ATRIAL PRESSURE CHANGES
Atrial pressure waves (JVP)
a wave: Atrial contraction. Rt. Atria; 4 – 6 mmHg, Lt. Atria; 7 – 8
mmHg. A – Atrial systole – x wave
c wave: Bulging of A – V valves because of ↑ing pressure in the
ventricles. C – Contraction of ventricle - x’ wave
v wave: At the end of ventricular contraction, slow flow of blood into
the atria from the veins while A – V valves are closed. V – Venous
filling – y wave
ECG RELATION WITH CARDIAC CYCLE
The P wave is caused by spread of depolarization through the atria,
and this is followed by atrial contraction, which causes a slight rise in
the atrial pressure curve immediately after the electrocardiographic
About 0.16 second after the onset of the P wave, the QRS waves
appear as a result of electrical depolarization of the ventricles, which
initiates contraction of the ventricles and causes the ventricular
pressure to begin rising. Therefore, the QRS complex begins slightly
before the onset of ventricular systole.
The ventricular T wave in the ECG represents the stage of
repolarization of the ventricles when the ventricular muscle fibers
begin to relax. Therefore, the T wave occurs slightly before the end of
Right atrial systole precedes left atrial systole, and contraction of the
right ventricle starts after that of the left.
Since pulmonary arterial pressure is lower than aortic pressure, right
ventricular ejection begins before left ventricular ejection.
During expiration, the pulmonary and aortic valves close at the same
time; but during inspiration, the aortic valve closes slightly before the
The slower closure of the pulmonary valve is due to lower impedance of
the pulmonary vascular tree.
The outputs of the two ventricles are equal, but transient differences in
output during the respiratory cycle occur in normal individuals.
Cardiac muscle has the unique property of contracting and repolarizing faster
when the heart rate is high and the duration of systole decreases from 0.3 s at a
heart rate of 65 to 0.16 s at a rate of 200 beats/min.
The duration of systole is much more fixed than that of diastole, and when the
heart rate is increased, diastole is shortened to a much greater degree.
This fact has important physiologic and clinical implications. It is during
diastole that the heart muscle rests, and coronary blood flow to the
subendocardial portions of the left ventricle occurs only during diastole.
Most of the ventricular filling occurs in diastole. At heart rates up to about 180,
filling is adequate as long as there is sufficient venous return, and cardiac
output per minute is increased by an increase in rate.
However, at very high heart rates, filling may be compromised to such a degree
that cardiac output per minute falls and symptoms of heart failure develop.
EDV, SV, ESV, EF
End diastolic volume: 110 to 120ml
Stroke volume: 70ml
End systolic volume: 40 to 50ml
Ejection fraction: 60 %
When the heart contracts strongly, the end-systolic volume can be decreased to as
little as 10 to 20 milliliters.
When large amounts of blood flow into the ventricles during diastole, the
ventricular end diastolic volumes can become as great as 150 to 180 milliliters in
the healthy heart.
By both increasing the end-diastolic volume and decreasing the end-systolic
volume, the stroke volume output can be increased to more than double normal.
The A-V valves prevent backflow of blood from the ventricles to the
atria during systole, and the semilunar Valves prevent backflow from
the aorta and pulmonary arteries into the ventricles during diastole.
These valves open passively and close somewhat actively. That is,
they close when a backward pressure gradient pushes blood
backward, and they open when a forward pressure gradient forces
blood in the forward direction.
Thin, filmy A-V valves require very low backflow to cause closure,
whereas the much heavier semilunar valves require rather rapid
backflow for a few milliseconds.
First, The high pressures in the arteries at the end of
systole cause the semilunar valves to snap to the closed
position, in contrast to the much softer closure of the A-V
Second, because of smaller openings, the velocity of blood
ejection through the aortic and pulmonary valves is far
greater than that through the much larger A-V valves.
Third, because of the rapid closure and rapid ejection, the
edges of the aortic and pulmonary valves are subjected to
much greater mechanical abrasion than are the A-V valves.
When the valves close, the surrounding fluids vibrate
under the influence of sudden pressure changes, giving off
sound that travels in all directions through the chest.
When the ventricles contract, one first hears a sound
caused by closure of the A-V valves. The vibration is low in
pitch and relatively long-lasting and is known as the first
When the aortic and pulmonary valves close at the end of
systole, one hears a rapid snap because these valves close
rapidly, and the surroundings vibrate for a short period.
This sound is called the second heart sound.
The first heart sound identifies the onset of ventricular systole.
The second heart sound identifies the onset of ventricular diastole.
The third heart sound – rapid filling phase of ventricle
The fourth heart sound – atrial systole
Phonocardiogram: The recording of the auscultatory cardiac
activity, using a transducer placed on the thorax.
Status of ventricles and atria
• whole heart is relaxed
1.Early diastole open
2. Atrial systole open
• ventricles are expanding and filling (passive filling,
~80% of volume)
• atria contract and pump blood
• additional 10–40% filling of ventricles due to active
contraction of atria
• ventricular myocytes begin to contract
• ventricle volume unchanged
• ventricles fully contract
• pump blood to rest of body
• ventricles relax
• ventricle volume unchanged
• atria expand and are filling
* AV (atrioventricular) valves:
1) mitral valve – between the left atrium and the left ventricle
2) tricuspid valve – between the right atrium and the right ventricle
1) aortic valve – between the left ventricle and the aorta