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Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
Pneumology - Ventilation perfusion-ratio-and-clinical-importance
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Pneumology - Ventilation perfusion-ratio-and-clinical-importance

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  • 1. Ventilation‐perfusion in health &  Ventilation‐perfusion in health & disease Arjun Srinivasan
  • 2. Where was the beginning ?
  • 3. Distribution of ventilation Distribution of ventilation • Spatial & anatomical variation • Rate of alveolar filling Rate of alveolar filling • Rate of alveolar emptying
  • 4. Ventilation distribution‐ RC t Ventilation distribution RC t f a s t s l o w R=1 C=.5 t = .5 R=2 C=1 C 1 t =2 R=1 C=1 C 1 t = 1 volume (% of final) % ) 100 75 50 25 0 0 1 2 sekundy seconds 3
  • 5. Clinical relevance  Clinical relevance • Perfusion is poor & pulsatile at apex • Pa & Pv proportionately increases from top to & P proportionately increases from top to  bottom • PA changes minimally with gravity h i i ll i h i • Pressures are max at bottom  – Pulm edema starts at bottom – Redistribution of blood flow to apex antler’s Redistribution of blood flow to apex – antler’s  horn
  • 6. Its not just gravity! Its not just gravity! Lung perfusion in zero gravity  situations is more uniform but  by  no means equally distributed Nunn’s Applied respiratory physiology, 6 th edition
  • 7. Understanding V/Q relationships Understanding V/Q relationships • C id l Consider lung as single unit i l it – Relationships  between PA O2, PA CO2, alveolar  l h b l l ventilation & pulmonary blood flow – Alveolar gas equation  • Consider lung as multiple units of varying V/Q – Clinical consequences in health & disease
  • 8. Alveolar PO and PCO Alveolar PO2 and PCO2 • D Determined by the ratio between ventilation and  i db h i b il i d blood flow: V/Q • PO2 and PCO2 are inversely related through alveolar  ventilation il i • Increasing V/Q produces higher PAO2 and lower PACO2 • Decreasing V/Q produces lower PAO2 and higher  PACO2
  • 9. Gas Composition in the Alveolar Space Gas Composition in the Alveolar Space PiO2 = (barometric pressure‐H2O vapor pressure) xFiO2 =  (760 – 47) x 0.21 =150 mmHg ( )
  • 10. Alveolar Gas Equation Alveolar Gas Equation PAO2 = (PiO2) – (PaCO2/R) PaCO2 approximates PACO2 due to the rapid diffusion of  CO2 R = Respiratory Quotient (VCO2/V02) = 0.8 In a normal individual breathing room air: PAO2 = 150 – 40/0.8 = 100 mmHg / g
  • 11. Ventilation/perfusion ratio (V/Q) il i / f i i ( / ) V Q
  • 12. V/Q distribution in health  West JB, Respiratory Physiology,  The Essentials, 6th ed. 2000, Lippincott, p. 54.
  • 13. V/Q ratio in disease V/Q ratio in disease obstruction alveolus vessel 50 40 “ideal” V/Q ↓ V/Q ↑ V/Q 30 PCO2 (mmHg) 20 ( ) dead space shunt/ venous admixture 10 0 0 embolus 40 80 120 PO2 (mmHg) 160
  • 14. Low V/Q Effect on Oxygenation Low V/Q Effect on Oxygenation One lung unit has One lung unit has normal ventilation and perfusion, while the  has inadequate ventilation has inadequate ventilation Low L V/Q Normal ↑ PCO2 ↓ PO2 PO2 50 PO2 100 PO2 ? PO2 ?
  • 15. CO2=(1.3 x HGB x Sat) + (.003 x PO2) ( ) ( ) % % Hemog globin Saturatio on 100 20 80 16 60 12 40 8 20 4 0 0 0 20 40 60 80 PO mmHg 2 100 Oxy ygen Content (ml/10 ml) C t 00 Oxyhemoglobin Dissociation Curve Dissociation Curve
  • 16. Low V/Q Effect on Oxygenation Low V/Q Effect on Oxygenation Low L V/Q Normal PO2 50 mmHg Sat 80% O2 content 16ml/dl PO2 50 PO2 100 mmHg g Sat 100% O2 content 20ml/dl PO2 100 PO2 = 60 Sat  90% O2 content 18ml/dl
  • 17. HIGH V/Q Effect on Oxygenation HIGH V/Q Effect on Oxygenation HIGH V/Q Normal PO2  130mmHg Sat 100% O2 content 20 ml/dl PO2 130 PO2 100 mmHg g Sat 100% O2 content 20ml/dl PO2 100 PO2 = 100 Sat  100% O2 content 20 ml/dl
  • 18. High + low V/Q = ? High + low V/Q = ? HIGH V/Q Low L V/Q PO2 50 mmHg Sat 80% O2 content 16ml/dl PO2 50 PO2 130 mmHg g Sat 100% O2 content 20ml/dl PO2 130 PO2 = 60 Sat  90% O2 content 18ml/dl
  • 19. Local ↑ V/Q above ~1 has minimal  effect on [O2] 160 23 PaO2 (mmHg) O2 content 21 ( / (ml/100 ml) ) 22 120 20 80 19 18 40 17 16 0 0.001 0.01 0.1 1 10 V/Q Thus ↑ V/Q in one part of lung can’t compensate for ↓ elsewhere 15 100
  • 20. PCO2 in V/Q Mismatch in V/Q Mismatch – Shape of CO2 curve Shape of CO2 curve • Total ventilation (VE)  ( ) must increase for this  compensation 80 CO2 CONTENT (ml/100 ml) T m • Increased ventilation  can compensate for  low V/Q units low V/Q units 60 40 20 0 20 40 60 P CO (mmHg) 2 80
  • 21. Infinity  fi i ↑V/Q Dead space
  • 22. Zero ↓V/Q Shunt Venous admixture
  • 23. Ventilation to Perfusion Mismatch   Ventilation to Perfusion Mismatch Pure Shunt Perfusion with  No Ventilation Pure Dead Space Shunt Like Units shunt Dead Space  Like Units Like Units Ventilation with No Perfusion Dead space
  • 24. 3‐ compartment model   3 compartment model 1 2 3
  • 25. Dead space Dead space • Defined as wasted ventilation • Classification – Anatomical ( 1 ml / pound of ideal body wt) – Alveolar – Physiological  • Anatomical + alveolar Anatomical + alveolar 
  • 26. Physiological Dead Space by Bohr’s  Method (for CO2) VT X FE = VA X FA X F V X F VT = VA + VD VA = VT – VD VT X FE = (VT – VD) X FA VD = FA – FE VT FA T  VD = PACO2 – PECO2 (Bohr Equation), so… VT PACO2 VD = PaCO2 – PECO2 PaCO CO VT PaCO2
  • 27. Physiologic Dead Space & V/Q Mismatch Hyperinflation • Airway Obstruction • Dynamic Hyperinflation  • Tidal Volume • PEEP Low Perfusion Low Perfusion • Low Cardiac Output • Pulmonary Vascular Injury • Extravascular Compression No Perfusion No Perfusion • Pulmonary Embolus • Vascular Obliteration • Emphysema
  • 28. Shunt equation  Shunt equation Qt x CaO2 = [(Qt – Qs) x Cc’O2] + [Qs x CvO2]  Qs Cc ' O2 − CaO 2 = Qt Cc ' O2 − CvO 2
  • 29. Causes of Shunt Causes of Shunt • Physiologic shunts – Bronchial veins, pleural veins ,p • P th l i h t Pathologic shunts – Intracardiac – Intrapulmonary • Vascular malformations • Unventilated or collapsed alveoli 
  • 30. Normal shunt fraction  Normal shunt fraction • ~ 5 % • Due to – Physiological shunt – Gravity related V/Q mismatch y • Contributes to A a D O2 Contributes to A‐a D O – 10 – 15 mm hg 
  • 31. A a A a DO2 • PAO2 ( l l PAO2 (alveolar gas equation)‐ arterial PaO2 ti ) t i l P O2 • I t t ll ffi i t l In a totally efficient lung unit with matched V/Q,  it ith t h d V/Q alveolar and capillary PO2 would be equal • Admixture of venous blood or V/Q scatter from low  V/Q lung units will  increase A a V/Q lung units will increase A a DO2 • Increases ~ 3 mm hg every decade after 30 yrs of age Increases  3 mm hg every decade after 30 yrs of age
  • 32. Shunt    VS. V/Q scatter Shunt VS V/Q scatter • C l l d h Calculated shunt fraction or A a DO2 f i O – Does not differentiate • Response of pa O2 to increasing Fi O2 • V/Q scatter  – Pa O2 increase with small increase in FiO2(.21‐.35) • Pure shunt – Not much response  p
  • 33. MIGET • • • 50 parallel gas exchange units  characterized by VA‐Q ratio. Fit predicted PE & Pa to  experimental data. Output:  Ventilation and  perfusion distributions.
  • 34. Compensation of V/Q inequality ? Compensation of V/Q inequality ? • ↑V/Q → local hypocapnia → ↑pH → local  bronchoconstriction (↓V/Q ) • ↓V/Q → ↑CO2 → ↑ ventilation ↓V/Q → – improves CO2 > O2 (dissociation curves) • ↓V/Q → hypoxic pulmonary vasoconstriction
  • 35. Points to remember Points to remember • Ventilation and Perfusion must be matched at the alveolar capillary Ventilation and Perfusion must be matched at the alveolar capillary  level • Most important cause of hypoxemia in most respiratory diseases Most important cause of hypoxemia in most respiratory diseases • V/Q ratios close to 1.0 result in alveolar PO2 close to 100 mmHg  and PCO2 close to 40 mmHg and PCO2 close to 40 mmHg • V/Q greater than 1.0 increase PO2 and Decrease PCO2.  V/Q less  than 1.0 decrease PO2 and Increase PCO2 than 1 0 decrease PO2 and Increase PCO2 • Shunt and Dead Space are Extremes of V/Q mismatching. • A‐a Gradient of 10‐15 Results from gravitational effects on V/Q and  Physiologic Shunt

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