Techniques of assessing lung volumes:

1
(No Transcript)
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

• _at_ 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 gt 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
• _at_ 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 gt60 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 Boyles Law PV P1V1

18
Alveolar Ventilation

• gt 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 _at_ 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
• _at_ 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
  bloods 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
• _at_ 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)