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CARDIAC CYCLE BY DR. MUDASSAR ALI ROOMI (MBBS, M. PHIL)
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Transcript of cardiac-cycle-by-dr-roomi
CARDIAC CYCLEBY
DR. MUDASSAR ALI ROOMI (MBBS, M. PHIL)
DEFINITION OF CARDIAC CYCLE:
Period between start of one beat to start of next.
It consists of one complete heart beat.
It consists of one systole & one diastole.
INITIATION OF CARDIAC CYCLE:
Initiated by Cardiac Impulse, which originates from SA node.
EVENTS THAT OCCUR IN THE
CARDIAC CHAMBERS DURING CARDIAC CYCLE
Pressure Changes. In ventricles In atria
Volume Changes. Production of Heart
Sounds. Closure & Opening
of Cardiac Valves. Electric Changes
(ECG recording).
VENTRICULAR SYSTOLE 0.31 sec(Peak of R wave of QRS complex to the end of T wave)
ISO-VOLUMETRIC CONTRACTION 0.06 sec
MAXIMUM EJECTION (2/3) 0.11 sec
REDUCED EJECTION (1/3) 0.14 sec
VENTRICULAR DIASTOLE 0.52 sec(End of T wave to the peak of R wave of QRS complex)
PROTODIASTOLE 0.04 sec
ISO-VOLUMETRIC RELAXATION 0.06 sec
RAPID INFLOW 0.11 sec
SLOW INFLOW / DIASTASIS 0.2 sec
ATRIAL SYSTOLE (after P wave) 0.11 sec
8 Phases of CARDIAC CYCLE 0.8 sec
8 Phases of CARDIAC CYCLE
PRESSURE CHANGES:
A) Pressure changes in left ventricle during cardiac cycle.
B) Pressure changes in right ventricle during cardiac cycle.
C) Pressure changes in atria.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle:‘Phase 1’ of cardiac
cycle / Iso-volumetric contraction of ventricle:
At the start of ventricular systole L.V is full of blood which is equal to EDV.
All the valves are closed. No change in blood volume.
Pressure in L.V at the start = 1-3 mm Hg.
Then pressure increases to just below 80 mmHg.
Duration of I.V.C of Ventricle = 0.06 sec.
Pressure changes in Left Ventricle (L.V) during cardiac cycle:
‘Phase 2’ of cardiac cycle / Maximal Ejection Phase (M.E.P) / Rapid Ejection Phase (R.E.P):
Ventricle muscle is contracting powerfully with opening of Aortic valve.
Blood is ejected from ventricle (2/3 of stroke volume) Aorta (at maximum rate). 70% EMPTYING occurs in first 1/3 of ejection phase.
In this phase: I.V.P maximum = 120 mm Hg.
Duration of M.E.P = 0.11 sec.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle:‘Phase 3’ of cardiac cycle /
Reduced Ejection Phase (R.E.P):
Blood ejection (remaining 1/3 of stroke volume, 30% EMPTYING occurs in last 2/3 time of ejection phase) from L.V Aorta, continues but at a reduced rate.
I.V.P falls from maximum.
This phase ends when I.V.P becomes equal to OR
slightly less than AORTIC PRESSURE.
Duration of R.E.P = 0.14 sec.
Duration of ventricular systole (3 phases):
1. Isovolumetric contraction = 0.06 sec
2. Maximum Ejection Phase = 0.11 sec
3. Reduced Ejection Phase = 0.14 sec
So, Ventricular Systole = 0.31 sec
Pressure changes in Left Ventricle (L.V) during cardiac
cycle: ‘Phase 4’ of cardiac cycle /
Protodiastole:
duration = 0.04 sec.
At the junction of systole & diastole, but included in diastole.
At this stage, I.V.P = Aortic Pressure or
I.V.P is slightly less than Aortic pressure, BUT SMALL AMOUNT OF BLOOD CONTINUES TO OOZE, because of momentum.
In protodiastole: THIS MOMENTUM IS OVERCOME due to further fall in I.V.P & there is some retrograde flow of Aortic blood in 1st part of Aorta closure of Aortic valve end of Protodiastole.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle: ‘Phase 5’ of cardiac
cycle / Isovolumetric Relaxation Phase (I.V.R):
Starts with closure of Aortic valve.
All the valves are closed.
Opening of left AV valve / mitral valve end of I.V.R phase.
Duration of I.V.R = 0.06 sec.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle
‘Phase 6’ of cardiac cycle / Rapid Inflow Phase (R.I.P) / Rapid filling phase (R.F.P):
Starts with opening of mitral valve.
Blood from Left Atrium rapidly flows into Left Ventricle.
2/3 of ventricular filling occurs in this phase (during first 1/3 of ejection phase)
Duration of R.I.P = 0.11 sec.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle:
‘Phase 7’ of cardiac cycle / Slow Inflow Phase / Diastasis:
It appears that: No blood is flowing from Lt. Atrium Lt. Ventricle because:
Only slight filling of Lt. Ventricle in this phase.
Duration of diastasis / Slow Inflow Phase = 0.20 sec.
THE LONGEST PHASE OF CARDIAC CYCLE.
Pressure changes in Left Ventricle (L.V) during cardiac
cycle: ‘Phase 8’ of cardiac cycle /
Atrial Systole:
Last phase of cardiac cycle
Lt. Atrium contracts 20% ventricular filling by atrial contraction.
Atria contract towards the end of ventricular diastole.
With atrial contraction, ventricular filling is complete.
Duration: 0.11 sec.
.
Duration of ventricular diastole (5 phases):
Protodiastole = 0.04 sec
Isovolumetric Relaxation = 0.06 sec
Rapid Inflow Phase = 0.11 sec
Slow Inflow Phase = 0.20 sec
Atrial Systole = 0.11 sec
Ventricular Diastole = 0.52 sec
Duration of Cardiac Cycle (8 phases):
= Duration of systole + diastole = (0.31) + (0.52) = [0.8
sec]
Pressure Changes in Right Ventricle:
Same phases as for Lt. ventricle.
Same duration as for Lt. ventricle.
Only change in pressure levels & in names of valves.
Aortic valve is replaced by pulmonary valve.
Mitral valve is replaced by Tricuspid valve.
Pressure Changes in Right Ventricle:
At the beginning of Rt. Vent. Systole: Pressure = 0-1 mm Hg.
During I.V.C just exceeds 8 mmHg opening of pulmonary valve
Maximum increase in pressure in Rt. Vent systole = 25 mmHg
Duration of cardiac cycle & heart rate:
Duration of cardiac cycle = 0.8 sec at heart rate = 70 beats / min.
When heart rate increases duration of cardiac cycle decreases.
Diastole is more affected as compared to systole with rapid heart rate.
At heart rate = 180 / min, cardiac cycle duration = 0.33 sec: (systole = 0.18 sec, diastole = 0.15 sec).
Cardiac output:
Output of heart per unit time = 5 L / min at rest.
Cardiac output = stroke volume x heart rate = 70 ml x 72 beats / min nearly equal to 5 L / min
Stroke volume (S.V): Difference between End Diastolic Volume
(EDV) & End Systolic Volume (ESV). S.V = EDV - ESV S.V = 120 – 50 S.V = 70 ml
EJECTION FRACTION:
Fraction of EDV that is ejected in one systole or one stroke = Ejection Fraction.
Value of Ejection Fraction = 60-65% (usually).
heart failure Ejection Fraction decreases.
Volume changes in Ventricles during Cardiac Cycle:
Beginning of ventricular systole: 130 ml (EDV)
Ejection Phases: Maximum Ejection Phase:
2/3 of Stroke Volume (total = 70 ml) is ejected out.
Reduced Ejection Phase: Remaining 1/3 is ejected out.
Iso-volumic Relaxation Phase: 50 ml = (ESV)
Rapid Inflow Phase: 2/3 of ventricular filling.
Diastasis / Slow Inflow Phase: Only slight filling occurs.
Atrial Systole: last 1/3 filling (30%).
Pressure changes in Atria during the Cardiac Cycle:
Atrial systole duration = 0.11 sec
Atrial diastole duration = 0.70 sec
Atrial systole + Atrial diastole = 0.8 sec = cardiac cycle.
Atrial diastole > Atrial systole, because basic function of atria is to receive blood from large veins & it can receive blood only when it is relaxed.
Right atrial pressure = Central Venous Pressure (CVP).
During most of cardiac cycle, this pressure remains almost zero.
During wave a, c & v pressure rises. Otherwise remains almost zero.
4-6 mm Hg Rt. Atrium (during a, c, v) 7-8 mm Hg Lt. Atrium (during a, c, v)
Pressure changes in Atria during the Cardiac Cycle:
3 waves can be recorded from atria which represent atrial pressure changes:
a-wave, c-wave & v-wave (Seen as Jugular Venous Pulse, not a true pulse, but a reflection of pressure changes in right atrium.
Two descents: x and y descent.
PRESSURE CHANGES IN ATRIA DURING THE CARDIAC CYCLE:
a-wave: Due to increase in atrial pressure during atrial systole.
PRESSURE CHANGES IN ATRIA DURING THE CARDIAC CYCLE:
c-wave: Recorded at beginning of contraction of ventricle. During isovolumetric contraction, ventricular pressure increases Cusps of AV valves are pushed into atrial cavity pressure rises in atria ascent of c-wave.
PRESSURE CHANGES IN ATRIA DURING THE CARDIAC CYCLE:
The top of c-wave coincides with opening of semi-lunar valves (Aortic & Pulmonary).
With opening of semi-lunar valves, ejection phase starts. AV valve is pulled to ventricular cavity pressure falls in the atria x-descent
PRESSURE CHANGES IN ATRIA DURING THE CARDIAC CYCLE:
v-wave: Due to gradual increase in atrial pressure, resulting from venous filling of blood (from the venae cavae) into the atria, with closed AV valves ascent of v-wave.
Top of v-wave coincides with opening of AV valves rapid inflow phase decrease pressure in atria y-descent
JUGULAR VENOUS PULSE:(a, c, v waves)
Normally arteriolar pulse ends in arterioles & in veins no pulsation.
But we can record pulsation in jugular vein, which is not a true pulse.
It is just backward transmission of pressure changes in Rt. Atrium (a, c. v waves) transmitted in neck veins.
Significance of J.V.P:
ac interval coincides with PR interval of ECG.
ac interval increases in delayed AV conduction (AV nodal blocks).
Significance of J.V.P:
a waves are absent in: ATRIAL FIBRILLATION.
Cannon a WAVES: (a wave) > (c wave) in COMPLETE AV BLOCK (3rd degree AV block).
‘Giant a waves’ in TRICUSPID & PULMONARY STENOSIS.
Pulsating Neck Veins in CCF (Congestive Cardiac Failure).
Closure & Opening of Heart Valves:
AV VALVES: Are closed at the beginning
of Isovolumic contraction Phase.
Are open at the beginning of Rapid Inflow phase.
AV valve closure is slow & soft & does not require backward flow of blood.
Cusps of AV valves are soft & thin because they are not subjected to increase in pressure & rapid blood flow.
Closure & Opening of Heart Valves:
SEMILUNAR VALVES: Are closed at the
beginning of Isovolumic relaxation phase.
Cusps of these valves are thick & heavier (as they are subjected to increased pressure & rapid blood flow).
Their closure is rapid & requires backward flow of blood (incisura in case of Aortic valve).
Closure & Opening of both AV & Semilunar Heart Valves:
Forward pressure gradient opening.
Backward pressure gradient closure.
AV valves prevent, leakage of blood from ventricle atria, during ventricular systole (when pressure rises in ventricle).
Semilunar valves prevent leakage of blood from large arteries ventricles, during ventricular diastole (when pressure falls in ventricle)
