Cardiac Cycle and Cardiac Output Flashcards
Stimulated by nerves and is self excitable
Heart Muscle
Self-excitable
Automaticity
How long is the Cardiac Cycle on Average
0.8 seconds (assuming 75 bpm)
Contraction of the heart muscle, blood is pumped into arteries, short period of time, approx. 0.1 seconds
Systole
Relaxation of the heart muscle, heart is filling with blood, longest period of time, approx. 0.7 seconds
Diastole
Explain Cardiac Cycle
- Atrial Systole
- Isovolumetric ventricular contraction
- Ejection
- Isovolumetric ventricular relaxation
- Passive ventricular filling
AV valves are open, semilunar valves closed
Atrial Systole
- Atria relaxes
- Ventricular pressure rises resulting in closing AV valves
Ventricular Systole
Ventricles are completely closed, pressure in the ventricles increases until the pressure is more than in the aorta/pulmonary trunks
Isovolumetric Ventricular Contraction Phase
Opens semilunar valves
Ventricular Ejection Phase
- Ventricles relax, ventricular pressure drops
- Back flow of blood in aorta and pulmonary trunk closes semilunar valves, dicrotic notch
Isovolumetric Ventricular Relaxation- Early Diastole
Brief rise in aortic pressure caused by back flow of blood rebounding off semilunar valves
Dicrotic Notch
Cardiac Cycle Pressure of Right Atrium
0-4 mmHg
Cardiac Cycle Pressure of Right Ventricle
25 systolic mmHg
Cardiac Cycle Pressure of Pulmonary Arteries
25 systolic mmHg
Cardiac Cycle Pressure of Left Atrium
8-10 mmHg
Cardiac Cycle Pressure of Left Ventricle
120 systolic mmHg
Cardiac Cycle Pressure of Aorta
120 systolic mmHg
The amount of blood pumped by each ventricular in one minute, best indicator of adequate blood flow to the peripheral tissues
Cardiac Output
Cardiac Output Equation
Stroke volume X Heart Rate
The percentage of blood pumped out of a ventricle with each contraction (average = 50%-65%)
Ejection Fraction
The volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction
Stroke Volume
Stroke Volume Equation
End diastolic volume (EDV) minus end systolic volume (ESV)
Amount of blood collected in a ventricle during diastole
End Diastolic Volume (EDV)
Amount of blood remaining in a ventricle after contraction
End Systolic Volume (ESV)
Factors Affecting Stroke Volume
- Venous return
- Preload
- Afterload
- Contractility
Amount of venous blood returned to the heart
Venous Return
Amount ventricles are stretched by contained blood
Preload
Cardiac cell contractile force due to factors other than EDV
Contractility
Back pressure exerted by blood in the large arteries leaving the heart
Afterload
What increases Stroke Volume?
Slow heartbeat and exercise increases venous return, increasing SV
What decreases Stroke Volume?
Blood loss and extremely rapid heart beat
Frank Sterling Law
- “More blood in = more blood out”
- The greater the volume of blood in the ventricle, the stronger the contraction
- Both an increased filling time and increased blood volume = increased stroke volume
Increase in Contractility come from:
- Increased sympathetic stimuli
- Certain hormones
- Ca2+ and some drugs
Agents/factors that Decrease Contracility:
- Acidosis
- Increased extracellular K+
- Beta blockers and calcium channel blockers (cardiac drugs)
Signs and Symptoms of Decreased Cardiac Output
- Acute changes in BP
- Acute changes in mental status
- Cold, clammy skin
- Colour changes in the skin and mucous membranes
- Crackles (rales)
- Dyspnea
- Dysrhythmias
- Orthopnea
- Restlessness
