Alveolar ventilation, Dead Spaces and Ventilation/perfusion ratio

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Alveolar ventilation, Dead Spaces and
Ventilation/perfusion ratio

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TOTAL PULMONARY VENTILATION

• It is total amount of new air that moves into
  lungs during each minute
• Total pulmonary ventilation or Minute respiratory
  volume
• Ventilation rate x Total volume
• 12 breaths/ mt x 500 ml/ breath
• 6000 ml / mt

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Dead Spaces

• Anatomic dead Space
• Physiological dead space
• Alveolar dead space

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Rate of Alveolar Ventilation

• Ventilation rate x ( Tidal volume dead
  space volume)
• 12 x 500 150
• 12 x 350
• 4200 ml / mt

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Effects of Breathing Pattern on Alveolar
Ventilation
Fresh Air to Alveoli
Respiratory Rate
Total Pulmonary (tidal volume
dead Alveolar Ventilation Tidal Volume (ml)
(Breaths / min ) Ventilation ( mL / min)
space volume ( mL / min) 500
(Normal) 12 (Normal) 6000
350 4200
300(Shallow) 20 ( rapid)
6000 150
3000 750 (Deep) 8( Slow)
6000 600
4800
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Types and Patterns of Ventilation
Eupnea Normal quiet breathing
Hyperpnea Increased respiratory
rate and / or volume Exercise
in response to increased metabolism
Hyperventilation increased respiratory rate
and / or volume Emotional
hyperventilationblowing up a without
increased metabolism balloon
Hypoventilation Decreased
alveolar ventilation
Shallow breathing / asthma/ restrictive lung
disease Tachypnea
Rapid breathing usually increased
Panting (hanpna, urdu) respiratory
rate with decreased depth Dyspnea
Difficulty in breathing (a subjective
Various pathologies or hard exercise
feeling sometimes described as air
hunger) Apnea Cessation of
breathing Voluntary breath-holding
depression of
CNS control centers
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Ventilation-perfusion(V/Q) ratio

• Physiologic Dead Space(V/Q greater than normal)
  
• Physiologic shunt is the total quantitative
• amount of shunted blood per minute
• (V/Q below normal)

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Respiratory membrane
Respiratory Membrane
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Physics of Diffusion
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Gas Exchange at alveoli Cell
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Partial pressure of O2 (Po2) at various sites.
Site Po2 (mm Hg)
Atmospheric air (dry) 159
Inspired air ( partially wet) 158
Air entering lungs 149.3
Alveolar air 100
Arterialized blood in pulmonary veins entering left atrium 97
Arterial blood ( in aorta, arteries, arterioles ) 95
Tissue cells 40 or less
Mixed venous blood 40
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Partial pressure of CO2 (PCo2) at various sites.
Site PCo2 (mm Hg)
Tissue cells 50 70
Venous Blood 46
Alveolar Air 40
Arterial Blood 40
Expired air 32
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