Pulmonary Ventilation during Exercise

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• Pulmonary Ventilation during Exercise

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Ventilation in Steady Rate Exercise

• During light moderate steady rate exercise,
  VEVO2 linear relationship.
• Ventilatory equivalent for oxygen (VEVO2) ratio
  of minute ventilation to oxygen uptake.
• Usually 25 1 during submaximal exercise up to
  55 max.

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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.

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Ventilation in Steady Rate Exercise

• Ventilatory equivalent for carbon dioxide
  (VEVO2) ratio of minute ventilation to carbon
  dioxide produced.
• Remains constant during steady rate exercise
  because pulmonary ventilation eliminates CO2 .

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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.

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Ventilation in Non-Steady-Rate Exercise

• The point at which ventilation increases
  disproportionately with oxygen uptake during
  incremental exercise is termed ventilatory
  threshold (VT).

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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

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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.

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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 gt 1
indicate CO2 production exceeds O2 consumption,
evidence of non-metabolic CO2 production.
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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, H,
  bicarbonate, RER.

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Ventilation in Non-Steady-Rate Exercise

• Although variables (CO2 production, blood pH,
  H, bicarbonate, 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.

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Ventilation in Non-Steady-Rate Exercise

• Common practice to use bloodless techniques
  e.g. R gt1, or break in ventilatory equivalent for
  oxygen to denote anaerobic threshold.

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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.

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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.

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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.

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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.