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

2. 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, PCO2, PO2, and temperature.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

3. 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
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

6. Plasma PO2 and Peripheral Chemoreceptors
Peripheral chemoreceptors are located in aorta and carotid arteries
Monitor PO2
During exercise
PCO2 increases
Temperature increases
Decreased pH stimulates peripheral chemoreceptors
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8. Hyperventilation & Breath Holding
Hyperventilation decreases alveolar PCO2 to near ambient levels.
This increases breath-holding time.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

9. Regulation of Ventilation During Exercise
Chemical control
Does not entirely account for increased ventilation during exercise
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

12. Integrated Regulation During Exercise
Phase I (beginning of exercise): Neurogenic stimuli from cortex increase respiration.
Phase II: After about 20 seconds, VE rises 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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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

13. 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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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

16. Ventilation in Steady-Rate Exercise
During light to moderate exercise
Ventilation increases linearly with O2 consumption and CO2 production
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

17. Ventilatory Equivalent
TVE / O2
Normal values ~ 25 in adults
25 L air breathed / LO2 consumed
Normal values ~ 32 in children
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

19. Ventilatory Threshold VT
The point at which pulmonary vent increases disproportionately with O2 consumption during exercise
Sodium bicarbonate in the blood buffers almost all of the lactate generated via glycolysis.
As lactate is buffered, CO2 is regenerated from the bicarbonate, stimulating ventilation.
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

20. Onset of Blood Lactation Accumulation
Lactate threshold
Describes highest O2 consumption 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.
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22. 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.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

23. Some Independence Between OBLA and O2max
Factors influencing ability to sustain a percentage of aerobic capacity without lactate accumulation
Muscle fiber type
Capillary density
Mitochondria size and number
Enzyme concentration
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25. Energy Cost of Breathing
At rest and during light exercise, the O2 cost of breathing is small.
During maximal exercise, the respiratory muscles require a significant portion of total blood flow (up to 15%).
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27. Respiratory Disease COPD may triple the O2 cost of breathing at rest.
This severely limits exercise capacity in COPD patients.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

28. 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.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

29. Does Ventilation Limit Aerobic Power and Endurance?
Healthy individuals overbreathe at higher levels of O2 consumption.
At max exercise, there usually is a breathing reserve.
Ventilation in healthy individuals is not the limiting factor in exercise.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

30. 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 PO2 equilibrium
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

32. Acid–Base Regulation Alkalosis increases pH. Acidosis decreases pH.
Three mechanisms help regulate internal pH.
Chemical buffers
Pulmonary ventilation
Renal function
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

33. 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
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

34. Bicarbonate Buffers H2O + CO2  H2CO3  H+ + HCO3− Result of acidosis
Result of alkalosis
H2O + CO2  H2CO3  H+ + HCO3−
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

35. Phosphate Buffer Phosphoric acid and sodium phosphate
Exerts effects in renal tubules and intracellular fluids
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

36. Protein Buffer
Intracellular proteins possess free radicals that, when dissociated, form OH−, which reacts with H+ to form H2O.
Hemoglobin is the most important protein buffer.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

37. Physiologic Buffers Ventilatory buffer
Increase in free H+ stimulates ventilation
Increase ventilation, decrease PCO2
Lower plasma PCO2 accelerates recombination of H+ + HCO3−, lowering H+ concentration
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38. Renal Buffer
Kidneys regulate acidity by secreting ammonia and H+ into urine and reabsorbing chloride and bicarbonate.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

39. Effects of Intense Exercise
During exercise, pH decreases as CO2 and lactate production increase.
Low levels of pH are not well tolerated and need to be quickly buffered.
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition