Flashcards in Hemodynamics Deck (61):
Basic physics of blood flow
What drives blood flow through vessels?
What is transmural pressure?
the difference in pressure between the inside and outside of a vessel (across the wall)
T or F: Gravitational pressure also affects blood flow
True, positional changes affect pressure.
Where is the highest mean pressure found?
T or F: cardiac output from left and right sides of heart are equal
True, but resistance and pressure are different — much lower in pulmonary circulation.
What is the Total blood volume?
Where is the greatest blood volume found?
What is Flow (Q)?
volume per unit time (ml/min)
T or F: Blood Flow (Q) is constant through the system
True. the cardiovascular system is a closed loop, so flow through the capillaries MUST be same as flow through the aorta (on average).
What is the Total flow in the cardiovascular system?
the CARDIAC OUTPUT (CO)
What is Velocity (v)?
distance per unit time (cm/sec), v=Q/A [A=cross sectional area]
Blood velocity is dependent on:
-Velocity depends inversely on cross-sectional area (A)
T or F: velocity is slowest through sections with biggest cross-sectional area
True, total sectional area is smallest in Aorta, yielding fastest flow
What is the Flow equation?
Q = (delta)P/R
-R = resistance
-(delta)P= pressure difference
What is the equation for Cardiac Output (CO)?
￼CO= (mean arterial pressure-venous pressure)/ total peripheral resistance (TRP)
T or F: Flow in doesn't necessarily have to equal equal flow out
T or F: Flow is directly proportional to pressure, inversely proportional to resistance
What are Assumptions of flow equation that are not really valid for cardiovascular system?
-straight rigid tube
T or F: The term (pi)r^4/8nl (from Poiseuille's equation) is the inverse of resistance in the flow equation
What happens when you increase size of vessel (radius)?
decrease resistance, increase flow
doubling the vessel radius increases flow by?
16-fold (2^4), flow varies with 4th power.
What is the the major mechanism by which flow is controlled in the CV system?
Vessel diameter (vasoconstriction & vasodilation).
What happens when you increase the length of the vessel?
increase resistance, decrease flow
What happens when you increase viscosity?
increase resistance, decrease flow. Viscosity dependent on hematocrit
Note: For the purposes of the exam, you do not have to memorize Poiseullie's quation per se, but you need to understand how each variable affects flow, and that the flow varies with the 4th power of the radius.
T or F: Poiseuille’s Law is only valid for single vessels
T or F: Total resistance of a network of parallel vessels is lower than the resistance of single lowest resistance vessel in the system.
True, Changing the resistance of a single vessel in a parallel system has little effect on the total resistance of the system.
T or F: pressure is the same in each parallel vessel, but the blood flow through each can be different
How do you calculate resistance in parallel vessels (uch as in most of the systemic circulation)?
Reciprocal of total resistance of a parallel network is the sum of the reciprocals of the individual resistances
How do you calculate resistance in series?
Resistances in series are additive, Total resistance of a series of vessels is higher than the resistance of any individual vessel
T or F: Largest proportion of total resistance is in arterioles
T or F: Blood flow through vessels in series is constant, but the pressure decreases through the series of vessels
T or F: Flow equation assumes non-pulsatile laminar flow
Explain Laminar flow
-smooth, streamlined, and most efficient
-velocity slowest at edge of tube, fastest in center
Define turbulent flow
-irregular, with eddies & vortices
-requires more pressure for same average velocity
compared to laminar flow
-factors that increase turbulent flow: large diameter, high velocity, low viscosity, abrupt
changes in diameter, irregularities on tube walls.
what is pulse pressure?
= systolic – diastolic
What is Systolic pressure?
peak aortic (~arterial) pressure; normal range for systolic pressure ~ 90– 120 mmHg; diastolic ~ 60 – 80 mmHg)
What is Diastolic pressure?
minimum aortic pressure
What decreases from Aorta to capillaries?
-mean pressure and
What is Mean arterial pressure (MAP)?
~ diastolic pressure + 1/3(systolic – diastolic)
T or F: MAP is NOT the arithmetic average of systolic and diastolic pressures
True, because diastole is longer than systole (at resting heart rates)
What is vascular compliance?
Compliance represents the elastic properties of vessels. Compliance (C, in ml/mmHg) equals change in volume (V, in ml) that results from a change in pressure (P, in mmHg)
T or F: Veins are less compliant than arteries – less deltaV per deltaP
False, veins are more compliant
how the pulsatile flow of blood produced by the heart is converted to steady flow in the capillary beds?
Degree of compliance in main arteries contributes to
transformation of pulsatile flow from heart into continuous flow in microcirculation (see Figure above)
What determines compliance?
Compliance is determined by relative proportion of elastin
fibers versus smooth muscle and collagen in vessel walls.
What is Arteriosclerosis?
general term for loss of compliance caused by thickening and hardening of arteries
What is LaPlace’s Law?
LaPlace’s Law describes the relationship between tension in a vessel wall and the transmural pressure.
T or F: Tension in the vessel wall increases as pressure and radius increase
True, hypertension increases stress on vessel (and chamber) walls.
What is LaPlace's equation?
u: wall thickness
What is Fick’s Principle?
The basic idea is that the amount of substance used is equal to the amount that enters the tissue minus the amount that leaves, and the amount can be determined as the flow times the concentration
What is the Fractional O2 Extraction (EO2)?
the amount of oxygen used by a tissue expressed as a fraction of the original (arterial) oxygen concentration.
What forces determine solvent movement across capillaries?
hydrostatic pressure and oncotic pressure
What is hydrostatic pressure (P)?
Hydrostatic pressure is simply fluid pressure, blood pressure in this case
T or F: Hydrostatic pressure promotes FILTRATION (movement of fluid out of capillaries)
what is oncotic pressure (π)?
Oncotic pressure (colloid osmotic pressure) is the osmotic force created by proteins in the blood and interstitial fluid. α Globulin and albumin are major determinants of oncotic
T or F: Capillary oncotic pressure promotes REABSORPTION of fluid (movement of fluid into
What is Starling's equation?
Flux = k[(Pc-Pi) – (πc – πi)]
What promotes filtration?
Factors that increase blood pressure (hypertension) or reduce oncotic pressure (liver disease) tend to promote filtration. Excess=edema
T or F: there is a tendency toward filtration on the venous side and reabsorption on the arterial side.
False, other way around