Download Cardiac physiology

Bio 194
Dr. Decker
Cardiac cycle
1- Ventricular relaxation (Quiescent period)
2- Ventricular filling (diastole)
3- Ventricular contraction/ejection (systole)
Cardiac cycle last about 0.8 seconds
1- Ventricular relaxation (Quiescent period):
In the beginning of this phase all four chamber are at rest. As the pressure inside
the ventricles drop, blood will flow back towards the pulmonary semilunar valve (from
the pulmonary artery) and aortic semilunar valve (from the aorta) causing those valves to
close. At this time all valves are closed. The heart is in isovolumetric relaxation. Blood
rebounding off those valves will cause a peak on the aorta pressure curve called the
dicrotic notch or dicrotic wave.
2- Ventricular filling (diastole):
As the walls of the ventricles continue to relax, the pressure inside the ventricles
continues to drop. This decrease in pressure will cause the atrioventricular valves to open
and blood to rapidly enter ventricles. This is known as rapid ventricular filling (denoted
as the first third of the filling phase). The second third of ventricular filling is called
diastasis. As the SA node depolarizes, causing the atria to contract, the final third of the
filling phase is accomplished. The amount of blood in each ventricle is approx. 130 ml.
This value is called the end diastolic volume (EDV)
3- Ventricular contraction/ejection (systole):
As the AV node is firing down the bundle of His (and bundle branches), the
ventricles will start to contract causing blood to push up against the AV valves closing
them. At this time all four valves are closed again. This is isovolumetric contraction.
As the pressure in the left ventricle exceeds a pressure of 80 mmHg over the aorta and a
pressure of 15-20 mmHg over that of the pulmonary trunk (artery), the semilunar valves
will open causing ventricular ejection. The amount of blood left in each ventricle
following ejection is approx. 60 ml. per ventricle. This value is called the end systolic
volume (ESV).
Stroke volume is the amount of blood that the ventricles eject per beat.
Stroke Volume (SV) = end diastolic volume (EDV) - end systolic volume (ESV).
SV= EDV - ESV
SV= 130ml. - 60ml.
SV=70ml.
Cardiac Output (CO) is the amount the ventricles eject per minute.
CO= SV x HR (heart rate)
CO= 70ml/beat x 75beats/min
CO= 5,250 ml/min or 5.25L/min.