1. Introduction to Cardiac Cycle and Cardiac Output

2. Objectives
Explain the ECG waves and correlate them with mechanical events.
Describe the phases of cardiac cycle.
Identify the origin of heart sounds.
Define heart rate, stroke volume, venous return and cardiac output.
Explain the Starling’s law of the heart.
List the function of autonomic nervous system on the heart.

3. Electrocardiogram ECG (EKG)

4. Electrocardiogram ECG (EKG)
Surface electrodes record electrical activity deep within body
Reflects electrical activity of whole heart not of single cell!
EC fluid = “salt solution” (NaCl)  good conductor of electricity to skin surface
ECG tracing =  of all electrical potentials generated by all cells of heart at any given moment

5. Electrocardiogram (ECG, EKG)
Electrodes placed on arms and legs (limb leads) + six positions on chest (chest leads).
Each lead records different electrical activity (each looks at heart from a different position)

6. 3 waves appear with each heart beat:
P wave: represents atrial depolarization
QRS complex: represents ventricular depolarization
T wave: represents ventricular repolarization

7. Depolarization = signal for contraction
Since:
Depolarization = signal for contraction
Segments of ECG reflect mechanical heart events

8. Correlation of ECG waves with Atrial and Ventricular Systole

9. ECG cont.
Comparing records with one another & normal records, allows determination :
if conductivity pathway is normal
if the heart is enlarged
if certain regions of heart are damaged
ECG time intervals or segments:
P-Q interval
S-T interval
Q-T interval

10. ECG cont.

11. Cardiac Cycle
One cardiac cycle (CC): all events associated with one heart beat.
(Systole and diastole of atria + systole and diastole of ventricles)
At HR 75 beats /min, CC lasts 0.8 secs.
In each CC, atria & ventricles alternatively contract & relax 
Force blood from areas of higher pressure
Areas of lower pressure

12. Cardiac Cycle cont. Cardiac Cycle comprises the following phases:
Atria systole:
atria contracting but Ventricles relaxing.
Lasts 0.1 sec
Ventricular systole:
Ventricular Contracting while atria relax
(atrial diastole). Lasts 0.3 sec.
Relaxation Phase
(Complete cardiac diastole ), Both atria
and ventricular relax. Lasts about 0.4 sec

14. Heart Sounds
Auscultation: act of listening to sounds within the body, usually done with a stethoscope
sounds are caused by vibrations set up within the walls of ventricles and major arteries during valve closure.
During each CC4 heart sounds
Only first & second (S1 &S2) heard in normal heart

15. First heard sound (S1) lubb:
- louder & longer than second
- caused by closure of A-V valves
(soon after beginning of ventricular systole)
Second heart sound (S2) dupp:
- shorter & not as loud as first
- caused closure of SL valves
(beginning of ventricular diastole)
S3 is due to turbulance during ventric filling
S4 is due to turbulance during atrial systole

16. Heart sounds
S1 &S2 are best heard at the surface of chest in specific locations

17. Cardiac output (CO) CO = SV X HR
CO is the volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute.
CO equals the stroke volume (SV) multiplied by heart rate (HR)
CO = SV X HR
SV volume of blood ejected by the ventricle during each contraction
HR number of heart beats per minute.
CO = SV X HR = 70 ml/beat X 75 beats/minute
= 5.25 L/min

18. Cardiac Output cont. CO may  to meet demands
During exercise CO can increase to L/ min
Cardiac reserve (CR): The difference between the maximum CO and CO at rest.
Average CR: 4 -5 X resting value (20-25 L/m)
higher in athletes (35 L/m)
little or no reserve in heart disease

19. Regulation of cardiac output
CO= SV x HR
Depends on the regulation of SV and HR

20. Cardiac Terminology End diastolic volume (EDV):
blood in the ventricles at the end of diastole.
Ejection fraction:
fraction of EDV that is ejected (%), used to measure heart efficiency.
End systolic volume (ESV):
blood that remains in the blood at the end of systole.
Preload:
the degree of stretch on the heart before it contracts.
Afterload:
the pressure that must be exceeded before ejection of blood from the ventricles can occur.

21. Regulation of stroke volume
THREE factors regulate SV:
Preload (EDV)
Contractility
Afterload

22. 1. Preload: effect of stretching
Frank-Starling (F-S) law of the heart:
Within limits, the more the heart fills during diastole (preload – stretching), the greater the force of contraction during systole.
the preload is proportional to EDV, the greater the EDV, the more forcefull the next contraction
“The heart will pump what it receives”- Starling’s law of the heart

23. Preload cont. Two factors determine EDV:
Duration of ventricular diastole (HR)
Ventricular filling occur during diastole
Tachycardia ( HR) diastole duration
ventricular filling end diastolic volume CO
Venous return (volume of blood flowing back to the heart through systemic veins)

24. 2. Contractility
Contractility: strength of contraction at any given preload
+ve inotropism:  contractility
Include: - sympathetic stimulation
- Hormones; adrenaline and noradrenaline
-ve inotropism:  contractility
May result from:
- inhibition of the sympathetic system
- anoxia
- acidosis

25. 3. Afterload
pressure in pulmonary tract is a bout 20 mm.Hg and in the aorta is about 80 mm Hg. This pressure must be overcome before the semilunar valves open.
Depend on:
Elasticity of large arteries
Peripheral resistance of arterioles
An  in afterload   SV  more blood remains in ventricle
at end of systole (ESV)
Conditions that  afterload include:
Hypertension
Narrowing of arteries by atherosclerosis

26. Regulation of heart rate
Several factors, the most important are
1. Nervous factors
2. Chemical factors
3. Others

27. Autonomic regulation of HR

28. Chemical regulation of HR
1. Hormones:
Adrenaline and noradrenaline (adrenal medulla) HR &  contractility
Adrenal medulla stimulated by:
exercise
stress
excitement
Thyroid hormones   HR & Contractility
Hyperthyroidism  tachycardia
2. Cations
 Na+ & K+   HR & Contractility
Ca2+   HR & Contractility

29. Other factors in HR regulation
Age: Newborn HR ~120 beats/min
Old people may also develop  HR
Gender: Adult females  higher HR than
males
Exercise: Athletic bradycardia (60 or
under) (more efficient heart)
Body temperature (BT):
 BT (fever or exercise)  HR
BT  HR & contractility