Control of Ventilation

1. Control of Ventilation • Respiratory control center • Receives neural and humoral input • Feedback from muscles • CO2 level in the blood • Regulates respiratory rate

2. Location of Respiratory Control Centers

3. Neural Input to the Respiratory Control Center • motor cortex - impulses from cortex may “spill over” when passing through medulla on way to heart and muscles • afferent - from GTO, muscle spindles or joint pressure receptors • mechanoreceptors in the heart relay changes in Q

4. Humoral Input to the Respiratory Control Center • central chemoreceptors - respond to changes in CO2 or H+ in CSF • peripheral chemoreceptors - aortic bodies and carotid bodies • both similar to central receptors, carotids also respond to increases in K+ and decreases in PO2

5. Ventilation vs. Increasing PCO2

6. Ventilation vs. Decreasing PO2

7. Ventilatory Control During Exercise • Submaximal exercise • Linear increase due to: • Central command • Humoral chemoreceptors • Neural feedback • Heavy exercise • Exponential rise above Tvent • Increasing blood H+

8. Respiration Control during Submaximal Exercise

9. Respiratory Control during Exercise • Central commmand initially responsible for increase in VE at onset • combination of neural and humoral feedback from muscles and circulatory system fine-tune VE • Ventilatory threshold may be result of lactate or CO2 accumulation (H+) as well as K+ and other minor contributors

10. Effect of Training on Ventilation • Ventilation is lower at same work rate following training • May be due to lower blood acidity • Results in less feedback to stimulate breathing

11. Training Reduces Ventilatory Response to Exercise

12. Final Note • the pulmonary system is not thought to be a limiting factor to exercise in healthy individuals • the exception is elite endurance athletes who can succumb to hypoxemia during intense near maximal exercise

13. Acid-Base Balance

14. Acids and Bases • Acid - compound that can loose an H+ and lower the pH of a solution • lactic acid, sulphuric acid • Base - compound that can accept free H+ and raise the pH of a solution • bicarbonate (HCO3-) • Buffer - compound that resists changes in pH • bicarbonate (sorry)

15. pH • pH = -log10 [H+] • pH goes up, acidity goes down • pH of pure water = 7.0 (neutral) • pH of blood = 7.4 (slightly basic) • pH of muscle = 7.0

16. Acidosis and Alkalosis

17. Acid Production during Exercise • CO2 - volatile because gas can be eliminated by lungs • CO2 + H2O <--> H2CO3 <--> H+ + HCO3- • The next point is erroneous • Lactic acid and acetoacetic acid - CHO and fat metabolism respectively • termed organic acids • at rest converted to CO2 and eliminated, but during intense exercise major load on acid-base balance

18. Sulphuric and Phosphoric acids - produced by oxidation of proteins and membranes or DNA • called fixed because not easily eliminated • minor contribution to acid accumulation

19. Sources of H+

20. Buffers • maintain pH of blood and tissues • accept H+ when they accumulate • release H+ when pH increases

21. Intracellular Buffers • proteins • phosphates • PC • bicarbonate

22. Insert table 11.1

23. Extracellular Buffers • bicarbonate - most important buffer in bodyremember the reactionhemoglobin - important buffer when deoxygenatedpicks up H+ when CO2 is being dumped into bloodproteins - not important due to low conc.

24. Buffering Capacity of Muscles vs. Blood

25. Respiration and Acid-Base Balance • CO2 has a strong influence on blood pH • as CO2 increases pH decreases (acidosis) CO2 + H2O > H+ + HCO3- • as CO2 decreases pH increases (alkalosis) • so, by blowing off excess CO2 can reduce acidity of blood

26. Changes in Lactate, Bicarb and pH vs. Work Rate

27. Lines of Defense against pH Change during Intense Exercise