Respiratory physiology


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Respiratory physiology

  1. 1. Ventilation<br />Diffusion<br />Ventilation-perfusion Relationships<br />Gas Transport by the Blood<br />Respiratory Physiology<br />
  2. 2. Lung Volumes<br />
  3. 3. LUNG VOLUMES AND CAPACITIES Remember: Capacities are always the summation of volumes.TIDAL VOLUME (TV): Volume inspired or expired with each normal breath.INSPIRATORY RESERVE VOLUME (IRV): Maximum volume that can be inspired over the inspiration of a tidal volume/normal breath. Used during exercise/exertion.EXPIRATRY RESERVE VOLUME (ERV): Maximal volume that can be expired after the expiration of a tidal volume/normal breath.RESIDUAL VOLUME (RV): Volume that remains in the lungs after a maximal expiration.  CANNOT be measured by spirometry.INSPIRATORY CAPACITY ( IC): Volume of maximal inspiration:IRV + TVFUNCTIONAL RESIDUAL CAPACITY (FRC): Volume of gas remaining in lung after normal expiration, cannot be measured by spirometry because it includes residual volume:ERV + RVVITAL CAPACITY (VC): Volume of maximal inspiration and expiration:IRV + TV + ERV = IC + ERVTOTAL LUNG CAPACITY (TLC): The volume of the lung after maximal inspiration.  The sum of all four lung volumes, cannot be measured by spirometry because it includes residual volume:IRV+ TV + ERV + RV = IC + FRCDEAD SPACE: Volume of the respiratory apparatus that does not participate in gas exchange, approximately 300 ml in normal lungs.  --ANATOMIC DEAD SPACE: Volume of the conducting airways, approximately 150 ml  --PHYSIOLOGIC DEAD SPACE: The volume of the lung that does not participate in gas exchange.  In normal lungs, is equal to the anatomic dead space (150 ml).  May be greater in lung disease.FORCED EXPIRATORY VOLUME in 1 SECOND (FEV1): The volume of air that can be expired in 1 second after a maximal inspiration.  Is normally 80% of the forced vital capacity, expressed as FEV1/FVC.  In restrictive lung disease both FEV1 and FVC decrease , thus the ratio remains greater than or equal to 0.8.  In obstructive lung disease, FEV1 is reduced more than the FVC, thus the FEV1/FVC ratio is less than 0.8.<br />
  4. 4. Ventilation<br />
  5. 5. Ventilation<br />PaCO2 – ventilatory status<br />Ventilation<br />PaCO2<br />Ventilation<br />PaCO2<br />
  6. 6. Ventilation<br />Minute ventilation (VE) = Tidal volume (VT) x RR<br /> = (VD + VA) RR<br /> VT (RR) = VD(RR) + VA(RR) <br /> VA(RR) = VT (RR) - VD(RR)<br />Alveolar ventilation = (tidal volume – VD ) RR<br />
  7. 7. VA = RR ( VT – VD )<br />
  8. 8. Ventilation<br />Anatomic dead space - volume of the conducting airways (150 ml)<br />Physiologic dead space - volume of gas that does not eliminate CO2<br />
  9. 9. Diffusion<br />Vgas = A . D . (P1 – P2 ) <br /> T<br />Fick’s Law<br />The rate of diffusion of a gas through a tissue slice:<br />proportional to the area, partial pressure difference, solubility of the gas in the tissue<br />inversely proportional to the thickness and the square root of the molecular weight <br />
  10. 10. Uptake of carbon monoxide, nitrous oxide, and O2 along the pulmonary capillary<br />
  11. 11. Diffusion of Oxygen Across the Blood-Gas Barrier:<br />
  12. 12. Measurement of Diffusing Capacity<br />Carbon Monoxide<br />Gas of choice<br />Diffusion-limited<br />Fick’s Law<br />Vgas = A . D . (P1 – P2 )<br /> T<br />
  13. 13. Measurement of Diffusing Capacity<br />Vgas = DL · (P1 – P2 )<br />DL – Diffusing capacity of the lung (area, thickness, and diffusion properties<br />DL CO = V•CO/P1-P2<br />DL CO = V•CO /PA co<br />NV DL CO =25ml/min/mmHg (increases 2-3x during exercise<br />
  14. 14. Ventilation-Perfusion Relationships<br />PO2 of air: 20.93%<br />Barometric pressure at sea level: 760mmHg<br />Water vapor pressure of moist inspired air: 47mmHg <br />PO2 of inspired air = (.2093) X (760 - 47) =149 mm Hg<br />
  15. 15. Ventilation-Perfusion Relationships<br />Scheme of the O2 partial pressures from air to tissues<br />
  16. 16. 5 Causes of Hypoxemia<br />Hypoventilation<br />Diffusion abnormality<br />Shunt<br />Ventilation-perfusion inequality<br />Decreased inspired oxygen<br />
  17. 17. Hypoventilation<br />
  18. 18. Hypoventilation<br />Causes:<br />Drugs (morphine and barbiturates)<br />Damage to chest wall or paralysis of respiratory muscles<br />High resistance to breathing (underwater)<br />
  19. 19. Hypoventilation<br />Increases the PCO2<br />Decreases the PO2 unless additional O2 is inspired<br />Hypoxemia is easy to reverse by adding O2<br />
  20. 20. 5 Causes of Hypoxemia<br />Hypoventilation<br />Diffusion abnormality<br />Shunt<br />Ventilation-perfusion inequality<br />Decreased inspired oxygen<br />
  21. 21. Shunt<br />Refers to blood that enters the arterial system without going through ventilated areas of lung <br />Bronchial artery collected by pulmonary veins<br />Coronary venous blood draining through thebesian veins<br />AV fistula<br />Hypoxemia responds poorly to added inspired O2<br />When 100% O2 is inspired, the arterial PO2 does not rise to the expected level- a useful diagnostic test<br />
  22. 22. VQ Mismatch/Inequality<br />O2 = 150 mmHg<br />CO2 = 0<br />
  23. 23. Regional Gas Exchange in the Lung<br />
  24. 24. Gas Transport by the Blood<br />Oxygen is carried in the blood in 2 forms:<br />Dissolved O2<br />Amount dissolved is proportional to the partial pressure (Henry’s Law)<br />0.003 ml O2 in 100ml blood/mmHg of PO2<br /> N Arterial blood w/ PO2 of 100mmHg has 0.3ml O2/IL blood<br />Combined with hemoglobin<br />
  25. 25. O2 + Hb↔ HbO2 (oxyhemoglobin)<br />O2 capacity - maximum amount of 02 that can be combined with Hb<br />O2 saturation - percentage of the available binding sites that have O2 attached, <br />O2 combined w/ Hbx 100<br />O2 capacity<br />O2 saturation of arterial blood with PO2 100mmHg is 97.5% <br />
  26. 26. O2 Dissociation Curve<br />
  27. 27. Carbon Dioxide<br />Carried in the blood in 3 forms:<br />Dissolved<br />As bicarbonate<br />As carbamino compounds<br />
  28. 28. Scheme of the uptake of CO2 and liberation of O2 in systemic capillaries<br />Chloride shift<br />
  29. 29. Some of the H+ ions liberated are bound to reduced hemoglobin (better proton acceptor)<br />H+ + HbO2 ↔ H+. Hb + 02<br />Reduced Hb in the peripheral blood helps unload CO2<br />Haldane effect: deoxygenation of blood increases its ability to carry CO2, mop up H+ ions, and form carbamino-Hb<br />
  30. 30. CO2 Dissociation Curve<br />
  31. 31. Acid-base Status<br /> HCO3 (Metabolic)<br />pH= (6.1) + log -------- <br /> PaCO2 (Respiratory)<br />HCO3<br />--------- = pH<br />PaCO2<br />
  32. 32. 32<br />iHCO3<br />------ = iipH<br />PaCO2<br />HCO3<br />------ = iipH<br />hPaCO2<br />Metabolic Acidosis<br />Respiratory Acidosis<br />hHCO3<br />------ = hhpH<br />PaCO2<br />HCO3<br />------ = hhpH <br />iPaCO2<br />Metabolic Alkalosis<br />Respiratory Alkalosis<br />
  33. 33. 33<br />hHCO3<br />------ = hhpH <br />iPaCO2<br />Combined<br />Respiratory & Metabolic<br />Alkalosis<br />iHCO3<br />------ = iipH <br />hPaCO2<br />Combined<br />Respiratory & Metabolic<br />Acidosis<br />
  34. 34. 34<br />iHCO3<br />------ = iipH <br />PaCO2<br />iHCO3<br />------ = ipH <br />iPaCO2<br />iHCO3<br />------ = N pH <br />iPaCO2<br />Compensated<br />Uncompensated<br />Partly Compensated<br />Metabolic Acidosis<br />
  35. 35. Thank YOU!<br />