Lecture 9 - Cardiovascular System 2 Flashcards
Blood flow
What are hemodynamics
A collection of mechanisms that influence the dynamic circulation of blood
- diff rates/min in diff areas
- greater activity requires greater blood flow
What are the 2 control mechanisms of hemodynamics
- Maintenance of circulation
2. Vary volume and distribution of blood
What causes fluids to flow in circulation
Pressure gradients from high to low
How does heart circulate blood
By changing pressure
What is a local pressure gradient known as
Perfusion pressure
Characteristics of arterial BP
- needs high pressure to keep blood flowing
- arterial BP is directly proportional to arterial blood volume
What are 2 important factors in arterial BP
- Cardiac output
2. Peripheral resistance
What does cardiac output influence
Amount of blood entering arteries
What does peripheral resistance influence
Amount of blood leaving arteries
Cardiac output formula
CO = SV x HR
CO= amount of blood that flows out of a ventrical/min Sv = volume/ beat Hr = beat/min
What is impacted by changes in SV or HR
CO, BP and arterial blood volume in the same direction
What is cardiac reserve
Amount that CO can increase above normal expressed as %
What is the typical resting cardiac output
5000 ml/min or 5L/min
What is inotropic factors
Factors caused by changes in myocardial contraction
Mechanical, chemical or neural (like length of myocardiac fibers at start of contraction)
What is Starlings law
Longer fibers make strong contractions up to a point (350 mL)
What is End Distal Volume (EDV)
More blood returned, more stretched fibers, stronger contractions
-too much blood will result in lowered elasticity
What does Norepinephrine do
Increases contractility of the heart
Where does Norepinephrine come from
Sympathetic nerve fibers or adrenal glands
What is ejection fraction
Ratio of SV to EDV
(SV/EDV x 100%),-55%
What is afterload
Work necessary to pump blood into arteries
What is mean pressure
Usually about (2 x diastolic + systolic) ÷3
What is result in increase of CO or PR
Increase in blood volume and thus increase in arterial BP
What typically controls chronotropic factors
Sinoatrial node
What affects stroke volume
Inotropic factors
Ejection fraction
Afterload