© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

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.

(AWOx •QAWO)in

VL

VA

PA

PPL

(a) (b)

(bx•Qb)in

AWO

QAWO

(bx•Qb)out

Ubx

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

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).

CstW

pPL

pA

pMUS

L qAWO

pMUS

CstL

pPL

RAW L

pA

qAWO

pAWO

pBS

pAWO

RAW

CstL

(b)(a)

+

pBS

CstW

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.3 Pneumotachometer flow-resistance elements (a) Screen. (b) Capillary tubes or channels.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.4 Pneumotachometer for measurements at the mouth (a) Diameter adapter that acts as a diffuser. (b) An application in which a constant flow is used to clear the dead space.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

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.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

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.

VL

TL

PA

Other signalprocessing

Strip-chartrecorder

Thermometer forspirometer gastemperature

One-wayvalves

Water seal

Bell

Uabs

Soda-limecanister

Pulmonarysystem

Spirometersystem

Mouthpiece

QAWO

Bloodflow

Kymograph

Counterweight

Rotationaldisplacementsensor

PS VS

TS

FS x

FA x

Ubs

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

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.

Nitrogenanalyzer

100% O2

O2

+N2

+CO2

VL

TL

FAN2

TS

VS

Spirometer

One-wayvalves

FSN2

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.8 A pressure-type total-body plethysmography is used with the shutter closed to determine lung volume and with the shutter open to determine changes in alveolar pressure. Airway resistance can also be computed if volume flow of gas is measured at the airway opening. Because atmospheric pressure is constant, changes in the pressures of interest can be obtained from measurements made relative to atmospheric pressure.

Pump

Shutter

(PM Patm )

Shutteropen

Calibration

=

PB

Shutterclosed

VB

VP

PB BPB

QAWO

QAWO

-QAWO

VL

(dPM)0(dPB)0

PB

PB

PM

PB

PA

TB

TL

NB

NL

VP

VP

dQAWO

dPB

(PB –Patm)

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.9 Idealized statically determined expiratory pressure-volume relations for the lung. The positions and slopes for lungs with different elastic properties are shown relative to scales of absolute volume and pressure difference.

NormalTLC

TLC

NormalFRC

Slope of linear approximationto curve (static compliance)

VL

Stiffer lung

TLC

FRC

FRC

Less stiff

Normal

RV

NormalRV

NormalVC

VC

VT

RV

VC

PL = PAWO –PPL

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.10 Idealized isovolume pressure-flow curves for two lung volumes for a normal respiratory system. Each curve represents a composite from numerous inspiratory-expiratory cycles, each with successively increased efforts. The pressure and flow values measured as the lungs passed through the respective volumes of interest are plotted and connected to yield the corresponding curves.

VL < 0.8 TLC

VL TLC

(PAWO –PA)

-QAWO

(Ins

pira

tion

)

(Exp

irat

ion)

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.11 Alternative methods of displaying data produced during a forced vital capacity expiration. Equivalent information can be obtained from each type of curve; however, reductions in expiratory flow are subjectively more apparent on the MEFV curve than on the timed spirogram.

Maximal expiratoryFlowvolume (MEFV) curves

Effortindependent

Time vital capacity (TVC) spirograms0 1 2 3 4 Time, s

TLC

(FVC QAWOdt)

Normal FVC

Reduced FVC

Normal

Effort independent

TL

C

QAWO

(Exp

irat

ion)

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.12 Essential elements of a medical mass spectrometer.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.13 General arrangements of the components of an infrared spectroscopy system.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.14 N2 analyzer employing emission spectroscopy.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.15 Oxygen analyzers (a) Diagram of the top view of a balance-type paramagnetic oxygen analyzer. The test body either is allowed to rotate (as shown) or is held in place by counter torque, which is measured to determine the oxygen concentration in the gas mixture. (b) Diagram of a differential pressure and a magneto-acoustic oxygen analyzer (see text for descriptions).

Pressuresensor F

A

Readoutscale

(a) (b)

Point ofsuspension

Dumbbell-shapedtest body

Samplein

Magnets

Lightsource

B

D JC

E

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.16 Distributions of volume and gas species at RV and TLC for a vital-capacity inspiration of air or pure oxygen.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.

Figure 9.17 single-breath nitrogen-washout maneuver (a) An idealized model of a lung at the end of a vital-capacity inspiration of pure O2, preceded by breathing of normal air. (b) Single-breath N2-washout curves for idealized lung, normal lung, and abnormal lung. Parameters of these curves include anatomical dead space, slope of phase III, and closing volume.

Normal slope 0.02/500 ml

Abnormal slope>0.02/500 ml

Anatomical dead spacevolume, V' D

CV

TLC RV

0 750 1250

Lung volume, vL

Expired volume, vS

(ml)

IVIIIIII

Ideal lung

Well-mixed alveolarcompartment

Conducting airwayfilled with 100% O2

Normal lung

Abnormal lung

(a)

(b)

FEN2