Mechanical Event&

Cardiac Output

Program Studi KeperawatanFAKULTAS KEDOKTERAN

UNIVERSITAS TANJUNGPURA PONTIANAK

Ariyani Pradana Dewi, S. Kep, Ners.

SUB TITLE . . .• Mechanical Events : Cardiac Cycle• Cardiac Output

Goals :• Describe the pressure and volume changes that

occur during a cardiac cycle.• Relate the timing of heart sounds to the ECG

waves and pressure changes during systole and diastole.

3

4

Pressure and Volume Changes During the Cardiac Cycle

• Atrial Systole• Ventricular Systole• Relaxation Period

5

Atrial Systole

Which lasts about 0,1 sec, the atria are contracting.

1. Depolarization of SA Node causes atrial depolarization.

2. Atrial depolarization causes atrial systole3. Atrial systole contributes a final 25 mL of blood

to the volume already in each ventricle (about 105 mL). Each ventricle contains about 130 mL at the end of its relaxation End-Diastolic Volume (EDV)

4. The complex in the ECG marks the onset of ventricular depolirazation.

6

7

Ventricular Systole

8

Which lasts about 0,3 sec the ventricles are contracting.

5. Ventricular depolarization causes ventricular systole. For about 0,05 sec both of SL & AV are closed isovolumetric contraction.

6. When LV pressure surpasses aortic pressure at about 80 mmHg & RV pressure rises above the pressure in pulmonary trunk (about 20mmHg), both SL valves open ventricular ejection, lasts for about 0,25 sec. The Pressure?

9

7. The volume remaining in each ventricle at the end systole, about 60 mL End-Systolic Volume (ESV). Stroke Volume??

8. Stroke Volume = volume ejected per beat9. The T wave in ECG marks on onset of

ventricular repolarization.

10

Relaxation Period

Which lasts about 0,4 sec the atria and ventricles are both relaxed.

10.Ventricular repolarization causes ventricular diastole. After SL valves close, there is a brief interval when ventricular blood does not change because all four valves are closed isovolumetric relaxation

11.When ventricular pressure drops below atrial pressure, the AV valves open and ventricular filling begins.

11

12

Goals :• Define Cardiac Output• Describe the factors that affect

regulation of stroke volume• Outline the factors that affect the

regulation of heart rate.

13

Cardiac Output• CO is the volume of blood ejected from the LV/RV

into the aorta/the pulmonary trunk each minute• CO is amount of the blood pumped out by each

ventricle in 1 minute. It is the product of Heart Rate (HR) and Stroke Volume (SV).

Formula :CO = HR x SV

14

Factors Affecting Cardiac Output• Regulation of Stroke Volume• Regulation of Heart Rate

15

Regulation of Stroke Volume1. Preload2. Contractility3. After Load

16

PreloadPreload is proportional to the amount of ventricular

myocardial fiber stretch (chamber blood volume) just before systole.

17

Contractility

The contractile strength achieved at a given muscle length. Notice that contractility is independent of

muscle stretch and EDV.

18

After load

Afterload is the pressure that the ventricles must overcome to force open the aortic and pulmonary

valves.

19

Regulation of Heart Rate

1. Autonomic Regulation of Heart Rate2. Chemical Regulation of Heart Rate

20

21

22

23