Arterial Blood Pressure & Flow

Question 1

What is responsible for the steady flow seen downstream in the capillaries opposed to a cyclical pulsating flow from the ventricle?

Answer 1

the resistance-compliance filter

Question 2

What is systolic pressure?

Answer 2

the highest arterial pressure reached during any given ventricular cycle

Question 3

What is diastolic pressure?

Answer 3

the lowest arterial blood pressure reached during any given ventricular cycle

Question 4

What is pulse pressure?

Answer 4

the variation in BP occurring in an artery during the cardiac cycle; the difference between systolic and diastolic PRESSURES

Question 5

At what level of the cardiac “tree” do we see the greatest drop in pressure?

Answer 5

arterioles

Question 6

What is the driving pressure throughout the entire system?

Answer 6

remember flow = difference in pressure / resistance. So the “delta p; change in pressure” throughout the entire CV system is about 90 mm Hg.

Question 7

Again, what is the mean arterial blood pressure (MAP or MABP)?
(know these equations for the test)

Answer 7

Pd + 1/3 Pp
That is the diastolic pressure plus one-third the pulse pressure. We multiply by one third because the systolic time isn’t equal in duration to the diastolic time, so this compensates for that difference.

Question 8

What are the 2 physical factors and 2 physiological factors that affect arterial BP?

Answer 8

Physical factors: arterial blood volume, arterial compliance
Physiological factors: CO (how much blood is entering the arterial system) and peripheral resistance.
* So just know that in order to increase BP, you either increase CO or increase peripheral resistance.

Question 9

What is arterial compliance?

Answer 9

compliance= change in volume/ change in pressure.

Aka the more compliant the more distensible it is.

Question 10

What is elasticity?

Answer 10

the reciprocal of compliance: 1/compliance
How easily it returns to its original shape.
So compliance is how easily it expands, and elasticity is how easily it springs back.

Question 11

So what happens to compliance at very high pressures?

Answer 11

it goes down (makes sense in terms of the equation bc pressure is in the denominator).

Question 12

What happens to compliance as we age?

Answer 12

it goes down (aka becomes more stiff), meaning it takes a greater pressure in order to fill them.

Question 13

What are the effects of compliance and elasticity by the aorta?

Answer 13

a steady stream of flow. This occurs because during systole, the compliance of the aorta allows it to expand, and during diastole, its elasticity allows it to contract, maintaining flow.

Question 14

What happens to flow during diastole in a very rigid aorta?

Answer 14

flow decreases drastically, due to less compliance and elasticity!

Question 15

What is the importance of resistance on flow?

Answer 15

allows for constant downstream flow. Otherwise, the pressures would be very intermittent.

Question 16

Why does the amplitude of pulse pressure drop as we go downstream in the arterial tree?

Answer 16

due to resistance (reduces flow) and compliance (dampens pressure)

Question 17

What does total peripheral resistance mean?

Answer 17

the resistance of the entire systemic circulation. So just go back to our flow equation (flow=difference in pressure/ resistance). If we solve for resistance, we have:
TPR= (MABP-MVP)/flow
TPR= 19 mm Hg/L/min
*MVP= mean venous pressure or central venous pressure

Question 18

Is TPR of the pulmonary vasculature greater or lower than TPR of the systemic vasculature?

Answer 18

LOWER. Remember CO to left and right side are equal, but pressure is lower in the pulmonary system (because you don’t want capillary pressure to be high or else you would lose fluid and increase distance between blood and air in the alveoli, and we want to keep fluid in the system, thereby decreasing the distance between blood and air for gas exchange, so pressures are lower by design), so resistance must also be lower.
Aside: if pulmonary pressure was high, this would lead to pulmonary edema, decreasing efficiency of gas exchange :(

Question 19

How else can we calculate MABP?

Answer 19

CO * TPR

Question 20

What determines the flow into the arterial system?

Answer 20

CO

Question 21

** Again what are the 2 ways to increase arterial BP?

Answer 21

1. increase the pump (CO)

2. increase the resistance (TPR)

Question 22

** What are the 2 components that affect pulse pressure?

Answer 22

1. SV

2. compliance

Question 23

What will you see with increases in SV?

Answer 23

increases in pulse pressure and increases in MABP. Because think pulse pressure is dependent on SV and compliance, and MABP is dependent on CO and TPR. Thus increases in SV cause increases in CO so both pulse pressure and MABP will rise.

Question 24

Will pulse pressure change with increases in TPR?

Answer 24

NO! Because both the systolic and diastolic pressure increase by the same amounts, and we know the definition of pulse pressure is (systolic - diastolic)

Question 25

What happens if we decrease the compliance (stiffen) of the arterial system?

Answer 25

MABP will stay the same (because this is only affected by CO and TPR), but the PULSE PRESSURE will INCREASE (because this is affected by compliance).

Question 26

What happens to pulse pressure and MABP if we increase resistance (TPR) and decrease compliance (make stiffer)?

Answer 26

both MABP and PULSE PRESSURE will INCREASE, because resistance affects MABP and compliance affects pulse pressure.