Hemodynamics 1 and 2

Question 1

Role of the Cardiovascular System (9)

Answer 1

• 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

Question 2

Pulmonary vs. Systemic Circulation

Answer 2

• 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

Question 3

Anatomy of the Cardiovascular System

Answer 3

• 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

Question 4

What heart is enclosed in and mainly comprised of

Answer 4

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

Question 5

Matching of Pulmonary and Systemic Blood Flow

Answer 5

• 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

Question 6

Blood

Answer 6

• 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

Question 7

Fluid Flow & Pressure

Answer 7

• 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

Question 8

Ohm’s Law

Answer 8

• ( 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

Question 9

Poiseuille’s Law

Answer 9

• 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

Question 10

Laminar vs. Turbulence / Tubulent Flow

Answer 10

• 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

Question 11

Reynold’s Number (Re)

Answer 11

• 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

Question 12

Poiseuille’s Law and Vasodilation/Vasoconstriction

Answer 12

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

Question 13

Poiseuille’s Law and Hematocrit

Answer 13

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

Question 14

Blood Pressure: Systole, Diastole, Pulse, Pulse Pressure

Answer 14

• 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

Question 15

Blood Pressure: Potential vs. Kinetic Energy

Answer 15

• 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

Question 16

Compliance

Answer 16

• 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

Question 17

Mean Arterial Pressure (MAP)

Answer 17

• 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

Question 18

Clinical Manifestations of Alterations in Vessel Properties

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

Answer 18

• 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

Question 19

Effect of Gravity on CV Control

Answer 19

• 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

Question 20

Pressure Waves in Arteries

Answer 20

• 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

Question 21

Dicrotic Notch / Incisura

Answer 21

• 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

Question 22

Pressure Waves in Arterioles

Answer 22

• 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

Question 23

Law of Laplace

Answer 23

• 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

Question 24

How blood flows from arterioles to capillaries to venules

Answer 24

• 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

Question 25

Flow Rate of Materials through Capillaries

Answer 25

• 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

Question 26

Venous Return to the Heart

Answer 26

• 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

Question 27

Veins vs. Arteries

Answer 27

• 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

Question 28

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

Answer 28

• 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

Question 29

Venous Compliance and its changes with Vascular Smooth Muscle and Aging

Answer 29

• 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

Question 30

Venous Return and Cardiac Output

Answer 30

• 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

Question 31

Cardiac Cycle

Answer 31

• 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

Question 32

Cardiac Cycle: Mechanical Events

Answer 32

• 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

Question 33

Pressure-Volume Graph

Answer 33

• 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

Question 34

Heart Sounds

Answer 34

• 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

Question 35

ECG

Answer 35

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

Question 36

Wiggers Diagram

Answer 36

• 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

Question 37

Relationships between MAP, aortic valve opening, & ESV

Answer 37

• 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