Physio. Ch13 Part 2 Cardiac Cycle

Cardiac Cycle

• All events associated with blood flow thorough the heart during one heart beat

• Comes in two major stages

- Systole: 35% of the cardiac cycle

- Diastole: 65% of the cardiac cycle

Driving force

• Ventricular contraction and relaxation

• Powers blood flow through the heart

Phases of the Cardiac Cycle

• 1: Ventricular filling

• 2: Isovolumetric contraction

• 3: Ventricular ejection

• 4: Isovolumetric relaxation

Ventricular filling

• 1st phases of the Cardiac Cycle

• Venous return passes through AV valves and into ventricles passively

- AV valves are open & Semilunar valves are closed

Isovolumetric contraction

• 2nd phases of the Cardiac Cycle

• Ventricles contract and ventricular pressure exceeds atrial pressure which closes the AV valves

• First stage of systole

• Creates “Lub” sound

• All valves are closed and blood neither enters or leaves the ventricle

Ventricular ejection

• 3rd phases of the Cardiac Cycle

• Ventricles contract and semilunar valves open & blood enters aorta and pulmonary arteries

- AV valves are still closed to prevent back flow

• Second stage of systole

• The stage controlling Stroke volume and End-systolic volume (ESV)

Isovolumetric relaxation

• 4th phases of the Cardiac Cycle

• Ventricular myocardium relaxes with all valves closed

- The pressure in that ventricles is to high to open the AV valves and to low to open the semilunar valves

• Moves back into phase 1 when the atrial pressure overcomes that of the ventricle

Venous return

• Blood that enters the heart from the veins

Stroke volume

• The amount of blood ejected from the heart with one beat

• Typically 70mL

• Calculated by subtracting end-systolic volume from end-diastolic volume

End-systolic volume (ESV)

• The amount of blood left in the heart at the end of one beat

• Typically 60mL

Cardiovascular pressures

• Pressure of blood in the heart chambers or in the vasculature

• Measured relative to atmospheric pressure (760mmHg)

Aortic Diastole

• No blood enters aorta

• AV valves open and semilunar valves closed

• Aortic pressure decreasing

Diastolic pressure (DP)

• Minimum aortic pressure at the end of Aortic Diastole

Aortic Systole

• Aortic pressure rises when aortic valve opens and ejection of blood occurs

Systolic pressure (SP)

• Maximum aortic pressure during ventricular ejection cphase

Dicrotic notch

• Closing of aortic valve causes brief increase in aortic pressure

Mean arterial pressure (MAP)

• Average aortic pressure occurring during the cardiac cycle

• Drives blood through the systemic circuit

End-diastolic volume (EDV)

• Maximum ventricular volume during cardiac cycle

- Reached just before ejection begins

End systolic volume (ESV)

• Minimum ventricular volume

• Reached just after ventricular ejection

Ejection fraction (EF)

• Fraction of end-diastolic volume ejected during a heartbeat

• Calculated by dividing strove volume by end diastolic volume

Ventricle compliance

• The ease with which the left ventricle can increase in volume/expand with a given change in pressure