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(bx•Qb)in 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. Ubx PPL QAWO PA (AWOx•QAWO)in VA AWO VL (bx•Qb)out (a) (b)
pAWO RAW uL qAWO CstW pA CstL RAW uL CstL qAWO pPL pPL pAWO CstW pA pBS pMUS + pMUS pBS 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). (a) (b)
Figure 9.3 Pneumotachometer flow-resistance elements (a) Screen. (b) Capillary tubes or channels.
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.
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.
Rotational displacement sensor Other signal processing Counterweight Strip-chart recorder Kymograph Bell PS VS TS Water seal Blood flow Uabs Mouthpiece FS x One-way valves Soda-lime canister VL Ubs TL Thermometer for spirometer gas temperature PA FA x QAWO 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.
100% O2 One-way valves TS TL VL FSN2 Spirometer FAN2 VS O2 + N2 Nitrogen analyzer + CO2 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.
dQAWO dPB ( dP ) M 0 ( dP ) B 0 P M Shutter closed ( P - P ) M atm P B Shutter QAWO QAWO VL PA TL NL -QAWO PB Shutter open VB PB Pump TB (PB –Patm) NB 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. Calibration VP VP VP = PB BPB PB
V L TLC Less stiff Normal TLC Normal VC FRC Slope of linear approximation to curve (static compliance) Normal VC RV VT TLC Normal FRC VC FRC Normal RV Stiffer lung RV PL = PAWO –PPL 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.
-QAWO VL TLC (Expiration) VL< 0.8 TLC (PAWO –PA) (Inspiration) 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.
Maximal expiratory Flow-volume (MEFV) curves -QAWO Effort independent Normal (Expiration) (FVC - QAWOdt) TLC TLC Reduced FVC Normal FVC Effort independent 0 1 2 3 4 Time, s Time vital capacity (TVC) spirograms 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.
Figure 9.12 Essential elements of a medical mass spectrometer.
Figure 9.13 General arrangements of the components of an infrared spectroscopy system.
Readout scale Light source Sample in A Pressure sensor D J F C E Magnets B Dumbbell-shaped test body Point of suspension (a) (b) 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).
Figure 9.16 Distributions of volume and gas species at RV and TLC for a vital-capacity inspiration of air or pure oxygen.
Conducting airway filled with 100% O2 Well-mixed alveolar compartment (a) Abnormal slope >0.02/500 ml FEN2 Normal slope 0.02/500 ml Ideal lung Normal lung I II III IV Abnormal lung CV 0 750 1250 Expired volume, vS (ml) 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. Anatomical dead space volume, V' D TLC Lung volume, vL RV (b)
