Download Physiology Chapter 23 [4-20

Physiology Chapter 23: Heart Valves and Heart Sounds; Valvular and Congenital Heart Defects
Closing of the heart valves causes audible sounds
Normally, there are no sounds made when the valves open
The “lub-dub” sounds:
-
-
“lub” – closing of the atrioventricular (AV) valves at the beginning of systole
o Includes tricuspid and mitral valves
o Called the first heart sound
“dub” – closing of the semilunar valves at the end of systole
o Semilunar valves are the aortic and pulmonary valves
o Called the second heart sound
Normal pumping cycle of the heart starts when the AV valves close at the start of ventricular systole
The cause of the heart sounds is the vibration of the valves after closure, along with the vibration of the
adjacent walls of the heart, and major vessels around the heart
-
-
-
For the first heart sound, contraction of the ventricles causes the blood in the ventricles to flow
backwards against the AV valves, causing the valves to close and protrude into the toward the
atria
o The chordae tendineae stop the valves from protruding into the atria any farther
o The elasticity of the valves and chordae tendineae let the back-surging blood bounce
forward into each ventricle
o This causes the blood, ventricular walls, and valves to vibrate and cause vibrating
turbulence in the blood
The second heart sound is made when back flow of blood causes the semilunar valves to
suddenly close at the end of systole
o The blood causes the valves to bulge backwards toward the ventricle
o Their elastic stretch then bounces the blood back into the arteries
o Causes reverberation of blood between the walls of the arteries and semilunar valves,
and a little in the ventricular walls
When these vibrations get to a sounding board like the chest, it creates a sound we hear
The first heart sound lasts about 0.14 seconds, and the second lasts about 0.11 seconds
-
Second sound lasts a little less because the semilunar valves are slightly more taut than the AV
valves, making them vibrate for less time
Pitch- audible range of frequency
Phonocardiograms can record heart sounds below what’s audible in a stethoscope
-
Most of the sound made in the heart sounds is below the audible level
-
Shows sound as waves – page 267
The second heart sound has a higher frequency than the first sound
-
Semilunar valve is more taut than the AV
Also happens because the arterial walls that carry the vibrations of the semilunar valve are more
elastic than the ventricles in the case of the AV valves
The third heart sound is an occasional weak, rumbling sound heard at the beginning of the middle 1/3 of
diastole (So between S2 and S1)
-
Sounds like “lub dub dub”
Thought to be made by oscillation of blood back and forth between the walls of the ventricles,
as the blood moves in from the atria
Takes until the middle 1/3 of diastole to show up because the ventricles haven’t filled with
enough blood to be elastic enough for sound until then
The third heart sound’s frequency is usually too low for the ear to hear it, but the
phonocardiogram can record it
The fourth heart sound is aka the atrial heart sound – sounds like “lalub dub”
-
Caused by atrial contraction, when blood moves into the ventricles, causing vibrations
Sometimes recorded on a phonocardiogram, but is very weak with such a low frequency that it
is almost never heard with a stethoscope
The third heart sound can be recorded in a phonocardiogram in at most half of people, and the fourth
heart sound in at most ¼ of people
Auscultation – listening to the sounds of the body
Page 266 - “Al Pacino, The Man” – Aortic, Pulmonary, Tricuspid, Mitral
-
Areas for listening to the heart sounds aren’t directly over the valve you’re listening to
Aortic valve is second intercostal space to right of sternum, due to transmission of vibrations up
the aorta
Pulmonary valve is heard at second intercostal space to left of sternum, due to the pulmonary
artery
Tricuspid valve is heard at 5th intercostal space to left of sternum, at the right ventricle
Mitral valve is heard at 5th intercostal space in midclavicular line, over left ventricle
Rheumatic fever is the most common cause for a valve lesion
-
Rheumatic fever is an autoimmune disease caused by strep infection
Starts with sore throat, scarlet fever, and middle ear infection
Antibodies are made against the strep, that also target body proteins
One area heavily affected by the antibodies are the heart valves
-
-
The amount of heart valve damage is directly correlated to the [antibody] and how long they are
around
Large hemorrhagic, fibrinous, bulbous lesions grow at the edges of the heart valves
Mitral valve is the most affected
Rheumatic fever lesions usually affect adjacent valve leaflets, causing them to stick together
o The lesions then turn into scar tissue that fuses the leaflets together
o If blood can’t get through this, it causes a stenosis
The valves can also become so destroyed by scar tissue, that they can’t even close, causing
regurgitation, which is blood backflow
o Usually, stenosis and regurgitation happen together in some degree
Heat murmur – abnormal heart sound
Systolic murmur – sounds like “lub swish dub”
Diastolic murmur – sounds like “lub dub swish”
Aortic stenosis causes a systolic murmur
-
-
Aortic stenosis causes only a small opening for blood to be ejected out the left ventricle through
o So left ventricle doesn’t empty completely
Because of this resistance to ejection, left ventricular pressure becomes very high
The high pressure causes a nozzle effect during systole, where blood enters the aorta at very
high velocity, causing severe turbulence of the blood in the aorta
The turbulent blood causes intense and loud vibrations in the aortic walls as far up as the neck
arteries
o So a loud murmur is heard in systole
The sound vibrations can often be felt, called thrill, by touching the upper chest and lower neck
Aortic regurgitation causes a diastolic murmur
-
-
In aortic regurgitation, blood flows backward from the aorta into the left ventricle during
diastole
o Causes turbulence leading to the murmur
Causes a “blowing” murmur of high pitch that sounds “swishy”
Heard best over left ventricle – 5th midclavicular
Mitral regurgitation causes a systolic murmur
-
In mitral regurgitation, blood flows backward from left ventricle into the left atrium, during
systole
Causes a “blowing, swishy” sound
Sound is made in the left atrium, but the left atrium is deep in the chest, so it’s heard best from
the left ventricle to the apex of the heart
Mitral stenosis causes a diastolic murmur
-
A stenosis in the mitral valve makes it hard for blood to pass from the left atrium into the left
ventricle
Left atrial pressure rarely gets higher than 30 Hg, so not too much pressure is made, and the
sound is weak and at a low frequency that’s below what’s audible to people
Sound won’t be heard until the middle 1/3 of diastole, because during the beginning of diastole,
the atria doesn’t have enough blood in it to stretch the atrial wall, so no reverberations can be
made
Both an aortic stenosis and an aortic regurgitation decrease the stroke volume output of the heart
-
-
-
What the heart does to compensate:
o The left ventricle hypertrophies due to the increased workload
 Although this increases pumping capability, most of what is pumped either is
stenosed or comes back to the ventricle through regurgitation, so the pumping
only increases the stroke volume enough to get back to normal
o The blood volume increases
 Triggered by slight decreases in arterial pressure, and peripheral reflexes the
pressure normally would induce
 The kidneys then hold onto more salt and water, increasing the blood volume to
increase the pressure
 Also causes increased venous return, which gives the left ventricle more power
to pump and overcome the aortic problem
So early in aortic stenosis or regurgitation, the body changes things so that the only early
problem seen is increased work output by the left ventricle
o So patient can be unaware of any issue
When the left ventricle can no longer keep up with the extra work it needs to do, it dilates,
causing the cardiac output to decrease
o Blood then dams up in the left atrium and lungs, increasing the left atrial pressure
enough to cause pulmonary edema
Both mitral stenosis and mitral regurgitation decrease the movement of blood into the left ventricle
-
-
The buildup of blood in the left atrium increases the left atrial pressure, causing pulmonary
edema
o Lethal pulmonary edema happens at left atrial pressure above 25 Hg
 Up to that point, the enlarging lymphatics of the lung can compensate
o The edema can cause arteriole constriction in the lungs, which increases systolic
pulmonary arterial pressure and right ventricular pressure
 Leads to hypertrophy of the right side of the heart
The increased left atrial pressure also causes the left atrium to get bigger, increasing the
distance needed for the cardiac impulse to travel
-
o Can cause circus movements, leading to atrial fibrillation
To compensate, the kidneys will excrete less water and salt to increase the blood volume
o The increased blood volume increases venous return, increasing the pumping of the left
atrium
o This keeps cardiac output from falling that much until late stages of the disease
Symptoms of a valve lesion show up quickly during exercise
-
Aortic valve lesions during exercise can cause acute left ventricular failure, followed by acute
pulmonary edema
Mitral valve lesions during exercise can cause so much damming of blood in the lungs that lethal
pulmonary edema happens
In mild cases of valve disease, the person fatigues quickly because they can’t increase the
cardiac output enough to properly get enough blood quick enough to the tissues
o This is a case where the cardiac reserve has decreased
Congenital anomaly happens when the heart or its associated blood vessels are malformed during fetal
life
-
3 major types:
o Stenosis
o Left-to-right shunts
o Right-to-left shunts – bypasses the lungs
Coarctation of the aorta – type of congenital stenosis that causes the pressure above the coarctation in
the upper body to be higher than the pressure in the lower body below the coarctation
-
Happens because of the great resistance to blood flow through the coarctation to the lower
body
Patent ductus arteriosus:
-
-
During fetal life the lungs are collapsed, including the lung vessels
This makes the resistance to blood flow through the lungs so high, that it increases the
pulmonary arterial pressure
Pressure in the aorta is lower than normal, and less than that in the pulmonary artery
All this causes the blood to flow through the ductus arteriosus, which connects the pulmonary
artery and aorta in order to bypass the lungs
When the baby is born, the lungs inflate on the first breath, decreasing pulmonary resistance
enough to open the pulmonary vessels
At the same time the aorta pressure rises, ending the normal shunt of the ductus arteriosus
o Instead, some blood now shunts from the aorta to the pulmonary artery
o This all leads to the ductus arteriosus closing within hours to days
Patent ductus arteriosus happens when it doesn’t close
o
o
o
o
o
May not cause problems early in life
As the child grows, the differential between the high pressure in the aorta and the lower
pressure in the pulmonary artery increases, causing backward flow from the aorta to the
pulmonary artery
Often blood shunted back to the pulmonary artery goes through the lungs again and
back through the left heart again
 Usually this cycle happens 2 or more times for every one time the blood makes
it out to systemic circulation
 Can make the blood better oxygenated than normal, and doesn’t cause
problems till later in life
The major effect of a patent ductus arteriosus is decreased cardiac and respiratory
reserve
 The left ventricle is pumping double the normal cardiac output, so it can’t reach
the rate of blood flow needed for to fuel the muscles during exercise
 So exercise causes weakness and can lead to heart failure
 Excess flow in the lungs increases the pressure, causing pulmonary edema
 The increased load on the heart and congestion from pulmonary edema cause
premature death if a patent ductus arteriosus isn’t fixed
Machinery murmur – murmur heard as a child ages that indicates a patent ductus
arteriosus
 A harsh, blowing murmur that is loud during high aortic pressure in systole, and
much quieter in the low pressure diastole
Tetralogy of fallot:
-
-
A right to left shunt that bypasses the lungs, making the blood pumped lack oxygen
Causes 4 things simultaneously:
o The aorta originates from the right ventricle instead of the left, and receives blood from
both ventricles (p.271)
o Pulmonary artery is stenosed, so less blood into lungs
o Blood from the left ventricle goes either into the right ventricle and into the aorta, or
directly into the aorta
o Right ventricle hypertrophies to deal with the high pressure in the aorta
Symptoms of tetralogy of fallot:
o Cyanosis
o High systolic pressure in right ventricle
o Radiology showing an enlarged right ventricle
Virus to mom during 1st trimester of pregnancy, especially measles, can cause a congenital anomaly
Heart-lung machines are used during surgery to replace the heart and lungs jobs and allow for surgery
on either
-
Called extracorporeal circulation
You can determine how much hypertrophy will happen in the heart by multiplying ventricular output by
the pressure the ventricle has to work against
Extreme heart hypertrophy can lead to heart failure
-
Due to the vessels not growing like the heart did, and fibrosis of the heart
Often there’s chest pain involved with heart hypertrophy