Lab 3

Question 1

What is the normal range of mean blood pressures within the arterial system and central venous system?

Answer 1

arterial: 70mmHg - 100mmHg
venous: 2mmHg - 6mmHg

Question 2

How can we measure forearm blood flow?

Answer 2

with venous occlusion plethysmography

Question 3

The underlying principle of forearm venous occlusion plethysmography is:
when _______ drainage from the arm is briefly interrupted, arterial ________ is
unaltered and blood can enter the forearm but cannot ________. This results in a __________
increase in forearm volume over time, which is proportional to arterial blood _________,
until venous pressure rises towards the ________ pressure. Under resting conditions,
∼_______% of total forearm blood flow (FBF) is through skeletal muscle, with _________ blood flow accounting for most of the remainder. If blood is prevented from leaving the
forearm without interfering with the arterial _______, then the forearm will swell at
the rate of the _________

Answer 3

when venous drainage from the arm is briefly interrupted, arterial inflow is unaltered and blood can enter the forearm but cannot escape. This results in a linear increase in forearm volume over time, which is proportional to arterial blood inflow, until venous pressure rises towards the occluding pressure. Under resting conditions, ∼70% of total forearm blood flow (FBF) is through skeletal muscle, with skin blood flow accounting for most of the remainder. If blood is prevented from leaving the
forearm without interfering with the arterial inflow, then the forearm will swell at
the rate of the inflow

Question 4

Venous occlusion plethysmography is done how? Why is this value important?

Answer 4

By inflating a sphygmomanometer cuff on the upper arm to about 50mmHg. This is important because this is below arterial pressure and above venous pressure

Question 5

What are we measuring with this technique?

Answer 5

We are not measuring blood directly but we are measuring a change in pressure over time as blood flows into the forearm.

Question 6

The rate of change of pressure related to the rate of change of what?

Answer 6

The rate of change of the blood flow.

Question 7

What does a fast blood flow indicate about the pressure change?

Answer 7

fast blood flow means more blood is coming in, P changes, there is more swelling, the slope of the increase in P will be steeper

Question 8

What does a low blood flow indicate about the pressure change?

Answer 8

Low blood flow means that there is less blood coming in, pressure change, less swelling, the slop of the increase in pressure will be less steep

Question 9

Why should be not occlude the cuff for more than 5-8 seconds?

Answer 9

As this changes the venous pressure which can change the Starling’s pressure

Question 10

What is the point of this experiment?

Answer 10

We will measure blood flow (indirectly) using venous occlusion plethysmography. We will measure blood pressure using a sphygmomanometer (automatic blood pressure machine). With pressure and flow we can calculate the resistance. Once we know blood flow and the resistance under normal conditions, we can change the cold conditions in the arm/body to see what happens with:

• cold
• exercise
• ischemia

Question 11

Forearm blood flow is proportional to the rate of _______ rise in the cuff. To put it another way, the slope of _________ change over _________

Answer 11

pressure
volume (change in amplitude)
time

Question 12

How do we calculate the forearm blood flow?

Answer 12

The forearm blood flow is the slope so we calculate it by dividing the change in amplitude (volume) by a change in time

Question 13

What would happen to the forearm volume if the cuff were inflated above the venous pressure (but below the arterial pressure) for a prolonged period of time?

Answer 13

If we left it inflated for longer, the pressure in the veins will increase as the volume in them has increased. The increase in venous pressure feedback to the increase the pressure in the arteries. This means that the hydrostatic pressure is increased. This is bad as there is now more fluid than normal flowing out to the interstitial fluid.

Question 14

What arm do we put in the cold water?

Answer 14

We put the right arm (non occlusive arm)

Question 15

Describe the relative changes from baseline, if any, in forearm blood flow in the cold stress test (BF and MABP and resistance)

Answer 15

The forearm blood flow decreases. The MABP stayed about the same (maybe slightly increased) so the resistance in the vessels must have increased so they must have vasoconstricted

Question 15

Describe the relative changes from baseline, if any, in forearm blood flow in the cold stress test (BF and MABP and resistance)

Answer 15

The forearm blood flow decreases. The MABP stayed about the same (maybe slightly increased) so the resistance in the vessels must have increased so they must have vasoconstrictor

Question 16

How is it possible that the placement of the right hand in cold water would change blood flow in the opposite arm?

Answer 16

Exposed to cold, the sympathetic nervous system releases NE which binds to α1 adrenergic receptors to cause vasoconstriction. We also get release of adrenaline which binds to the same receptors to cause vasoconstriction. This happens everywhere so even though the cold happened on the right arm, we can see the effect on the left arm

Question 16

How is it possible that the placement of the right hand in cold water would change blood flow in the opposite arm?

Answer 16

Exposed to cold, the sympathetic nervous system releases NE which binds to α1 adrenergic receptors to cause vasoconstriction. We also get release of adrenaline which binds to the same receptors to cause vasoconstriction. This happens everywhere so even though the cold happened on the right arm, we can see the effect on the left arm

Question 17

How fast the arm swells (detected by the second cuff) depends on what?

Answer 17

how fast blood is flowing into the arm

Question 18

Describe the relative changed to baseline, if any, in forearm blood flow in response to the exercise? (MABP, BF, resistance)

Answer 18

There will be more blood flow but MABP stays about the same (maybe slightly increased) which means that resistance must have decreased and therefore vasodilation must have occurred

Question 19

Discuss potential physiological mechanisms underpinning the change in flow in response to exercise

Answer 19

We are using more O2 and producing more CO2 which means that there is increased metabolic activity of the organ. Via the process of active hyperaemia, there is dilation of the organ and increased blood flow to support the organ’s needs.
Sympathetic nerve also release NE which can bind to the β2 adrenergic receptors in the skeletal muscle and this causes vasodilation

Question 20

What is ischemia?

Answer 20

This is when there is insufficient blood flow to the organ

Question 21

When we were measuring the forearm blood flow in response to ischemia, what did we pump the cuff up to? Why is this?

Answer 21

170 mmHg

this was to stop the blood flow in or out of the arm

Question 22

Describe the relative changes from baseline, if any, in forearm blood flow in response to the ischemia.

Answer 22

There was increased blood flow in the forearm, MABP remains about the same so the resistance decreases so vasodilation must have occurred.

Question 23

Discuss potential physiological mechanisms underpinning the change in flow in response to ischemia

Answer 23

Flow auto regulation due to the change in blood pressure in the organ. There was a decrease in blood pressure so there was a drop in blood flow. But the tissues are still using O2 and producing metabolites, and there is less stretch on the vessel walls. There is dilation of the arteriole supplying that organ so that there is restoration. Once we get dilation, there is a decrease in resistance which increases the flow and everything gets back to normal

Question 24

Discuss the physiological reasons as to why this person has become so severely dehydrated.

Answer 24

This person is cold so peripheral vasoconstriction has occurred to preserve heat which brings the volume into the core. The organs and pressure/volume detecting systems are fooled to thinking there is more blood volume so there is ANP released so you get increased fluid excretion by the kidneys and less ADH Is released so there is lower thirst sensation and lower fluid intake.

Question 25

Discuss other ways in which water loss is enhanced by the cold

Answer 25

You will be wearing more clothes and you are working harder to move so you produce more sweat. Exercise increases water loss due to increased ventilation