Pressure Curves In Cvs

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 Question

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.

Don’t Forget to Solve all the previous Year Question asked on Pressure Curves In Cvs

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