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
What is ischemia?
A decrease in blood flow to a specific organ
What does occluded mean?
An occlusion is a complete or partial blockage of a blood vessel.
What occurs in response to exercise?
Active hyperaemia
What occurs in response to ischemia?
Flow autoregulation (reactive hyperemia)
*Ischemia is a less-than-normal amount of blood flow to part of your body. This lack of blood flow means your tissues aren’t getting the oxygen they need.
What is the order of events in flow autoregulaltion?
Decrease in arterial pressure causes a decrease in blood flow to an organ > in the organ there is a decrease in PO2, increase in metabolites and less stretch of vessel walls > dilation of the arteriole supplying that organ > restoration of appropriate blood flow to the organ.
What are the primary causes of dehydration?
Decreased water intake and increase urine production
In cold temperatures what percentage does body thirst diminish?
up to 40% (even when dehydrated)
Why do you become more dehydrated when cold?
Because periphery vasoconstriction is occurring to conserve body heat therefore more blood volume is now in the core. Our vital organs, and pressure/volume detecting systems are fooled into thinking there is an increase blood volume.
ANP is secreted in response to an increase in blood volume leading to increased fluid excretion by the kidneys as well as inhibition of ADH = less water reabsorption and more urine production + lower thirst sensation and less water intake.
Why does wearing extra clothes increase water loss?
Working harder to move therefore produce more sweat (sweat evaporates more quickly in cold air so we don’t even notice we are sweating).
Increase ventilation during exercise increases what?
Water loss
What is the equation for MAPB?
MABP = DP + 1/3 (SP-DP)
What is the equation for forearm BP?
Forearm BP = change in volume / change in time
What is the equation for resistance?
Resistance = MABP / Forearm BP
MABP = DP + 1/3 (SP-DP)
