1. Respiratory Changes During Exercise, Oxygen Debt,By
Dr. Mudassar Ali Roomi

2. 2 main respiratory changes in exercise:
1) increase in pulmonary ventilation
2) increase in both rate & depth of
respiration.

3. Regulation of Respiration during exercise:
What causes intense ventilation during exercise?

4. O2 consumption in moderate & severe exercise:
In healthy athlete  alveolar vent. is directly proportional to oxygen metabolism.
The arterial PO2, PCO2 and pH remain almost normal.
Conclusion: Hypoxia, hypercapnia & acidosis have no role in inducing hyperventilation during exercise!!

5. 4 main factors that increase rate of respiration during exercise:
Anticipatory increase in rate of ventilation:
When a person intends to perform exercise impulses from cerebral cortex  skeletal muscle  to initiate contraction & simultaneously collateral impulses  respiratory centre increase ventilation.

6. 2. Impulses from proprioceptors: (receptors for position & movement present around joints, in the muscles, tendons and joint ligaments).
This is the major stimulus for respiratory centre during exercise.

7. 3. Increase in temperature:
During exercise  metabolism increases  body temperature increases  stimulates respiration directly & indirectly.

8. 4. Chemical factors:
Decrease in PO2
Increase in PCO2
Increase in H+ conc.
The effect of PO2, PCO2 & H+ is minimum to stimulate respiration in exercise because there is increased ventilation  so PO2 & PCO2 remain in normal limits.

9. Metabolic systems during exercise:
3 types:
Phosphagen system:
consist of ATP & Creatine phosphate in muscle (ATP can maintain muscle contraction for 5-6 sec; energy from creatine phosphate can sustain contraction for another 10 sec)

10. 2) Glycogen-Lactic Acid System: (another
30-40 sec)
Glucose stored as glycogen in the muscle
undergoes glycolysis  ATP.

11. 3) Aerobic System: (For long long time)
Nutrients,
Glucose,
Amino Acids
Fatty Acids
are oxidized.
It is the ultimate source of energy.

12. Changes in Respiration during Exercise:
1) Normal respiratory minute volume
(RMV) at rest = 500 x 12 = 6 L / min
in severe exercise:
RMV = up to 100 – 110 L / min
2) Maximum Breathing Capacity (MBC):
Up to 150 – 170 L / min

13. 4) Utilization Co-efficient (U.C): 25% (at rest)
3) Oxygen Consumption (O.C): It is the percentage of arterial blood which gives its O2 while passing through the tissues.
250 ml / min (at rest)
may increase to 4-5 L / min in exercise
4) Utilization Co-efficient (U.C):
25% (at rest)
75 – 85 % in severe exercise

14. 5) Diffusion Capacity for O2:
At rest: 20 – 30 ml / mm Hg / min
in exercise: 65 ml / mm Hg / min
6) Chemical parameters in skeletal muscles:
PO2 decreases,
PCO2, H+, Temp increases  Right hand shift of oxy-Hb dissociation curve  easy dissociation of O2 to supply skeletal muscle.

15. 7) Effect on Respiratory Quotient (RQ):
In moderate exercise: RQ remains about 1.
In severe exercise: May increase up to due to extra CO2 formation
After severe exercise: RQ falls up to 0.5.

18. Interrelation between chemical & nervous factors in control of respiration during exercise:
At the onset of exercise  alveolar vent. increases instantaneously, without an initial increase in arterial PCO2
There is initial decrease in arterial PCO2 due to great increase in alv. Vent.
Conclusion: brain  anticipatory stim. of resp. at the onset of exercise.

19. Neuro-genic drive from respiratory centre during heavy exercise
Arterial PCO2 remain normal (40 mm Hg) at rest & during heavy exercise.
If PCO2 does change from 40, there is stim. of vent. above 40 & depression of vent. below 40.
This shift in exercise is partly a learned response that involves cerebral cortex.
Conclusion:
Neurogenic factor shifts the curve about 20- fold in upward direction so that vent. Matches the rate of CO2 release keeping normal level of Arterial PCO2

20. Oxygen Debt: Definition:
Extra amount of oxygen, that must be supplied to body after exercise, in order to restore metabolic system back to pre-exercise state.

21. During exercise  oxygen consumption is increased by skeletal muscle.
Oxygen is present:
In combination with Hb
In myoglobin &
In dissolved form

22. Oxygen used in severe exercise:
0.3 L
O2 combined with Myoglobin
1 L
O2 combined with Hemoglobin
0.5 L
O2 in
alveolar air
0.25 L
dissolved form
TOTAL OXYGEN = 2 L (approx.)
TOTAL OXYGEN = 2 L (approx.)
This much oxygen must be repaid.

23. Debts: To restore phosphagen & glycogen system: 2 L is required.
To restore Aerobic system: 8 L is required.
So, a total of L oxygen is used in exercise & is paid in 90 min after exercise  respiratory rate remain increased for 90 min after exercise to repay oxygen debt = L.