Definition
– Amount of blood pumped to the body from each of the ventricles are called as cardiac output.
-Normal cardiac output of the heart is 5 liters per minute
Stoke volume and HEART RATE are the 2 main components that controls the cardiac output
CARDIAC OUTPUT=
STROKE VOLUME *HEART RATE
Definition
STROKE VOLUME:-
– It is an amount of blood pumped in 1 heart beat.
-Normal stroke volume of heart is 70ml/beat
HEART RATE:-
-It is the amount of heart beats to supply 5 liter of blood to all the parts of the body.
-Normal heart beat is 72 beats / min
.CARDIAC OUTPUT =70*72
=1540mL /min
=5Liters/min
Factors affecting cardiac output
Physiological condition
1)Age -: Children has less cardiac output then adults
2)Sex -: Male has more cardiac output then female
3)AFTER MEAL-: Cardiac output increases during 1st hour of meal
4)EXERCISE-: Cardiac output increases during exercise
5)POSTURE-: From lying to standing cardiac output decreases
6)SLEEP -: Cardiac output decreases slightly during sleep
PATHOLOGICAL CONDITION
1)INCREASE CARDIAC OUTPUT
a)Fever
b)Anemia
2)DECREASE CARDIAC OUTPUT
a)Hypothyroidism
b)Shock
c) Hemorrhage
Factors affecting cardiac output are ,
a) VENOUS RETURN
b)FORCE OF CONTRACTION
c)HEART RATE
d)PERIPHERAL RESISTANCE.
a)VENOUS RETURN
-Amount of blood which return to heart from different part of the body
-Cardiac output is directly proportion to venous return
It depends upon the following
1) RESPIRATORY PUMP
2)MUSCLE PUMP
3)GRAVITY
4) VENOUS PRESSURE
1)RESPIRATORY PUMP
-Respiratory activity helps in returning of blood to the heart.
During inspiration
-The inter thoracic pressure increases during the inspiration
-These decends the diaphragm and increases the intra abdominal pressure.
– Due to increase in abdominal pressure the abdominal veins gets suppressed
-It increases the diameter of the inferior vena cava
-It pushes the blood upward towards the heart
-Which results in the increase of venous pressure.
2)MUSCLE PUMP
-Muscular activity helps in muscle pump
– During muscle contraction the veins gets compressed.
-There are valves present in between the muscles
-which help the blood to move towards the heart
-These increases the venous return of the heart.
3)GRAVITY
-Due to the pull of the gravitational force the venous blood flow gets decreased .
-These gravitational force pulls the blood downwards
4)VENOUS PRESSURE
-The pressure of the veins gets decreased from lower veins to higher veins
– These decrease in pressure between the veins decreases the venous return of the heart.
-Normal pressure of veins is 12to 16mmHg
– In SVC( SUPERIOR VENA CAVA) AND IVC(INFERIOR VENA CAVA) the pressures falls to 5 mmHg.
b)FORCE OF CONTRACTION
-Cardiac output is directly proportional to the force if contraction.
-According to FRANK-STARLING LAW,
” The Force of contraction of heart is directly proportional to the initial lenght of muscle fiber.”
c) HEART RATE
-Cardiac output is directly proportional to heart rate.
-Moderate change in the heart rate does not alter the cardiac output.
– If there is marked increase in heart rate the cardiac output increases
-If there is marked decrease in heart rate the cardiac output decreases.
d)PERIPHERAL RESISTANCE
-Peripheral resistance is the resistance offered to blood flow at the peripheral blood vessel.
-It is the resistance against which the heart has to pump
– As a result peripheral resistance is inversely proportional to cardiac output.
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