L27 Central and Peripheral Limitations to Oxygen Uptake

Question 1

Discuss the evidence against a ventilatory limitation to aerobic capacity at sea level.

Answer 1

pulmonary function is not a weak link in oxygen transport system of healthy individuals
A max steady state (vo2 max) additional anaerobic exercise raises ventilation
Subjects can still hyperventilate at VO2 max

Question 2

how is the oxyhaemoglobin dissociation curve is influenced by pH and temperature. Explain how this effects haemoglobin-oxygen affinity at the lung and tissues

Answer 2

pH
Decreased pH lowers Hb-O2 affinity - results in a rightward shift to favour offloading of O2 to tissues

Temperature
Increased blood temp lowers O2-hb affinity - results in a rightwards shift favouring offloading of O2 to the tissues

Question 3

Explain why some elite endurance athletes may experience arterial hypoxemia.

Answer 3

High pulmonary blood flow and short mean transit time

- not enough oxygen can associate over

Question 4

Describe some of the early experimental work proposing a cardiac limitation to aerobic capacity

Answer 4

The pump capacity of the heart
- skiers - those with bigger hearts got placed higher in the race

• for a given sub max - heart rate was lower in the physically active

Question 5

Interpret the results of Davies & Sargeant (1974) with regards to how exercising muscle mass influences the limiting factor to aerobic capacity

Answer 5

2 legs vs 1 leg
- 1 leg cycling deals with half the muscle mass so you’d expect a relatively higher Vo2 max in 1 leg cycling compared with 2 leg. but this is not the case.

Normoxia vs Hyperoxia
If tissue O2 uptake is a problem, increasing oxygen delivery by hyperoxia should not increase oxygen uptake in 1 leg exercise - central circulation is not the problem in this mode

Question 6

Why is 1 leg knee extension exercise a good experimental model to explore how high skeletal muscle blood flow can go in humans

Answer 6

To test how high muscle blood flow can you you must activate maximally a mass of muscle that is too small to overwhelm the hearts ability to pump blood. Single leg knee extension is good because the quadriceps are isolated and the vasodilation is not counteracted by whatever degree of vasoconstriction is needed to maintain blood pressure

Question 7

How does blood doping with erythropoietin (EPO) improves aerobic performance

Answer 7

It increases Hb concentration, arterial oxygen content and improves aerobic performance through the induction of red blood cell production.
After 4 weeks treatment of EPO subjects cycling Vo2 max thresholds increased by about 13%

Question 8

explain the difference between responders and non responders and how this related to adaptation

Answer 8

The more you train per week, the more percentage change in vO2 max.
Rather than people being non-responders to adaptations, the may just not being doing an adequate amount of training for them

Question 9

List the factors contributing to maximal SV and Maximal A-V difference for oxygen

Answer 9

SV
- Increased RBC volume and Increased plasma volume increases blood volume. this increases venous return which then increases end diastolic volume. This and decreased cardiac afterload both cause an increase in ejection fraction which increases stroke volume.

A-V O2 diff
- increased vascular function. Increased capillarity. Increased mitochondrial volume density and oxidative capacity. Increased plasma volume and RBC volume .
Better distribution of blood to active fibres. Increased muscle O2% extraction