Mechanisms of the filling:
a) „Vis a tergo“ – residual energy from the left ventricle
b) „Negative“ intrathoracic (interpleural) pressure:
Quiet breathing:
- expiration: P
pl
= -2.5 mm Hg (relative to atmospheric)
- inspiration: -6 mm Hg during = thoracic pump.
Pressure is transmitted to the great veins and atria – aids venous return.
The movement of diaphragm – rise of P
abd.
c) Shifting down of the A-V ring by contraction of ventricles „vis a fronte“.
d) Gravity – from head and vessels above cardiac level
e) Muscular pump
Filling of the ventricles
Accumulation of blood in the atria – elevated atrial pressure - decrease of ventricular pressure to
diastolic value (near Ø) → pressure in the atria push open the A-V valves – blood flows
into the ventricles
1) Period of rapid filling (first 1/3 of the diastolic time)
2) Period of slow filling – diastasis (next 1/3)
3) Atrial systoly (last 1/3) + 20-30 % of the filling of the ventricles
Ventricular systole
1) Period of isovolumic .- isometric contraction
At the start of ventricular contraction, the ventricular pressure rises – causing the A-V valves to
close. Also semilunar valves are closed – during first about 0.05 s – until the pressures in LV
and RV and RV exceed the pressures in the aorta and pulmonary artery – opening of the
semilunar valves →
2) Period of ventricular ejection
a) Phase of the rapid ejection (1/2 of V is ejected in the first ¼ of the ventricular systole)
b) Phase of the slow ejection (remaining ½ of V-during next 2/4 of the ventricular systole)
3) Protodiastole (last ¼ of the ventricular systole)
The ventricular pressure ralls to a value below that in aorta, closing of the semilunar valves
– early diastole.
Ventricular diastole
1) Period of isovolumic (isometric) relaxation – the valves are closed,V pressures continues
to drop
2) Filling of the ventricles:
Period of the rapid ventricular filling – when the ventricular pressure falls below atrial pressure
and the AV valves open .……….a new cycle.
HR = 72/min – 1 cycle lasts 0.83 s.
Length of Systole/Diastole
HR – 65/min: S - 0.3 s
D - 0.6 s
1 : 2
HR – 200/min: S - 0.16 s
D - 0.14 s
1 : 1