Hemodynamics Flashcards
What are the most important determinants of blood flow in the CV system?
the pressure gradient and radius to the fourth power
Resistance is equal to…
pressure differential over blood flow
For resistances in series, the total resistance of the entire system equals_________.
the sum of the individual resistances
The primary site of arterial resistance is_______.
the arterioles
What are examples of vessels in parallel in the circulatory system?
organs and vessels within a category of vessels (ex: the special circulations we discussed, including cerebral, coronary, renal, splanchnic, and cutaneous circulations)
For resistances in parallel, the total resistance is____ than any individual resistance
less
What is Reynold’s number?
it describes the propensity for turbulent blood flow (higher Reynold’s # = greater chance for turbulent flow)
What is one of the most common places for turbulent blood flow to develop?
in the aorta, where the vessel diameter is large
Is dense fluid more or less likely to exhibit turbulent flow?
more likely
Is hematocrit higher or lower in smaller vessels compared to larger vessels? Why?
Hematocrit is lower in smaller vessels due to plasma skimming, in which blood from periphery of main vessel is shunted into a branching vessel (and the blood on the periphery contains less RBCs).
What is axial streaming and what does it compensate for?
the tendency of RBCs to accumulate in axial laminae at high shear rates; compensates for the high viscosity expected to be experienced in small vessels (ie, capillaries) with low velocities
What does the venous system vs. arterial system vs. lymphatic system vs. capillary network control?
- venous: volume
- arterial: pressure
- lymphatic: fluid drainage/return
- capillary: exchange
Why is blood pressure on the arterial side NOT a good way to assess whether or not blood volume has been lost?
The arterial side controls blood pressure and has several mechanisms to maintain pressure; thus, even with a lower blood volume, the arterial side will maintain pressure. This is why central venous pressure is a much better indicator of blood volume.
Muscular arteries serve as ______ resistance conduits that deliver blood quickly to tissues with _____ energy expenditure.
low; minimal
Why are venous vessels known as capacitance vessels?
They are able to store large blood volumes without experiencing a large increase in blood pressure.
Why is the right heart known as a “volume pump”?
It delivers large volumes of blood to the pulmonary circulation at low pressure.
Define Bernoulli’s Principle and its application to the circulatory system.
Bernoulli’s states that in a constant flow system, the total energy (potential+kinetic+gravitational) remains constant. This principle can be applied to the circulatory system when considering stenosis. With stenosis, there is an abrupt decrease in vessel CSA, thus increasing velocity. Potential energy (pressure) is converted to kinetic energy (flow). Thus, transmural (static) pressure decreases as the velocity of blood flow increases in a stenotic area.
What are other words we have used to refer to transmural pressure?
static pressure, lateral pressure, blood pressure (only when tissue pressure is negligible)
Rather than understanding blood flow as movement from higher to lower pressure, it is more correct to understand blood flow as what?
flow from higher to lower total energy (and blood loses energy as it flows due to frictional forces against vessel wall)
How does velocity of blood flow affect blood pressure?
higher velocity of flow = lower pressure
How does Bernoulli’s Principle relate to heart sounds?
The smaller the aortic valve gets (ie, the more it closes, or the more stenotic it gets due to a pathological condition), the faster the blood flow through the valve and the louder the heart sound.
What does Poiseuille’s Law state?
Flow is proportional to pressure gradient and inversely proportional to resistance.
R=(8Lη)/(πr^4)
Q=(πr^4)/(8Lη)
Why are right and left ventricular pressures different if they generate the same cardiac output?
This is due to the vast change in resistance between the systemic and pulmonary circuits.
What is the Reynold’s number needed to generate turbulent blood flow?
> 3000
What are the determinants of turbulent flow?
- high density, large tube diameter, and high velocity all increase propensity for turbulent flow
- a more viscous fluid is less likely to exhibit turbulent flow
Is an anemic patient more or less likely to exhibit turbulent flow? Why?
More likely- this is because less with anemia, there are less RBCs per volume of blood, which means the patient’s blood is less viscous. A decrease in viscosity increases the propensity for turbulent flow, based on Reynold’s equation.
What is the difference b/t a Newtonian and non-Newtonian fluid?
A Newtonian fluid is one whose viscosity remains constant over a range of shear rates and shear stress (homogeneous). A non-Newtonian fluid is one whose viscosity changes over a range of shear rates and shear stress (non-homogeneous).
What is the normal range for hematocrit?
35-50%
