Download Transcripts/4_13 1-2 (McNicholas)

Cardio: 1:00 - 2:00
Scribe: Hunter Neill
Monday, April 13, 2009
Proof: Taylor Nelson
Dr. McNickolas
The Cardiac Cycle
Page 1 of 5
Note: R-right, L-left, AP-action potential, HR-heart rate, BP-Blood pressure, SA-Sinoatrial, A-Atria, V-Ventricle
AV-atrioventricular
1.
Introduction [1]:
2.
The Cardiac Cycle [2]
a. The heart relaxes and contracts regularly
b. The SAN pacemaker or pacemaking activity of the heart is determined the duration of the cardiac cycle
c. The electrical properties of the cardiac conduction system and cardiac myocytes determine the relative
duration of contraction and relaxation
i. Diastole is the relaxation (filing) phase of the cardiac cycle
ii. Systole is the contraction (ejection) phase of the cardiac cycle
3.
The Four Events [3]
a. Artial Systole
b. Atrial Diastole
c. Ventricular Systole
d. Ventricular Diastole
4.
[4] The sequence of mechanical and electrical events that repeats every heartbeat is called the cardiac cycle.
a. The duration of the cardiac cycle is the reciprocal of the heart rate and can be obtained from the ECG
i. Which wave forms determine the length of a cardiac cycle (calculate the HR from the ECG)
1. The R-R interval
b. Duration (s/beat) = 60 (s/min) / Heart Rate (beats/min)
i. e.g. for a heart rate of 75 beats/min, the cardiac cycle lasts 0.8 s (normal length)
c. [5] The duration of the cardiac cycle varies considerable among humans and also during an individuals
lifetime and from one person to another
i. The duration of the cardiac cycle can be really short as it is in newborns .25-.30 sec
ii. What is the result of that happening in a newborn in relation to the heart rate?
1. Its going to be really high
2. So the shorter the duration of the cardiac cycle, the faster the hart rate
a. Can be really long in trained athletes (resting HR of 40 beats/min) 1 or more seconds
b. That means that their cycle length is going to be longer
3. In normal people the length of the cardiac cycle is between .7 and .8 seconds depending
on the capability to contract and the functional integrity of the conduction system
a. If there are any delays that occur in any part of the conduction system it will delay the
movement of the action potentials (AP) downward into the ventricles
b. i.e. a delay in the AV node, prolongs the cardiac cycle
5.
Pressure changes [6]
a. Produced within the heart chambers are a direct result of cardiac muscle contraction
i. Pressure changes responsible for blood movement because blood moves from areas of higher
pressure to areas of lower pressure.
1. Same principles apply as when compared to moving ions or solute down its concentration
gradient
b. [7] Each cycle is initiated by spontaneous generation of an action potential in the sinoatrial (sinus) node.
i. The SA node is located in the R atria
c. Just to reiterate: The SA node is the normal pacer of the heart.
i. Why is that the case? (Difference in the rates) – because it’s the fastest
ii. In the case of a normal heart the “sinus” node or SA node will initiate the HR and AP that
transfers down through the intermodal pathways of the R atrium across to the L atrium.
1. There is a convergence of the waveform at the AV node
2. Slowing of the conduction pathway
3. The waveform diverges into the bundle branches and out through the Purkinje system
4. The Purkinje system – the purkinje fibers fire very rapidly and reach all of the
myocardium so that all are excited at the same time – concerted Ventricular contraction
6.
[8] Conducting System
a. Because of this special arrangement of the conducting system from the atria into the ventricles, there is a
delay of more than 0.1 second during passage of the cardiac impulse from the atria into the ventricles
b. This allows the atria to contract ahead of ventricular contraction, thereby pumping blood into the
ventricles before the strong ventricular contraction begins.
i. That contraction only contributes 20% of volume of blood that moves into the ventricles
c. –NOTE: the remaining 80% of blood moves passively from the atria to the ventricles because of the
pressure gradient between the two
Cardio: 1:00 - 2:00
Scribe: Hunter Neill
Monday, April 13, 2009
Proof: Taylor Nelson
Dr. McNickolas
The Cardiac Cycle
Page 2 of 5
d. Under normal circumstances you can get by with out the atrial (20%) contraction because the heart will
pump ~300-400% blood around the body than is required
i. Would notice a problem with atrial contraction because you would become breathless because
you don’t have the extra reserve being pumped into the ventricle
e. Thus, the atria act as primer pumps for the ventricles, and the ventricles in turn provide the major source
of power for moving blood through the body's vascular system.
7.
[9] Healthy Heart
a. In a healthy heart, oxygen-depleted blood is collected by the right-sided heart chambers via the vena
cava and then pumped to the lungs to be re-oxygenated.
i. The first place that the blood is received is the R atria.
ii. Passively blood moves into the R ventricle and then blood is pumped by the R atria into the R
ventricle (extra 20%)
iii. The pumped from the R ventricle through to the lungs,
1. Re-oxygenated
b. Oxygen-rich blood returns from the lungs to the to the left-sided heart chambers.
i. First it passes through the atrium, then the ventricle and
ii. It is then pumped out through the aorta to circulate around the body.
c. Four valves located in the heart chambers open and close like one-way gates to keep the blood moving in
the right direction.
i. Principle of a valve – if the pressure is greater on one side that the other, a valve with ope
ii. If the pressure increases on the other side it pushes the valves shut (flaps of tissue that open and
close passively dependent upon the pressures that are present)
d. 4 main valves
i. Tricuspid valve (atrioventricular - right),
ii. Pulmonary valve (semilunar - right),
iii. Mitral valve (atrioventricular - left)
iv. Aortic valve (semilunar - left) from the L ventricle into the aorta and to the body
8.
[10] Heart Valves - Diagram
a. Right side of diagram is the left side of the heart
b. The superior vena cava bring blood back into the R atrium
c. The Tricuspid valve is located between the R atrium and Ventricle
i. The blood passively moves because of the pressure gradient from the R atrium into the R
ventricle during diastole, during the relaxation phase of the cardiac cycle
d. As the pressure increases in the right ventricle, that pressure pushes back up into the R atrium and
causes the Tricuspid valve to close
i. As the R ventricle contracts (systole) the pulmonary valve will open as the pressure in the
chamber increase as compared that within the pulmonary artery
ii. Pumps blood into the pulmonary artery and into the lungs
iii. The blood becomes re-oxygenated
e. Comes back into the left atria via the pulmonary vein. The L atrium and ventricle are connected via the
mitral valve
i. As the blood increases in the atrium the blood passively moves into the L ventrical via the mitral
valve during the diastolic phase when relaxation of the heart or ventricular muscle occurs
ii. Then the atria contracts to pump the extra 20% into the ventricle
f. The left ventrical contracts, the aortic valve opens, the pressure gradient increase in the L ventricle as
compared to the aorta, the blood pumps out into the aorta
g. As the pressure in the aorta increases, the back pressure closes the aortic valve
h. Diagram
i. Shows the difference between the mitral valve (connected by fibrous tissue) to the Papillary
muscles
1. The U wave in the ECG may be caused by the repolarization of the papillary muscles
2. Cordae tendinae connect that valve with the chambers of the ventricles
3. [I interpreted her gibberish] The bicuspid valves between the ventricles and their
respective arteries do not have fibrous attachment and are stronger than the valves
between the atria and ventricles (tricuspid and mitral).
9.
[11] Valves a. The cardiac valves open and close with every heartbeat.
b. Most adults have about 80-100,000 heartbeats each day.
i. Calculated by the number of hours, minutes times the number of beats per second
Cardio: 1:00 - 2:00
Scribe: Hunter Neill
Monday, April 13, 2009
Proof: Taylor Nelson
Dr. McNickolas
The Cardiac Cycle
Page 3 of 5
c. ~2000 gallons of blood will be pumped through the valves and out to the body every day.
d. Lots of wear and tear on those vessels which in some cases do wear out and have to be replaced
10.
[12] Relaxation - Diastole
a. Pressure increases in the atrium verses the ventricle (relaxed) and blood passes through the AV valve
(noted by the fibrous tissues attached to the papillary muscles)
b. During relaxation the pressure within the vessels that supply those ventricles is greater than the pressure
within the ventricles. Thus, those valves are closed. The valves that connect the ventricle to the blood
vessel (pulmonary or aortic valve) are closed
11. [13] Contraction – Systole
a. Because the pressure increases within the ventricle compared to the atria thus closing the AV valves
b. As the pressure within the ventricles increases in respect to the vessel then the semilunar valves open
and enter the blood system
12. [14] Valves – diagram
a. The lower valves are the AV valves and are open during diastole because of the pressure gradient
i. the valves between the ventricle and vessels are closed
b. During Systole, when the pressure is greater in the ventricle than the vessel it is supplying, than the
vessel valves will open and the AV valves will close preventing backflow during systole
13. [15] Graph
a. Scheme of the cardiac cycle with breakdown
b. Dotted line on the top shows the aortic pressure and the changes in the aortic pressure (upper part of
diagram) on the y axis
i. Changes throughout each cardiac cycle (2 shown)
ii. One ECG tracing to the next illustrating two heart beats
c. The red line shows the ventricular pressure
i. In relation to the L ventricle due to the pressures generated in that chamber
d. Lower dotted line is the atrial pressure. Much less than that in the ventricles
e. The changes in the volume of blood (lower portion of Y axis) changes throughout the cardiac cycle
f. NOTE: the cardiac volume never goes to 0. You always have a residual blood volume in the chambers of
the heart
g. The brown tracing is the ECG
h. What is the P wave due to?
i. Atrial contraction so you can see that here
ii. Remember the waveform that you look at for an ECG compared to the contraction of the muscle
tissue has a slight phase shift. Notice that the P wave occurs slightly before contraction of the
muscle.
i. What is the QRS complex due to?
i. Ventricular depolarization
ii. As they depolarize contraction begins to occur and then they T wave is Ventricular repolarization
j. The last portion (pink) shows the sounds that occur due to the blood flow through the chambers
14. [16] Pressure and ventricular volumes during the Cardiac Cycle
a. Take home message of slide: Concentrate on pressure changes in the R verses the L side of the heart
b. Looking at the R ventricular pressure verses the L, there is a much greater pressure generated in the L
i. What is the cause of the greater pressure in the L?
1. Due to how far it has to pump
2. Where as the R side of the body only pumps to the lungs, the L side of the heart has to
pump to the entire body and therefore require more pressure
ii. Note that the volumes are essentially the same between the L and the R
1. If there is a discrepancy between the two you know there is an underling pathological
problem
c. The ventricular pressure generated during each heart beat is greater in the L ventricle than the R,
whereas the volumes of each are approx. the same
15. [17] Phases of the Cardiac Cycle
1. Inflow phase occurs when the Inlet valve is open and the outlet valve closed (diastole)
i. The inlet valve in this case = the AV valve
ii. The outlet valve connects the ventricle with the vessel its it supplying
2. Isovolumetric contraction. Both valves are closed with no blood flow (systole)
i. Because the pressure generated has not overcome the pressure in the vessel that the ventricle is
about to supply. That valve is still closed because the back pressure of the vessel
3. Outflow phase. Outlet valve open, inlet valve closed (systole)
Cardio: 1:00 - 2:00
Scribe: Hunter Neill
Monday, April 13, 2009
Proof: Taylor Nelson
Dr. McNickolas
The Cardiac Cycle
Page 4 of 5
i. The contraction within the ventricle increases the ventricular pressure greater that of the aorta
(vessel) and the outlet valve is open
4. Isovolumetric relaxation - Both valves are closed with no blood flow (diastole)
i. NO blood flow
ii. There must be enough blood brought back to the atria to over come the ventricular pressure to
open the AV valve.
5. For a cycle length of 800 ms (.8s): Systole = 300 ms and diastole = 500 ms. If heart rate increases, and
thus cycle length decreases, diastole shortens relatively more than systole.
i. Must shorten the cycle length for the next cycle to occurs
b. NOTE: last word on slide should say systole
16. [18] Phase 1
a. Middle of phase 1 -DIASTASIS
b. Mitral valve open, little blood flow A→V.
i. Atrial pressure approximately the same as ventricular pressure.
ii. Slowly pressure in the LA increases it overcome the ventricular pressure and blood passively
moves from the A to the V
iii. You need the atrial contraction during exercise
c. End of phase 1 - ATRIAL CONTRACTION
i. ~20% of the subsequent stroke volume is transferred from the atria to ventricle (~40% during
exercise). Corresponding small increase in volume and pressure in the LV.
d. The ventricular volume will begin to increase towards the end of phase 1
17. [19] Phase 2
a. ISOVOLUMETRIC CONTRACTION
b. Pressure within the aorta is not changing. Why?
i. Blood isn’t going into the aorta so its not going to change. It hasn’t reached the aortic phase yet
c. Upon ventricular depolarization the ventricles contract and soon the pressure in the LV exceeds the LA.
The mitral valve closes as a result. The aortic valve is also closed. The blood is therefore trapped within
the ventricle and isovolumetric contraction occurs. Hence, the pressure in the ventricle increases rapidly.
When LV pressure exceeds aortic pressure (at the “crossover” point starred on the slide), the aortic valve
opens (volume remains about the same at 120 mm – no movement yet)
i. Isometric so the overall volume stays the same but the pressures changes to open the valve
1. Only talking about the L side but same principles apply to the R
18. [20] Phase 3
a. EJECTION (OUTFLOW) - LV blue/green; Aortic pressure - red
b. Initially, rapid ejection coupled with a continued increase in LV pressure accompanied by an increase in
aortic pressure. A corresponding reduction in LV volume ensues. Even though there is a crossover in LV
and aortic pressures, blood continues to flow. Aortic pressure decreases as blood flows into the aortic
tree. At the latter end of phase 3, pressures in both LV and aorta fall off.
c. ~70 ml blood is ejected and ~ 50 ml remains behind
d. The blood volume doesn’t decrease to 0 so all the blood is not pumped out of the ventricular chamber
e. When the ventrical is completely full (120mL of blood are retained) – during contraction ~70 is ejected
thereby leaving ~50 behind (used in times of need for increased blood flow out into the tissues
19. [21] Phase 4
a. ISOVOLUMETRIC RELAXATION – green portion
b. Blood volume remains the same. Thus isometric. Whereas the pressure with in the V decrease
i. The myocardium is relaxing so the volume is the same but the pressure deceases
ii. At this point blood is still flowing into the aorta [Think that she misspoke since no volume change]
Blood flow across the aortic valve falls and the aortic valve closes. This is accompanied by a brief increase in
pressure (Dicrotic notch) followed by a decrease in aortic pressure. Because the aortic and mitral valves are
closed, no blood can enter the LV and there is a rapid fall in pressure. LV volume ~constant.
iii. The pressure in the atria is less that that in the ventricle so the gradient doesn’t allow for that AV
valve to open.
20. [22] Beginning of Phase 1
a. RAPID VENTRICULAR FILLING
b. When LV pressure falls below LA pressure, the mitral valve opens and there is a rapid filling of the LV.
Diastole begins. LA and LV pressures are parallel because the mitral valve is wide open. Toward the end
of this period, the period of diastasis discussed earlier begins.
i. Increase in blood volume because the myocardium is still relaxed – no change in pressure
c. Cycle then repeats itself
Cardio: 1:00 - 2:00
Scribe: Hunter Neill
Monday, April 13, 2009
Proof: Taylor Nelson
Dr. McNickolas
The Cardiac Cycle
Page 5 of 5
21. [23] Pressure Changes in the Atria
a. 3 major pressure elevations in the atria reflected as a complex pulse wave in the jugular vein:
i. Why is this the case? Think anatomy
1. Jugular vein is supplying the atria so that pressure changes in those chambers of the
heart are reflected in the vein – R side of heart
ii. “a” wave is caused by RA contraction (red line)
1. as the RA contracts, the pressure increase so an A wave is detected
iii. “c” wave occurs when RV begins to contract, it is caused by the slight backflow of blood into the
atria and by the bulging of tricuspid valve (just closed) backward into the RA.
1. Remember the tricuspid valve is not as fibrous tissue as the aortic and pulmonary valves.
As the pressure increases a small bulging of the valve back into the RA
iv. “v” wave occurs towards the end of ventricular contraction; results from the slow build up of blood
in the atria while the tricuspid valve is closed. This wave begins to wane as the tricuspid valve
opens.
1. As the tricuspid valve opens the pressure decreases. This that valve is closed the
pressure increases within the atria and is detected. See decrease as pressure overcome
that of the ventricle and blood flows
22. [24] Blood Flow in the Aorta
a. Aortic blood flow parallels the increase in pressure during the LV rapid ejection phase.
b. At the peak of aortic flow, the decreased ejection phase ensues.
c. As pressure decreases in the V and the blood flows out into the vessels than a decrease in aortic
pressure occurs along with the aortic flow
23. [25] Events relation to the ECG
a. Important to remember the events correspond to the events of the cardiac cycle and the mechanical
events that happen within the heart related to the electrical events
b. The P wave of the ECG corresponds to atrial depolarization (contraction).
i. Ca influx occurs here that translates into contraction of the myocardium thus increasing pressure
ii. The gold line corresponds to the pressure changes within the ventrical
c. The QRS complex occurs immediately before the upswing of LV pressure.
i. The gold line is corresponding pressures changes in the V
ii. As the QRS occurs V depolarization occurs translating into an influx of Ca into the cell and
contraction
iii. Recall from depolarization there is a phase shift in the actual contraction actually occurring
1. Therefore a phase lag occurs between the contraction of the muscle and the actual
depolarization
iv. Repolarization of the V is the beginning of the relaxation phase
1. As this occurs the pressure also decreases within the V
d. The T wave occurs in the decreased-ejection phase.
24.
[26] Heart Sounds
a. 4 sounds usually heard
b. Of four heart sounds, only two (S1 & S2) generally are heard with a stethoscope.
c. S1 is generally the longest and loudest. It occurs at the beginning of systole.
d. S2 occurs at the end of systole, early diastole.
e. S3 is low pitched and occurs early in ventricular filling. Normal in children, abnormal in adults, may
indicate V dilation
f. S4 vibration of V wall during atrial contraction, abnormal - heard when V compliance is reduced.
i. As the blood moves through the various chambers of the heart you can hear sounds on the
surface of the body
ii. Can tell if there are problem with valves as you would hear murmers
25. [27] Chart and illustration
a. Spend some time studying this diagram
b. Blue represents atrial contraction (systole)
c. Pink is relaxation (diastole)
d. Will take you through the mechanical events of the cardiac cycle
26. Heart Sounds: Is S1 sound from the mitral valve closing?
a. Answer: its actually not the valves themselves that you hear but the turbulence within the chambers that
you can detect (not the slapping of the valves) can hear actually valve sounds if there is a problem with
them directly
27. End [38:53]