copyright © 2007 lippincott williams & wilkins.mcardle, katch, and katch: exercise physiology:...
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Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Chapter 14
Dynamics of Pulmonary Ventilation
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, PCO2, PO2, and temperature.
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
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Hyperventilation & Breath Holding
• Hyperventilation decreases alveolar PCO2 to near ambient levels.
• This increases breath-holding time.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, 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 O2
consumption and CO2 production
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Ventilatory Equivalent
• TVE / O2
• Normal values ~ 25 in adults
– 25 L air breathed / LO2 consumed
• Normal values ~ 32 in children
V
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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
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.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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
V
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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%).
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Respiratory Disease
• COPD may triple the O2 cost of breathing at rest.
• This severely limits exercise capacity in COPD patients.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, 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 O2 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. 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 PO2 equilibrium
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.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Acid–Base Regulation
• Alkalosis increases pH.
• Acidosis decreases pH.
• Three mechanisms help regulate internal pH.– Chemical buffers– Pulmonary ventilation– Renal function
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
Bicarbonate Buffers
• Result of acidosis
H2O + CO2 H2CO3 H+ + HCO3−
• Result of alkalosisH2O + CO2 H2CO3 H+ + HCO3
−
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, 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 H2O.
• Hemoglobin is the most important protein buffer.
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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 PCO2
• Lower plasma PCO2 accelerates recombination of H+ + HCO3
−, lowering H+ concentration
Copyright © 2007 Lippincott Williams & Wilkins. McArdle, 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. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition
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.