Aortic Pressure (I) – arteries are pressure resovoirs
Phase 1 and 2 – Aortic valve is closed but there is
still flow of blood out of the aorta: ↓ aorta
In the early and late stages of diastole, aortic
pressure is decreasing
The first (slow) decrease of aortic pressure
occurs when the semi-lunar valves are close
(i.e. there is no blood being pumped from the
ventricles into the aorta or pulmonary artery).
This is because even though the heart is no
longer pumping blood through the aortic valve
into the aorta, blood is still flowing to the systemic circulation.
The is because arteries function as pressure reservoirs – the larger the artery,
the greater this function
The aorta under healthy conditions is relatively plastic
1. The blood flows through the aorta and forms a bulge (when the heart is
2. When the heart is relaxed (valve close) the aorta returns to its normal (pre-
contraction) diameter and forces the blood in the bulge down the aorta and into
the systemic circulation (when the heart is its relaxation phase)
Aortic Pressure (II)
Phase 3 – the aortic valve opens flow into aortaflow out aortaherefore, ↑ P (aorta).
Aorta pressure continues to fall from the maximum until the point between
ventricular ejection phase and isovolumetric relaxation phase
Here ventricular pressure is less than the aortic pressure and this causes the
semi-lunar valve to close
Aortic Pressure (III)
The smooth decrease in aortic pressure is
interrupted by a very abrupt but slight upward
pressure or deflection followed by a linear decrease
in aortic after the upswing.
The dichrotic notch is a pressure
reverberation associated with the closing of
the aortic valve – this closing (when the
ventricle pressure is less than aortic Thiruvarangan
pressure) momentarily interrupts the smooth flow of blood which causes a small
pressure wave upwards.
o P (ventricle) < P (aorta)
o aortic (semi-lunar) valve closes
o produces small increase in P aorta
Systolic and Diastolic Pressure
o Minimum Aortic Pressure = Diastolic Pressure (DP)
o 80 mm Hg
o It is called diastolic pressure even though it is not achieved until slightly
o Diastolic pressure is an important indicator of stroke volume
o Maximum Aortic Pressure = Systolic Pressure (SP)
o 120 mm Hg
Blood Pressure – measured in brachial artery.
o 120/80 – used to calculate mean arteriole pressure
o Blood Pressure (BP) = CO X Total Peripheral Resistance (TPR)
o TPR is the resistance to blood flow in the circulation. There are five factors
that influence resistance and blood flow in the next couple of lectures
Pulse Pressure (PP)
Pulse Pressure (PP) = Systolic Pressure – Diastolic Pressure =
= 120 mm Hg – 80 mm Hg = 40 mm Hg (normal)
It can be used to identify cardiovascular diseases including hardening of the arteries.
o The pulse pressure is in part determined by how well arteries can contract and
expand when filled with blood
o But as arteries age and acquire fatty deposits, the ability to expand and contract
is reduced (lose elasticity)
o In the aorta, this has the consequence of inhibiting blood flow during diastole.
Additionally, leads to increases in blood pressure.
o The hardening causes increases in systolic and diastolic pressure (but much
greater in systolic) and therefore the pulse pressure increases.
Mean Arterial Pressure (MAP) – the driving force for blood flow
The mean arterial pressure isn’t simply equal to (SP + DP) / 2. This is because Aortic
pressure is closer to the minimum value for longer than it is close the maximum value. It
can be calculated in two ways:
o MAP = 1/3 SP + 2/3 DP or MAP = PP/3 + DP
o 40 mmHg / 3 + 80 mmHg = 13 mmHg + 80 mmHg = 93 mmHg Thiruvarangan
In a clinical setting, blood pressure is measured at the arm and it is a good
approximation of aortic blood pressure.
o Mild Hypertension – SP > 140 mmHg or DP > 90 mmHg
o Moderate Hypertension – SP > 160 mmHg or DP > 100 mmHg
o Severe Hypertension – SP > 180 mmHg or DP>110 mmHg
o Hypotension – SP < 90 mmHg or DP < 60 mmHg
Stroke Volume – is the amount of blood pumped in one heartbeat
Stroke Volume (SV) = EDV (mL) – ESV (mL)
o End Diastolic Volume (EDV) – Maximum ventricular volume
o It is the amount of blood in the heart just as the heart finishes the
relaxation phase and is beginning to contract (blood available to be
o End Systol