Control Of Cardiac Output Flashcards
What is preload?
The amount the ventricles are stretched via filling in diastole- related to the end diastolic volume/ central venous pressure.
What is afterload?
The pressure the heart must eject against, roughly equivalent to aortic pressure
Describe total peripheral resistance
Resistance to blood flow offered by all of the systemic vasculature
What happens to the capillaries and venous side if arterioles constrict/ increase BP?
The capillaries and venous side has a lower blood pressure (as they are located away from the arterioles. The vessels before the arterioles such as arteries will have increased pressure.
In what order to we find blood vessels in the body?
Arteries —> arterioles —> capillaries —> venues —> veins
Impact of decreasing TPR and maintaining the same CO
Total peripheral resistance falls. Arterial pressure falls. Venous pressure increases (but is still lower than arterial).
Impact of increasing TPR and maintaining CO?
Arterial pressure increases, venous pressure falls (blood finding it harder to get through arteries).
Effect of increasing CO and maintaining TPR?
Arterial pressure increases as more blood pumped here, venous decreases as more blood is pumped out of venous circulation to arteries.
Effect of decreasing CO and maintaining TPR?
Reduces arterial pressure (not as much pumped), increases venous pressure as less blood is being pumped into the heart.
What happens at a local level if tissues need more blood?
Arterioles and pre-capillary sphincters dilate to allow more blood flow.
Equation for cardiac output?
Stroke volume x heart rate
Equation for stroke volume?
End diastolic volume EDV- end systolic volume ESV
What’s the cardiac output at rest for a 70kg man?
5L blood per minute
If there is a higher venous pressure what impact does this have on the heart?
The more the heart fills
High level of heart filling does what to the left ventricular pressure?
Increases
Decreased/ increased compliance of the heart has what impact on left ventricular pressure?
If you have a compliant heart this decreases left ventricular pressure. If you have decreased compliance you have a higher pressure in the left ventricle.
Briefly describe the Frank- Starling law of the heart
The greater the heart fills the more it will contract up to a certain point (increased preload). The harder the heart contracts the greater the stroke volume. An increase in venous pressure will fill the heart more.
As the cardiac muscle fibres are stretched the sensitivity for calcium….?
Increases
The pulmonary and systemic circulations must operate in series, what does this mean?
The same volume of blood pumped to the body must also be pumped to the lungs
Extrinsic factor that increases contractility and force of contraction?
Circulating adrenaline and sympathetic circulation
Increased peripheral resistance has what impact on aortic pressure?
Increase
What factors determine cardiac output?
- How hard the heart contracts (determined by end diastolic volume- how much the heart fills) and contractility (increased by sympathetic NS)
- How hard it is to eject blood (determined by aortic impedance - roughly equivalent to arterial pressure)
What happens to total peripheral resistance and the heart if metabolism increases?
Reduced total peripheral resistance as more blood is needed at the tissues, decrease in arterial BP, increase in venous blood pressure, heart responds by pumping more.
What happens to venous, arterial and CO output when standing?
Blood pools in the legs due to gravity and venous pressure is reduced - harder for blood to return to the heart, this reduces CO and arterial pressure. Reflex: baroreceptor reflex and sympathetic nervous system detects and increases contractility and heart rate which increases TPR.
