TOTAL PULMONARY VENTILATION Total pulmonary ventilation or Minute respiratory volume = Ventilation rate x Total volume =12 breaths/ mt x 500 ml/ breath =6000 ml / mt

Dead Spaces Anatomic dead Space + Physiological dead space Alveolar dead space }

Rate of Alveolar Ventilation =Ventilation rate x ( Tidal volume – dead space volume) = 12 x 500 – 150 = 12 x 350 = 4200 ml / mt

Respiratory Unit

Respiratory membrane

Physics of Diffusion D  P x A x S d x MW

Gas Exchange at alveoli & Cell

Partial pressure of gases in air at various respiratory levels Atmosphere Inspired air Air entering the lungs Alveolar air Expired air PN2 (including traces of other gases 600.6 596 563.4 573 565 PO2 PCO2 159.1 0.3 158 149.3 100 116 40 32 PH2O Total Nil 760 5.7 47.0 47 47 760 760

Partial pressure of O2 (Po2) at various sites. 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

Partial pressure of CO2 (PCo2) at various sites. PCo2 (mm Hg) Tissue cells 50 – 70 Venous Blood 46 Alveolar Air 40 Arterial Blood Expired air 32