1. Ch 09 Measurement of the Respiratory System

2. 9.1 Modeling the respiratory system
Respiratory function:
Gas transport in the lung (extrapulmonary airway, pulmonary capilaries)
--changes in concentration of gas species
-- gas volume flow
Mechanics of the lung and chest wall
-- pressure, lung volume, d/dt (lung volume)

3. Balance

4. (AWOx •QAWO)in VL VA PA
PPL
(a)
(b)
(bx•Qb)in
AWO
QAWO
(bx•Qb)out
Ubx
Figure 9.1 Models of the lungs (a) basic gas-transport unit of the pulmonary system. Here (x  Q) is the molar flow of X through the airway opening, AWO, and the pulmonary capillary blood network, b. Ubx is the net rate of molar uptake –that is, the net rate of diffusion of X into the blood. VD and VA are the dead-space volume and alveolar volume, respectively. (b) A basic mechanical unit of the pulmonary system. PA is the pressure inside the lung – that is, in the alveolar compartment. PPL and PAWO are the pressures on the pleural surface of the lungs and at the airway opening, respectively. VL is the volume of the gas space within the lungs, including the airways; QAWO is the volume flow of gas into the lungs measured at the airway opening.

5. (AWOx •QAWO)in VL VA PA
PPL
(a)
(b)
(bx•Qb)in
AWO
QAWO
(bx•Qb)out
Ubx
Figure 9.1 Models of the lungs (a) basic gas-transport unit of the pulmonary system. Here (x  Q) is the molar flow of X through the airway opening, AWO, and the pulmonary capillary blood network, b. Ubx is the net rate of molar uptake –that is, the net rate of diffusion of X into the blood. VD and VA are the dead-space volume and alveolar volume, respectively. (b) A basic mechanical unit of the pulmonary system. PA is the pressure inside the lung – that is, in the alveolar compartment. PPL and PAWO are the pressures on the pleural surface of the lungs and at the airway opening, respectively. VL is the volume of the gas space within the lungs, including the airways; QAWO is the volume flow of gas into the lungs measured at the airway opening.

6. Chest wall (ribs, respiratory muscles, abdominal contents)
pPL pA
uL  qAWO
 pMUS
pAWO
RAW
CstL
(b) +
pBS
CstW
Chest wall (ribs, respiratory muscles, abdominal contents)
Interpleural space (filled with liquid)
Lung
CstW
pMUS
CstL
pPL
RAW uL pA
qAWO
pAWO
pBS
(a)
Figure 9.2 Models of normal ventilatory mechanics for small-amplitude, low-frequency (normal lungs, resting) breathing (a) Lung mechanical unit enclosed by chest wall. (b) Equivalent circuit for model in Figure 9.2(a).

7. ‘
Spatial difference: ΔY = Yi – Yj

8. Transpulmonary pressure difference:

9. An example pAWO RAW pA CstL pPL CstW   pMUS + pBS
Q1. (10 points) (From Spring Semester 2007)
pPL pA
 pMUS
pAWO
RAW
CstL  +
pBS
CstW
An equivalent circuit model of a normal respiratory mechanics is shown to the right. The modeling is based on the correspondence between the respiratory mechanics and the equivalent circuit model:
Pressure of air  Electrical voltage
Volume of air  Electrical charge
Flow of air  Electrical current
Explain the respiratory mechanism in terms of the circuit model. (i.e., how does our body do to make the air flow into and out of the lung.)
Assume that a pathological condition causes the reduction of the compliance in the alveolar membranes. How will this condition affect the respiration of the patient. (The answer must be based on an analysis on the circuit model.)

10. An example patm patm + pwa Q2. (5 %) (From Spring Semester 2007)
Draw an equivalent circuit to represent the normal respiratory mechanics of a person standing in a swimming pool, as shown to the right. Assume the water pressure at the lung level is pwa above one atmospheric pressure patm. Explain, in terms of the equivalent circuit model, why it becomes more difficult to breath when one stands in the water than in the air.
pPL pA
 pMUS
pAWO
RAW
CstL  +
pBS
CstW

11. 9.4 Lung volume TLC Total lung capacity FRC
Functional residual capacity RV
Residual volume IC
Inspiratory capacity
ERV
Expiratory reserve volume VC
Vital capacity VT
Tidal volume CV
Closing volume CC
Closing capacity

12. 肺活量
Figure 9.5 Volume ranges of the intact ventilatory system (with no external loads applied). TLC, FRC, and RV are measured as absolute volumes. VC, IC, ERV and VT are volume changes. Closing volume (CV) and closing capacity (CC) are obtained from a single-breath washout experiment.

14. Changes in lung volume
Measurement method 1:
Plethysmography --- to measure the volume changes of the gas space within the body during breathing
Measurement method 2:
Spirometry --- to measure the gas passing through the airway opening
(Assumption – the compression of the gas in the lungs is sufficiently small)

15. Changes in lung volume – math model

16. Spirometer Rotational displacement sensor Other signal processing
Strip-chart
recorder
Counterweight
Kymograph
Bell PS VS TS
Water seal
Blood
flow
Uabs
One-way
valves
FS x
Mouthpiece
Soda-lime
canister VL
Ubs
Thermometer for
spirometer gas
temperature TL PA
QAWO
FA x
Spirometer
system
Pulmonary
system
Figure 9.6 A water-sealed spirometer set up to measure slow lung-volume changes. The soda-lime and one-way-valve arrangement prevent buildup of CO2 during rebreathing.

17. The main components of soda lime are :
Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.
It is made by slaking quicklime (生石灰 ) with concentrated caustic soda (NaOH) solution.
The main components of soda lime are :
Calcium hydroxide - Ca(OH)2 (about 75%)
Water - H2O (about 20%)
Sodium hydroxide - NaOH (about 3%)
Potassium hydroxide - KOH (about 1%)
From Wikipedia, the free encyclopedia

18. Spirometry, mass balances of

19. The change in lung volume --- measurable

20. Absolute volume of the lung – how to measure?
Difficulty in measuring absolute lung volume
* complex geometry, irregular
* inaccessibility

21. Absolute volume of the lung – three methods
Nitrogen-washout
-- based on static mass balances and washout of a test gas
2. Helium dilution
-- based on static mass balances and dilution of a test gas
3. Total body plethysmography – based on dynamic mass balances and gas compression

22. Absolute volume of the lung
Dalton's law of partial pressures:
the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture

23. Absolute volume of the lung
Nx Vx P
Nx mole of X only
N V P
Nx mole of X and other gases
N moles totally

25. Absolute volume of the lung – Nitrogen-washout estimation
analyzer
100% O2 O2 + N2
CO2 VL TL
FAN2 TS VS
Spirometer
One-way
valves
FSN2
Figure 9.7 Diagram of an N2 washout experiment The expired gas can be collected in a spirometer, as shown here, or in a rubberized-canvas or plastic Douglas bag. N2 content is then determined off-line. An alternative is to measure expiratory flow and nitrogen concentration continuously to determine the volume flow of expired nitrogen, which can be integrated to yield an estimate of the volume of nitrogen expired.

26. Absolute volume of the lung – Nitrogen-washout estimation

27. Nitrogen
analyzer
100% O2 O2 + N2
CO2 VL TL
FAN2 TS VS
Spirometer
One-way
valves
FSN2

28. Absolute volume of the lung – Helium-dilution estimation
Tracer gases:
* Properties: nontoxic, insoluble
* Examplea: He, Ar, Ne

29. Spirometer Rotational displacement sensor Other signal processing
Strip-chart
recorder
Counterweight
Kymograph
Bell PS VS TS
Water seal
Blood
flow
Uabs
One-way
valves
FS x
Mouthpiece
Soda-lime
canister VL
Ubs
Thermometer for
spirometer gas
temperature TL PA
QAWO
FA x
Spirometer
system
Pulmonary
system
Figure 9.6 A water-sealed spirometer set up to measure slow lung-volume changes. The soda-lime and one-way-valve arrangement prevent buildup of CO2 during rebreathing.

30. Absolute volume of the lung – Helium-dilution estimation