Module 5 Section 5 Flashcards
Explain how CO is calculated.
Cardiac output (CO) = heart rate (HR) x stroke volume (SV)
Describe the Frank-Starling law of the heart.
Is the relationship b/a EDV and SV such that increasing EDV increases SV, the greater the diastolic filling, the greater the systolic emptying. This law of the heart allows for beat to beat regulation of stroke volume.
Explain why end diastolic volume is so important for the regulation of cardiac contractility.
As more blood returns to the heart, more blood is pumped out.
The volume of blood in the ventricles cause the chamber to distend and this puts a stretch on the cardiac muscle fibres. This stretch changes the length tension relationship of the cardiac muscle fibres.
As cardiac muscle is stretched (b/c there’s more blood in the ventricle), muscle fibre length increase and a greater contraction can occur.
Preload (venous return)
- it’s the amount of blood returning to the ventricle.
- it’s increased by increasing venous return and thus EDV and SV. It stretches the RV and LV to its greatest dimensions.
Afterload
- it’s the force that the ventricle is pushing against.
- if increased pressure on the aorta and the LV is contracting against itself -> net result = aortic valve shuts early and the SV is decreased.
- if normal blood volume returns to the heart during diastole, the EDV is increased and so will be the force of the next contraction.
Explain how CO is regulated.
Factors affect cardiac output by changing heart rate and stroke volume. Primary factors include blood volume reflexes, autonomic innervation, and hormones. Secondary factors include extracellular fluid ion concentration, body temperature, emotions, sex, and age.
What would happen if the RV was to pump an increased V of blood into the pulmonary circulation? Would there be an increase or decrease in EDV in the LV? What about SV?
An increase of blood volume from the RV would return to the LA to be pumped to the LV and increase end diastolic volume and stoke volume.
What are some ways in which sympathetic stimulation stimulates the heart?
- increases the force of contraction
- increase SV
- shift the Frank starling curve upwards
- increase AV node excitability
- increase contractility of cardiac muscles
For each cardiac activity, indicate if CO would increase or decrease
1) increased parasympathetic activity
2) increased HR
3) increased sympathetic activity
4) decreased SV
5) decreased end-diastolic volume
1) increased parasympathetic activity = decrease
2) increased HR = increase
3) increased sympathetic activity = increase
4) decreased SV = decrease
5) decreased end-diastolic volume = decrease
