L10 . Physics blood pressure

Question 1

What is Mean systemic Arterial Pressure and how do you calculate it

Answer 1

The force exerted by the blood against any unit area of vessel wall usually in the great arteries.
MAP: Diastolic pressure + 1/3 (difference between systolic and diastolic pressure)

Question 2

What is Pulse pressure

Answer 2

The difference between the systolic (max) and diastolic (min) pressure.

Question 3

What are the determinants of MAP

Answer 3

MAP = Cardiac out put X Total peripheral resistance.

Question 4

What are the determinants of pulse pressure

Answer 4

Systolic pressure: 
1. Aortic compliance: 
2. Stroke volume (ejection rate)
Diastolic pressure; 
1. AC and Diastolic run off : 
HR and TPR

Question 5

What is aortic compliance and its effect on BP

Answer 5

Compliance reflects elasticity of the vessel. Given by change in Volume/ change in Pressure.

• High compliance= stretchy, store more elastic energy/volume with little change in pressure
• Low compliance= stiff, high pressure increase compared to volume increase, has to work harder to push out blood because can’t store it.
  This also means that in diastole there isn’t a lot of blood left to push out, so the diastolic pressure is lower than normal.

Question 6

What is Stroke volume and its effect on systolic pressure

Answer 6

• How much being pumped out: so: increasing the stroke volume delivered to the aorta increases the arterial pulse pressure
• SV affected by: preload, afterload, chronotropy and inotropy -> can increase with exercise.

Question 7

What is diastolic run off and its effect on systolic pressure

Answer 7

The ability of the blood to flow forward

• This can be hindered by having a lot of TPR. This will make flow slow so pressure will remain high.
• Having high heart rate means that there is less time for the blood to run out during diastole so diastolic pressure can stay higher
• Basically if blood can leave early it will reduce the diastolic pressure

Question 8

what factors alter CO

Answer 8

HR, inotropic state, neural, humoral

Renal fluid volume control

Question 9

what factors alter TPR

Answer 9

sympathetic vasoconstriction, vasodilation

Question 10

How does gravity affect blood pressure

Answer 10

The pressure measured is also dependent on gravity. This is hydrostatic pressure and has to be overcome. Therefore
Total pressure = hydrostatic pressure + vascular pressure generated by the heart.

Question 11

What mechanisms are involved in regulating Blood pressure within seconds

Answer 11

Nervous mechanisms (baroreceptor feedback mechanisms, central nervous system ischemic mechanism, chemoreceptor mechanism) combine to powerfully cause

• constriction of the veins and transfer of blood into the heart,
• increased heart rate and contractility of the heart,
• constriction of most peripheral arterioles to impede flow out of the arteries

Question 12

What mechanisms are involved in regulating Blood pressure within minutes

Answer 12

• The renin-angiotensin vasoconstrictor mechanism (changes in angiotensin II levels in response to changes in perfusion of the kidney),
• stress-relaxation of the vasculature
• shift of fluid through the capillary walls into the circulation to readjust the blood volume.

Question 13

What mechanisms are involved in regulating Blood pressure long term: Hours/days

Answer 13

The kidneys play a vital role in returning the blood pressure all the way to normal by restoring the salt and water levels. The interaction with the renin-angiotensin-aldosterone system and kidney function is especially important to ensure blood pressure regulation is not salt intake dependent.