The cardiac cycle is the rhythmic sequence of relaxation and contraction of the heart chambers that pumps blood throughout the body. Here's a breakdown of the key points you mentioned:
1. Atrial Systole :-
• Dynamic phase (contraction) : The atria contract, actively pushing additional blood into the ventricles. This contributes about 20% of total ventricular filling.
• Adynamic phase (relaxation) : The atria briefly relax after contraction, allowing for further blood flow from the veins.
2. Atrial Diastole :-
• The atria are completely relaxed, allowing for maximum filling with blood returning from the body. This is the longest phase of the cardiac cycle.
3. Ventricular Systole :-
• First heart sound (S1) : Caused by the closure of the atrioventricular valves (tricuspid and mitral valves) as the ventricles contract. The sound of these valves slamming shut is the iconic first heart sound, often described as a "lub" sound.
• Isometric contraction : The ventricles contract without a change in chamber volume as the pressure builds to overcome the pressure in the arteries.
• Period of ventricular systole :
(a) Maximum ejection period : The ventricles forcefully contract, ejecting a large volume of blood into the aorta (left ventricle) and pulmonary artery (right ventricle).
(b) Reduced ejection period : The rate of blood ejection slows as the ventricles begin to relax.
4. Ventricular Diastole :-
• Second heart sound (S2) : Caused by the closure of the semilunar valves (aortic and pulmonary valves) at the end of ventricular ejection. This closure creates the second heart sound, often described as a "dupp" sound.
• Phase of ventricular diastole :
(a) Prot-odiastolic phase (rapid relaxation) : The ventricles rapidly relax, creating a slight suction effect that draws blood into the ventricles.
(b) Isometric relaxation phase : Ventricular pressure drops rapidly, but the chambers haven't yet changed volume.
(c) First rapid filling phase (third heart sound - not always audible) : Blood rapidly flows into the ventricles due to the pressure difference between the atria and ventricles. This sound is sometimes audible in healthy young adults.
(d) Slow inflow phase (diastasis) : A period of slower, steady blood filling from the atria.
(e) Last rapid filling phase (fourth heart sound - very faint) : A final, small rush of blood into the ventricles just before atrial systole. This sound is very faint and rarely audible.
Additional Points :-
• The entire cardiac cycle typically lasts around 0.8 seconds.
• The duration of each phase can vary depending on factors like heart rate and blood pressure.
Filling of Heart (Ventricles) :-
• Blood normally flows from the great veins into the atria.
• About 75% of the blood flows directly through the atria into the ventricles even before the atria contracts.
• Usually causes an additional 25% filling of the ventricles.
• The period of Atrial Systole Fills 25% of ventricles.
• The period of Atrial Diastole Fills 75% of ventricles.
Volumes of Blood Related to Cardiac Cycle :-
• During diastole, filling of the ventricles normally increases the volume of each ventricle to about 120 milliliters.
• The volume decreases by about 70 milliliters, which is called the stroke volume. (i.e. the volume of blood pumped by left ventricle in the aorta in one stroke or brat).
• The remaining volume in each ventricle is now about 50 milliliters is called end systolic volume.
• The fraction of the end diastolic volume which is ejected out is called the ejection fraction.
• Around 60% or 7/12.
EF = SV/EDV
• Cardiac output it is the amount of blood pumped by the left ventricle in the aorta in a minute.
• Its value in a normal adult is about 5 litre/minute.
CO = SV × HR
Cardiac output (ml/minute) = Stroke volume (ml/beat) × Heart rate (beats/min)
a. Average heart rate = 70 bpm
b. Average stroke volume =70 - 80ml /beat
c. Average cardiac output =5, 500ml /minute
Heart-Sound :-
1. First Sound :
• This is a contraction sound which denotes the beginning of ventricular-contraction.
• It arises due to closing of mitral valve and the tricuspid valve.
• It is weak and appears in the form of "Lubb" (L-U-B -B)
2. Second Sound :
• This is a diastolic sound which denotes the beginning of ventricular diastole.
• This arises due to the closing of the semilunar valves of the two arches and is heart in the from of " Dup " .
• It is shrill than the first sound and takes less time.
3. Heart Murmur : In case of defective or damaged heart valves, their improper closure leads to leakage of blood which produces an abnormal sound referred to as heart murmur.
Blood Pressure :
Blood-pressure is measured in two stages -
1. Systolic Pressure :- It is the higher limit of blood pressure that shows the state of heart (systole) contraction for man this limit is 120 mm Hg (normal).
2. Diastolic pressure :- It is the lower limit of B.P. that shows the state of heart relaxation (expansion = Diastole) for man this limit is 80 mm Hg (normal).
• The instrument by which we can measure B.P. is called sphygmomanometer.
• In man B.P. is measured in the brachial artery of arm. [Normal B.P. of a healthy person is 120/80 mm Hg]
• Hales measured B.P. in horse first of all.