Lecture 22: Skeletal Muscle Blood Flow Flashcards
What is functional sympatholisis?
Switching off of vasoconstriction by local vasodilatory factors
At what point is muscle blood flow lowest during dynamic exercise?
When IMP and blood pressure are high, therefore when the muscle is contracting
At what point is muscle blood flow highest during dynamic exercise?
When the muscle is relaxed
What is the relationship between blood flow and isometric contractions?
During the isometric contraction, metabolites build up as blood flow is restricted by mechanical pressure produced by the contraction.
When the contraction stops, blood flow rapidly increases as large amounts of metabolites stimulate large amounts of vasodilation.
How do differing patterns of force contraction effect fatigue of muscles?
Same overall metabolite production, but continuous exercise causes less fatigue than intermittent as metabolite build-up doesn’t occur as much during the contraction.
What exercise factors determine blood flow?
Duty Cycle (contraction ON or Off) and force of contraction
What are the 4 factors that effect skeletal muscle blood flow?
Method of blood flow measurement
Force of contraction
Static vs dynamic exercise
Fibre type composition
What are the PO2 and PCO2 values for blood going to muscle tissue at rest?
PO2 = 100mmHg PCO2 = 40mmHg
What are the PO2 and PCO2 values for blood leaving the muscle tissue at rest?
PO2 = 40mmHg PCO2 = 46 mmHg
Why does the partial pressure of oxygen decrease in the trachea?
Because it gets saturated by water
What changes occur to the values of PO2 and PCO2 leaving the muscle tissue during exercise?
PO2 = 0 PCO2 = 90mmHg
What two ways is oxygen carried in the blood?
In the blood (myoglobin) and by haemoglobin
In skeletal muscle, how much oxygen saturation is there at 40mmHg?
Around 70%
How do we calculate the blood’s O2 capacity?
O2 capacity = quantity of haemoglobin * o2 capacity of haemoglobin
If haemoglobin is fully saturated, what is its carrying capacity?
20 ml O2 per 100 ml of blood
What is the A-VO2 difference for active skeletal muscle?
18 ml o2 per 100 ml of blood (20 –> 2)
What is the microvascular unit?
The terminal arterioles and all of the capillaries it supplies
Define tortuous.
Lengthy and complex
What is a key property of capillaries that aid their supply to muscle tissue?
They are tortuous
What two methods can be used to calculate the number of capillaries?
Density: muscle biopsy and count number of capillaries
Ratio: count number of capillaries in proportion to fibres
What two factors influence diffusion distance for oxygen from haemoglobin to reach tissues?
Capillary density and muscle fibre size (increased hypertrophy means decreased O2 delivery)
Do all capillaries have RBC flux?
No
80% have flux and 100% have plasma concentration
Do capillaries differ in the amount of RBC flux they have?
Yes, massively
What is RBC flux?
The speed and number of RBC’s moving through a capillary
How is RBC flux regulated?
By smooth muscle running along the whole of the capillary, that regulate diameter and flow (not the pre-capillary sphincter)
What is transit time?
The time it takes for a RBC to move through a capillary
How is transit time effected at high intensity exercise?
High intensity exercise = increased blood flow
Increased blood flow = increased RBC velocity
Increased RBC velocity = decreased transit time
Decreased transit time = decreased time for oxygen dissociation
What are the 5 determinants in microcirculaton oxygen delivery in exercise?
Diffusion distance (short = better) Capillary CSA (tortuosity) Heamoconcentration RBC transit time Capillary perfusion (regulated by smooth muscle not sphincters)
What governs the pressure gradient between blood plasma and the muscle tissues in the microcirculation?
The pressure difference between the tissue and the plasma
