PHYL3002 Lecture Notes - Lecture 9: Central Venous Pressure, Viscosity, Vascular Resistance
LECTURE NINE: Blood Pressure and Cardiac Loads
Mean and Pulse Pressure:
• Pressure wave produced by contraction of the heart
• Include
o Systolic pressure → when ventricles are in systole
o Diastolic pressures → when ventricles are in diastole
• Mean pressure → closer to diastolic pressure
• Pa = Pd + 1/3 (Ps-Pd) → only an approximation
• Not dependent on diastolic/systolic pressures
• SBP and DBP are not directly measured or controlled
• Pulse pressure also directly controlled by CVS
• Pulse pressure is determined by stroke volume and arterial compliance
Mean Arterial Pressure:
• Pressure is dependent on cardiac output and total peripheral resistance
• Q’ → Pa-Pv/R
• Pa-Pv = Q’ x R
• Pa = Q’R
• Sets the average driving pressure, controls flow
• Measured by the baroreceptors
Control of Stroke Volume:
• Frank-Starling law
• Increasing venous return increases cardiac output
• Venous return changes cardiac pre-loads
• Inotropy increases force of contraction
Pre-Loads and After-Loads:
• Pre-loads
o Load that stretches a muscle to its current operating length
o Increasing pre-load increases resting muscle length
• After-load
o The load a muscle contracts against
o Increasing after-load reduces velocity of shortening and amount of
muscle shortening during a twitch
Cardiac Muscle Length-Tension Curve:
• Cardiac muscle has similar length-tension
properties to other muscles
• Increasing ventricular volume stretches the
ventricular muscle
• Stretching the ventricles changes the pressure
they can generate
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Document Summary
Mean and pulse pressure: pressure wave produced by contraction of the heart. Mean arterial pressure: q" pa-pv/r, pa-pv = q" x r, pa = q"r, sets the average driving pressure, controls flow, measured by the baroreceptors. Control of stroke volume: frank-starling law, venous return changes cardiac pre-loads. Cardiac muscle length-tension curve: cardiac muscle has similar length-tension properties to other muscles. Increasing ventricular volume stretches the ventricular muscle: stretching the ventricles changes the pressure they can generate. Cardiac cycle: during diastole the ventricle fill with blood. Isovolumic contraction of ventricles when all heart valves are closed at start of systole: similarly during relaxation there is an isovolumic phase when all heart valves are closed, after-load increases during systole. Cardiac pre-load: venous pressure sets the pre-load, cardiac filling stops when ventricular pressure equals central venous pressure. Increasing venous pressure increases end diastolic volume and pre-load. Cardiac after-load: with constant end diastolic volume increased after-load reduces stroke volume, after-load = arterial pressure.
