PHYL3002 Lecture Notes - Lecture 10: Central Venous Catheter, Block Cipher Mode Of Operation, Vascular Resistance
LECTURE TEN: Venous Pressure and Vascular Function Curves
Pre-Loads and Cardiac Filling:
• Venous pressure controls cardiac filling
• Blood flows until venous and ventricular pressure are equal
• Venous pressure control cardiac filling and hence venous return
• Ventricular diastolic pressure depends on the pressure in the veins
emptying into the heart
• Control of end diastolic pressure and cardiac output is dependent on
venous pressure
Steady State:
• On average heart is in steady state
• Not equilibrium as heart is continually using energy to pump blood
• Flow is 5 L/min = total blood volume is 5L
• Blood going into arteries increases pressure
• Blood in arteries is significantly less compared to veins
• Blood flows from arteries to veins due to pressure difference
• If flow is not 5 L/min t → not steady state
• E.g. constricting veins
o Activating venous smooth muscle and increasing venous tone
o Pressure in vein increases from ~ 2mmHg-5mmHg
o Causes increasing in ventricular volume
o Stroke volume increases resulting in increase in cardiac output
o Flow output increases to match flow input → if not, then the heart
will expand until flow rate is the same going into/out of heart
o Increase in blood flow to arteries increases mean arterial pressure
as it is not equal to blood flow out of arteries
o Once arterial pressure increases → blood flow out of arteries will
increase
o Now back to steady state
Venous Pressure at Stasis:
• No blood flow
o Arterial and venous pressures are equal
o Pressure determined solely by blood volume and capacitance of
vascular system
• Pv = Pa = Qt/Ct
• Pressure during stasis is the mean circulatory pressure (MC)
• ~7mmHg for normal vessels and blood volume
Arterial and Venous Pressure:
• To generate flow the heart pumps blood volume from veins into arteries
• Change in venous volume is equal and opposite that of the arteries
• Arterial volume goes up and venous volume goes down by same amount
• Increased arterial volume = increased arterial pressure
• Decreased venous volume = decreased venous pressure
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Document Summary
Lecture ten: venous pressure and vascular function curves. Increased arterial volume = increased arterial pressure: decreased venous volume = decreased venous pressure, arteries are less compliant than veins so larger pressure changes in arteries. Increasing cardiac output or total peripheral resistance increases arterial pressure and decreases venous pressure. Cardiac output and venous pressure: no flow mean arterial and central venous pressures are equal. Increasing cardiac output increases arterial pressure but decreases venous pressure. Increasing peripheral resistance has the same result: volume changes are the same but pressure differences are unequal (more pressure difference with arteries) Vascular function curve: vascular function curve is the relationship between blood flow and venous pressure, more or less linear relationship, with no flow venous pressure = mc pressure, once venous pressure falls below ventricular end diastolic pressure filling. Increasing cardiac output reduces venous pressure can not occur. Increased blood volume increases mc pressure and venous pressure at any cardiac output parallel slopes.
