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

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?

7. 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

8. 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

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

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

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

14. 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

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

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

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

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

20. 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

21. 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)

25. 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)

26. Source: http://www.daviddarling.info/images/deep_vein_thrombosis.jpg

29. Factors that increase the risk of a DVT • Hip or leg fractures • Standing or sitting for long periods of time (airplanes) • Obesity • Smoking • Pregnancy, birth control bills, estrogen replacement therapy

30. 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)

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

32. 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).

33. CCHS

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

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

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

39. . 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

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

42. 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)

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

44. 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.

45. 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

47. 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

48. “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