It is defined as the volume of blood ejected out from the ventricles each minute, blood is ejected from left ventricle to the aorta and from the right ventricle to the pulmonary trunk.
Cardiac output = stroke volume*heart rate , its unit is ml/min
In a normal resting male , the average stroke volume is 70ml/beat and the heart rate is 75 beats/min, therefor the cardiac output will be
CO = SV * HR
CO = 70ml/beat*75 beats/min
CO= 5250 ml/min
- During exercise , stroke volume increases to the 100ml/beat and the heart rate reaches 100 beats/min so the cardiac output becomes approx 10ml/min.
- Cardiac reserve is the difference between the person’s maximum cardiac output (during exercise) and the person’s minimum cardiac output (during rest).
Regulation of cardiac output:-
Cardiac output is regulated by two mechanism
• Regulation of stroke volume
If more volume of blood return to the heart during diastole, then more I amount of blood is ejected during next contraction., this is known as Frank – Starling Law of Heart. stroke volume depends upon 3 factors-
I. Preload:-it is defined as the stretch required before the contraction takes place, more the preload more forceful is the contraction and stroke volume increases.
II. Contractility:- it refers to the strength of contraction, more the strength more is the cardiac output, substances which increases contractility are positive inotropic agents and the one decreases are negative inotropic agents.
III. Afterload it is the pressure that must be overcome before the SL valves open ,more the afterload lesser is the stroke volume.
• Regulation of heart rate:-
- Heart rate increases or decreases in effect of certain changes in the body, like certain receptors say proprioceptors which monitors the position of limbs and muscle during exercise provide signals to the cardiovascular center and the heart rate increases, similarly the baroreceptors for BP and chemoreceptors which regulates the chemical composition of blood also send responses to the CV center.
- Sympathetic stimulation increases heart rate while parasympathetic decreases.
- Hormones like epinephrine, non epinephrine thyroid hormones increases heart rate, increased body temp also increases heart rate.
MULTIPLE CHOICE QUESTION(MCQs)
1. What do you mean by cardiac output?
A. the volume of blood received in atrium
B. the volume of blood received in ventricles
C. the volume of blood ejected from atrium to the ventricles
D. the volume of blood ejected from ventricles to the aorta and pulmonary artery
2. What do you mean by cardiac reserve?
A. difference between max cardiac output and min one
B. difference between the max cardiac output and stroke volume
C. difference between the max cardiac output and heart rate
D. addition of max stroke volume and heart rate
3. Complete the following sentence “the more volume of blood enters during diastole,————————.
A. More blood is ejected during next diastole
B. more blood is received during next systole
c. more blood is ejected during next systole
D. more blood is received during next diastole
4. which of the following nerve provide parasympathetic stimulation to the heart which decreases the heart rate?
A. cardiac accelerator nerve B. vagus nerve
C. accessory nerve D. optic nerve
5. Which of the following factors decreases the heart rate?
A. parasympathetic stimulation B. increase level of Na and k+ ions
C. release of acetyl – choline D. all of the above
6. Which of the following is NOT the example of positive inotropic agents?
a. increased Ca ions B. anoxia
c. epinephrine and non epinephrine D. drug digitalis
7. Match the following:-
a. positive inotropic 1. Parasympathetic stimulation
B. negative inotropic 2. Drug digitalis
c. increases stroke volume 3. Acidosis
D. decreases heart rate 4. Greater end – diastolic volume
8. which of the following nerve takes the sympathetic stimulation to the heart regarding heart rate?
A. vagus nerve B. glossopharyngeal nerve
C. cardiac accelerator nerve D. accessory nerve
9. Which of the following statement is true?
A. greater the afterload, more is the stroke volume
B. greater the venous return, more is the stroke volume
C. longer the duration of diastole increases heart rate
D. anoxia is an positive inotropic agent
10. Which of the following is the correct formula for cardiac output?
A. stroke volume/ heart rate B. stroke volume*resistance
C. heart rate / resistance D. none of the above
1. the volume of blood ejected from ventricles
2. difference between the max and min cardiac output
3. more blood is ejected during next systole
4. vagus nerve
5. all of the above
7. a – 2 b – 3 c – 4 d – 1
8. cardiac accelerator nerve
9. greater the venous return more is the stroke volume
10. none of the above
REFRENCES:- Gerard J. Tortora -Principles of anatomy and physiology; edition twelfth ; page no.-: 741-744.