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Lecture 8

PHGY 210- Lecture 8- Dr. Lauzon.docx.docx

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PHGY 210
Ann Wechsler

thLecture Eight Wednesday January 20 2010I Spirometry Measuring lung volumes Spirometer upside down canister floating in water All the air in the lungstotal lung capacity Spirometer can measure only what you can breathe in and out However total lung capacity cannot be measured because youre not breathing out residual volume Clinically it is useful to be able to measure the volume of air inhaled during inspiration under a number of different circumstances Subdivisions of the lung volumes can be determined by means of a spirometer Figure 8 a spirometer measures volumes of inhaled or exhaled gas so can be used to measure tidal volume vital capacity inspiratory capacity expiratory reserve volume and inspiratory reserve volume Figures 89 It cannot be used to measure functional residual capacity total lung capacity or residual volumesee pictures in slidesJ Measurement of FRC Helium dilution technique subject hooked up to a spirometer helium is in the tube dissolved in air Subject breathes out to FRC thats when valve is opened up and subject breathes helium Can use mass spectrometer to measure new helium which is lower because it is now over a larger volume C2 V2V1FRC FRC can be measured by helium dilution Figure 10 Let C1 be the helium concentration in a spirometer of volume V1 and let the subject breath out to FRC Then open the valve and ask the subject to breath in and out from the spirometer After equilibration with the subjects lungs the concentration in the spirometer is C2 Since the total amount of helium is conserved we have C1 x V1C2 x V1FRCso thatFRCC1 x V1C2V1Note Think of the lung as a balloon not as a jar see picture in slidesIIVENTILATION A Minute ventilation vs Alveolar ventilationThe amount of air inspired into the lungs over some period of time is called ventilation Usually it is measured for one minute and therefore we call it minute ventilation VE Therefore VE is the amount of air inspired or expired during one minutedot on top of VE VEVT x ftidal volume x frequency of breathsminute where VT is the tidal volume and f is the number of breaths per minute A dot above a symbol means a change with respect to time In a normal adult male VT500ml and f 12 breathsminute Therefore VE6000mlmin However not all the air inhaled into the lungs reaches the gas exchanging area the respiratory zone Some of the air remains in the conducting airways ie in the anatomical dead space VD Figure 12 The volume of the
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