Department of Medical Physics and Informatics MEASUREMENT OF LUNG VOLUMES
I.
Background Respiratory volumes can be determined by the measurement of volume or airflow during inspiration and expiration. Tidal (quiet breathing) volume, the maximal inspiratory and expiratory reserve volumes and their relationships reflect the normal or pathological conditions prevailing in the respiratory system. The spirogram in Figure 1 illustrates the characteristic lung volumes recorded during quiet respiratory manoeuvres.
Figure 1. Definition of lung volumes
Figure 2. Forced expiratory lung volumes
Medical Physics laboratory practicals
1
spirometry
University of Szeged
Department of Medical Physics and Informatics
II. Principles of measurement Closed-circuit and open-circuit spirometries are the two basic means to measure lung volumes. The closed-circuit spirometer measures volume directly, for example via the displacement of an upper cylinder, suspended in a double-walled, water-insulated bottom part (Fig. 3), which is moved up and down in proportion to the expiratory and inspiratory volume, respectively. The open-circuit spirometer (pneumotachograph) measures airflow (V') into or from the ambient air. The most common type of the pneumotachograph measures V' by sensing the pressure drop across a fine metal or plastic mesh screen. In the case of a laminar flow, the pressure drop is proportional to the velocity (Hagen-Poiseuille law). the volume signal is obtained via integration of flow: V=∫V’dt.
Figure 3. Schematics of a closed-circuit (bell type) spirometer (left) and a pneumotachograph (flow meter; open-circuit spirometer- right)
III. Experimental objectives 1.
Measurement of tidal volume (TV), inspiratory and expiratory reserve volumes (IRV and ERV, respectively) and the vital capacity (VC); comparison of the measured VC with the normal value predicted for the corresponding sex, height and age.
Medical Physics laboratory practicals
2
spirometry
University of Szeged 2.
Department of Medical Physics and Informatics
Measurement of the forced expiratory volume following maximum inspiration (FVC), and its fraction expired in the first 1 s (FEV1) in 3 successive manoeuvres; calculation of the FEV1/FVC ratios.
IV. Measurement protocol 1. 2. 3.
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Select Lesson 12 (Pulmonary Function I) in the BSL Lessons 3.7 program on the data acquisition computer Specify the measurement file name by typing the ETR code of the tested subject (without .SZE) and extending the code with „VC” (e.g. ABCDEFG_VC). Calibration: recording of zero flow, connection of the 600-ml calibration syringe to the flowmeter via the bacterial filter and recording of 5 push-and-pull cycles with 1-s strokes and 2-s breaks. The arm of the pneumotachograph must be kept in a vertical position throughout. Insert the mouthpiece into the filter and put on the nose clip. Start the measurement (Record) with at least 5 quiet breathing cycles followed by a quiet inspiration to maximum lung volume and a quiet expiration to minimum lung volume and the return to normal breathing for at least 5 cycles. Remove the noseclip and detach from the mouthpiece only after the full recording; irregular or interrupted recordings should be replaced (Redo). Save the recording (Done). Forced expiratory maneouvres. Select Record from another Subject; however, since the same subject will be measured the previous file name should be modified (ABCDEFG_F1). Calibration consists only of zero-flow recordings. After at least 5 quiet brathing cycles, start a maximum inspiratory manoeuvre followed by a forced „explosive” maximum expiratory effort lasting for min. 5-6 s; return to normal breathing for min 5 cycles. By repeating steps 5.-7., record two more forced expiratory manoeuvres (file names ABCDEFG_F2 and ABCDEFG_F3). End the recordings (Quit) and close the BSL Lessons 3.7 program.
V. Data analysis – „static” lung volumes 1. Start the BSL Pro 3.7 program and open the VC recording from C:\TEMP\MEASURE (file type: LDD, name: ETRcode_VC-L12). 2. Open the Report (Excel) file from C:\TEMP\MEASURE (JKV… XLS). 3. Close the „Journal” text window („Hide journal” in the toolbar). 4. Measure the inspiratory volumes of 3 tidal breathing cycles preceding the deep inspiration (TV1, TV2 and TV3) with the p-p function, and type the medium value in the record (Fig. 4). 5. Measure the volume of the deep inspiration (TV+IC) (Fig. 5) and report. 6. Measure the difference between maximum and minimum lung volume (VC) (Fig. 6) and report. 7. Determine the expiratory reserve volume as the difference between VC and the volume of deep inspiration(TV+IC).
Medical Physics laboratory practicals
3
spirometry
University of Szeged
Department of Medical Physics and Informatics
8. Type in the data of the tested subject in the record and obtain the predicted value of VC. Compare the measured and predicted values and comment on this in the record. VI. Data analysis – forced expirations 1. Open the first forced expiratory measurement file from C:\TEMP\MEASURE (file type: LDD, file name: ETRcode_F1-L12). 2. Close the „Journal” text window („Hide journal” in the toolbar). 3. Zoom in the interval of deep inspiration and expiration and measure the forced expiratory volume (FVC) (Fig. 7). 4. Measure the volume expired in the first second after the start of the expiration (FEV1) (check Delta T) (Fig. 8). 5. Evaluate the other two forced expiratory manoeuvres (F2 and F3) by repeating steps 2.-4.. 6. Assess the reproducibility of the FVC és FEV1 values and their ratios (FEV1/FVC) and comment on this in the record. 7. Close the recording files without saving the changes, and submit your record.
Figure 4. Reading the inspiratory volumes of 3 breaths preceding the deep inspiration
Medical Physics laboratory practicals
4
spirometry
University of Szeged
Department of Medical Physics and Informatics
Figure 5. Measurement of the volume of the deep inspiration (TV+IC)
Figure 6. Measurement of the difference between maximum and minimum lung volume (VC)
Medical Physics laboratory practicals
5
spirometry
University of Szeged
Department of Medical Physics and Informatics
Figure 7. Measurement of the forced expiratory lung volume (FVC)
Figure 8. Reading of the volume expired in the first second of the forced expiratory manoeuvre
