Download - Cardiac Cycle by Bala Goyal
-
8/12/2019 Cardiac Cycle by Bala Goyal
1/14
The cardiac cycle
Describing the sequence of events in one heart beat
-
8/12/2019 Cardiac Cycle by Bala Goyal
2/14
Cardiac Contraction
Contraction is initiated byaction potentials thatnormally originates in SAnode in right atrium
Action potentialdepolarizes cells, causingcontraction
Sequence of contraction-
Atria and ventricles AV node delays impulses
by 0.1 seconds.
-
8/12/2019 Cardiac Cycle by Bala Goyal
3/14
Definitions
Systole= Begins with ventricular contractionand ends when ejection ceases.
Diastole= Begins when ejection ceases asventricles relax, ventricular filling starts after
sufficient relaxation occurs. Duration = Each Cardiac cycle - 0.80 sec,
systole 0.27,diastole 0.53 (HR = 75/MIN)
-
8/12/2019 Cardiac Cycle by Bala Goyal
4/14
Cardiac cycle
General Principles
Contraction of the myocardium generates pressurechanges which result in the orderly movement ofblood.
Blood flows from an area of high pressureto anarea of low pressure, unless flow is blocked by avalve.
Events on the right and left sides of the heart are thesame, but pressures are lower on the right.
-
8/12/2019 Cardiac Cycle by Bala Goyal
5/14
Phases of cardiac cycle
Phase 1 ATRIAL CONTRACTION
Phase 2 ISOVLUMETRIC CONTRACTION
Phase 3 RAPID EJECTION Phase 4 REDUCED EJECTION
Phase 5 ISOVOLUMETRIC RELAXATION
Phase 6 RAPID FILLING
Phase 7 REDUCED FILLING
-
8/12/2019 Cardiac Cycle by Bala Goyal
6/14
Atrial
systole
The heart is full of bloodand the ventricles arerelaxed (diastole)
Both the atria contract andblood passes down to theventricles
70% of the blood flowspassively down to theventricles so the atria do nothave to contract a great
amount Narrows the vena cava
orifices but some there issome regurgitation of bloodin to the veins.
-
8/12/2019 Cardiac Cycle by Bala Goyal
7/14
Atrial Diastole
Blood continuously enter
atria except when
transiently impeded during
atrial systole
Occurs throughout
ventricular systole and
diastole until p wave on
ECG.
AV valve suddenly openswhen ventricular pressure
falls below atria (creating v
wave)
-
8/12/2019 Cardiac Cycle by Bala Goyal
8/14
Ventricular
Systole
AV valve closes
Isovolumetric ventricularcontraction(0.05 sec), AV valvebulges.
Pressures in ventriclesexceeds than aorta(80 mmhg)and pulmonaryartery(10mmhg).
Aortic and Pulmonary valvesopen, rapid ejection phase
begins. Pressures in ventricles rises to
120 and 25 mmhg (left andright
-
8/12/2019 Cardiac Cycle by Bala Goyal
9/14
Ventricular Diastole
Aortic and pulmonary valvescloses.
Isovolumetric relaxation.
Ventricular pressures fallsbelow atrial and AV valves
opens, permitting ventricles tofill.
Filling is rapid at first, thenslows as next cardiaccontraction approaches.
Atrial pressures continues to
rise after vent. systole until AVvalves open and slowly risesagain until the next atrialsystole.
-
8/12/2019 Cardiac Cycle by Bala Goyal
10/14
Heart Sounds
FirstLow pitched, slightlyprolonged ``LUB, caused byvibrations due to suddenclosure of AV valves.
SecondHigh pitched, shorter``DUB caused by vibrationsassociated with closure ofsemi lunar valves.
ThirdSoft, low pitched dueto rapid ventricular filling
(normal in young) Fourthsome times heard
before first heard sound whenatrial pressures are high (rarein normal individuals)
-
8/12/2019 Cardiac Cycle by Bala Goyal
11/14
STROKE VOLUME
Ventricular stroke volume is
difference between
ventricular end diastolic
(EDV) and end systolic
volumes (ESV)
SV(70 to 90) = EDV(130) -
(50)ESV
In normal heart stroke
volume is the volume ofblood as ejected in to aorta
during each contraction.
-
8/12/2019 Cardiac Cycle by Bala Goyal
12/14
Ejection Fraction (EF)
EF is fraction of blood ejected by ventricle
relative to its filled volume (EDV)
EF = SV / EDV
EF is a measure of ability of heart to eject
blood.
Normally about .55 to .65 (55 to 65%)
-
8/12/2019 Cardiac Cycle by Bala Goyal
13/14
Length of systole and diastole
High heart rate- duration of systole decreases from 0.27 (65) to
0.16 (200 beats/min)
Duration of diastole decreases from 0.62 seconds to 0.14 (200
beats/min)
This fact has important clinical and physiological implicationsbecause during diastole heart muscle rests, coronary blood flow to
subendocardial portion of LV occurs and most of ventricle filling
occurs.
At heart rates up to 180, filling is adequate as long as there is ample
venous return and CO per minute is increased by an increase inrate.
At very high HR, filling may be compromised to such a degree that
CO per minute falls.
-
8/12/2019 Cardiac Cycle by Bala Goyal
14/14
TH NKS