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Understanding the Importance of Breathing in Oxygen and Removing CO2 in Human Physiology

Explore the vital role of breathing in taking in oxygen for ATP production and expelling CO2 as a waste product. Discover the consequences of oxygen deprivation and CO2 buildup in the body, along with factors affecting breathing rates and gas exchange. Learn about partial pressure of gases, hypoventilation causes, and conditions like emphysema. Gain insights into phenomena such as hypercarbia, dead space changes, hypoxemia, diffusion impairment, and shunt effects on oxygen saturation. Demystify the intricate mechanisms of lung function and gas exchange processes in the human body.

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Understanding the Importance of Breathing in Oxygen and Removing CO2 in Human Physiology

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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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