Dynamics of Pulmonary Ventilation in Exercise: Control and Regulation

1. Chapter 14 Dynamics of Pulmonary Ventilation 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. 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 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 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 McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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8. Hyperventilation & Breath Holding • Hyperventilation decreases alveolar PCO2 to near ambient levels. • This increases breath-holding time. 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 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. 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 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 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. 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 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 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. 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. 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

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

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

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

38. Renal Buffer • Kidneys regulate acidity by secreting ammonia and H+ into urine and reabsorbing chloride and bicarbonate. 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition