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Other Factors Contributing to Non-Uniform Distribution of Perfusion

Other Factors Contributing to Non-Uniform Distribution of Perfusion. Right pulmonary artery comes off at an acute angle. Therefore, there is more flow to the left lung. Factors Contributing to Non-Uniform Distribution of Ventilation. Diaphragm and ribcage association with lungs provides for

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Other Factors Contributing to Non-Uniform Distribution of Perfusion

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  1. Other Factors Contributing to Non-Uniform Distribution of Perfusion • Right pulmonary artery comes off at an acute angle. Therefore, there is more flow to the left lung.

  2. Factors Contributing to Non-Uniform Distribution of Ventilation • Diaphragm and ribcage association with lungs provides for • greater expansion at the base than at apex • outer parencyma expands more than inner • Weight of the lung and blood at the base • greater starting volume at apex (less ventilation upon inhalation) • results in less negative pleural pressure at base, favoring greater expansion at apex • Net result: more ventilation at the base than at the apex.

  3. V/Q Matching Concentration (x mg / total ml) Powder Dye (x mg)

  4. V/Q Matching Concentration (V/Q) Fluid Flow (Q) Powder Dye (V)

  5. Powder Dye (V) Concentration (V/Q) Fluid Flow (Q)

  6. Powder Dye (V) Concentration (V/Q) Fluid Flow (Q)

  7. V/Q Matching Powder Dye (V) Concentration (V/Q) Fluid Flow (Q)

  8. Powder Dye (V) Concentration (V/Q) Fluid Flow (Q)

  9. Powder Dye (V) Concentration (V/Q) Fluid Flow (Q)

  10. L/min or V /Q % lung volume A C 0.15 3 VA / QC 0.10 2 Blood Flow Ventilation 0.05 1 Rib Number BOTTOM 5 4 3 2 TOP

  11. V/Q Matching 60 40 Low VA/Q PCO2 (mmHg) High VA/Q 20 0 40 60 80 100 120 140 PO2 (mmHg) mixed venous blood Tracheal air

  12. V/Q Matching VA Q VA/Q (L/min) 0.24 0.07 132 28 0.82 1.29 89 42 PO2 PCO2 pH mmHg 3.3 7.51 0.63 7.39

  13. Why is arterial PO2 lower than average (ideal) alveolar PO2? • When pulmonary veins joins combining volumes of blood that have different oxygen concentrations, the final concentration of oxygen is a simple, linear function of • Oxygen content of each volume • Sum of the volumes (final volume)

  14. V/Q Matching mv (pa) pv O2 Concentration 20 18 20.5 inVol% (100) (PO2) 18.0 X 10 = 180 60 X 10 = 600 20.0 X 10 = 200 100 X 10 = 1000 20.5 X 1 = 20.5 150 X 1 = 150 400.5 / 21 = 19.1 1750 / 21 = 83.3 V/Q=1/10 V/Q=10/10 V/Q=10/1 19.1 (70) (60) (150)

  15. Total O 2 22 100 18 80 14 60 O2 Content (ml O2/dl blood) Hb Saturation (%) 10 40 6 20 2 0 20 40 60 80 600 100 P (mmHg) O 2 Oxygen Transport

  16. Why is arterial PO2 lower than average (ideal) alveolar PO2? • When pulmonary veins joins combining volumes of blood that have different oxygen concentrations, the final concentration of oxygen is a simple, linear function of • Oxygen content of each volume • Sum of the volumes (final volume) • PO2is not a simple linear function of oxygen content or concentration.

  17. The PO2 of blood leaving the lungs of an upright individual will be slightly less than ideal (average) alveolar PO2 as a result of • the largest quantity of blood coming from regions with the lowest V/Q ratios, coupled with the non-linear characteristics of the oxyhemoglobin dissociation curve, skews the PO2 of arterial blood toward the alveolar PO2 values at the base • shunts

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