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Pulmonary Ventilation during Exercise

Pulmonary Ventilation during Exercise. Ventilation in Steady Rate Exercise. During light & moderate steady rate exercise, V E :VO 2 linear relationship. Ventilatory equivalent for oxygen (V E :VO 2 ): ratio of minute ventilation to oxygen uptake.

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Pulmonary Ventilation during Exercise

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  1. Pulmonary Ventilation during Exercise

  2. Ventilation in Steady Rate Exercise • During light & moderate steady rate exercise, VE:VO2 linear relationship. • Ventilatory equivalent for oxygen(VE:VO2): ratio of minute ventilation to oxygen uptake. • Usually 25 : 1 during submaximal exercise up to 55% max.

  3. Ventilation in Steady Rate Exercise • Ventilatory response to fixed level of submaximal exercise can be divided into 4 phases. • Sudden increase at onset. • Ventilation gradually increases to higher steady-rate level. • Steady state level of ventilation maintained. • Recovery period gradual return to resting levels. • Phase IV higher than resting levels coincide with EPOC.

  4. Ventilation in Steady Rate Exercise • Ventilatory equivalent for carbon dioxide (VE:VO2): ratio of minute ventilation to carbon dioxide produced. • Remains constant during steady rate exercise because pulmonary ventilation eliminates CO2 .

  5. Ventilation in Non-Steady-Rate Exercise • Minute ventilation (VE) increases in proportion to oxygen consumption over range from rest to moderate exercise. • VE increases dispropor-tionately to oxygen consumption over range from moderate to strenuous.

  6. Ventilation in Non-Steady-Rate Exercise • The point at which ventilation increases disproportionately with oxygen uptake during incremental exercise is termed: ventilatory threshold (VT).

  7. Ventilation in Non-Steady-Rate Exercise • Lactic acid generated during anaerobic glycolysis is buffered in blood by sodium bicarbonate. Lactic acid + NaHCO3→ Na Lactate + H2CO3→ H20 + CO2

  8. Ventilation in Non-Steady-Rate Exercise • The excess, non-metabolic CO2 stimulates ventilation. • Recall that metabolic CO2 is produced in Krebs Cycle in oxidation of acetyl CoA.

  9. Ventilation in Non-Steady-Rate Exercise • The non-metabolic CO2 from buffering HLa drives increased VE to eliminate it, so VE: VCO2 remains constant. • The increased in VE exceeds increase in VO2 disproportionately. • The point at which VEO2 breaks with linearity is the ventilatory threshold. RER = 1 where two lines intersect. R values > 1 indicate CO2 production exceeds O2 consumption, evidence of non-metabolic CO2 production.

  10. Ventilation in Non-Steady-Rate Exercise • As exercise intensity increases, blood lactate begins to systematically increase over a baseline value of 4 mM/L termed onset of blood lactate. • Blood lactate accumulation associated with changes in CO2 production, blood pH, bicarbonate, [H+], RER.

  11. Ventilation in Non-Steady-Rate Exercise • Although variables(CO2 production, blood pH, bicarbonate, [H+], RER)are related to OBLA, doubtful that VT can be used to denote onset of anaerobic metabolism. • OBLA directly assessed by measuring lactate level in blood.

  12. Ventilation in Non-Steady-Rate Exercise • Common practice to use “bloodless” techniques e.g. R >1, or break in ventilatory equivalent for oxygen to denote anaerobic threshold.

  13. Does Ventilation Limit Aerobic Capacity for Average Person? • If inadequate breathing capacity limited aerobic capacity, ventilatory equivalent for oxygen would decrease. • Actually, healthy person tends to over-breathe in relation to VO2. • In strenuous exercise, decreases arterial PCO2 & increase Alveolar PO2.

  14. Work of Breathing • Two major factors determine energy requirements of breathing • Compliance of lungs • Resistance of airways to smooth flow of air • As rate & depth of breathing increase during exercise, energy cost of breathing increases too. • At maximal exercise when VE= 100 L/m, oxygen cost of breathing represents 10-20% of total VO2.

  15. Work of Breathing • Acute effects of 15 puffs on a cigarette during a 5-minute period • 3 fold increase in airway resistance • Lasts an average 35 minutes • Smokers exercising at 80% • Energy requirement of breathing after smoking was 14% of oxygen uptake • Energy requirement of breathing no cigarettes was only 9%.

  16. References • Axen and Axen. 2001. Illustrated Principles of Exercise Physiology. Prentice Hall. • Kapit, Macey, Meisami. 1987. Physiology Coloring Book. Harper & Row. • McArdle, Katch, Katch. 2006. Image Collection Essentials of Exercise Physiology, 3rd ed. Lippincott William & Wilkens.

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