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Dynamics of Pulmonary Ventilation in Exercise: Control and Regulation

This chapter explores the complex mechanisms and factors that control and regulate pulmonary ventilation during exercise. It covers neural, humoral, and nonchemical factors, as well as the integrated regulation and recovery of ventilation. Additionally, it discusses the relationship between ventilation and energy demands, the ventilatory threshold, and lactate accumulation.

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Dynamics of Pulmonary Ventilation in Exercise: Control and Regulation

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  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

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

  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

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

  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

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

  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

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

  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

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

  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

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

  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

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

  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

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