Download Respiratory Changes During Exercise, Oxygen Debt

Respiratory Changes
During Exercise, Oxygen Debt,
By
Dr. 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 / min
2) 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
1L
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.