Respiratory Changes During Exercise, Oxygen Debt, By Dr. Mudassar Ali Roomi
Mar 19, 2016
Respiratory Changes During Exercise, Oxygen Debt,
ByDr. Mudassar Ali Roomi
2 main respiratory changes in exercise:
• 1) increase in pulmonary ventilation• 2) increase in both rate & depth of respiration.
Regulation of Respiration during exercise:
• What causes intense ventilation during exercise?
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!!
4 main factors that increase rate of respiration during exercise:
1. 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.
• 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.
• 3. Increase in temperature: During exercise metabolism increases
body temperature increases stimulates respiration directly & indirectly.
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.
Metabolic systems during exercise:
3 types:
1) 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)
2) Glycogen-Lactic Acid System: (another 30-40 sec) Glucose stored as glycogen in the muscle undergoes glycolysis ATP.
3) Aerobic System: (For long long time) Nutrients, Glucose, Amino Acids Fatty Acids are oxidized. It is the ultimate source of energy.
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 / min2) Maximum Breathing Capacity (MBC): Up to 150 – 170 L / min
• 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
• 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.
• 7) Effect on Respiratory Quotient (RQ): – In moderate exercise: RQ remains about 1.
– In severe exercise: May increase up to 1.5-2 due to extra CO2 formation
– After severe exercise: RQ falls up to 0.5.
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.
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
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.
• During exercise oxygen consumption is increased by skeletal muscle.
Oxygen is present:• In combination with Hb• In myoglobin &• In dissolved form
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
O2 in dissolved form
TOTAL OXYGEN = 2 L (approx.) This much oxygen must be repaid.
Debts:
• To restore phosphagen & glycogen system: 2 L is required.
• To restore Aerobic system: 8 L is required.
• So, a total of 10-12 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 = 10-12 L.