بسم الله الرحمن الرحيم Cardiac cycle Lecture by Dr.Mohammed Sharique Ahmed Quadri Assistant professor ,Physiology
Objectives • To know about different phases of cardiac cycle • To understand the volume, pressure and electrical changes during the cardiac cycle • To emphasize the inter-relationship between all these changes • To know the event that leads to the heart sounds • Recognize the relation ship of heart sounds with events of cardiac cycle
Cardiac cycle • Cardiac events that occur from beginning of one heart beat to beginning of next are called the cardiac cycle . • Cardiac cycle consist of alternate period of systole (contraction/emptying)& diastole(relaxation/filling) • Contraction results from spread of excitation across the heart & relaxation follows subsequent repolarisation of cardiac musculature.
CARDIAC CYCLE • Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute. • Atria and Ventricle go through separate cycles of systole and diastole. • When we use the term Systole and Diastole, we refer to ventricles, until unless specified for atria.
CARDIAC CYCLE Atrial Cycle (0.8 Sec.) Ventricular Cycle (0.8 Sec.)
We will discuss mechanical & electrical changes during Cardiac Cycle Mechanical changes: • Phases of cardiac cycle • Pressure changes during cardiac cycle • Volume changes during cardiac cycle • Heart sounds Electrical Changes • Electrocardiogram (ECG)
ECG • ECG ( Electrocardiogram) – These electrical events can be recorded by putting electrodes on the surface of body • P wave – Atrial depolarization • QRS - Ventricular Depolarization • T wave – Ventricular Repolarization We will discuss ECG in detail in coming lectures.
Events during cardiac cycle • Atrial systole 0.1 second • Atrial diastole 0.7 second • Ventricular systole 0.3 second • Isovolumic contraction 0.01 seconds • Rapid ejection period • Slow ejection period • Ventricular diastole 0.5 seconds • Isovolumicrelaxation 0.02 seconds • Rapid Passive filling phase • Slow passive filling (Diastasis) • Atrial contraction
Semilunar valves closed AV valves opened Events during cardiac cycle (continued) • Ventricular filling: • When ventricular pressure falls below atrial pressure AV valves opens & ventricular filling begins • The first part of this period is known as Rapid Passive ventricular filling phase (3rd heart sound) • Large part of ventricular filling takes place during this period
Semilunar valves closed AV valves opened Events during cardiac cycle (continued) • Ventricular filling: • In the next phase of diastole ventricular filling slows down . • As the ventricles are already full to a large extent & ventricular pressure slowly rises • This phase is known as diastasis or slow Passive ventricular filling phase • Amount of filling during this period is minimum
Semilunar valves closed AV valves opened Events during cardiac cycle (continued) • Ventricular filling: • Than comes the last phase of ventricular filling known as last rapid filling • This phase corresponds with atrial systole (contributes to 20-30% of ventricular filling)
Semilunar valves closed AV valves opened Events during cardiac cycle • Atrial systole: • Caused by atrial depolarization • Left ventricle is relaxed • As AV valves are open ,ventricles are filling with blood even prior to atrial systole • Atrial systole causes further increase in ventricular volume • Through out atrial contraction atrial pressure exceeds ventricular pressure so AV valves remain open
Events during cardiac cycle (continued) • Ventricular systole : • After the atrial contraction impulse travels through AV node & specialized conduction system to excite the ventricle. • As the ventricular contraction begins pressure in the ventricles exceeds that of atria and this backwards pressure forces the AV valves to close
Events during cardiac cycle (continued) • Isovolumetric ventricular contraction: • To open the semilunar valves ventricular pressure must exceeds that of aortic & pulmonary pressure • After closing of AV valves & before opening of Semlunar valves ,a brief period of time when ventricles contracts as a closed chamber • Ventricular pressure continues to increase
Semilunar valves opened Semilunar valves closed AV valves closed AV valves closed Events during cardiac cycle (continued) Systole: Period venticular ejection.
Events during cardiac cycle (continued) • Ventricular diastole (repolarization): • As the ventricles starts to relax on repolarisation ,ventricular pressure falls below aortic & pulmonary pressure & semilunar valves closes .
Semilunar valves closed AV valves closed Events during cardiac cycle (continued) • Isovolumetric relaxation: • when semilunar valves closes AV valves is not yet open because pressure in vetricles still exceeeds that of atria. • Therefore all valves are once again closed for short period of time when ventricles are relaxing
Tachycardia, Effect on Cardiac Cycle • During Tachycardia, when heart rate is increased, both systole and diastole time decreases. • Diastole length (time) is shortened much more than systole length. Therefore it reduces the time for ventricular relaxation and filling. But still ventricular filling takes place is adequate because maximum filling takes place during first rapid PASSIVE filling phase
Pressure changes during cardiac cycle Rt- Atrium = 0-7mm Hg. Lt- Atrium = 2-10 mm Hg. Rt – Ventricle = 25 / 6(2-8) mm Hg. Lt – ventricle = 120 / 8(2-10) mm Hg. Aorta = 120 / 80 mm Hg. Pul. Artery = 25 / 10 mm Hg.
Define Stroke Volume (SV) • Define End Diastolic Volume (EDV) • Define End Systolic Volume (ESV) • Define Ejection Fraction (EF)
Stroke Volume: It is a volume of blood pumped out by each ventricle per beat. It is about 70 - 80 ml. Stroke volume (SV) = EDV – ESV • End Diastolic Volume: Volume of blood in each ventricle at the end of diastole. It is about 120 – 130 ml. • End Systolic Volume: Volume of blood in each ventricle at the end of Systole. It is about 50 to 60 ml
Events of cardiac cycle showing left ventricular pressure, volume changes, & phonocardiogram
SV (EDV – ESV) X 100 EDV • Ejection fraction (EF) is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke. EF = 75 X 100 = 62.5% 120 Normal ejection fraction is about 60 – 65 %. Ejection fraction is good index of ventricular function.
Relation Of Heart Sounds With Phases Of Cardiac Cycle 1 st Heart Sound 2 nd Heart Sound 3 rd Heart Sound 4 th Heart Sound HEART SOUNDS
Relation ship of heart sounds with events of cardiac cycle • 1st heart sound = closure of AV valves at start of ventricular systole • 2nd heart sound= closure of semi lunar valves at end of ventricular systole • 3rd heart sound = first rapid filling phase • 4th heart sound = end of ventricular filling phase
Heart Sounds • We will discuss Heart Sounds in next lecture.
References • Text book of physiology by Linda .S .Costanzo third edition • Text book of physiology by Guyton & Hall • review of medical physiology by william F.Ganang