Lecture 32: Central and Peripheral Limitations to O2 Uptake Flashcards
Is respiration a limiting factor on O2 uptake?
No
How is it known that respiration is not a limiting factor on O2 uptake?
Because ventilation increases at VO2 max when anaerobic exercise continues
Can oxygen dissociation be a limiting factor in O2 uptake?
Yes
Name two major factors in a decreased O2-haemoglobin affinity and name one minor factor.
Major: Temperature and pH
Minor: 2-3 DPG (from RBC glycolysis and increases when exposed to high altitudes)
Is RBC concentration of the blood a limiting factor on O2 uptake?
Yes
How can RBC concentration’s effect be tested in athletes? What is the result of the injection a certain chemical?
Injection of erthyropoietin
Increased time to exhaustion by 54%
Is the pumping capacity of the heart a limiting factor in O2 uptake?
No, it is in fact the amount of muscle O2 uptake that is limiting
Why could the pumping capacity of the heart be a limiting factor in O2 uptake?
Increasing pumping capacity of the heart results in increased stroke volume; heart rate; cardiac output
What part of the heart has seen to be a major limiter in its pumping capacity?
Pericardium
What did Davis & Sargaent’s research on muscle mass effect on O2 uptake show?
The fact that the one leg value was 70% of the two leg value implied that central circulation was the limiting factor as there was not enough blood to be supplied to both legs
Increased O2 uptake by muscles in 2 leg exercise when under hyperoxic conditions implies that it is central circulation as the limiting factor
The fact that O2 uptake remains the same in hyperoxic conditions in one leg, implies that skeletal muscle is the limiting factor in O2 uptake
Conclusion: amount of muscle mass active and amount of skeletal muscle blood flow are limiting factors in O2 uptake
When exercising do we use all of our available blood flow?
No
What is the commonly known blood flow range in a maximum intensity exercise?
50-80 ml.100g.min
What is the effect of an increase in active muscle on blood flow per unit of volume?
The blood flow per unit volume decreases as more muscle is active (kg)
What kind of muscle is required to identify skeletal muscle blood flow?
A muscle that is small enough not to overwhelm the pumping capacity of the heart
What were the results of a knee extensor exercise measuring maximum blood flow and its effect on O2 uptake?
Blood flow increased to 240 ml.100g.min
O2 uptake increased
MAP increased at higher intensities
AVO2 difference plateau’d very early on
Why is there less O2 extraction as intensity of exercise increases?
Because there is less transit time for RBC’s
How long does blood remain in the capillaries at rest and then under intense exercise?
Rest: 0.75 seconds
Exercise: 0.3-0.4 seconds
Why do elite endurance athletes have increased transit time?
Because they have a greater capillary density
What is the main symptom of decreased transit time in the muscles?
Muscle hypoxia (not enough O2 extraction therefore decreased saturation)
What causes the vasoconstriction of muscle blood flow to already working muscles, when new muscles become activated during exercise?
Catacholamine spillover
What must be achieved to ensure muscle blood flow is maintained during strenuous exercise?
Vasoconstriction must prevail over vasodilatory tone
What are the limiters of O2 uptake during exercise?
Cardiac circulation Muscle mass activated Heamoglobin affinity with oxygen RBC concentration Capillary density (transit time) Blood flow Vascular conductance (catacholamine spillover)
What are the physiological responses to decreased temperature?
Decreased heart rate Decreased lipid mobilisation Decreased skin blood flow Increased central blood volume Increased submaximal VO2
