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

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Presentation on theme: "Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition."— Presentation transcript:

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

2 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, P CO 2, P O 2, and temperature.

3 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

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

5 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

6 Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Plasma P O 2 and Peripheral Chemoreceptors Peripheral chemoreceptors are located in aorta and carotid arteries Monitor P O 2 During exercise –P CO 2 increases –Temperature increases –Decreased pH stimulates peripheral chemoreceptors

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

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

9 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

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

11 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.

12 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, V E rises exponentially to reach steady state. –Central command –Peripheral chemoreceptors Phase III: Fine tuning of steady-state ventilation through peripheral sensory feedback mechanisms

13 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

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

15 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.

16 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 O 2 consumption and CO 2 production

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

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

19 Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Ventilatory Threshold V T 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.

20 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 O 2 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.

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

22 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.

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

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

25 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 O 2 cost of breathing is small. During maximal exercise, the respiratory muscles require a significant portion of total blood flow (up to 15%).

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

27 Copyright © 2007 Lippincott Williams & Wilkins.McArdle, 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.

28 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.

29 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 O 2 consumption. At max exercise, there usually is a breathing reserve. Ventilation in healthy individuals is not the limiting factor in exercise.

30 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 PO 2 equilibrium

31 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.

32 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

33 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

34 Copyright © 2007 Lippincott Williams & Wilkins.McArdle, 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

35 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

36 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 H 2 O. Hemoglobin is the most important protein buffer.

37 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 P CO 2 Lower plasma P CO 2 accelerates recombination of H + + HCO 3, lowering H + concentration

38 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.

39 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 CO 2 and lactate production increase. Low levels of pH are not well tolerated and need to be quickly buffered.


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