Cardiac Output Flashcards
How do you calculate cardiac output?
Stroke volume x heart rate
Describe the intrinsic method for increasing stroke volume
Frank-Starling mechanism - Increased preload means a greater end diastolic volume which increases the force of contraction meaning more blood is pumped out.
What is preload?
The venous pressure and venous return to the heart, can increase or decrease.
What is afterload?
The aortic/pulmonary pressure, this doesn’t really vary, needs to stay constant.
Describe the extrinsic mechanism of increasing stroke volume
Sympathetic stimulated contraction. Overall volume in ventricles stays the same but force of contraction is increased.
What occurs if you overfill the heart?
You stretch the actin and myosin too far that you can’t generate enough force to cause a contraction - important to remember for pathology
Other than an increase in stroke volume, what else does Frank-Starling’s law allow for?
Automatic adjustment for the small imbalances between the left and right ventricles.
Can you have both intrinsic and extrinsic control of stroke volume?
Yes, you can either have them working alone or together. Obviously when you have them working together then you generate greater tension.
Summerise the ways in which you can control cardiac output
- Increase EDV to increase SV.
- Increase sympathetic nerve activity to increase SV and HR.
- Decrease activity of parasympathetic NS to increase HR.
Describe the pressure in the systemic and pulmonary vessels
High, oscillating pressure that decreases between LV and arterioles. When reaches capilaries it is of a low pressure and doesn’t oscillate till it reaches the right atrium. Then lower pressure in pulmonary vessels that again is similar when reaches capillaries.
Describe the control of the continuous blood flow through the aorta in systole and diastole
Systole - The systemic vascular resistance limits how fast blood can escape, this prevents blood going through the whole body at once.
Diastole - Energy stored in arterial walls during systole drives blood forward during diastole.
What is meant by vascular compliance?
Non compliance means the tubes are rigid and resist expansion. Compliance means tubes are elastic and they swell when internal pressure rises.
How do you calculate mean arterial pressure (MABP)
Diastolic pressure + 1/3 pulse pressure
How do you calculate pulse pressure?
Systolic pressure - diastolic pressure
What factors determine the magnitude of pulse pressure
Stroke volume, speed of ejection of stroke volume and arterial compliance (decreases with age due to atherosclerosis)
