Volume Changes During Cardiac Cycle.

 

Stroke Volume (SV)

          It is a volume of blood pumped out by each ventricle per beat. It is about 70 – 80 ml.

            Stroke volume (SV) = End diastolic volume – End systolic volume

 

End Diastolic Volume (EDV)

          Volume of blood in each ventricle at the end of diastole. It is about 120 – 130 ml.

 

End Systolic Volume (ESV)

          Volume of blood in each ventricle at the end of systole. It is about 50 – 60 ml.

 

Ejection Fraction (EF)

It is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke.

EF = SV (EDV – ESV) * 100

                 EDV

• ·       Normal ejection fraction is about 60 – 65 %
• ·       Ejection fraction is good index of ventricular function

 

Brachial Artery Pressure Curve

Atrial Pressure

·      Systolic blood pressure – peak pressure during systole in atrial blood

·      Diastolic blood pressure – lowest pressure during diastole in the atrial blood

·      Pulse pressure – different between systolic blood pressure and diastolic blood pressure

·      Mean atrial pressure – average pressure = diastolic blood pressure + 1/3^rd of pulse pressure

Atrial Pulse

·      Blood forced into the aorta during systole not only moves the blood in the vessels forward but also sets up a pressure wave that travels along the arteries

·      The pressure wave expands the arteries walls as it travels, and the expansion is palpable as the pulse

·      The strength of the pulse is determined by the pulse pressure and bears little relation to the mean pressure

·      The pulse is weak (“thready” pulse) in hypovolemia.

·      It is strong (bounding pulse) when stroke volume is large: for example, during exercise or after the administration of histamine

 

Jugular Venous Pulse

·       Atrial pressure fluctuates during cardiac cycle

·       It gives rise to a characteristic pressure waves in the internal jugular vein

·       The atrial pressure changes are transmitted to the great veins, producing three characteristic waves in the record of jugular pressure waves

•     3 waves – a, c, v
• 2 descents – x and y descent

a Wave

·       Due to atrial systole

·       Blood regurgitates into the great veins when the atria contract. In addition, venous inflow stops and the resultant rise in venous pressure contributes to a wave

c Wave

·       Due to the rise in atrial pressure produced by the bulging of the tricuspid valve into the atria during isovolumetric contraction

v Wave

·       Due to the rise in atrial pressure before the tricuspid valve opens during diastole

Genesis of x descent

·       Decreased atrial pressure due to pulling down of AV valves during right ventricular ejection

Genesis of v wave

·       Filling of right atrium

·       Passive rise in pressure in right atrium as venous return to the atrium continues during ventricular systole while the tricuspid valve is closed

Genesis of y descent

·       Tricuspid valve open

·       Blood flows from right atrium to right ventricle

·       Pressure drops in right atrium

 

v the jugular pulse waves are superimposed on the respiratory fluctuations in venous pressure

v venous pressure falls during inspiration as a result of the increased negative intrathoracic pressure and rises again during expiration

    Heart Sounds

        1^st lub sound

Cause         -due to vibrations set up by sudden closure of mitral valve and tricuspid valve

Site             - apex of the heart

Character - low pitched and prolonged (compared to 2^nd)

Timing       - beginning of ventricular systole

                           Good clinical of systole

 

2^nd dup sound

            Cause             - due to vibrations setup by sudden closure of AV and PV (physiological                        splitting during inspiration)

            Site                 - in 2^nd inter costal space

            Character      - high pitched and short duration

            Timing            - end of ventricular systole

 

Heart sounds functions of valves

·       open with a forward pressure gradient

eg- when left ventricle pressure > the aortic pressure the aortic valve is opened

·       close with a backward pressure gradient

eg – when aortic pressure > left ventricle pressure the aortic valve is closed

 

The course for heart sound is due to the vibration of the valves immediately after closure.