Lab 3 - Blood Flow Control Flashcards
What is a Venous occlusion plethysmography?
A Venous occlusion plethysmography is a standard method for measurement of limb blood flow.
When using a venous occlusion plethysmography where can and can’t blood flow and why?
Blood can enter the forearm (because occlusion cuff is below arterial pressure) but cannot leave the forearm (because occlusion cuff pressure is greater than venous pressure).
What causes an increase in pressure due to venous occlusion plethysmography?
The blood cannot leave the forearm and collects in the forearm causing it to swell - this pushes on the pressure cuff increasing the pressure inside it which is recorded on the computer as a graph.
How fast the forearm swells during venous occlusion plethysmography depends on what?
Depends on how fast blood is flowing into the arm
If blood flows into the forearm faster than normal how is this represented on a graph and what does it represent?
Steeper slope - meaning faster increase in pressure in forearm cuff
If blood flows into the forearm more slowly how is this represented on a graph and what does it represent?
Represents a slower increase in pressure in the forearm cuff and shown as a shallower slope on the recording
How did we measure blood flow?
Using venous occlusion plethysmography
How did we measure blood pressure?
Using sphygomomanometer (autonomic blood pressure machine)
With pressure and flow what can be calculated?
Resistance
Once we had measured blood flow and resistance under normal conditions we changed the condition to understand the effects of what three things?
Cold
Exercise
Ischemia
What do sympathetic neuron’s release for extrinsic neural vasoconstriction?
Noradrenaline
What are the extrinsic hormonal control vasoconstrictors?
Adrenaline
Angiotensin 2
Vasopressin / ADH
What are the extrinsic hormonal control vasodilators?
Adrenaline
Atrial natriuretic peptide
What are the intrinsic local controls for vasoconstriction?
Endothelin
What are the intrinsic local controls for vasodilation?
Hypoxemia
Nitric oxide
CO2, H+, K+
Adenosine
What would happen to the forearm ‘volume’ if the cuff were inflated above venous pressure (but below diastolic pressure) for a prolonged period of time?
There would be an increase in venous pressure causing retrograde movement of blood.
The increase in venous pressure causes an increase in capillary hydrostatic pressure and causes a net movement of fluid into the interstitial space.
During cold stress what nervous system is stimulated?
Sympathetic nervous system
What is the SNS response to cold stress?
Release of noradrenaline increasing its concentration in extracellular fluid which causes activation of adrenaline 1 mediated vasoconstriction (as the skin mainly have a1 receptors). Overall this causes a decrease in forearm blood flow which mainatains warm blood at the bodies core.
What is the order of events in active hyperemia?
Increased metabolic activity of an organ > decrease in oxygen and build up of metabolites > arteriole dilation in organ > increase in organ blood flow to support the organs metabolic needs
What type of receptors do skeletal muscle have higher proportion of?
Beta 2 adrenergic receptors
What does adrenaline bind to in skeletal muscles to mediate vasodilation during exercise?
B2
How does forearm flow, MAP and resistance change in response to cold stress?
Forearm Flow = decrease
MAP = stays the same or slight increase
Resistance = Increase
How does forearm flow, MAP and resistance change in response to exercise?
Forearm Flow = Large increase
MAP = stays the same or slight increase
Resistance = large decrease
How does forearm flow, MAP and resistance change in response to ischemia?
Forearm Flow = increase
MAP = stays the same
Resistance = decrease
