PHYS20008 Lecture Notes - Lecture 17: Mean Arterial Pressure, Wiggers Diagram, Pulse Pressure
12 Jun 2018
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Lecture 17
PHYS20008 - HUMAN PHYSIOLOGY
LECTURE 17
REGULATION OF BLOOD PRESSURE
OVERVIEW
•Blood pressure
•Distributing blood to the body
•Mean arterial blood pressure
•Cardiac output: stroke volume and heart rate
•Resistance to blood flow
•Making adjustments to MAP- influence of:
•Total Peripheral Resistance
•Cardiac Output
•Control of Blood Pressure
•Short term
•Longterm
MOVEMENT OF BLOOD
•Heart – source of energy
•Other influences/aids
•Gravity
•Skeletal muscle
•Diaphragm movements
•Elastic tissue
•Skeletal muscle pump; when a muscle is contracting, it is squeezing the blood vessels, forcing
blood upward past the valves, which helps us with moving blood around system against gravity.
•Breathing in and out hangs pressure in thorax. Rhythmic pressure changes in thorax help to move
blood around the system.
BLOOD PRESSURE TERMINOLOGY
•Systolic BP: Max. pressure exerted in arteries when blood is ejected into them during systole
(heart contracting phase).
•Diastolic BP: Min. pressure within arteries when blood draining off into remainder of vessels
during diastole (heart relaxing/filling phase).
•Difference between above two is pressure being exerted by the heart; the pulse pressure.
•Pulse pressure: A measure of strength of pressure wave (Difference between Systolic & Diastolic
BP)
•Mean arterial pressure (MAP): Average pressure responsible for driving blood forward into
tissues throughout cardiac cycle.
•(MAP = Diastolic BP + 1/3 Pulse pressure)
MEAN ARTERIAL PRESSURE
•Average pulse between the two
•Loss of energy due to friction
•Difference reduced to zero by capillaries
•Left ventricular pressure is rising and falling dramatically, like
we know from the Wiggers diagram, but as soon as we come
into the arteries, the diastolic pressure in arteries is way up
compared to ventricles. This is to do with the smooth muscle
within the arteries maintaining their vasomotor tone. The
smooth walls maintain some level of pressure, meaning they
never fully relax.
•MAP decreases as we move through the system.
Lecture 17
PHYS20008 - HUMAN PHYSIOLOGY
•Resistance increases moving through smaller
and smaller vessels so that by the time we get
to the capillaries the waveform is very steady.
Not like the initial waves.
•By the time it’s coming back to the right
atrium, it’s coming back at a fairly steady
pressure.
•We can increase blood pressure in this part of
the system by putting more blood into the
system (cardiac output).
•Or, with the resistance of the arterioles. If
they are overall constricting and forcing
blood inwards, this will increase blood
pressure because we are inhibiting the ability
for it to flow out.
•The resistance in these vessels is called total
peripheral resistance (TPR).
•MAP is proportional to CO (cardiac output) * TPR
•Can also change heart rate. Requiring more beats per minute.
•CO = Heart rate * stroke volume (SR)
•Sympathetic NS can squeeze the veins, increasing venous return coming back to heart, therefore
increasing what’s coming out of the heart, affecting BP.
•If you lie down and stand up suddenly, we are temporality reducing venous return.
IMPORTANCE OF MAP
•Essential for efficient function and life: extremes dangerous
•Low bp (Eg. dizziness, organ failure)
•High bp (Eg. stroke, aneurysm).
•What determines it?
•How much blood is pumped out per unit time
•depends on stroke volume and heart rate
•‘cardiac output’ = CO
•How difficult/easy it is for the blood to move through the system
•i.e. the resistance of the peripheral circulation
•‘total peripheral resistance’ = TPR
HOW MUCH BLOOD IS PUMPED OUT?
•Cardiac output (CO)
•Volume of blood pumped by one ventricle in a given period of time
•CO = HR * SV (Heart Rate x Stroke Volume)
•Average = 5 L/min
•Stroke volume (SV)
•Amount of blood pumped by one ventricle during a contraction
•SV = EDV – ESV (end diastolic volume - end systolic volume)
•SV = 135mL - 65mL = 70mL (average value at rest)
•Usually we pump out about 70mLs, leaving about 65mLs behind. Because we want a bit of
wiggle room.
WHAT AFFECTS STROKE VOLUME?
•Force of ventricular contraction
•Affected by:
Document Summary
Overview: blood pressure, distributing blood to the body, mean arterial blood pressure, cardiac output: stroke volume and heart rate, resistance to blood flow, making adjustments to map- influence of, total peripheral resistance, cardiac output, control of blood pressure, short term, longterm. Rhythmic pressure changes in thorax help to move blood around the system. Bp: mean arterial pressure (map): average pressure responsible for driving blood forward into tissues throughout cardiac cycle, (map = diastolic bp + 1/3 pulse pressure) This is to do with the smooth muscle within the arteries maintaining their vasomotor tone. The smooth walls maintain some level of pressure, meaning they never fully relax: map decreases as we move through the system. Phys20008 - human physiology: resistance increases moving through smaller and smaller vessels so that by the time we get to the capillaries the waveform is very steady. Because we want a bit of wiggle room. What affects stroke volume: force of ventricular contraction, affected by:
