Hemodynamics 1 and 2 Flashcards
1
Q
Role of the Cardiovascular System (9)
A
- 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
2
Q
Pulmonary vs. Systemic Circulation
A
- 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
3
Q
Anatomy of the Cardiovascular System
A
- 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
4
Q
What heart is enclosed in and mainly comprised of
A
- Heart is enclosed in a tough membranous sac: pericardium
- Heart is mainly comprised of cardiac muscle: myocardium
5
Q
Matching of Pulmonary and Systemic Blood Flow
A
- 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
6
Q
Blood
A
- 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
-
Red cells (erythrocytes)
7
Q
Fluid Flow & Pressure
A
- 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
8
Q
Ohm’s Law
A
- ( 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
9
Q
Poiseuille’s Law
A
- 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
10
Q
Laminar vs. Turbulence / Tubulent Flow
A
- 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
11
Q
Reynold’s Number (Re)
A
- 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
12
Q
Poiseuille’s Law and Vasodilation/Vasoconstriction
A
- Can affect blood flow by altering blood vessel size via vasodilation/vasoconstriction
- Vasodilation –> decreased resistance –> increased blood flow
- Vasoconstriction –> increased resistance –> decreased blood flow
13
Q
Poiseuille’s Law and Hematocrit
A
- Increased hematocrit –> increased viscosity –> increased resistance –> decreased blood flow
- Anemia: low hematocrit, increased blood flow
- Polycythemia: high hematocrit, decreased blood flow
14
Q
Blood Pressure: Systole, Diastole, Pulse, Pulse Pressure
A
- 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
15
Q
Blood Pressure: Potential vs. Kinetic Energy
A
- 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
16
Q
Compliance
A
- 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
17
Q
Mean Arterial Pressure (MAP)
A
- 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
18
Q
Clinical Manifestations of Alterations in Vessel Properties
- Effects of smooth muscle vasoconstriction
- Nutrient delivery
- Myogenic autoregulation
- Advantages of increasing BP
- Compliance during aging
A
- 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
19
Q
Effect of Gravity on CV Control
A
- 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
20
Q
Pressure Waves in Arteries
A
-
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
21
Q
Dicrotic Notch / Incisura
A
- 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
22
Q
Pressure Waves in Arterioles
A
- 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
23
Q
Law of Laplace
A
- 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
24
Q
How blood flows from arterioles to capillaries to venules
A
-
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
25
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
26
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
27
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
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
* 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
29
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
30
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
31
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
32
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
33
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
34
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
35
ECG
* _P wave_: atrial depolarization
* _QRS waves_: ventricular depolarization (& atrial repolarization)
* _T wave_: ventricular repolarization
* _RR interval_: heart rate
36
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
37
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
