Oxygen consumption and ventilation
Liner relationship below Owles point
Relationship between minute volume and oxygen consumption is approximately linear
* Up to about oxygen consumption of 2 L/min in an untrained person.
Slope of the linear part
= ventilation equivalent for oxygen
--> About minute volume of 20-30 L/min per 1 L/min of oxygen consumption
--> Doesn't alter with training
NB:
- Resting level of oxygen consumption = 250 mL/min
- Resting level of minute volume = 6-8L/min
- Oxygen consumption for exercise = 12mL of O2 per minute for each watt (watt = joule/sec)
Owles point
- Above a critical level of oxygen consumption (Owles point)
--> Ventilation increases more in proportion to oxygen consumption
* (Probably due to lactic acidosis)
- In an untrained person
--> Owles point ~ 2L/min of oxygen consumption
- In a trained person
--> Owles point is higher
##See diagram 20050306(03) - "Oxygen consumtion and ventilation"
Limitation to exercise
- Limitation to exercise is usually determined by the breathlessness
- Breathlessness occurs when exercise ventilation uses a high proportion of the maximal breathing capacity (MBC)
--> Rising levels of lactate increass ventilation, leading to breathlessness
- There is a close correlation between MBC and maximal oxygen uptake
NB:
- Diffusion capacity normally doesn't limit exercise in normal person at sea level.
Maximal breathing capacity (MBC)
(aka maximal voluntary ventilation)
--> maximal minute volume of ventilation that a subject can maintain for 15 seconds.
- Average young fit male: 170L/min
- Male: 47-253 L/min
- Female: 55-139 L/min
Significance
- Dyspnoea occurs at about 1/3 of MBC
- Ventilation is about 60% of MBC at maximal oxygen uptake
* Can be changed by training
Maximal oxygen uptake
--> about 3 L/min for young fit adult male
- Can be increased by exercise
- Can be decreased by sedentary lifestyle