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CARDIOVASCULAR SYSTEM CARDIAC CYCLE. LECTURE – 3 DR. ZAHOOR ALI SHAIKH. CARDIAC CYCLE. Cardiac events occurring during one beat (systole & diastole) are repeated during the next beat Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute. CARDIAC CYCLE.
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CARDIOVASCULAR SYSTEM CARDIAC CYCLE LECTURE – 3 DR. ZAHOOR ALI SHAIKH
CARDIAC CYCLE • Cardiac events occurring during one beat (systole & diastole) are repeated during the next beat • Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute.
CARDIAC CYCLE • 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.
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.
PHASES OF CARDIAC CYCLE • Atrial systole: 0.1 second • Atrial diastole : 0.7 seconds • Ventricular systole : 0.3 seconds • Ventricular diastole : 0.5 seconds
CARDIAC CYCLE Atrial Cycle (0.8 Sec.) Ventricular Cycle (0.8 Sec.)
Ventricular events • Ventricular systole • Isovolumetric contraction • Ejection phase • Rapid ejection • Slow ejection • Protodiastolic phase • Ventricular Diastole • Isovolumetric relaxation phase • Filling phase • Rapid filling • Slow filling • Last rapid filling
Ventricular events Ventricular systole • Isovolumetric Contraction • When blood has come from Atria into the ventricle, ventricle will start contracting, when pressure increases in ventricle than atria, AV valves close. • This phase of ventricular contraction when all valves are closed is called ISOVOLUMETRIC CONTRACTION.
Ventricular systole • During Isovolumetric Contraction, volume remains same, but pressure in the ventricle must continue to increase till it exceeds aortic pressure.
Ventricular systole 2.Ejection Phase • When ventricular pressure increases, semi-lunar valve [aortic and pulmonary valves] will open and blood will flow into aorta and pulmonary artery. This is Ejection Phase [pumping of blood out]. • Ejection is rapid first and then slow.
Protodiastolic phase • Once ventricle muscle is fully contracted, than it will relax and ventricular pressure will drop rapidly. • When ventricles are relaxing, but aortic and pulmonary valves have not closed yet, this period is called Protodiastole. • It lasts for 0.04 sec. • It ends when aortic and pulmonary valve close.
Ventricular Diastole • Isovolumetric Relaxation During diastole, When ventricular pressure falls below the Aortic pressure, aortic valve closes, and AV valves are not open yet , ventricle is close cavity with all valves closed. This phase is called Isovolumetric Relaxation (means volume remains same but pressure is decreasing).
Ventricular Diastole 2. Filling phase • When ventricular pressure falls below the atrial pressure, AV valve open and blood moves rapidly from the atria into the ventricles – first rapid filling phase [causes 3rd heart sound]. • Then blood comes slowly – slow filling phase. • Then atria contract for 0.1sec and blood comes fast into the ventricle – last rapid filling phase [causes 4th heart sound]. • NOTE Last rapid filling phase is due to atrial systole and contributes to 20-30% of ventricular filling. After atrial systole, cardiac cycle will re-start.
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
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.
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.
Draw pressure curve for Lt.ventricle, Aorta & Lt. Atrium • Draw pressure curve for Rt. Ventricle & Pul. Artery.
Events of cardiac cycle showing pressure changes in left ventricle, aortic pressure, atrial pressure, ECG & phonocardiogram
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.
Heart Sounds • We will discuss Heart Sounds in next lecture.
What You Should Know From This Lecture • Cardiac Cycle – Definition • Phases of Cardiac Cycle • Pressure Changes • Volume Changes • Period of Systole & Diastole During Tachycardia • Relationship of Heart sounds with Cardiac Cycle