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Flashcards in Physio Deck (22)
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Main determinant of blood flow.

Tissue needs


How are velocity and cross section area related?



Which blood vessels act as the control conduits that control blood flow?

Muscular Arteries


Main determinant for systolic blood pressure.

Stroke Volume


Main determinant for diastolic blood pressure.

Total Peripheral Resistance


Major determinant for cardiac output.

Venous Return


How is blood flow calculated?

F = change in pressure/resistance


How is velocity calculated?



How is pulmonary vascular resistance calculated?

PVR = (mean pulmonary artery pressure - left atrial pressure)/cardiac output


What happens to resistance with turbulent blood flow?

Increase in resistance


What does Reynold's Number measure and what factors are involved?

Measures tendency of blood flow to become turbulent.

Re = (velocity of flow x diameter of vessel x density of blood)/viscosity of blood


What the hell was he talking about with the energy gradient crap?

It basically is energy conservation. We know that velocity and cross sectional area are inversely related. So if a vessel narrows (decreasing area) the velocity increases.

When velocity increases, the kinetic energy of the blood increases. To compensate for the increase in kinetic energy, the only other factor (that we have to worry about), the pressure energy, has to decrease.

This maintains a conservation of energy in the system.


If blood flow is dependent on a pressure gradient, how does it flow from a stenotic portion of a blood vessel with low pressure to a region of higher pressure distal to the stenosis?

Energy Gradient Crap.
-even though the pressure is higher distal to the stricture, the increase in kinetic energy provides the energy to flow from a section of low pressure to a section of high pressure.


What are the variables in Poiseulle’s equation to calculate blood flow?

Flow = (pressure change x radius^4)/(viscosity x length)

Radius changes have the biggest effect on blood flow


Biggest contributor to autoregulation.

Local mechanisms such as tissue needs


How are compliance, volume and pressure related?

C = change in volume/change in pressure


How does distensibility help to maintain blood pressure?

It accommodates extra blood volume in the vessels and ""buffers" the system to prevent much of a blood pressure increase.


Describe the change in systolic and diastolic blood pressure in patients with Primary Systolic Hypertension due to atherosclerosis.

Systolic: increases
Diastolic: decreases

Atherosclerosis decreases the distensibility of the major elastic arteries (mainly the aorta). When blood is pumped into these vessels in systole the blood pressure rises to a high level.

Meanwhile, the muscular arteries further distal to the heart are dealing with increased blood flow due to the high pressure. They will distend (decrease resistance) the best that they can but once they reach their limit, they will send blood out through the capillaries and into the interstitial space to dissipate the pressure.

This loss of fluid in the vasculature leads to decreased heart filling and a lower diastolic blood pressure. Dumb.


Where is central venous pressure measured?

In the right atrium where the IVC and SVC enter.


What does inhalation and intubation do to pulmonary venous pressure upon inhalation.

Normal inhalation: an already negative pressure becomes more negative with inhalation. This expansion of the chest wall also decreases resistance in the pulmonary blood vessels leading to a drop in venous pressure.

Intubation: inhalation caused by positive pressure forcing air into the lungs causes an increase in pulmonary pressure. The decrease in resistance from the chest expanding does not account for the increased pressure from the air forced into the lungs.


Cause of varicose veins.

Venous valve insufficiency.


What happens to the blood vessels during anaphylaxis?

Capillaries normally only have blood flow when surrounding tissues require nutrients and waste removal. This prevents too much blood from entering the capillaries at one time. During anaphylaxis, the arterioles dilate all the sphincters regulating flow to the capillaries and blood fills them.

This results in severe hypotension and shock. It is treated with a vasoconstrictor like epinephrine.