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Flashcards in Hemodynamics & Vasculature Deck (60)

What does transmural pressure refer to?

• The pressure difference between inside of the vessel and the outside of the vessel
• Pressure across the vessel wall


Where is most of the body's blood at any given time?

• Veins - capacitance vessels


What is the overall blood volume? (number)

• 5 liters


How does the aorta handle the pulsatile pressure from the left heart?

• The elastic fibers help dampen pulsatile pressure while maintaining overall systemic pressure


The pressures of the pulmonary and systemic circulations are not equal. Does that mean the cardiac output of the right vs. left heart are also unequal?

• Nope. They are equal at the level of output from the right vs. left heart
• The pressures are different, however, as the resitances are different


Why are arterioles called reistance vessels?

• There is a large drop in pressure through arterioles (compared to arteries)
• Thus, they are resistance vessels. They should be as they need to get capilaries to have very little pressure


What is the letter that designates flow and what are the units of measurement?

• Volume per unit time
○ mL/min
• Q= flow


Is the velocity of blood faster in aorta or in capillaries and why?

• You have to think of capillaries as TOTALING MORE THAN ONE CAPILLARY (because of their arrangemnt in series?)
• Total cross secitonal area in capillaries is super large compared to aorta, meaning velocity in capillaries is slower than in aorta


What are the characteristics of blood flow in the CV

• Total flow in CV system is known as CARDIAC OUTPUT
• Must be constant through the system
○ Closed loop, so flow through all capillary beds must be same as flow through aorta


What is the letter that designates velocity and what are the units of measurement?

• V= velocity
• V= Q/A (a= cross sectional area)
• Thus, velocity is inversely proportional to the cross-sectional area of a vessel


What is the flow equation?

• Q= deltaP/R
○ Q- flow
○ deltaP- pressure difference
○ R- resistance


What are the consequences of increased vessel resistance?

• Increased resitance = decreased flow


What are the consequences of increased vessel viscosity?

• Increased viscosity increases resitance and decreases flow


What are the consequences of increased vessel length?

• Increase length of vessel increases resistance and decreases flow


What are the consequences of increased vessel size?

• Increased radius of vessel decreases resistance and increases flow


What does the term (pi*r^4)/(8nl)) mean in the Poiseuille's Equation?

• Inverse of resistance in the flow equation
• Increased radius of vessel decreases resistance and increases flow
• Increase length of vessel increases resistance and decreases flow
• Increased viscosity increases resitance and decreases flow


What is Poiseuille's Equation?

• An expanded version of the flow equation
• Q= deltaP*((pi*r^4)/(8nl))
○ R- radius
○ Pi - number pi
○ N- viscosity
○ L-length


What is true of flow?

• Requires a pressure difference
• Flow in must equal flow out in a closed system
• Flow is directly proportional to pressure, inversely proportional to resistance
• Individual vessels are less accurately modeled by flow equation, but the whole closed system IS well approximated by flow equation


What is Cardiac output?

• CO= (mean arterial pressure - venous pressure)/TPR
○ TPR = total peripheral resistance


What mostly dermines "n" or viscosity of blood?

• Hematocrit
○ 38-46% in women
○ 42-54% in men


What does changing the radius of a vessel have to do with flow?

• Flow varies with the 4th power of the radius so little changes mean lots of flow change
• Thus diameter of vessels being major way flow is regulated in CV system


What is an example of additive resistance in the CV system?

• Total resistance to blood flow to a particular organ system is determined by additive combination of resitances in all vessels leading to said orgain
○ Rt= R-artery + R-arteriole + R-capillaries


What is the consequence on resistance of a SERIES set up (not parallel)?

• Resitances in series are additive
• The total resistance then is higher than any one vessel in that series
• The blood flow through vessels in series is constant, but the pressure decreases through the series of vessels
○ Pressure drops through systemic circulation


Why is resitance in the capillaries so low when they are so tiny?

• An individual capillary has high resistance, but there are so many capillaries set up in parallel the total resistance of the system in parallel is low


What is the consequence on resistance of a system set up in PARALLEL?

• Poiseuill'es law is only valid for single vessels
• Parallel vessels decrease total vascular resistance
• Changing the resistance of a single vessel has little effect on the resitance in the whole system


What is laminar flow?

• Smooth, streamlined, most efficient
• Straight vectors, not turbulent
• Slowest at edge of tube, fastest in center


What happens to MAP at higher heart rates?

• At higher heart rates, MAP approaches average btw systolic and diastolic pressures because diastole is shorter


MAP is best for resting heart rate

• At higher heart rates, MAP approaches average btw systolic and diastolic pressures because diastole is shorter


What is meant by MAP?

• Mean arterial pressure
• NOT the arithmetic average of systolic and iastolic pressures because diastoly is longer than systole
• MAP depends on HR…the equation for approximating


How do you come up with mean arterial pressure?

• MAP is approximated by
• MAP= diastolic pressure +1/3(systolic pressure - diastolic pressure)


What does turbulent flow produce?

• Shearting force
○ Viscous drag of fluid flowing through tube, exerting force on walls
○ Shear force can damage endothelium, forming throbi and embolisms
• Damage to endothelium is first step in plaque build-up


How do you increase turbulent flow?

• Large diameter
• High velocity
• Low viscosity
• Abrupt changes in diamter
• Irregulaties on vessel wall


What is turbulent flow?

• Irregular, eddies and vortices
• Requires more pressue for same average veloscity compared to laminar flow


What is Compliance?

• C= detlaV
• mL/mmHg
• Change in volume that results in a change in pressure
• Represents the elastic properties of vessels or chambers of the heart


What are the consequences of LaPlace's Law?

• Hypertension increases stress on vessels and chamber's walls because increase pressure increases tension
• In an aneurysm, the weakened vessel wall bulges outward, increasing the radius, thus increasing the tension that cells within the wall have to withstand to resist splitting open
• Eventually the aneurism rupturs as it bulges more and more


What is LaPlace's Law?

• Describes the relationship between tension in a vessel wall and the transmural pressure
• T= (deltaPtm*r)/(mu)
• Tension (wall stress) = change in transmural pressure times the radius of the vessel divided by the thickness of the wall
• Increase thickness of the wall, decrease tension
• Increase transmural pressure, increase tension


What is ateriosclerosis?

• NOT atherosclerosis
• General term for loss of compliance caused by thickening and hardening of arteries
• Some of it happens with age


How does capillary flow become constant in a system with a pulstaile pump?

• Because of the compliance of the aorta and lager arteries


Which are more compliant, veins or arteries?

• Veins, more deltaV per deltaP


What are the two major processes of CV transport?

• Bulk transport
○ Point A to point B. think of O2 movement
• Transcapillary tansport
○ Cargo btw capillaries and tissue


What is Fick's principle?

• Expansion of the bulk transport idea
• Helps approximate how much of a substance is used by a tissue
• The amount used by the tissue is the difference between the amount that arrives and the amount that leaves


How can you use bulk transport to determing how much O2 is carried to muscle in 1 min?

• O2/min = Q*[O2]
• Q= cardiac output in this instance
• O2/min = transport rate


How can you determine bulk transport rate?

• Flow times concentration
• X = Q*[x]
• X is amount of substance
• [x]=concentration of x substance
• Q=flow


What is meant by Q([x]I - [x]o)?

• This is Fick's principle in equation format, suggesting that you can approximate the amount of a substance (like O2) used by a tissue by knowing the amount of the substance entering the tissue and leaving the tissue


What is the expression for Fractional Oxygen extraction?

• E-O2 = ([oxygen arterieal] - [oxygen venous])/[oxygen arterial]


How can you get a number for the oxygen comsuption of the whole body?

• Difference between oxygen in pulmonary vein minus pulmonary artery


What is the upper limit of myocardial oxygen consumption?

• 70mL Oxygen per minute per 100g tissue


What is typical myocardial oxygen consumption at rest?

• 8 ml oxygen per minute per 100g tissue


What is the typical oxygen content?

• Typically 0.2 mL oxygen in 1 mL of blood


How is myocardial oxygen consumption usually defined?

• mL of oxygen per minute
• Often expressed as mL of oxygen per minute per 100g of tissue
• Typically 0.2 mL oxygen in 1 mL of blood


What is the best example for Fick's principle?

• Originally developed to measure CO based on myocardial oxygen consumption
○ mVO2 = CO*([o2]I - [o2]o)
○ Remember CO = Q in this system
○ Cardiac output is equal to flow
○ [o2]i is arterial
○ [o2]o is venous


What are the forces that determine transcapillary transport?

• Solvent movement determined by opposing forces
• Hydrostatic pressure
• Oncotic pressure


Why is there more viltration on arterial s side of capillary and more reabsorption on venous side?

• Pi capillary is lower on arterial side


What diseased promote filtration?

• Liver disease and hypertension
• Increase blood pressure
• Reduce oncotic pressure
• Leads to edema


The net oncotic pressue id usually what direction?

• Pi capillary - pi interstitium is usually inward
○ Reabsorption


The net hydrostatic pressure is usually what direction?

• Pc - Pi means outward (filtration)


What is Sterling's law of the capillary?

• Flux = k[(Pc-Pi) - (pi capillary - pi intersti
• K = constant
• Flux = net movement across the wall
• Pc = capillary hydrostatic pressure
• Pi - intertitial hydrostatic pressure
• Pi capillary - capillary oncotic pressure
• Pi interstitium - interstitial oncotic pressure


Where is oncotic pressure higher, capillaries or interstitial tissue?

• Capillaries. You want fluid reabsorption to happen in the capillaries on the venous side.
* on the arterial side, hydrostatic pressure should take fluid into interstitial tissue, and the dissolved goodies with it
* on the venous side, you want the metabolic waste and other dissolved "baddies" to move with fluid back into the capillary to be delivered to venous system (liver, lungs)


What's up with oncotic pressure?

• The pressure formed by proteins in the blood and insterstitial fluid
• Roughly the same as osmotic forces
• Alpha-gluboulin and albumin are major determinants of oncotic pressure
* fluid will move TOWARD high concentration of protein, and capillaries are usually higher in protein concentration than interstitium, promoting fluid movement into the venous side of the capillary network


What is net hydrostatic pressure in a capillary bed?

• Difference between capillary blood pressure and interstitial pressure
• Usually 25mmHg in the capillary and 0(ish) outside of it