Chapter14 Dynamics of Pulmonary Ventilation (2).ppt

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1. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Chapter 14
Dynamics of Pulmonary Ventilation

2. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Ventilatory Control
•Complex mechanisms adjust rate and depth
of breathing in response to metabolic
needs.
•Neural circuits relay information.
•Receptors in various tissues monitor pH,
PCO
2, PO
2, and temperature.

3. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Neural Factors
•Medulla contains respiratory center
•Neurons activate diaphragm and intercostals
•Neural center in the hypothalamus integrates
input from descending neurons to influence
the duration and intensity of respiratory
cycle

4. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition

5. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Humoral Factors
•At rest, chemical state of blood exerts the
greatest control of pulmonary ventilation

6. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Plasma PO
2and Peripheral
Chemoreceptors
•Peripheral chemoreceptors are located in
aorta and carotid arteries
•Monitor PO
2
•During exercise
–PCO
2increases
–Temperature increases
–Decreased pH stimulates peripheral
chemoreceptors

7. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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8. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Hyperventilation & Breath Holding
•Hyperventilation decreases alveolar PCO
2to
near ambient levels.
•This increases breath-holding time.

9. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Regulation of Ventilation
During Exercise
•Chemical control
–Does not entirely account for increased
ventilation during exercise

10. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition

11. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Nonchemical Control
•Neurogenic factors
–Cortical influence
–Peripheral influence
•Temperature has little influence on
respiratory rate during exercise.

12. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Integrated Regulation During
Exercise
•Phase I (beginning of exercise): Neurogenic
stimuli from cortex increase respiration.
•Phase II: After about 20 seconds, V
Erises
exponentially to reach steady state.
–Central command
–Peripheral chemoreceptors
•Phase III: Fine tuning of steady-state ventilation
through peripheral sensory feedback
mechanisms

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In Recovery
•An abrupt decline in ventilation reflects
removal of central command and input from
receptors in active muscle
•Slower recovery phase from gradual
metabolic, chemical, and thermal
adjustments

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15. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Ventilation and Energy
Demands
•Exercise places the most profound
physiologic stress on the respiratory
system.

16. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Ventilation in Steady-Rate
Exercise
•During light to moderate exercise
–Ventilation increases linearly with O
2
consumption and CO
2production

17. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Ventilatory Equivalent
•TV
E/ O
2
•Normal values ~ 25 in adults
–25 L air breathed / LO
2consumed
•Normal values ~ 32 in childrenV


18. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Ventilation in Non–Steady-Rate
Exercise
•V
Erises sharply and the ventilatory
equivalent rises as high as 35 –40 L of air
per liter of oxygen.

19. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Ventilatory Threshold V
T
•The point at which pulmonary vent increases
disproportionately with O
2consumption during
exercise
•Sodium bicarbonate in the blood buffers almost all
of the lactate generated via glycolysis.
•As lactate is buffered, CO
2is regenerated from the
bicarbonate, stimulating ventilation.

20. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Onset of Blood Lactation
Accumulation
•Lactate threshold
–Describes highest O
2consumption of exercise
intensity with less than a 1-mM per liter increase
in blood lactate above resting level
•OBLA signifies when blood lactate shows a
systemic increase equal to 4.0 mM.

21. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition

22. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Specificity of OBLA
•OBLA differs with exercise mode due to
muscle mass being activated.
•OBLA occurs at lower exercise levels during
cycling of arm-crank exercise.

23. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Some Independence Between OBLA
and O
2max
•Factors influencing ability to sustain a
percentage of aerobic capacity without
lactate accumulation
–Muscle fiber type
–Capillary density
–Mitochondria size and number
–Enzyme concentrationV


24. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition

25. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Energy Cost of Breathing
•At rest and during light exercise, the O
2cost
of breathing is small.
•During maximal exercise, the respiratory
muscles require a significant portion of total
blood flow (up to 15%).

26. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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27. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Respiratory Disease
•COPD may triple the O
2cost of breathing
at rest.
•This severely limits exercise capacity in
COPD patients.

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Cigarette Smoking
•Increased airway resistance
•Increased rates of asthma and related
symptoms
•Smoking increases reliance on CHO during
exercise.
•Smoking blunts HR response to exercise.

29. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Does Ventilation Limit Aerobic
Power and Endurance?
•Healthy individuals overbreathe at higher
levels of O
2consumption.
•At max exercise, there usually is a breathing
reserve.
•Ventilation in healthy individuals is not the
limiting factor in exercise.

30. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
An Important Exception
•Exercise-induced arterial hypoxemia may
occur in elite endurance athletes.
•Potential mechanisms include
–V/Q inequalities
–Shunting of blood flow bypassing alveolar
capillaries
–Failure to achieve end-capillary PO
2
equilibrium

31. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Acid–Base Regulation
•Buffering
–Acids dissociate in solution and release H
+.
–Bases accept H
+to form OH
−
ions.
–Buffers minimize changes in pH.

32. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Acid–Base Regulation
•Alkalosis increases pH.
•Acidosis decreases pH.
•Three mechanisms help regulate internal
pH.
–Chemical buffers
–Pulmonary ventilation
–Renal function

33. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Chemical Buffers
•Chemical buffers consist of a weak acid
and the salt of that acid.
•Bicarbonate buffers = weak acid, carbonic
acid, salt of the acid, and sodium
bicarbonate

34. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Bicarbonate Buffers
•Result of acidosis
H
2O + CO
2H
2CO
3H
++ HCO
3
−
•Result of alkalosis
H
2O + CO
2H
2CO
3H
++ HCO
3
−

35. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Phosphate Buffer
•Phosphoric acid and sodium phosphate
•Exerts effects in renal tubules and
intracellular fluids

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Protein Buffer
•Intracellular proteins possess free radicals
that, when dissociated, form OH
−, which
reacts with H
+to form H
2O.
•Hemoglobin is the most important protein
buffer.

37. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Physiologic Buffers
•Ventilatory buffer
–Increase in free H
+stimulates ventilation
–Increase ventilation, decrease PCO
2
•Lower plasma PCO
2accelerates
recombination of H
++ HCO
3
−,lowering H
+
concentration

38. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
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Renal Buffer
•Kidneys regulate acidity by secreting
ammonia and H
+into urine and reabsorbing
chloride and bicarbonate.

39. Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy,
Nutrition, and Human Performance,Sixth Edition
Effects of Intense Exercise
•During exercise, pH decreases as CO
2and
lactate production increase.
•Low levels of pH are not well tolerated and
need to be quickly buffered.