Circulation Flashcards
What is ohm’s law?
Blood flow (F)= pressure difference/resistance
Where is fastest blood flow in a vessel, if flow is laminar?
At the center, blood flow is parabolic because liquid molecules cling to vessel walls and flow slower there
What is Poiseuille’s Law?
Increase in conductance when diameter increases is explained by this law. Conductance is a measure of blood flow through a vessel for a given pressure difference.
What is blood flow autoregulation?
The ability of each tissue in the body to adjust its vascular resistance and to maintain normal blood flow during changes in arterial pressure between 70 and 175 mmHg
What’s the fourth power law for arteriolar resistance mean?
It means that in the systemic circulation, two thirds of the total systemic resistance to blood glow is in the small arterioles. The diameter of these changes tons. And because of Poiseuille’s law, you know that a 4x increase in diameter of thevessel will increase flow by 256x.
This is important because it means that tha arterioles have the potential to either almost completely stop blood flow or cause huge increase in blood flow by changing diameter alone.
Does resistance to blood flow in a circuit get higher or lower as you add more vessels to the circuit?
It becomes lower! The total peripheral vascular resistance is equal to the sum of the resistances of the arteries, arterioles, capillaries, venules, and veins. If you increase number of vessels, you increase conductance (ability of blood to flow thru the vessels), thus decreasing resistance. Thus, if you amputate a limb, you remove a parallel circuit and reduce vascular conductance and total blood flow, while increasing total peripheral vascular resistance
How much more viscous is blood compared to water?
3x more viscous than water.
What is autoregulation?
The ability of each tissue to adjust its vascular resistance to maintain normal blood flow during changes in arterial pressure between about 70-175 mmHg is called blood flow autoregulation
What is stress-relaxation of the blood vessels?
This is a characteristic of all smooth muscle. As the volume of a blood in a vessel increases, this will raise the pressure. Over time it’ll decrease to normal. This is because the blood in the vessel causes elastic distention of the ein, but then the smooth muscle fibers of the vein begin to creep to longer lenghts, and their tensions correspondingly decrease. This is stress relaxation.
This is important because delayed compliance is a mechanism by which the circulation can accomodate extra blood when necessary.
What factors affect the pulse pressure?
- Stroke volume output of the heart
- compliance (the total distensibility of the arterial tree)
Pulse pressure= stroke volume/arterial compliance
What kind of pulse wave contours would the following conditions produce: arteriosclerosis, aortic stenosis, PDA, aortic regurgitation?
In atherosclerosis- the arteries are hardened and noncompliant, so pulse pressure rises. In aortic stenosis- pulse pressure decreases because of diminished blood flow thru mitral valve. In PDA, the diastolic pressure is super low because the L to R shunt means that the blood leaving the aorta gets shunted into the pulmonary artery (not systemic circulation). In aortic regurgitation, the pressure falls to 0 (super low diastolic) because blood pumped into the aorta can flow backwards in diastole into the heart. No incisura in this contour because no aortic valve to close.
See diagram in Guyton, Pg 169 for more details.
Explain ‘transmission of the pressure pulse’ in the arteries
When the heart ejects blood into the aorta during systole, at first, only the proximal portion of the aorta becomes distended because of the inertia of blood prevents sudden blood movement all the way to the periphery. However, rising pressure in the proximal aorta overcomes inertia, and the wave front of distention spreads farther and farther down the aorta.
The greater the compliance of each vascular segment, the slower the velocity, which explains the slow transmission in the aorta, and much faster transmission of the pulse pressure in the distal arteries. The velocity of transmission of pulse pressure is FASTER than actual velocity of blood flow because this is basically a moving wave of pressure that involves little blood movement.
What is dampening of pressure pulses and what does it mean?
This is when the pulse pressure diff between systole and diastole becomes progressively less, because of the resistance to blood movement and the compliance of the vessels.
Resistance to blood flow damps pulsations because a small amount of blood must flow forward at the pulse wave front t odistend the next segment of the vessel; the greater the resistance, the harder this is for this to happen. The compliance damps pulsations because the more compliant a vessel is , the greater amount of blood required at pulse wave front to cause an increase in pressure!
Thus, the degree of damping is almost directly proporitional to the product of resistance times compliance.
What is right atrial pressure determined by?
The ability of the heart to pump blood out of the right atrium and the ventricle into the lungs or the tendency for blood to flow from the peripheral veins into the right atrium
What are three things that increase venous return?
Increased blood volume, increased large vessel tone throughout the body, resulting in increased peripheral venous pressures, and dilatation of the arterioles.
