© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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. U b x is the net rate of molar uptake –that is, the net rate of diffusion of X into the blood. V D and V A are the dead-space volume and alveolar volume, respectively. (b) A basic mechanical unit of the pulmonary system. P A is the pressure inside the lung – that is, in the alveolar compartment. P PL and P AWO are the pressures on the pleural surface of the lungs and at the airway opening, respectively. V L is the volume of the gas space within the lungs, including the airways; Q AWO is the volume flow of gas into the lungs measured at the airway opening. (  AWO x Q AWO ) in VLVL VAVA PAPA P PL (a)(b) (  b xQ b ) in  AWO Q AWO (  b xQ b ) out UbxUbx

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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). Cst W p PL pApA  p MUS  L  q AWO  p MUS Cst L p PL R AW LL pApA q AWO p AWO p BS p AWO R AW Cst L (b)(a) + p BS Cst W

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, Figure 9.3 Pneumotachometer flow-resistance elements (a) Screen. (b) Capillary tubes or channels.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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. 3 rd ed. New York: John Wiley & Sons, 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 V T 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. 3 rd ed. New York: John Wiley & Sons, 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 CO 2 during rebreathing. VLVL TLTL PAPA Other signal processing Strip-chart recorder Thermometer for spirometer gas temperature One-way valves Water seal Bell U abs Soda-lime canister Pulmonary system Spirometer system Mouthpiece Q AWO Blood flow Kymograph Counterweight Rotational displacement sensor PSPS VSVS TSTS F S x F A x U bs

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, Figure 9.7 Diagram of an N 2 washout experiment The expired gas can be collected in a spirometer, as shown here, or in a rubberized-canvas or plastic Douglas bag. N 2 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. Nitrogen analyzer 100% O 2 O2O2 + N2N2 + CO 2 VLVL TLTL FAN2FAN2 TSTS VSVS Spirometer One-way valves FSN2FSN2

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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 (P M  P atm ) Shutter open Calibration = PBPB Shutter closed VBVB VPVP PBPB BPBBPB Q AWO -Q AWO VLVL (dP M ) 0 ( B ) 0 PBPB P B P M PBPB PAPA TBTB TLTL NBNB NLNL VPVP VPVP dQ AWO dP B (P B –P atm )

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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. Normal TLC Normal FRC Slope of linear approximation to curve (static compliance) V L Stiffer lung TLC FRC Less stiff Normal RV Normal RV Normal VC VTVT RV VC  P L = P AWO –P PL

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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. V L < 0.8 TLC V L  TLC (P AWO –P A ) -Q AWO (Inspiration) (Expiration)

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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 expiratory Flow  volume (MEFV) curves Effort independent Time vital capacity (TVC) spirograms 01234Time, s TLC (FVC  Q AWO dt) Normal FVC Reduced FVC Normal Effort independent TLC  Q AWO (Expiration)

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, Figure 9.12 Essential elements of a medical mass spectrometer.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, Figure 9.13 General arrangements of the components of an infrared spectroscopy system.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, Figure 9.14 N 2 analyzer employing emission spectroscopy.

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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). Pressure sensor F A Readout scale (a)(b) Point of suspension Dumbbell-shaped test body Sample in Magnets Light source B D J C E

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 rd ed. New York: John Wiley & Sons, 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. 3 rd ed. New York: John Wiley & Sons, 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 O 2, preceded by breathing of normal air. (b) Single-breath N 2 -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 space volume, V' D CV TLC RV Lung volume, v L Expired volume, v S (ml) IVIIIIII Ideal lung Well-mixed alveolar compartment Conducting airway filled with 100% O 2 Normal lung Abnormal lung (a) (b) FEN2FEN2