12/2/2014 Medical Physiology Systemic Circulation Amit S. Dhamoon Flashcards
What does the concept of compliance refer to in general?
Compliance = V/P
- blood vessels have finite compliance
In blood vessels, the greater the volume of fluid, the ___ the pressure
greater
Define compliance (C) of an elastic vessel
Proportionality factor that relates the change in volume, ∆V, to a change in transmural pressure, ∆P(tm) ∆V = C∆P(tm) or C = ∆V/∆PTM
What is another name for compliance?
Capacitance (ml/mm Hg)
Define transmural pressure
P(tm) –> difference in pressure between the inside and the outside of the vessel
A rigid tube has a compliance of ___
zero
Define elastance (E)
Inverse of compliance
E = ∆P(tm)/∆V
Define distensibility (D) or specific compliance
Fractional change in volume for a given change in pressure
D = ∆V/V∆P(tm) = C/V.
What determines vascular compliance?
The relative proportion and arrangement of smooth muscle, and elastin and collagen fibers in the vessel wall
Describe the function of each type of vessel
1) aorta
- conduit of blood from the heart
- high pressure vessel.
2) arterioles
- resistance vessels
- regulate blood flow through individual organs
- affected by sympathetic nervous system
3) capillaries
- exchange vessels
4) veins
- capacitance vessels
- contain >50% of blood volume
Because blood vessels are ___, they can expand and contract depending upon the pressure, changing blood volume contained within
distensible
Compliance is the medically important measure of how the distensible ___ changes volume with pressure
blood vessel
Vascular compliance is determined by arrangement of ___ and ___ and is not homeostatically regulated parameter like pressure
elastic fibers; smooth muscle
Compliance is measured from the ___ of a Pressure-Volume curve
slope
Another way to quantify the elastic properties of vessels is ___
distensibility
Why do arteries function as resistance vessels?
They have low volume capacity, expand modestly and maintain resistance over wide pressure levels
Why do veins function as volume reservoirs or capacitance vessels?
They expand greatly (also change shape) with small pressure changes due to the high compliance and have large volume changes
With increasing age, vascular compliance ___ dramatically, and the heart must work
___ to pump blood through stiffer vessels
decreases; harder
A given stroke volume would produce a ___ pulse pressure in older individuals than in younger ones
greater
With increasing age the Windkessel effect is ___, causing pulsatile flow to persist in the capillaries
decreased
Regular exercise ___ cardiac contractility and stroke volume so that the heart may pump
blood through vessels that are stiffer and that may also have higher resistance due to ___
increases; atherosclerosis
What is the Windkessel effect?
German for wind chamber –> the storage of blood during systole by the aorta, pulmonary artery and their major branches
What is the consequence of the Windkessel effect?
The maintenance of blood flow during diastole
For a given cardiac output, Q, the mean pressure decreases with increasing distance from the heart in accordance with Poiseuille’s law:
P2 = P1 - (8ηQ/πr4)L
The greatest pulse pressure is in the ___
left ventricle
Why does blood flow?
Because cardiac contractions create pressure in the fluid contained within the heart, thus establishing a pressure gradient of about 100 mm Hg between the aorta and the vena cava
Is the pressure on the arterial side pulsatile in the systemic circulation?
Yes
What facilitates the damping of the pressure oscillations and the steadiness of the blood pressure as the large resistance of the smaller arterioles is encountered?
The Windkessel effect
Why is pulmonary resistance less than systemic resistance?
Because in the pulmonary capillaries the pressure remains pulsatile, oscillating between lower limits than in the systemic circulation
The arterial pulse contour shows the time course of the ___ in the arteries of the systemic circulation during a single cardiac cycle
transmural pressure
As the heart beats, a continuous sequence of ___ pressure waves is generated at a frequency of 1-2 Hz (hertz, cycles per second)
pulsatile
Define systolic pressure, Ps
Maximum pressure reached by the arterial pressure as blood is ejected from the heart during systole
Define diastolic pressure, Pd
Minimum pressure reached by the arterial pressure as the heart relaxes and refills during diastole
The mean arterial pressure is equal to the steady pressure required to maintain the ___ through the total peripheral resistance
cardiac output
What does the shape of arterial pulse contour reflect?
Events of cardiac cycle and elastic properties of the vessels
What is the anacrotic limb?
Rising part of aortic pressure wave
What causes the anacrotic limb?
Blood entering aorta from left ventricle during systolic ejection
What is peripheral runoff?
Flow of blood from arteries into capillaries
What is the dicrotic notch or incisura?
Momentary reversal of blood flow, which closes the aortic valves and creates a transient increase in aortic pressure
Pulse pressure is directly proportional to ___ and inversely proportional to ___
stroke volumen; compliance
