What is oxygen extraction?
- pulling oxygen from circulation to support cellular production of energy for muscle contraction
- normal 5vol% a-vO2 difference
- more O2 extracted by working muscles
What is oxygen diffusion?
- A-C membrane, gas exchange
- increased cardiac output, increased perfusion, increased pulmonary vascular pressure thus more uniform distribution
What is oxygen consumption?
- resting VO2 = 3.5 ml/kg/min
- exercising VO2 increases directly with level of muscular work
- maximum VO2 depends on genetics, conditioning, presence/absence of disease
At rest, what does 1 MET equal?
3.5 ml/kg/min
What is normal VO2 max?
> 84% of predicted
How can O2 consumption be predicted?
from work rate
What is VO2 peak?
where exercise is stopped below maximal capacity for O2 transport due to dyspnea, pain, peripheral vascular disease
What is carbon dioxide production?
- VCO2, normal 200 ml/min or 2.8 ml/min/kg
- exhaled CO2 depends on matching alveolar ventilation
What is the respiratory exchange ratio (RER)?
- VCO2/VO2 at mouth
- one way of determining lactate threshold
- normal 0.8 (greater than 1.0 reflects increased CO2 lactate buffering)
- affected by hypo/hyperventilation
What is the respiratory quotient (RQ)?
- usually not measured directly
- ratio of VCO2 to VO2 at tissues
- CHO RQ 1.0, Fat RQ 0.7, combined at rest 0.8
What is minute ventilation?
- depends on PaCO2 and dead space
- evaluates respiratory response
- healthy individuals < 70% of ventilatory capacity
How do you measure breathing reserve?
MVV - VEmax
In healthy individuals, how is end expiratory lung volume affected during exertion?
decreases
In COPD patients, how is end expiratory lung volume affected during exertion?
increases causing a decrease in IC
What is the dead space to tidal volume ratio?
- normally <0.25 with maximal exertion
- (PaCO2 - PeCO2)/PaCO2
What is the normal P(A-a)O2?
10 mmHg
What is the P(A-a)O2 with maximal exercise?
20-30 mmHg
When does P(A-a)O2 increase?
heavy exertion and age
What is PETCO2 and (Pa-ET)CO2?
- end tidal CO2
- estimates PaCO2
- resting normal difference is 2-3 mmHg
- maximal exertion 4 mmHg
- diseased lung values >10 mmHg
What is PETO2?
- end tidal PO2
- plotted as a function of workload
- increase with hyperventilation associated with lactic acidosis
- can utilize to determine LT
What is lactate threshold?
- commonly called the anaerobic threshold
- VCO2 and VE do not rise in proportion to VO2
- where pH stable until oxygen delivery does not meet demand
How would you detect LT?
- normal value is 50-60% of VO2 max
- clinically breathlessness, muscle burning, muscle fatigue
What is maximum heart rate?
- predicted HR max is 220-age
- HR increased linearly with increased workload
- maximum HR achieved just prior to exhaustion
What is heart rate reserve?
- (HR predicted - HR actual)
- should be less than 15
- HR % of predicted >90%
- values outside this range indicate non-cardiovascular limitations
