Cardiac Output Flashcards
What occurs when the left (and right) ventricle is relaxed? What is this period called?
When relaxed, the left (and right) ventricle is filling with blood - this period is called diastole
What do the atria mainly act as?
Reservoirs - store blood for entry into the ventricles and subsequent blood pumping
Which circulation does the left side of the heart supply blood? Which circulation does the right side supply?
The left side of the heart supplies blood to systemic circulation - the right side of the heart supplies blood to the pulmonary circulation (the lungs)
Define the term systole.
Systole relates to the contraction of the ventricles, where blood is forced from the heart due to increases in intraventricular pressure, entering pulmonary (the lungs) and systemic circulation (the aorta)
What is myocardium?
The muscular tissue responsible for the contraction responsible for the contraction of the heart
What is regarded as the pacemaker of the heart? Where is it located?
The sinoatrial node - this is located in the right atrium
What causes the atria to contract?
Direct innervation from the sinoatrial node
What structure is responsible for delaying the electrical stimulus leading to ventricular contraction? Why does this delay occur?
The atrio-ventricular node - this ensures the ventricle pumps inferiorly from the apex of the heart upwards
Define afterload.
The load that the heart must eject against
What is after load roughly equivalent to?
Aortic pressure
Define preload.
The load that causes the ventricles to stretch of fill in diastole
Mathematically, define stroke volume.
End diastolic volume - end systolic volume = stroke volume
What will vasoconstriction of an arteriole do the the blood pressure either side of the constriction?
The BP preceding the constriction will increase, while the BP proceeding the constriction will decrease
What does the FRnk-Starling Law of the heart suggest?
The more the fibres of the heart are stretched (upon filling) the greater the contraction of the heart
How does total peripheral resistance influence cardiac output?
The greater the TPR the lower the venous pressure and the lower CO
The lower the TPR the greater the venous return and the greater the CO
How does venous pressure influence cardiac output?
The greater the venous pressure the greater the preload, and the greater the stroke volume - therefore CO is increased
The lower the venous pressure the lower the preload, and the lower the stroke volume - therefore CO is decreased
Define contractility.
The force of contraction for a given fibre length
What is aortic impedance?
The pressure that the heart has to pump against (the afterload)
Describe how standing up influences cardiac output.
Standing up means blood pools in the legs due to gravity - there is reduced venous return, leading to decreased cardiac output, and decreased total peripheral resistance - this is called postural hypotension
What mechanism is used to counter-act postural hypotension?
The baroreceptor reflex
What does the Frank-Starling Law of the heart suggest about contractility?
The greater the contractility, the greater the force of contraction
How does cardiac output influence the venous pressure?
The greater the CO, the lower the venous pressure
The lower the CO, the greater the venous pressure
State the 2 factors that determine how much blood the heart pumps in systole?
- how hard the heart contracts - contractility, related to the filling (preload)
- how hard it is to eject blood - the arterial pressure, related to total peripheral resistance (afterload)
Describe how exercise affects cardiac output.
An increase in exercise will reduce the total peripheral resistance to supply blood to tissue, increasing the amount of Venus return - this I’ll ac to increase preload and increase stroke volume, leading to an increased CO
Define diastole.
The filling of the heart, where the ventricles are relaxed
