1. Ventilatory and Blood Gas Response to Exercise

2. Rest to work Transitions
Change in pulmonary ventilation
Observed below lactate threshold

3. Rest to work Transitions
Transition from rest  constant-load-submaximal exercise
Arterial tensions of PCO2 and PO2 are relatively unchanged during transition during submaximal exercise
BUT: arterial PO2 decreases & PCO2 increases slight in transition from rest  steady-state exercise
Therefore: at the start of exercise:
Increase in ventilation is NOT as fast as increase in metabolism

4. Rest to work transitions
At the onset of constant-load submaximal exercise:
Initially, ventilation increases rapidly
Then, a slower rise toward steady-state
PO2 and PCO2 are maintained
Slight decrease in PO2 and increase in PCO2

5. Changes in Ventilation, PO2 and PCO2 in transition from rest to steady state submaximal exercise

6. Prolonged Exercise in a hot Environment
Cool, low humidity environment = 19°C, 45% humidity
Hot, high humidity = from 28°C, 75% humidity
Hot environments hamper heat loss from the body
Increase in body temperature which directly affects respiratory control centre = Minute ventilation increases (with increased breathing frequency)

7. Prolonged Exercise in a hot Environment
During prolonged sub maximal exercise:
Ventilation tends to drift upwards
Little change in PCO2
Higher ventilation not due to increased PCO2

8. Incremental Exercise
Linear increase in ventilation - Up to 50 – 75% VO2max
Exponential increase beyond this point
Ventilatory threshold - Point where minute ventilation increases exponentially

9. Ventilatory Threshold
Reflects aerobic fitness without the need to directly measure maximal oxygen uptake
Point during exercise training at which pulmonary ventilation becomes disproportionately high with respect to oxygen consumption during an incremental exercise test
Used as a guide to determine exercise intensity

10. Therefore: Ventilatory threshold = intensity of exercise that shows a larger ventilation than required to do work.   
At this point, the contribution of anaerobic metabolism becomes significant to produce larger concentrations of lactic acid.   
Lactic acid accumulates, reducing pH & increasing metabolic acidosis.  
 Because one of the functions of the respiratory system is acid-base balance, respiration must increase to compensate for the increased acidosis.   
The point were ventilation deviates from linearity is termed the ventilatory threshold (TVENT).  

11. Ventilatory response to exercise
Trained vs. Untrained:
Trained:
Decrease in arterial PO2 near exhaustion
pH maintained at a higher work rate
Ventilatory threshold occurs at higher work rate

12. Effect of Training on Ventilation
Untrained: able to maintain PO2 in arteries within 10–12 mmHg of resting value
Trained: PO2 decreases by mmHg during heavy exercise
*low arterial PO2 vales during exercise = exercise induced hypoxemia
* Low arterial Po2 values are also seen in patients with severe lung disease

13. Males Vs. Female athletes
50% of highly trained male endurance athletes develop exercise induced hypoxemia
Females are suggested to have experience exercise induced hypoxemia more often than males

14. Causes Failure of pulmonary system?
Ventilation perfusion mismatch? Indicates matching of blood flow to ventilation
Ideal: ~1.0
Light exercise improves
Heavy exercise = inequality
Diffusion limitations during exercise ? Reduced amount of time that red blood cells spend in the pulmonary capillaries...caused by high cardiac outputs from athletes  less time for gas equilibrium to be achieved

15. Ventilatory Response to exercise: Trained Vs. Untrained

16. Revision questions
Describe the changes in PO2 and PCO2 with different exercises (6)
What happens during prolonged sub maximal exercise? Why does this occur? (6)
What happens during incremental exercise? (3)
Explain the Ventilatory Threshold (8)
How do trained and untrained athlete’s ventilatory responses differ? (6)
How do male and female ventilatory responses differ? (2)
What is hypoxemia and how does it relate to exercise? (4)
What are the suggested causes to hypoxemia in athletes? (6)