Mini-Test 1 Flashcards
Factors affecting mean arterial pressure
- Downstream resistance changes
- compliance
Def: Compliance
Ability for a vessel to change in volume for a given change in pressure
How does compliance change
- Decrease with age, sedentary and hypertension
- increase with exercise
Purpose of compliance
-Buffers the change in pressure
- acts as an intermittent pump due to the recoil of elastin (windkessel effect)
Def: Total peripheral resistance
the resistance of all downstream vessels
Factors affecting TPR
- vasculature anatomy (diameter)
- blood viscosity
Poiseuille’s law
R= 8uL/pir^4
Def: Vascular resistance (tone)
How difficult it is for blood to flow through a vessel
Ohm’s Law
Ohms (vascular resistance) = Voltage (change in pressure) / amperes ( blood flow)
Def: Augmented Pressure
The increase in peak blood pressure due to reflective waveforms
Isolated Systolic Hypertension
Systole: with age, stiffer aorta and large arteries do not expand as much with the injection of blood volume into the vascular space (less damping)
Diastole: Decrease in compliance = decrease in recoil - blood not pushed along the vascular tree & DBP decreasesDe
Def: Pulse Pressure
the difference between DBP and SBP
What are the effects of exercise on vascular compliance
- Greater compliance in endurance trained individuals compared to sedentary individuals of same age
- Increase in compliance following training intervention
What lines all vessels
Endothelium
Smooth muscle and vessels
- Surrounds in rings
- Causes vasodilation and vasoconstriction
Elastin and vessels
- Runs parallel to vessel
- involved in mechanical dilation that results from shear force produced by increased blood flow
Are vessels closer or further away from the heart more compliant and how does that affect reflective wave forms
- Vessels become less compliant the further you move away from the aorta
- need to accommodate less significant changes in pressure
- reflect waves because not all energy can be transferred
Steady state conditions vascular control
DOWNSTREAM VASCULATURE
1. Vascular resistance to flow
2. Resistance, CO, MAP
3. Resistance vs conductance
Pulsatile Flow vascular control
HEART LEVEL
1. Vascular Compliance
Variables which determine VO2 (equation)
Q*(aO2 - vO2)
How does local blood flow increase with workload
linearly
Def: Functional/exercise hyperemia
The increase in blood flow (decrease in vascular resistance) in response to muscle contraction
Variables affecting stroke volume
- Venous Return
- Cardiac Mechanisms
Variables affecting heart rate
- Neural Control
Variables affecting TPR
- Vascular constriction
- Vascular dilation
Role of Cardiac output compared to vascular conductance during exercise
- Q increases with exercise
- Mechanical constraints on heart limit Q (Pericardium)
-Skeletal muscle blood flow increases linearly with workload
-Q cannot provide enough blood flow to exercising muscles - requires changes in local vascular conductance to direct blood flow
Mechanical constraints of on SV of the Pericardium
- ridged structure limits distension
- shown through increase in SV, CO and VO2 in a heart with the pericardium removed
How does the pattern of blood flow increase during exercise
- Redistribution of blood flow in body
- Muscle takes most of CO
- More CO going to the heart with exercise
-less going to viscera - Rapid blood flow/vasodilation response
- Single contraction causes immediate increase in muscle blood flow - Ascending vasodilation
Factors involved in vasomotor control
- Mechanical
- Muscle Pump
- Myogenic - Neural
- SNS (Vasoconstriction) - Biochemical
- Metabolic
- endothelium
- neural
Muscle Pump
Mechanically changing the pressure gradient across the capillary bed
- Collapse of vein during exercise changes the venous pressure from 40 mmHg at rest to 0 during muscle contraction
- increases venous return back to heart
Myogenic Mechanism
- increase in arterial pressure due to increased Q
- Natural cause increase in arterial radius
- constriction due to detection of stretch
- returns capillary pressure to baseline
Mechanism used to protect capillaries - form of local flow autoregulation in response to changes in pressure
Effect of potassium on vasodilation
- K released rapidly from skeletal muscle ( release related to workload)
- outside smooth muscle because more positive
- hyperpolarization leads to vasodilation
Effect of adenosine originating form the skeletal muscle
Metabolite leads to vasodilation through the stimulation of receptors
Effect of lumen originating metabolites and ACh
- ACh, ATO and adenosine bind to receptors on endothelial cell
- Cause an increase in Ca+ in endothelial cell
- Leads to the upregulation of COX and NOS
- increase in prostacyclin and NO production
- PGI2 and NO more into SMC
- Activates cAMP and cGMP which causes a decrease in Ca+ leading to SM relaxation
How does shear force cause vasodilation?
- Shear force causes phospholipid breakdown of the glycocalyx which line the endothelial cell
- Phospholipid breakdown causes an increase in Ca+ increasing NOS activity and produces arachidonic acid
- arachidonic acid then produces prostaglandins via the enzyme cyclooxygenase
- Both leading to dilation
Def: Reactive Hyperemia
Increased blood flow due to muscle ischemia
Def: Flow mediated dilation
the conduit vessel dilation due to shear stress typically following an increase in blood flow
how can flow-mediated vasodilation be used to assess how well the endothelium is working
- We inflate cuff
- release it to cause a shear stress stimulus on an artery
- Measure dilation in artery
- 10-15% dilation is normal
- <5% = bad
How can the rate and % change following reactive hyperemia change
- normally there is a delay between increase in shear and % change in diameter
- Age effects the time it takes
- training effects the % change
What conditions does endothelial control of blood flow have the greatest effect on
Rest and Heavy exercise
Red Blood cell Hypothesis
- ATP released, binds into P2Y receptors on endothelium
- Cascade of events leads to eNOS activation
- NO production increases
- NO diffuses to smooth muscle cell
