Chapter 14 Dynamics of Pulmonary Ventilation Copyright 2007

Ventilatory Control • Complex mechanisms adjust rate and depth of breathing in response to

Neural Factors • Medulla contains respiratory center • Neurons activate diaphragm and intercostals •

Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology:

Humoral Factors • At rest, chemical state of blood exerts the greatest control of

Plasma PO 2 and Peripheral Chemoreceptors • Peripheral chemoreceptors are located in aorta and

Hyperventilation & Breath Holding • Hyperventilation decreases alveolar PCO 2 to near ambient levels.

Regulation of Ventilation During Exercise • Chemical control – Does not entirely account for

Nonchemical Control • Neurogenic factors – Cortical influence – Peripheral influence • Temperature has

Integrated Regulation During Exercise • Phase I (beginning of exercise): Neurogenic stimuli from cortex

In Recovery • An abrupt decline in ventilation reflects removal of central command input

Ventilation and Energy Demands • Exercise places the most profound physiologic stress on the

Ventilation in Steady-Rate Exercise • During light to moderate exercise – Ventilation increases linearly

Ventilatory Equivalent • TVE / O 2 • Normal values ~ 25 in adults

Ventilation in Non–Steady-Rate Exercise • VE rises sharply and the ventilatory equivalent rises as

Ventilatory Threshold VT • The point at which pulmonary vent increases disproportionately with O

Onset of Blood Lactation Accumulation • Lactate threshold – Describes highest O 2 consumption

Specificity of OBLA • OBLA differs with exercise mode due to muscle mass being

Some Independence Between OBLA and O 2 max • Factors influencing ability to sustain

Energy Cost of Breathing • At rest and during light exercise, the O 2

Respiratory Disease • COPD may triple the O 2 cost of breathing at rest.

Cigarette Smoking • Increased airway resistance • Increased rates of asthma and related symptoms

Does Ventilation Limit Aerobic Power and Endurance? • Healthy individuals overbreathe at higher levels

An Important Exception • Exercise-induced arterial hypoxemia may occur in elite endurance athletes. •

Acid–Base Regulation • Buffering – Acids dissociate in solution and release H+. – Bases

Acid–Base Regulation • Alkalosis increases p. H. • Acidosis decreases p. H. • Three

Chemical Buffers • Chemical buffers consist of a weak acid and the salt of

Bicarbonate Buffers • Result of acidosis H 2 O + CO 2 H 2

Phosphate Buffer • Phosphoric acid and sodium phosphate • Exerts effects in renal tubules

Protein Buffer • Intracellular proteins possess free radicals that, when dissociated, form OH−, which

Physiologic Buffers • Ventilatory buffer – Increase in free H+ stimulates ventilation – Increase

Renal Buffer • Kidneys regulate acidity by secreting ammonia and H+ into urine and

Effects of Intense Exercise • During exercise, p. H decreases as CO 2 and

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

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

Plasma PO 2 and Peripheral Chemoreceptors • Peripheral chemoreceptors are located in aorta and carotid arteries • Monitor PO 2 • During exercise – PCO 2 increases – Temperature increases – Decreased p. H stimulates peripheral chemoreceptors Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

Regulation of Ventilation During Exercise • Chemical control – Does not entirely account for increased ventilation during exercise Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

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

In Recovery • An abrupt decline in ventilation reflects removal of central command input from receptors in active muscle • Slower recovery phase from gradual metabolic, chemical, and thermal adjustments Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

Ventilation in Steady-Rate Exercise • During light to moderate exercise – Ventilation increases linearly with O 2 consumption and CO 2 production Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Ventilatory Equivalent • TVE / O 2 • Normal values ~ 25 in adults – 25 L air breathed / LO 2 consumed • Normal values ~ 32 in children Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

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

Onset of Blood Lactation Accumulation • Lactate threshold – Describes highest O 2 consumption of exercise intensity with less than a 1 -m. M per liter increase in blood lactate above resting level • OBLA signifies when blood lactate shows a systemic increase equal to 4. 0 m. M. Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, 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. Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

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

Respiratory Disease • COPD may triple the O 2 cost of breathing at rest. • This severely limits exercise capacity in COPD patients. Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

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

Acid–Base Regulation • Alkalosis increases p. H. • Acidosis decreases p. H. • Three mechanisms help regulate internal p. H. – Chemical buffers – Pulmonary ventilation – Renal function Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

Bicarbonate Buffers • Result of acidosis H 2 O + CO 2 H 2 CO 3 H+ + HCO 3− • Result of alkalosis H 2 O + CO 2 H 2 CO 3 H+ + HCO 3− Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Phosphate Buffer • Phosphoric acid and sodium phosphate • Exerts effects in renal tubules and intracellular fluids Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Protein Buffer • Intracellular proteins possess free radicals that, when dissociated, form OH−, which reacts with H+ to form H 2 O. • Hemoglobin is the most important protein buffer. Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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

Renal Buffer • Kidneys regulate acidity by secreting ammonia and H+ into urine and reabsorbing chloride and bicarbonate. Copyright © 2007 Lippincott Williams & Wilkins. Mc. Ardle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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