L19 Skeletal Muscle Blood Flow in Exercise

Question 1

What are the methods uses to measure blood flow to exercising muscle in human

Answer 1

Venous occlusion Plethysmography

Thermodilution

Doppler Ultrasound

Microdialysis

Question 2

Describe thermodilution to measure blood flow to exercising muscles and the typical values it yields

Answer 2

Catheter in femoral vein with temperature probe at tip. Cold saline infused into vein. Drop in blood temperature is proportional to the flow rate.
+ real time measurements, can be used in exercise
- Invasive, femoral vein drains quad

Typical values - 5.7l per min for quads. Knee extensor = 250ml per min per 100g

Question 3

Describe Venous occlusion Plethysmography to measure blood flow to exercising muscles and the typical values it yields

Answer 3

upper limb cuff inflated to 40 mmHg so venous outflow is occluded but arterial inflow is maintained - rate of swelling is proportional to the rate of arterial inflow
+ non-invasive, easy, widely used
- Not suitable during exercise, only post-exercise, limb includes skin and fat as well as muscle

Typical values ~50-70ml per 100g per min

Question 4

Describe Doppler Ultrasounds to measure blood flow to exercising muscles and the typical values it yields

Answer 4

ultrasound used to measure the Doppler shift in velocity from red blood cells passing below a probe. Measures blood flow velocity. Can also image vessel diameter .
Flow = velocity x cross sectional areas

+ non-invasive, real time used during exercise
- restricted to large arteries near the skin, angle of probe to vessel is important for good images and true velocity

yield = 300ml per min per 100g

Question 5

Describe Microdialysis to measure blood flow to exercising muscles and the typical values it yields

Answer 5

measures clearance and recovery of substance

+ during exercise. can sample interstitial fluid and measure metabolites
- Invasive, equation to relate clearance rate to actual flow is complex

yield - 500 ml per min per 100g

Question 6

Graph the time course of hyperaemia (increase in blood flow) at the initiation of exercise

Answer 6

Yeah look this up

Question 7

Explain how sympathetic neural factors, the muscle pump or metabolic vasodilator substances might. might not account for the rapid rise in muscle blood flow at exercise onset.

Answer 7

Mechanical –> the muscle pump. Compression and relaxing facilitate flow by lowering venous pressure

Metabolic vasodilator substances –> active tissues have a change in metabolism which causes vasodilation. Potassium plays a big role

neural - possible sympathetic nerve activity withdrawal

Question 8

Discuss evidence for involvement of metabolic factors in steady-state exercise hyperaemia

Answer 8

Interstitial levels of adenosine increase in proportion to work during exercise.
Infusion of ATP matches/mimics the increase of ATP in exercise and vasodilation is closely linked

Question 9

Define the phenomenon of functional sympatholysis

Answer 9

the local modulation that optimises muscle blood flow . During exercise, local factors in skeletal muscle can overcome sympathetic vasoconstrictor tone to allow vasodilation

Question 10

Discuss how, when and why local factors override sympathetic vasoconstriction

Answer 10

i dunno

Question 11

Discuss how, when and why local factors restrains metabolic vasodilation

Answer 11

i dunno