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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.
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Pressure and Volume Changes During the Cardiac Cycle
• Atrial Systole• Ventricular Systole• Relaxation Period
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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.
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Ventricular Systole
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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?
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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.
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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.
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Goals :• Define Cardiac Output• Describe the factors that affect
regulation of stroke volume• Outline the factors that affect the
regulation of heart rate.
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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
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Factors Affecting Cardiac Output• Regulation of Stroke Volume• Regulation of Heart Rate
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Regulation of Stroke Volume1. Preload2. Contractility3. After Load
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PreloadPreload is proportional to the amount of ventricular
myocardial fiber stretch (chamber blood volume) just before systole.
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Contractility
The contractile strength achieved at a given muscle length. Notice that contractility is independent of
muscle stretch and EDV.
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After load
Afterload is the pressure that the ventricles must overcome to force open the aortic and pulmonary
valves.
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Regulation of Heart Rate
1. Autonomic Regulation of Heart Rate2. Chemical Regulation of Heart Rate
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