Lecture 7 - Heart Flashcards
Where does the heart sit in the body?
Chest NOT directly on the midline slightly rotated most obvious part=ventricles Heart of Males and Immature Females is at Nipple level
Base=area where heart is attached to the rest of the body=”anchoring point”=where vessels enter/exit
Apex=pointy part of LV
=point INferiorly(down), ANTeriorly(forward), to the LEFT
2/3 of mass lies to the LEFT of the midline, slightly Rotated
1/3 of mass lies to right of midline
How is the heart orientated relative to the midline?
2/3 of the heart is on the LEFT of the midline (sqewd to the left), and is SLIGHTLY ROTATED
1/3 of the heart is on the right if the midline
How is the heart protected?
most of the heart is protected by the Sternum
the Left Ventricle (LV) ISNT protected by the sternum
What are the borders of the heart?
RIGHT border is formed mainly by the R.Atrium
INFERIOR border is formed mainly by the R.Ventricle
LEFT border is formed mainly by the L.Ventricle
What is the Base and Apex of the heart?
Base=TOP=area where the heart is attached to the rest of the body
=attachment/entry and exit point
=ANCHORING point
Apex=BOTTOM
Heart sits free to move/unattached other than at the base
Why are the borders of the heart important?
Cadaver= brown skin with not alot of colour
Chest X-rays
when the shape changes, you can see what part of the heart is causing the problem
What is the Diaphragm?
Boundary between the Abdomen and Thorax
What is Cardiohypertrophy?
Enlarged
Boot shaped heart
(bulging out LV
Deformed RA)
x-ray shows Cardio-throacic ratio is LArger than normal (greater than 50% of rib-to-rib line)
aortic stenosis (narrowing due to rheumatic fever) causes cardiohypertrophy= LV becomes even thicker and ore muscular to compensate the decreased integrity of the valve opening (due to lumpy/vegetation/scar tissue formation) =pressure
LV wall significantly thicker but LUMEN TINY
=less space to fill
heart struggles to INFLATE=doesn’t pump as well
Decrease in Flexibility (LOSS of COMPLIANCE)=harder to fill
cardiac OUTPUT DROPS=(GREATER AFTERLOAD)
So large that they OUTSTRIP ability to SUPPLY OXYGEN to all the LV muscle cells= fail
What do Radiographers look out for?
Cardiac Thoracic ratio
Line from Rib to Rib
Heart should be LESS than 50% between the two lines
too big=heart occupies and area greater than 50% of the Rib-to-Rib line
What is composed of alot of collagen?
Valve leaflets
the mass of collagen in Valve Leaflets contributes to them being Tough but Flexible
What is Aortic Stenosis?
Narrowing
Stiffer Outlet
often due to Rheumatic Fever=STREPTOCOCCUS infection
body produces antibodies(immune system) which attacks your own bodily CT tissue (endocardium,myocardium and pericardium)
tends to attack collagen heavy tissues especially=valve leaflets (e.g aortic valve)
Able to Rebuild, but doesn’t rebuild as well=
scar tissue + vegetation + lumps on valve flaps form
= different efficiency in function
=RUINS INTEGRITY of the valve flaps
Narrower and Stiffer outlet RESTRICTS blood flow, as the L.V. has to Squeeze/WORK HARDER and become MORE MUSCULAR, undergoing hypertrophy to compensate and get the blood UP through the NARROW HOLE
(muscle which works harder builds muscle)
LV wall significantly thicker but LUMEN TINY
=less space to fill
heart struggles to INFLATE=doesn’t pump as well
Decrease in Flexibility (LOSS of COMPLIANCE)=harder to fill
cardiac OUTPUT DROPS=(GREATER AFTERLOAD)
So large that they OUTSTRIP ability to SUPPLY OXYGEN to all the LV muscle cells= fail
What is the Pericardium?
the Bag the Heart sits in
what you see when the rib cage is first opened
“a continuous layer of PARIETAL and VISCERAL Pericardium which SURROUNDS and PROTECTS the heart”
most of the Pericardium is serous membrane/mesothelial cells
How fast does your heart beat?
50-80 times per minute
dependant on health status
What are the surrounding structures of the heart?
Lungs either side
infront = Sternum
behind= Boney rod= Vertebral Column
Heart and lungs both move upon breath
Heart will rub up against its neighbours
What is the universal method that the body uses to deal with friction?
2x Serous membranes with serous liquid between them
Thin, Transparent, really slippery when wet
What is a serous membrane?
Thin= simple=single layer flattened cells (squamos) attached to each other forms a continuous sheet secretes serous fluid "Mesothelial cells"
MESOthelial cells are similar to epithelial cells but are found INSIDE your body
ORGANS which are INSIDE your body (not gut lining as that is Epithelial cells) typically have mesothelium/serous membrane around them
= great at reducing friction
What is the Visceral Pericardium?
the VISCERAL pericardium is the INNER walls of the serous membrane of the heart (pericardium) which ADHERES to the heart’s outer surface (EPIcardium)
“viscera”=organ=”belongs to the organ”
What is the name of the heart’s Outer surface?
EPIcardium
What is the Parietal Pericardium?
the PARIETAL pericardium is (away from organ) the OUTER wall of the heart’s serous membrane (pericardium) which LINES a TOUGH FIBROUS SAC called the FIBROUS PERICARDIUM -DENSE IRregular
What is the Fibrous Pericardium?
the TOUGH fibrous SAC (on the outside of the heart)
LINED with PARIETAL Pericardium
“outer layer of collagenous tissue”
more of a PROTECTIVE layer, rather than a lubricating layer
FIBRES/COLLAGEN can RESIST TENSION
DENSE IRRegular CT
What is the Pericardial Space?
capillary thin space
contains serous fluid
“pericardinal space is a very thin film of fluid”
=contains only fluid, not the heart=IMPORTANT
REDUCES friction
acts as a LUBRICANT to PREVENT HEAT from rubbing against the THORACIC CAVITY with friction, as the heart beats
surrounded by the inner and outer wall of the Pericardium/Serous membranes, which is comprised by a singe layer of squamous mesothelial cells which SECRETE serous fluid
What is inside the Peritoneal cavity?
*Exam question
fluid
no organs inside the peritoneal cavity
What is the distribution in the heart wall?
composed of 3x layers “fist against water filled balloon”
Thin Inner layer=Lumen=ENDOcardium
Thick Middle layer =MYOcardium(muscle)
Very Thin Outer layer =EPIcardium (epi=outside)=Visceral pericardium
What types of layers are there in the heart?
PROTECTIVE layer and LUBRICATING layer(s)
PROTECTIVE layer=FIBROUS pericardial sac
LUBRICATING layer(s)=Visceral and Parietal Pericardium(s)
What is the Fibrous Skeleton of the Heart?
DENSE CT rings Coarse fibres
purpose:
1. STRENGTHEN HOLES/valves (inlet/outlets)
2. ELECTRICAL INSULATOR b/w atria/ventricles (nerve impulses cannot pass through)
3. PREVENT OVER-STRETCHING of valves
inlet/outlet valves form a continuous line/plateau across the heart
openings=weakened area =
b/w Thin-walled Atria and Thick-walled Ventricle
Want to be strong as valve leaflets are attached to here
Stops the distortion of valve leaflets, which otherwise would compromise valve
Mitral Inlet and Aortic Outlet valves are HIGH PRESSURE valves and have FULL SKELETAL RINGS to Prevent Stretching
TRIcuspid Inlet has a PARTIAL ring and the PULMONARY valve has NO ring.
instead the Tricuspid and Pulmonary valves have LOOSE Fibres and FATTY tissue (not a true fibrous ring)
What is Cardiac Tamponade?
During a MYOCARDIAL INFARCTION “dying of the muscles of the heart” (heart attack) part of your heart muscle dies
(tissue INFARKTs) (not enough blood supply/oxygen)
Infections causes puss and fluid to enter the Pericardium = PERICARDITIS = inflammation
Although macrophages clean up dead tissue and our line area becomes replaced with scar tissue, which makes it THIN and WEAKER
the High PRESSURE of LEFT.V, blood can move out through weakened area and blood moves into the Pericardial Space as L.V. RUPTURES
Every time the LV contracts, blood squirts into the Pericardial Space (affecting the hearts ability to fill every beat)
FIBROUS Pericardium is quite RIGID, so instead of the bag (pericardium) EXPANDING (due to the COLLAGEN which RESISTS TENSION), the heart will be SQUEEZED SMALLER and smaller, due to the ACCUMULATION of blood in the pericardial space
Causes:
- COMPRESSING of the heart
- Ventricular FILLING DECREASED
- CARDIAC OUTPUT Decreased
- VENOUS RETURN to heart Diminishes
- Blood PRESSURE FALLS
- BREATHING Difficulty
What is a heart attack called?
Myocardial Infarction
“dying of the muscle of the heart”
What does infarkt mean?
tissue dying
What is an infection of the heart called?
Puss and fluid enter the Pericardial Space
Pericarditis
“inflammation of the heart”
What is the Conduction System of the heart?
The method by which the HEART BEATS are INITIATED and
he method by which the heart is ELECTRICALLY STIMULATED
No in-built nerves within its muscle fibres
ONLY INFLUENCED by nerves
Instead has highly modified cardiac muscle fibres
What is special about cardiac muscle fibres?
designed to conduct nerve impulses
AUTO-rhythmic fibres
SELF-Excitable = can repeatedly Generate ACTION POTENTIALS triggering heart contraction
allows for a WAVE of EXCITATION
-but still Weakly Contractile UNLIKE nerve fibres
What is the function of a Pacemaker?
sets the RHYTHM of electrical excitation –> contraction
in the SinoAtrial Node (SA)
What is the function of the Cardiac Conduction System?
Cardiac Conduction System is a network of Specialised cardiac muscle fibres that PROVIDE PATH for each cycle of Cardiac Excitation to pass through the heart
What are the differences between Myocytes and Purkinje Cells?
Myocytes in the Atria
Purkinje Cells in the Ventricles
Purkinje cells are LARGER and WIDER than cardiac myocytes
(Larger=good WIRING for the heart)
Purkinje cells DONT BRANCH and DONT CONDUCT action potentials well
Purkinje cells are WEAKLY CONTRACTILE
are the “WIRING of the heart”
What is the overall pathway in the conduction system?
- SA node/Atrial Muscle
- AV Node
- AV bundle/Purkinje cells
What is the overall transitions in speed of conduction during the conduction pathway? What does each step result in?
1. slow=0.5m/s Atrial contraction (Uniformly)
- very slow=0.05m/s
100m/s delay
Smaller Diameter between junctions - fast=5m/s
Even, Rapid Ventricular Contraction = SYSTOLE
What is the First step in the Propagation of Cardiac Action Potentials?
A. Cardiac excitation BEGINS at the SA NODE (SLOW)
- SA node (collection of specialised cardiac muscle fibres) depolarises to threshold spontaneously via the Pacemaker Potential
- AP is fired
- each AP from the SA Node PROPOGATES through BOTH of the ATRIAs via GAP JUNCTIONS in the INTERCALATED DISCS of atrial muscle fibres (MYOCYTES)
- following the AP, the TWO ATRIAS CONTRACT at the SAME TIME
What is the SA node?
Sino-Atrial Node
a KNOT of cardiac muscle fibres which have an UNSTABLE RESTING POTENTIAL
so it DEPOLARISES to threshold SPONTANEOUSLY (intrinsic ability to generate activity) via the Pacemaker Potential
spontaneously depolarises and repolarises 60-100x per minute (own internal clock)
SA node is the MOST RAPID
What does Spontaneous Depolarisation?
INTRINSIC ability to generate activity
What is the AV Node?
Atrio-Ventricular Node
“CLUSTER of fibres with its own AUTO-Rhytmicity, located at the TOP of the inter-atrial septum which forms a HOLE through the FIBROUS SKELETON so most of the AP STOPS but the rest GOES THROUGH the hole”
rapid contraction
“Fast STIMULATING HIGHWAY”
Only electrical link between the Atrium and Ventricle
HOLE in the Fibrous skeleton
VERY GOOD INSULATOR
TOP of the INTRA-VENTRICULAR SEPTUM (wall between ventricles) Allows Excitation to pass through it
What is the Wall between Ventricles called?
Intra-Ventricular Septum
Allows Electrical Stimuli to pass through it
What is the Second step in the Propagation of Cardiac Action Potentials?
B. Action Potential reaches the AV Node (VERY SLOW)
- AV Node Hole in the FIBROUS SKELETON causes most of the AP to STOP, with the Rest GOING THROUGH the hole (hits fibrous skeleton and mostly stops)
- AP Considerably SLOWS, due to the DIFFERENCE in CELL STRUCTURE and results in a 100ms DELAY BETWEEN the ATRIA and VENTRICLES contracting
- the delay provides time for the Atria to EMPTY BLOOD into the Ventricles
What is the Third Step in the Propagation of Cardiac Action Potential?
C. From AV Node, AP reaches the BUNDLE of HIS (FAST)
- electrical impulses pass through here as it provides ELECTRICAL LINK between the Atria and Ventricles
- is the only site where AP ___propogate?____ without being insulated by the fibrous skeleton
What is the Bundle of His?
Electrical Link between the Atria and Ventricles
What is the Fourth Step in the Propagation of Cardiac Action Potential?
D. AP enters BOTH the Right and Left BUNDLE Branches
- AP extends through the Inter-ventricular septum and towards the APEX of the Heart
What is the Fifth step in the Propagation of Cardiac Action Potentials?
E. AP conducts through the Purkinje Fibres
- the LARGE DIAMETER of Purkinje Fibres RAPIDLY CONDUCTS the AP from the APEX UPWARDS to the REMAINDER of the Ventricular Myocardium
- VENTRICLES CONTRACT (both sides of the ventricular muscles SQUEEZE SIMULTANEOUSLY) “Main event!”
- EVEN Ventricular CONTRACTION
- Pushes blood towards the SEMI-LUNAR VALVES
What would a typical cardiac muscle fibre look like?
Branching Fibres
Intercalated Discs
Contractile
At what speed will the SA node initiate an AP?
90-100 times/min the SinoAtrial Node will initiate an ActionPotential
What happens if the SinoAtrial Node becomes diseased or damaged?
the CONDUCTION is blocked
AV Node can pick up the PACEMAKER TASK
will have a different intrinsic rate (slower) 40-60 time/min via Spontaneous Depolarisation
or
a Pacemaker can be Installed
How is the rate of spontaneous depolarisation and repolarisation of cardiac fibres Influenced?
by HORMONES and by NERVES (Vagus Nerve in particular)
What does the Propagation of Cardiac Action Potentials result in?
EVEN contraction of ventricular walls (SYSTOLE)
What is Systole? Why is it needed?
refers to when things are CONTRACTING
e.g. the even contraction of the Ventricular Walls in isovolumetric ventricular contraction
Ventricle will only fill up until 80% of its volume PASSIVELY
so it requires the ATRIA to CONTRACT AHEAD of it, in order to squeeze in the las 20% of blood REMAINING in the atria BEFORE it CONTRACTS ITSELF
What does the Ventricular Filling stage in the Cardiac Cycle consist of?
LONGEST phase (HALF the cycle)
SHORTENS FASTEST than other phases during EXERCISE (Influenced the most)
Resting –> diastole
Little bit of reserve present if you have a healthy heart
- RELAXED heart wall. PRESSURE of VENTRICLE drops BELOW pressure of the Atria
- Mitral Valve OPENS quietly as blood travels from HP–>LP i.e. Atria(high/80mmHG) –> Ventricle(less than 5mmHG) (Needs a Pressure Gradient)
- Ventricle PASSIVELY (from left over pressure) fills to 80% of total capacity
What does the Atrial Contraction stage in the Cardiac Cycle consist of?
“topping up”
- SA Node DEPOLARISES
- Atria CONTRACTS and completes the LAST 20% FILLING of the atrium (pressure increase)
- Lasts about 0.2 sec
- AV node has a 0.1 sec DELAY
Small rise in atrial pressure
Atria is a poor pump as
a. Atria has a THIN muscle wall
b. NO INLET valves - some of the blood goes into the VEINS as there is NOTHING to Prevent Backflow of blood
Is the Atria a good or bad pump? Why?
Poor pump
only small rise in atrial pressure
- THIN atrial wall
- NO INLET Valves
therefore some of the blood goes back into he veins as there is NOTHING TO PREVENT Backflow back into Veins
What does the Isovolumentric Ventricular Contraction Stage in the Cardiac Cycle consist of?
Isovolumentric Ventricular Contraction = SYSTOLE
- Ventricles Contract
(INCREASE in PRESSURE) and a (Decrease in Volume) - will slowly start to EXCEEDS Atrial Pressure
- Blood TRIES to flow back into the atria but this causes blood to ABRUPTLY STOP as the VALVES CLOSE
- closing of valves causes TURBULENCE and therefore the FIRST HEART SOUND (LUB) deeper and at the BEGINNING
- at this brief period (0.05sec), Ventricular pressure is STILL BELOW arterial pressure so the OV(Aortic valve) closes.
Both valves are closed = ISOvolumentric = fluid volume cannot change
Atrial.P.
What are the differences between the Right and Left sides of the heart during the Cardiac Cycle?
Right side has LOWER PRESSURE but the Volume is the Same/Beat
What is another name for systole?
ISOVolumentric VENTRICULAR Contraction
systole refers to when things are Contracting
What does the Ventricular Ejection stage in the Cardiac Cycle consist of?
systole continues
- Ventricular Pressure EXCEEDS AORTIC pressure
- Aortic Valves/outlet OPEN quietly
- Blood LEAVES to the Ventricle (70ml into the aorta)
- Aorta/Elastic Artery Expands
- blood is EJECTED into the AORTA FASTER THAN is can RUN-OFF into Distributing Arteries
- Pressure in Ventricles and Aorta RISE STEEPLY
- Later in the phase rate of EJECTION FALLS BELOW rate of run-off
- Aortic and ventricular pressures LEVEL OFF and Begin too DECREASE (runs out of strength)
What does the Isovolumetric Ventricular Relaxation Stage in the Cardiac Cycle consist of?
Short –> 0.05s
repolarisation/rest phase
- Limit of contraction so VENTRICLE RELAXES, walls move outwards (INCREASE VOLUME) and a (Decrease in Pressure). inflation of outlet valves
- HIGH Pressure blood just got EJECTED into the ARTERY
- Flow tries to reverse but the AORTIC VALVE CLOSES (the Cusps of the Ventricular Valves come together)
- Blood comes to an ABRUPT STOP.
- TURBULENCE occurs due to stopped blood, and results in Second heart beat (DUB)
- MITRAL Valve CLOSES due to Atrial.P.
What are the names of the phases of the Cardiac Cycle?
5 phases to the Cardiac Cycle
- Ventricular Filling
- Atrial Contraction
- Isovolumetric Ventricular Contraction
- Ventricular Ejection
- Isovolumetric Ventricular Relaxation
Doesn’t matter where you start as it is a Cycle
How long does the Cardiac Cycle take to complete?
1 sec
What does x symbolise in the cardiac cycle?
contraction
What does . symbolise in the cardiac cycle?
pressure
Which phase in the cardiac cycle is the longest?
Step 1. : Ventricular Filling
Most affected by exercise (shortens the most)
acts as a reserve if require to eat into its time in the cycle
What is Atrial Fibrillation?
CAN live with this fine
Chamber DOESNT UNIFORMLY contract
Heart quivers/FLUTTERS(non-rhythmic/non-cyclic contraction) due to the effect of OVERWHELMING IMPULSES that s____ from and to other organs
NOT a rhythmic contraction
Atrium cant Squeeze
Lots of people live with this, especially as they get older, live fine
- extra 20% is Not Nescessary
- Blood POOLS in the ATRIA
- Blood Clot may form
What is Ventricular Fibrillation?
CANNOT live with this fine
INSUFFICIENT CO (Cardiac Output)
- UNCONSCIOUS
- can die
Defibrillator = Stops Fibrillation
- Zaps heart with a LARGE ELECTRICAL CHARGE
- DEPOLARIZES EVERYTHING
- chance for the first cells (SA NODE) which will REpolarise again to TAKE OVER normal Pacemaker Function of the Heart and restart the Heart Beat
Purpose: QUIETEN down the RANDOM INTERFERING SIGNALS in the heart which are INTERFERING with its normal RHYTHM
and
to REBOOT the heart via letting the SA Node TAKE OVER the PACEMAKER function
Sinus Rhythm
What is Sinus Rhythm?
normal heart beat, referring to BOTH the heart RATE and heart RHYTHM
What is the Defibrillator?
Zaps the Heart with a LARGE ELECTRICAL CHARGE
DEPOLARISES the entire heart
Purpose: to QUIETEN down the heart’s RANDOM SIGNALS which INTERFERE with RHYTHM. It REBOOTS the heart, and lets the SA NODE take over the role of the PACEMAKER
Which heart beat is the deeper one?
LUB
the first heart beat
What does Isovolumetric mean?
Same volume
due to both the inlet and outlet valve being closed therefore total volume cannot change
DUE to the PRESSURE of the VENTRICLE being INBETWEEN atrial and arterial pressures
is WHILE the Ventricle is Contracting
word which follows (contraction/relaxation) describes pressure change
What is the duration of systole?
Atrial systole + ventricular systole
Atrial Contraction + Isovolumetric Ventricular Contraction + Ventricular Contraction
What is the change in pressure on the left side of the heart?
120mmHg - 0mmHg
What is the change in pressure on the right side of the heart?
25mmHg - 0mmHg
What is the maximum volume of blood in one side of the heart?
120 mL
What is the minimum volume of blood in one side of the heart?
60 mL (can only squeeze out about half of total volume)
can change, depending on your demand
When does Diastole occur?
- Ventricular Filling
5. Isovolumetric Ventricular Relaxation
Why does the aortic pressure drop during ventricular filling and atrial contraction?
As blood is being drained out to vascular tree into the systemic circuit
What is responsible for initiating contraction?
SA Node
What happens to atrial pressure during atrial contraction?
A small increase in pressure
is quite pathetic, this shows that the atrial muscular wall isn’t strong enough to generate significant movement
this is only “topping up”
however don’t need it to survive, many people live without functioning atria
What changes almost instantaneously with ventricular contraction?
Increase in ventricular pressure
closes inlet valve
=SIMULTANEOUS increase in Ventricular PRESSURE = first HeartBeat= LUB
step increase but remains “middle” pressure throughout isovolumetric ventricular contraction
ventricular volume only starts decreasing during ventricular ejection. v.VOL remains SAME as is during ISOvolumetric ventricular contraction
What occurs to pressures during ventricular ejection?
both the pressure of the Aorta and Ventricle increase simultaneously “in communication”
Ventricular pressure still remains higher than Aortic Pressure. whilst Left Atrium remains very low
What is special about the rate blood is squeezed out of the Ventricle during Ventricular Ejection?
rate CHANGES THROUGHOUT this phase
starts rapid
rate slows down
Ventricles run out of their ability to SHORTEN FIBRES
blood is still flowing from ventricle–>artery throughout the whole phase still
reflects in pressure
What happens almost immediately when the heart relaxes/stops contracting?
decrease in pressure (most significantly the ventricular pressure)
What physically makes the heart beat sound?
NOT the leaflets
the leaflets are SOFT and PLIABLE
is actually the ABRUPT STOPPING of blood
blood TRIES to come BACK down, the valve LEAFLETS CLOSE causing the blood comes to a SHUDDERING stop and causes the WALLS of the heart to VIBRATE (TURBULENCE) creating the HEART BEAT SOUND
What does the pressure spike represent?
The blood BOUNCING as it comes to a SHUDDERING HALT
SECOND H.B.
Why are heart sounds LUB DUB?
1st heart sound is meant to be LOW FREQ.
as the IN-let valve is a BIG HOLE with BIG FLAPS
has a DEEPER, more RESONANT sound
2nd heart sound is meant to be HIGH FREQ.
as the OUT-let valve is a SMALL HOLE/AREA with SMALL LEAFLETS resulting in a HIGHER PITCH sound
slightly SPLIT
What is special about one of the heart sounds?
The SECOND heart beat is SLIGHTLY SPLIT
- aortic 2. pulmonary
the AORTIC valve is CLOSING just BEFORE the Pulmonary Valve
these two ventricles are squeezing side by side, but the AORTIC ARTERY has a Higher PRESSURE (120mmHg : 25mmHg)
The elastic recoil of the aorta pushes the blood down faster as it higher pressure, and therefore closes the aortic valve just marginally before the pulmonary valve
Why is there an increase in atrial pressure during isovolumetric ventricular relaxation?
Blood POOLING in the atrium while it CANT get into the ventricle
= doing its job and acting as a RESERVOIR
When a doctor takes your blood pressure, what are they actually measuring?
The Pressure RANGE in your BRACHIAL ARTERY in your arm
previously: stethoscope and sphygmomanometer
measure PEAK PRESSURE
120/80
P.P/Minimal Pressure
Minimal pressure= how low the pressure in the artery is allowed to drop down to (healthy is about 80)
Females are a little lower
115/75
stays around about that
