فسلجة

• Ventilation (V)


  The flow of air into and out of the alveoli

  
• Perfusion (Q)


  The flow of blood to alveolar capillaries
• Ventilation-perfusion ratio


  Expressed as Va/Q
• When there is both normal Va (alveolar ventilation) and normal Q (alveolar perfusion), exchange of oxygen and carbon dioxide through the respiratory membrane is nearly optimal, and alveolar Po2 is normally at a level of 104 mm Hg (40 mm Hg in venous blood), and alveolar Pco2 40 mm Hg (45 mm Hg in venous blood)

  
• When the ventilation (Va) is zero, yet there is still perfusion (Q) of the alveolus, the Va/Q is zero
• When Va/Q is equal to zero (without any alveolar ventilation), the air in the alveolus comes into equilibrium with the blood oxygen and carbon dioxide because these gases diffuse between the blood and the alveolar air

  
• The blood that perfuses the capillaries is venous blood returning to the lungs from the systemic circulation, normal venous blood has a Po2 of 40 mm Hg and a Pco2 of 45 mm Hg
• When there is adequate ventilation (Va) but zero perfusion (Q), the ratio Va/Q is infinity
• When Va/Q equals infinity the alveolar air becomes equal to the humidified inspired air
• Normal inspired and humidified air has a Po2 of 149 mm Hg and a Pco2 of 0 mm Hg
• Physiologic Shunt


  Whenever Va/Q is below normal, there is inadequate ventilation to provide the oxygen needed to fully oxygenate the blood flowing through the alveolar capillaries
• A certain fraction of the venous blood passing through the pulmonary capillaries does not become oxygenated, this fraction is called shunted blood
• Some additional blood flows through bronchial vessels rather than through alveolar capillaries, normally about 2 per cent of the cardiac output, this too is unoxygenated, shunted blood
• Physiologic Dead Space


  When ventilation of some of the alveoli is great but alveolar blood flow is low, there is far more available oxygen in the alveoli than can be transported away from the alveoli by the flowing blood, so the ventilation of these alveoli is said to be wasted
• In a normal person in the upright position, both pulmonary capillary blood flow and alveolar ventilation are considerably less in the upper part of the lung than in the lower part, but blood flow is decreased considerably more than ventilation

  
• At the top of the lung, Va/Q is as much as 2.5 times as great as the ideal value
• تلاصيوحلا ةيئاوهلا


  عن قيرط مدلا قفدتملا
• ةيوهت هذه تلاصيوحلا ةيئاوهلا

  ةردهم
• Abnormal VA/Q in the Upper and Lower Normal Lung
• يف صخشلا يعيبطلا يف عضولا ميقتسملا

  1. قفدت مدلا يرعشلا يوئرلا ةيوهتلاو ةيخنسلا لقأ ريثكب يف ءزجلا يولعلا نم ةئرلا ةنراقم ءزجلاب يلفسلا

  2. قفدت مدلا ضفخني لكشب ظوحلم رثكأ نم ةيوهتلا

  3. ةميق Va/Q ربكأ رادقمب 2.5 ةرم نم ةميقلا ةيلاثملا
• امم ببسي ةجرد ةلدتعم نم ةحاسملا ةتيملا ةيجولويسفلا يف هذه ةقطنملا نم ةئرلا
• يف ءزجلا يلفسلا نم ةئرلا كانه ةيوهت ةليلق اًدج اميف قلعتي قفدتب مدلا ثيح لصت ةميق Va/Q ىلإ 0.6 فعض ةميقلا ةيلاثملا
• يف هذه ةقطنملا لشفي ءزج ريغص نم مدلا يف لوصحلا ىلع نيجسكلأا لكشب يعيبط اذهو لثمي ةليوحت ةيجولويسف
• ءانثأ نيرمتلا


  • دادزي قفدت مدلا ىلإ ءزجلا يولعلا نم ةئرلا لكشب ظوحلم
  • ثدحي ةحاسم ةتيم ةيجولويسف لقأ ريثكب
  • برتقت ةيلاعف لدابت تازاغلا نلآا نم ىوتسملا لثملأا
• ببسب مدع ةيافك قفدت مدلا لقنل تازاغ مدلا

  متي رادهإ مظعم ةيوهتلا
• يف ضرم دادسنلاا يوئرلا نمزملا رهظت ضعب قطانم ةئرلا ةليوحت ةيجولويسف ةريطخ
• رهظت قطانم ىرخأ ةحاسم ةيجولويسف ةتيم ةريطخ
• اتلك نيتلاحلا نلالقت لكشب ريبك نم ةيلاعف نيتئرلا ءاضعأك لدابتل تازاغلا
• يف ضعب نايحلأا نم امهتيلاعف ىلإ لقأ نم رشُع لدعملا يعيبطلا
• اذه وه ببسلا رثكلأا اًعويش ةقاعلإل ةيوئرلا مويلا