Lecture 32: Arterial Pressure and Arterial System Flashcards
Roles of arterial system
- Primarily: distribute blood to capillary beds
- Hydraulic filter
- Arterial elasticity
Arterioles
- Terminal components of this arterial system
- Regulate distribution of blood among the various capillary beds
Vessels between heart and arterioles
- System of tubes
- Considerable volume and distensibility
Arterial system composed of
- Elastic tubes with high resistance at the end
- “Hydraulic filter”
Hydraulic filter role
- Converts pulsatile flow from heart to steady flow in capillaries
- Minimizes workload of heart
Stroke volume enters arterial system
- During diastole
Part of energy developed (or conveyed to blood as pressure) during systole is dissipated as
- Forward capillary flow
- Rest (majority) is stored as potential energy in the walls of the arterial system
During diastole the elastic recoil of vessel walls
- Converts potential energy into capillary blood flow
If walls were inelastic (rigid tubes)
- No energy could be “stored” in walls and used to propel blood during diastole
- Flow would cease during diastole in rigid tubes
- 2x pressure would have to be developed for same flow in rigid tubes
Primary determinants (physical factors) of arterial blood pressure
- Arterial volume
- Compliance of arterial system
Secondary determinants (physiological factors) of arterial blood pressure
- Heart rate
- Stroke volume
- Cardiac output
- Peripheral resistance
Mean arterial pressure (MAP)
- Average pressure over time in aorta and large arteries
Formula for determining MAP
- MAP = Pd + 1/3(Ps - Pd)
- MAP = Pd + 1/3(PP)
- (Ps - Pd) is pulse pressure (PP)
Pulse pressure
- Essentially same factors that determine mean arterial pressure
- Thus, stroke volume and arterial compliance determine pulse pressure
Increase in HR at constant Q results in
- Decreased SV
- Deceased PP
Decreased TPR results in
- Allowing rapid flow of blood from arteries to veins
- Increased venous return
- Increased SV as in exercise
- Increased PP
Increases in mean circulatory filling pressure (Pmcf) such as rapid transfusion blood volume results in
- Increased SV
- Increased PP
Sudden ejection vs. prolonged ejection
- Sudden ejection increases PP more than prolonged ejection
Atherosclerosis leads to
- Decreased elasticity of arteries
- Decreased compliance
- Increased PP
An increase in Pd is often used as indicator of
- Changes in TPR
- Seen in hypertension (but not always the case)
increase in TPR leads to an increase in
- MAP (both Ps and Pd) if Q is unchanged
- But if there is concomitant decrease in Q by a decrease in SV, then MAP (Pd + Ps) may not be changed
Radial stretch of aorta as blood is ejected from heart initiates
- Pressure wave that is propagated down aorta
- Branches with finite velocity
Peripheral arterial pressure curve/wave characteristics
- Propagated wave is faster than forward movement of blood itself
- Perceived when counting pulse rate
- In aorta velocity of pressure wave may be 15 times that of blood flow
- In more distal arteries, velocity of wave may be 100 times the velocity of blood flow
Velocity of transmission of pressure wave varies inversely with
- Vascular compliance
- Decreased vascular compliance (seen in more distal parts of arterial tree) leads to increased velocity
Measurement of transmission velocity can be used to measure
- Elastic characteristics
- Degree of compliance of arterial tree
Three major things are seen as distortion of wave happens (wave moves more distally)
- High frequency components of pulse (like incisura) dampen and disappear
- Systolic portion becomes narrower and attains greater peak
- A hump may become prominent in diastolic portion of pressure wave
Narrowed and greater peak (augmentation) of systolic portion of wave occurs due to
- Phenomena of reflection
- Vessel tapering
- Vessel resonance
As wave travels to less compliant areas of arterial tree, the decreasing compliance causes
- Retrograde or backward traveling wave of pressure
- Backward wave then summates with next forward moving wave, producing a higher wave (thus arterial augmentation)
Retrograde augmentation of wave has little functional significance, but relates to
- Blood pressures in peripheral arteries
- Systolic pressure in peripheral arteries may be 20-30% greater than that of central aorta
- Diastolic pressure may be reduced as much as 10-20% over aortic values
