Review Lung Volumes

2. Review Lung Volumes

3. Tidal Volume (Vt) • volume moved during either an inspiratory or expiratory phase of each breath (L)

4. Inspiratory Reserve Volume (IRV) • Reserve ability for inspiration (L) • Volume of extra air that can be inhaled after a normal inhalation (L)

5. Expiratory Reserve Volume (ERV) • Volume of extra air that can be exhaled after a normal exhalation (L)

6. Forced Vital Capacity (FVC or VC) • Maximal volume of air that can be moved in one breath, from full inspiration to full expiration (L) • SVC may be greater due to air trapping

7. Residual Volume (RV) • Volume of air remaining in lungs following a maximal exhalation (L) • Usually increases with age • Allows for uninterrupted exchange of gases

8. Functional Residual Capacity (FRC) • Volume of air in the lungs at the end of a normal tidal exhalation (end tidal) (L) • Important for maintaining gas pressures in the alveoli

9. Total Lung Capacity (TLC) • Maximal amount of air in the lungs • RV + VC = TLC (L)

10. Maximal Ventilatory Volume (MVV or MBC) • Maximal amount of air that can be moved in one minute (L/min)

11. Pulmonary Ventilation • @ rest, usually ~ 6 l/min • Increase due to increases in rate and depth • Rate: inc. 35-45 breaths/min, elite athletes: 60-70 breaths/min, max. ex. • Vt 2 lit, Ve > 100 lit/min • Vt may reach 2 lit, still 55-65% if VC (Tr and UNTr)

12. Anatomic Dead Space • Volume of air that is in conducting airways, not in alveoli, not involved in gas exchange • Nose, mouth, trachea, other non-diffusible conducting portions of the respiratory tract • Air is identical to ambient air, but warmed, fully saturated with water vapor

13. 350 ml of 500 ml tidal volume will enter into and mix with existing alveolar air • 500 ml will enter alveoli, but only 350 ml is fresh air • 350 ml is about 1/7 of air in alveoli • This allows for maintenance of composition of alveolar air (concentration of gases)

14. Dead space versus tidal volume • Anatomic dead space increases with increases in tidal volume • Increase in dead space is still less than increase in tidal volume • Therefore, deeper breathing allows for more effective alveolar ventilation, rather than an increase in breathing rate

15. Physiologic Dead Space • Gas exchange between the alveoli and blood requires ventilation and perfusion matching: V/Q • @ rest, 4.2 l of air for 5 l of blood each minute in alveoli, ratio ~.8 • With light exercise, V/Q ratio is maintained • Heavy exercise: disproportionate increase in alveolar ventilation

16. When alveoli do not work adequately during gas exchange, it is due to • Under perfusion of blood • Inadequate ventilation relative to the size of the alveoli • This portion of alveolar volume with poor V/Q ratio is physiologic dead space • Small in healthy lung • If physiologic dead space >60% of lung volume, adequate gas exchange is impossible

17. Techniques of assessing lung volumes: • Spirometry (cannot determine RV and FRC) • Helium dilution • Oxygen washout • Plethysmograph (what we have) • based on Boyle’s Law: PV = P1V1

18. Alveolar Ventilation • > 300 million alveoli • elastic, thin-walled membranous sacs • surface for gas exchange • blood supply to alveolar tissue is greatest to any organ in body • are connect to each other via small pores

19. capillaries and alveoli are side by side • at rest, 250 ml of O2 leave alveoli to blood, and 200 ml of CO2 diffuse into alveoli • during heavy exercise, (TR athletes) 25X increase in quantity of O2 transfer

20. Gas exchange in the lungs • molecules of gas exert their own partial pressure • total pressure = mixture of the sum of the partial pressures • Partial pressure = % concentration X total pressure of the gas mixture

21. Ambient Air @ sea level • Oxygen: 20.93% X 760 mm Hg = 159 mm Hg • Carbon Dioxide: 0.03% X 760 mm Hg = 0.2 mm Hg • Nitrogen: 79.04% X 760 mm Hg = 600 mm Hg • Partial pressure is noted by P in front, e.g., PO2 = 159

22. Tracheal Air • as air enters respiratory tract, it is completely saturated with water vapor • water vapor will dilute the inspired air mixture • @ 37 degrees C, water exerts 47 mm Hg • 760 - 47 = 713 • Recalculate pressures, PO2 = 149

23. Alveolar Air • different composition than tracheal air • b/c of CO2 entering alveoli from blood and O2 leaving alveoli • average PO2 in alveoli ~103 mm Hg • PCO2 = 39 • these are average pressures, it varies with the ventilatory cycle, and the ventilation of a portion of the lung

24. FRC is present so that incoming breath has minimal influence on composition of alveolar air • therefore, partial pressures in alveoli remains stable

25. Gas Transfer in lungs • PO2 is about 60 mm Hg higher in alveoli than capillaries • b/c of diffusion gradient, oxygen will dissolve and diffuse through alveolar membrane into capillary • CO2 pressure gradient is smaller, ~ 6 mm Hg • adequate exchange still occurs b/c of high solubility of CO2

26. Nitrogen is not used nor produced, PN is relatively unchanged • Equilibrium is rapid, ~ 1 sec, the midpoint of blood’s transit through the lungs • during exercise, transit time decreases ~ 1/2 of that seen at rest • during exercise, pulmonary capillaries can increase in blood volume 3X resting • this maintains the pressures of oxygen and carbon dioxide

27. Gas Transfer in the Tissues • Partial pressures can be very different than those seen in the lung • @ rest, PO2 in fluid outside a muscle cell are rarely less than 40 mm Hg • PCO2 is about 46 mm Hg • During exercise, PO2 may drop to 3 mm Hg, and PCO2 rise to 90 mm Hg

28. O2 and CO2 diffuse into capillaries, carried to heart and lungs, where exchange occurs • body does not try to completely eliminate CO2 • blood leaves lungs with PO2 of 40 mm Hg, this is about 50 ml of carbon dioxide/100ml of blood • PCO2 is critical for chemical input for control of breathing (respiratory center in brain) • By adjusting alveolar ventilation to metabolic demands, the composition of alveolar gas will stay constant, even during strenuous exercise (which can increase VO2 and CO2 production by 25X)