PRESSURE CURVES IN CVS

PRESSURE CURVES IN CVS

Pressure & volume changes during different phases of cardiac cycle can be represented by,

Aortic pressure curve.

Pressure-volume loop.

Jugular venous pressure.

1. AORTIC PRESSURE CURVE:

Onset of rapid ejection phase of ventricular systole.

↓

Aortic pressure steeply rises to maximum.

To about 120 mm/Hg

↓

Ejection of blood into aorta → Causes aortic wall stretch → Blood in entire arterial system moves at a faster rate.

↓

Sets up pressure wave traveling along arteries, expanding their walls.

This is palpable as “Pulse”.

↓

Aortic pressure declines throughout diastole.

↓

Up to min of 80mm/Hg until isometric contraction of next cardiac cycle.

NOTE:

Aortic elastic recoil property & arteriolar resistance –

– Maintains relatively high aortic pressure during diastole.

An incisura/dicrotic notch corresponds to aortic valve closure –

Recorded in early part of downstroke of aortic pressure curve

Produced by sudden backward flow of aortic blood.

Followed by immediate cessation of backflow.

Pulse:

Strength/amplitude/volume of pulse depends on,

Stroke volume –

– Volume of blood ejected out with each beat.

Extent of arterial wall elasticity/compliance.

In turn both are determinants of Pulse Pressure.

2. PRESSURE-VOLUME LOOP:

Represents “Relationship between ventricular pressure & volume throughout cardiac cycle”.

X-axis: Presents ventricular blood volume.

Y-axis: Presents left ventricular pressure.

Loop width:

– Represents “Stroke volume”.

– Ie., Difference between end-diastolic volume & end-systolic volume.

Area under loop – “Ventricular stroke work”/”External cardiac work”.

– Four phases of cardiac cycle, each representing one side of closed loop.

Pressure & volume variations in cardiac cycle:

1. Starting with “End-diastolic volume” –

Increased ventricular pressure.

Volume is constant-

– Hence, isovolumetric contraction.

2. During ejection phase –

Decreased volume.
Pressure – Small change.

3. Isovolumetric relaxation –

Decreased intraventricular pressure.

Volume – No change.

4. Filling phase –

Increased volume.

CONDITIONS SHIFTING CURVE:

LOOP SHIFTING LEFT –

When less volume is handled by same pressure.

Occurs in conditions with decreased compliance & increased contractility.

Eg:

In Pressure overload – Aortic stenosis.

In sympathetic stimulation.

Concentric hypertrophy.

LOOP SHIFTING RIGHT-

In volume overload – Eg. Mitral & aortic regurgitation.

3. JUGULAR VENOUS PRESSURE (JVP):

Variations in right atrial pressure are transmitted to jugular veins producing,

– Three positive waves (a, c & v)

– Two negative waves/descents (x & y).

a wave –

Presystolic ‘positive’ wave.

Due to right atrial systole.

x-descent –

Negative wave.

Due to right atrial relaxation.

c-wave –

Positive wave.

Produced by bulging of tricuspid valve into right atrium.

Happens during right ventricular isovolumetric contraction.

v-wave –

Positive systolic wave.

Due to tricuspid valve closure.

Resulting in increased vena cava blood volume during systole.

y-descent (Diastolic collapse) –

Negative wave.

Due to tricuspid valve opening.

Causing rapid blood flow into right ventricle.

Exam Important

PRESSURE CURVES IN CVS

Aortic elastic recoil property & arteriolar resistance maintains relatively high aortic pressure during diastole.

An incisura/dicrotic notch in an aortic pressure curve, corresponds to aortic valve closure.

Strength/amplitude/volume of pulse depends on,

– Stroke volume – Volume of blood ejected out with each beat.

– Extent of arterial wall elasticity/compliance.

– In turn are pulse pressure determinants.

PRESSURE-VOLUME LOOP:

Loop shifting left – Aortic stenosis.

Loop shifting right – Mitral regurgitation & aortic regurgitation.

JUGULAR VENOUS PRESSURE (JVP):

a wave – Due to right atrial systole.

v-wave – During tricuspid valve closure.

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PRESSURE CURVES IN CVS