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Why do we breathe? Take in O 2 (which we need to make ATP)

Why do we breathe? Take in O 2 (which we need to make ATP) Get rid of CO 2 (which is a waste product of ATP synthesis). Thought questions What happens to our cells and our bodies if we don’t get enough O 2 , or if CO 2 is made but never removed from the body?

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Why do we breathe? Take in O 2 (which we need to make ATP)

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  1. Why do we breathe? • Take in O2 (which we need to make ATP) • Get rid of CO2 (which is a waste product of ATP synthesis)

  2. Thought questions • What happens to our cells and our bodies if we don’t get enough O2, or if CO2 is made but never removed from the body? • Is the amount we breathe always the same? • What kinds of things change it?

  3. Partial pressure of a gas (P) P = F x Patm F = fraction of the gas in the atmosphere that is that gas Patm: atmospheric pressure

  4. Partial pressure of a gas (P) P = F x Patm F = fraction of the gas in the atmosphere that is that gas Patm: atmospheric pressure • Example: partial pressure of O2 in this room • 21% of the atmosphere is O2 • Atmospheric pressure in Boston (see level) is 760 mmHg PO2 = 0.21 x 760 = 160 mmHg

  5. Hypercarbia: PaCO2 greater than set point of 40 mmHg What determines the PaCO2?

  6. What determines the PaCO2? Answer: The PACO2 What determines the PACO2?

  7. What determines the PaCO2? Answer: The PACO2 What determines the PACO2? Answer: Alveolar ventilation

  8. Minute Ventilation = tidal volume (VT) x frequency .8 Change in volume (liters) .6 .4 VT .2 0 0 1 2 3 4 5 6 7 Time (sec) Breathing frequency: 1 breath/ 4 sec = 15 breaths/min VT = 0.6 liters

  9. Is all the air that we take in useful?

  10. A useful model of the lung – balloon on a tube Tube: airways Balloon: alveoli

  11. End Expiration VD = volume of cylinder Begin Inspiration Mid Inspiration

  12. VT = total volume of white area End Inspiration Mid Expiration End Expiration

  13. PANTING: high frequency but low volume breathing (assume a dead space of 0.1 L) Breathing at rest: VT = 0.5 L f = 10 breaths/min VE=5 L/min VA = 4 L/min Panting: VT = 0.14 L f = 100 breaths/min VE = 14 L/min VA = 4 L/min

  14. Examples of things that can cause hypoventilation • drugs (i.e. morphine) that suppress respiratory drive • diseases of the muscles (like myasthenia gravis) • diseases of the nerves • diseases that affect central respiratory drive: • - CCHS (Ondine’s curse).

  15. CCHS

  16. What causes changes in dead space? • 1) Breathing through a piece of equipment • Gas mask • Snorkel • Ventilator circuit • 2) Loss of blood flow to a ventilated region of lung • pulmonary embolism • Certain lung diseases (emphysema)

  17. What causes changes in dead space? • 1) Breathing through a piece of equipment • Gas mask • Snorkel • Ventilator circuit • 2) Loss of blood flow to a ventilated region of lung • pulmonary embolism • Certain lung diseases (emphysema)

  18. EMPHYSEMA Jeffrey et al, Am. J. Respir. Crit. Care Med. 2001 164: 28S-38S

  19. Hypoxemia: PaO2 less than the set point of about 80 mmHg

  20. CAUSES OF HYPOXEMIA • Hypoventilation • Diffusion Impairment • Shunt • V/Q abnormalities

  21. Diffusion Impairment What determines how fast O2 (or CO2) diffuses across the alveolar wall?

  22. . VO2 = K x A x (PAO2 – PaO2)/T . VO2 = flux of O2 across the lung K = a constant A = surface area of the lung T = thickness of the lung (distance between air and red blood cell) PAO2 and PaO2 = partial pressure for O2 in alveolus and in capillary blood

  23. EMPHYSEMA Jeffrey et al, Am. J. Respir. Crit. Care Med. 2001 164: 28S-38S

  24. Shunt: blood passes from the right heart to the left heart without becoming oxygenated • 1.Blood goes from the right to the left heart without going • through the lungs • Bronchial circulation • Foramen ovale, ductus arteriosus • 2. Blood goes through the lungs but never comes into close • contact with alveolar gas • Foreign object lodged in an airway • Pneumonia (accumulation of fluid and pus in the alveoli)

  25. How much does a shunt affect PaO2? “Good” lung “Bad” lung Air Pus and fluid 40% of C.O. 60% of C.O.

  26. How much does a shunt affect PaO2? “Good” lung “Bad” lung Air Pus and fluid PO2 = 100 mmHg PO2 = 40 mmHg 40% of C.O. 60% of C.O.

  27. How much does a shunt affect PaO2? “Good” lung “Bad” lung Air Pus and fluid PO2 = 100 mmHg PO2 = 40 mmHg 40% of C.O. 60% of C.O. In Out 40 mmHg 100 mmHg In Out 40 mmHg 40 mmHg PO2

  28. O2 carrying capacity of hemoglobin 1 g Hemoglobin (Hg) can carry 1.34 ml O2 (when fully saturated) Normal: 15 g Hg/ 100 ml blood x 1.34 = 20 ml O2/100 ml blood = 200 ml O2/L blood

  29. “Good” lung “Bad” lung 100% x 200 ml O2/L blood x 3L 75% x 200 ml O2/L blood x 2L 300 ml O2 600 ml O2 Blood mixes in left atrium 900 ml O2 in 5L blood 180 ml O2/L (Fully saturated 200 mlO2/L) 90% saturated PaO2 of 60 mmHg Assume the cardiac output is 5 L/min: 60% to good lung and 40% to bad lung 3 L/min 2 L/min

  30. Volume (L) Pressure (cm H2O)

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