3. Overview of Gas Exchange in the Lungs Adapted from: Costanzo, LS. Physiology , 1 st ed. 1998.
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10. Oxygen Transport (cont) Total O 2 content of blood (C a O 2 ) = + Dissolved O 2 O 2 bound to hemoglobin
11. Oxygen Transport (cont) Total O 2 content of blood (C a O 2 ) = P a O 2 Solubility of O 2 in blood + O 2 binding capacity of Hb x x x [Hb] O 2 sat
12. Oxygen Transport (cont) Total O 2 content of blood (C a O 2 ) = P a O 2 Solubility of O 2 in blood + O 2 binding capacity of Hb x x x [Hb] O 2 sat (During Normal Gas Exchange)
13. Oxygen Transport (cont) Total O 2 content of blood (C a O 2 ) = 100 mmHg 0.003mL O 2 ___ 100mL blood ∙ mmHg + 1.34mL O 2 1g Hb x x x 15g Hb 1dL blood 0.98 (During Normal Gas Exchange)
14. Oxygen Transport (cont) Total O 2 content of blood (C a O 2 ) = 0.3mL O 2 _ 100mL blood + 19.7mL O 2 _ 100mL blood (During Normal Gas Exchange) (Dissolved O 2 ) (Hb-bound O 2 )
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16. Hypercapnia - Etiologies P a CO 2 = (V CO 2 x P I ) / V A Alveolar Ventilation Equation V A = RR (V T – V D ) V A – Alveolar Ventilation RR – Respiratory Rate V T – Tidal Volume V D – Dead Space
17. Hypercapnia - Etiologies V CO 2 x P I RR (V T – V D ) P a CO 2 = ↑ V CO 2 (Hypermetabolism) Fever Seizures Sepsis Hyperalimentation ↓ RR (Central hypoventilation) Drugs Brainstem lesions Obesity-hypoventilation syndrome ↓ V T Skeletal muscle weakness Impaired neuromuscular transmission ↓ Lung / chest wall compliance Airway obstruction COPD Asthma Obstructive sleep apnea ↑ V D Excessive PEEP
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20. Hypoxia - Etiologies A-a Gradient = P A O 2 – P a O 2 Rearrangement: P a O 2 = P A O 2 – A-a gradient Alveolar Gas Equation P A O 2 = [F I O 2 (P I – P H 2 O )] – (P a CO 2 / RQ) Substitution: P a O 2 = [F I O 2 (P I – P H 2 O )] – (P a CO 2 / RQ) – (A-a gradient)
21. Hypoxia - Etiologies P a O 2 = [F I O 2 (P I – P H 2 O )] – (P a CO 2 / RQ) – (A-a gradient) ↑ A-a gradient V/Q mismatch COPD Pulmonary embolus Pneumonia Pulmonary edema Anatomic shunt Right to left intracardiac shunts Pulmonary AVMs Impaired diffusion Emphysema Pulmonary fibrosis ↓ F I O 2 Suffocation ↓ P I High altitude ↑ P a CO 2 As above
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