The Cardiac Cycle

The Cardiac Cycle

The repeating pattern of contraction (systole) and relaxation (diastole) of the heart

Duration of cardiac cycle = 0.8 seconds

Diastole longer than systole Ventricular contraction follows

atrial contraction (0.1 to 0.2 second later) remember the delay from AV node that’s why

The end diastolic volume: the total volume of blood in the ventricles at the end of diastole (120 ml)

Stroke volume is the volume of blood pumped by each ventricle per beat (70 ml)

Residual volume: amount of blood left in each ventricle at the end of systole (50 ml)

The Cardiac Cycle

Ventricles contract Ventricular pressure: increasing Ventricular volume: no change AV valves: closed.. prevent

backflow of blood Semilunar valves: closed (P in

ventricles < P in vessels)

The Cardiac Cycle Isovolumetric ventricular

contraction

Ventricular pressure: increasing > the pressure in the aortic and pulmonary vessels

Left ventricular pressure up to 120 mmHg (thicker wall , aorta artery higher pressure than polmunary)

Right ventricular pressure up to 25 mmHg

Ventricular volume: decreasing Semilunar valves: open AV valves: closed.. prevent

backflow of blood

The Cardiac CycleEjection phase

Ventricles relax Ventricular pressure:

decreasing Ventricular volume: no

change AV valves: closed Semilunar valves: closed

The Cardiac CycleIsovolumetric relaxation

Ventricular pressure: below atrial pressure ( slightly above zero)

Ventricular volume: increasing

AV valves: open when pressure in the atria> the pressure in the ventricles

Semilunar valves: closed Passive ventricular filling via

AV valves (80%)

The Cardiac Cycle Rapid filling of the ventricles

Active filling of the ventricles (20%)

Ventricular volume: slight rise Ventricular pressure: slight rise Semilunar valves: closed AV valves: open

The Cardiac CycleAtrial systole

The Cardiac Cycle

1. Isovolumetric contraction

2. Ejection phase

3. Isovolumetric relaxation

4. Rapid filling of the ventricles

5. Atrial systole

Heart Sounds

The first heart sound: Cause: closure of the AV valves

The second heart sound: Cause: closure of the semilunar

valves

Cardiac Output Cardiac output is the volume

of blood pumped by each ventricle per minute

CO = Stroke volume x Heart rate(L/min) (ml/beat) (beat/min) = 70 X 70

= 4900 ml/min= 5 L/min

Normal cardiac output (CO) = 5 L/min

Cardiac Output

Sympathetic stimulation HR (positive chronotropic

effect) CO

Parasympathetic stimulation HR CO

Cardiac centers in the medulla oblangata

Cardiac OutputRegulation of Heart Rate

End Diastolic Volume (EDV) Frank- Starling Law of the

Heart venous return EDV length

of cardiac muscle (stretch) force of contraction stroke volume cardiac output

Cardiac OutputRegulation of Stroke

Volume

Positive ionotropic effect strength of contraction

Sympathetic stimulation Adrenaline (neurotransmitter for

Sym.) Negative ionotropic effect

strength of contraction Parasympathetic stimulation Acetylcholine (neurotransmitter

for parasym.) Vagal stimulation

Cardiac Output Regulation of Stroke

Volume