
  • MAP decreases as the pressure wave propagates as resistance is overcome


Dicrotic Notch / Incisura

  • Aorta absorbs energy during systole and resorbs it during diastole
  • In the left ventricle, when it relaxes, BP drops significantly
  • Pressure doesn't drop as rapidly in the aorta as in the left ventricle
  • There's a brief period at the end of systole when blood flows backwards from the aorta in the ventricle
  • Triggers closure of the aortic valve and termination of retrograde flow
    • Aortic valve opens when pressure in left ventricle > aorta
    • Aortic valve closes when pressure in left ventricle < aorta
  • Dicrotic Notch / Incisura: discontinuity in the pressure tracing, marker for aortic valve closing


Pressure Waves in Arterioles

  • As arteries divide into smaller branches, the amount of connective tissue in the walls diminishes but muscularity increases
  • Arterioles: major resistance vessels, so BP drops when blood flows through them
    • As the pressure wave progresses through them, the pulse is almost completely damped out


Law of Laplace

  • Describes surface tension and why large arteries contain more connective tissue than small arteries
  • T = Pr
    • T = wall surface tension
    • P = transmural pressure
    • r = radius
  • Small vessels can sustain a high pressure w/o having a high surface tension and breaking
  • Large vessels need a lot of connective tissue reinforcement to sustain pressure since surface tension is high


How blood flows from arterioles to capillaries to venules

  • Capillaries: single layer of endothelial cells + basement membrane
    • Thickness of the wall is only ~0.5 micrometers
  • Metarterioles: specialized blood vessels that permit large white cells to flow form the arterial to the venous side of circulation
  • Precapillary sphincters: small bands of vascular smooth muscle at the junciton b/n a metarteriole and a capillary
    • When contract, they diminish blood flow into capillaries and shunt blood away from capillary beds


Flow Rate of Materials through Capillaries

  • V = Q / A
    • V = velocity of blood flow
    • Q = flow rate
    • A = cross sectional area
  • Flow rate through capillaries is lower than arteries veins b/c the toal surface area of capillaries is enormous
    • Surface area of capillaries > arteries b/c there are more capillaries than arteries in the CV system


Venous Return to the Heart

  • Most of the blood volume in the CV system is in the veins, so venous pressure primarily determines CO
    • When lying down: the pressure left in blood after it has moved through the capillary bed is sufficeint to return blood to the heart
    • When standing: force of gravity increases the pressure needed to return blood to the heart
  • Orthostatic hypotension: drop in BP results in insufficient perfusion of the brain
    • Occurs during postural alterations when venous return, CO, and BP decrease


Veins vs. Arteries

  • Thinner walls
  • Larger diameters
  • More numerous
  • More compliant, so expand easily when filled with blood
  • During standing
    • Blood is translocated form the thorax to the abdomen and legs
    • Blood pools more in dependent veins (subjected to gravity) as intravenous pressure increases
    • Blood flow decreases
  • During large-amplitude head-up tilts
    • ​Femoral venous blood flow drops at the onset but then increases toward baseline levels


Major mechanisms that assist in returning blood to the heart when standing

  • Venous valves
  • Compression of veins by skeletal muscle
  • Smooth muscle venoconstriction
  • Blood reservoirs
  • Heart location
  • Ventricular contraction

  • Venous valves
    • Permit unidirectional flow back to the heart
    • Located every 2-4 cm
    • Varicose veins: when veins become stretched due to venous pressure over time, valves don't expand to fill the vessel
      • Valves stretch out, don't adequately close, and blood pools
      • Venous return ot the heart diminishes and pressure in leg veins becomes high during standing
  • Compression of veins by skeletal muscle
    • During movement, leg muscle contractions force blood from intramuscular veins toward the heart
  • Smooth muscle venoconstriction
    • SNS --> venoconstriction --> translocates blood from the periphery to the heart
  • Blood reservoirs
    • Veins store blood to be liberated if more CO is required
    • 4 important venous beds: spleen, liver, abdominal (splanchnic), venous plexus beneath the skin
  • Heart location
    • Heart is located in a cavity whose pressure changes with breathing
    • During inspiration, descent of the diaphragm produces negative pressure in the throax, which sucks air into the lungs and sucks blood into the chest
    • Limited capacity to aid in venous return
  • Ventricular contraction
    • Ventricular contraction --> increased atria size --> small suction effect that pulls blood into the atria
    • Negligible effect


Venous Compliance and its changes with Vascular Smooth Muscle and Aging

  • ΔP = ΔV/C
    • At higher pressures and volumes, vein compliance decreases and vessels become stiffer (similar to arterial compliance)
    • At lower pressures and volumes, compliance is greater, so veins can accommodate a large change in blood volume w/ a small change in pressure
  • Vascular smooth muscle
    • Contraction --> increased vascular tone --> decreased vascular compliance
    • Relaxation --> decreased vascular tone --> increased vascular compliance
  • Aging --> increased compliance --> increased blood pooling --> reduced venous return --> orthostatic hypotension


Venous Return and Cardiac Output

  • Striated & cardiac muscle contract best w/ maximal actin & myosin overlap
    • When the heart relaxes, cardiac muscle rests shortens, & contraction is weak
    • When blood fills a heart chamber, cardiac muscle stretches to its optimal length, sensitivity of Ca2+-binding protein troponin for calcium increases, rate of cross-bridge attachment & detachment increases, & contraction is strong
  • Frank-Starling Law of the Heart
    • Volume of blood returning to the heart increases
    • Myocardial cells stretch to a more efficient resting length
    • Force produced by contraction and stroke volume incrase
    • Heart pumps out as much blood as is returned


Cardiac Cycle

  • Cardiac cycle: one "pumping cycle" of the heart
    • If blocked, ventricles will contract at a different rate than atria
    • Pacemaker cells: all elements in conduction pathway
  • Autorhythmic cells: generate action potentials to control cardiac muscle contraction
    • Initiation of an AP at one cell --> electrical activity spread throughout heart --> coordinated contraction of atria & ventricles
    • Coupled via gap junctions so electrical activity can pass from autorhythmic cells to myocardial cells
  • ​Depolarization
    • SA node: in right atrium near superior vena cava, conducts faster
    • atria: contract
    • AV node: near floor of righ atrium, conducts slowly to ensure ventricles contract after atria
    • Bundle of His: conducts rapidly
    • ventricles: contract from bottom to top to squeeze blood up to pulmonary artery
    • Purkinje fibers: carry impulses from bottom of heart to top


Cardiac Cycle: Mechanical Events

  • Late diastole: atria & ventricles are relaxed, passive ventricular filling
    • Atrial pressure > ventricular pressure
    • AV valves are open, semilunar valves are closed
    • ~80% of ventricular filling occurs during this phase
  • Atrial systole: atrial contraction forces ~20% of additional blood into the ventricles
    • End-diastolic volume (EDV): max amount of blood in ventricls at the end of ventricular relaxation (135ml)
  • Isovolumic ventricular contraction: first phase of ventricular contraction pushes AV valves closed but doesn't create enough pressure to open semilunar valves
    • Systole: geneconsidered the time when ventricles contractrally 
  • Ventricular ejection: as ventricular pressure rises & exceeds pressure in the arteries, the semilunar valves open & blood is ejected
    • End-systolic volume (ESV): minimum amount of blood in ventricles (65ml)
    • Stroke volume: amount of blood ejected during each cardiac cycle (70ml)
      • SV = EDV - ESV
    • Ejection fraction (EF): fraction of EDV ejected out of the ventricles during each contraction
      • EF = SV/EDV = 70ml / 135ml = 0.52
  • Isovolumetric ventricular relaxation: as ventricles relax, pressure in ventricles drops, blood flows back into cups of semilunar valves & snaps them closed


Pressure-Volume Graph

  • A: AV valves open
    • AV valve opens when atrial pressure > ventricular pressure
    • Ventricular diastole: ventricles fill
    • Ventricular pressure increases slightly as volume increases
    • Atria contract, & ventricles contain the max amount of blood
    • End-diastolic volume (EDV) = 175ml
  • B: AV valves close
    • AV valve closes when ventricular pressure > atrial pressure
    • Ventricles begin to contract
    • Isovolumetric contraction: ventricular pressure increases as volume stays constant
  • C: Semilunar valves open
    • When semilunar valves open, blood is ejected into the aorta & pulmonary arteries
    • Ventriuclar pressure continues to increase as ventricular volume drops
    • Ventricles begin to relax, & semilunar valves close
    • End-systolic volume (ESV) = 65ml
  • D: Semilunar valves close
    • isovolumetric relaxation: pressure drops as volume remains the same
    • AV valves remain closed b/c ventricular pressure > atrial pressure
    • When ventricular pressure drops below atrial pressure, AV valves open


Heart Sounds

  • Closing of heart vavles generates vibrations --> heart sounds ("lub-dub")
  • "Lub": closing of tricuspid & mitral valves
  • "Dub": closing of semilunar valves
  • 3rd heart sound: turbulent blood flow into the ventricle near the beginning of ventricular filling
  • 4th heart sound: additional turbulent flow into the ventricle during atrial contraction



  • P wave: atrial depolarization
  • QRS waves: ventricular depolarization (& atrial repolarization)
  • T wave: ventricular repolarization
  • RR interval: heart rate


Wiggers Diagram

  • a wave: atrial contraction
  • c wave: ventricular contraction due to...
    • Backflow of blood from ventricle to atrium when mitral valve closes
    • Bulging of the closed mitral valve backward into the atrium when ventricular pressure increases
  • v wave: blood flowing from the veins into the atrium during ventricular contraction


Relationships between MAP, aortic valve opening, & ESV

  • If total peripheral reisstance increases, then left ventricular pressure increases to open the aortic valve
  • The aortic valve closes earlier when the ventricle begins to relax
  • Stroke volume decreases
  • ESV increases
  • Increased volume is added to the volume transferred from the left atrium to the left ventricle after the mitral vavle opens
  • EDV increases
  • Next ventricular contraction is stronger due to the Frank-Starling Effect
  • Thus, if TPR is high, the heart must work harder & use more ATP to maintain constant cardiac output