Lab 10 Respiratory Physiology

Transcription

1 Bio 202 Human Anatomy & Physiology II Lab 10 Respiratory Physiology Background Gas exchange between air and blood occurs in the alveolar air sacs. The efficiency of gas exchange is dependent on ventilation; cyclical breathing movements alternately inflate and deflate the alveolar air sacs (Figure 1). Inspiration provides the alveoli with some fresh atmospheric air, and expiration removes some of the stale air, which has reduced oxygen and increased carbon dioxide concentrations. Figure 1. Basic Lung Anatomy is becoming more important as respiratory diseases are increasing worldwide. is the method of choice for a fast and reliable screening of patients suspected of having Chronic Obstructive Pulmonary Disease (COPD). COPD is the 12 th leading cause of death worldwide and the 5 th leading cause in Western countries. Studies suggest COPD could climb to be the 3 rd leading killer by Most COPD cases are completely avoidable as 85-90% of cases are caused by tobacco smoking. Asthma is another respiratory disease and can be confused with COPD. People with asthma can experience a shortness of breath (dyspnea), wheezing, coughing, and tightness in their chest. In these people, the bronchi are always red and inflamed, even when they are not suffering an asthma attack. During an attack, the airways constrict and become filled with mucus; this can make physical activity difficult. Many important aspects of lung function can be determined by measuring airflow and the corresponding changes in lung volume. In the past, this was commonly done by breathing into a bell spirometer, in which the level of a floating bell tank gave a measure of changes in lung volume. Flow, F, was then calculated from the slope (rate of change) of the volume, V: More conveniently, airflow can be measured directly with a pneumotachometer (from Greek roots meaning breath speed measuring device ). The PowerLab pneumotachometer is shown in Figure 2. Figure 2. The PowerLab Pneumotachometer Written by staff of ADInstruments. Edited by Udo Savalli

2 Lab 6: Cardiovascular Physiology Page 2 Several types of flow measuring devices are available and each type has advantages and disadvantages. The flow head you will use today is a Lilly type that measures the difference in pressure either side of a mesh membrane with known resistance. This resistance gives rise to a small pressure difference proportional to flow rate. Two small plastic tubes transmit this pressure difference to the Spirometer Pod, where a transducer converts the pressure signal into a changing voltage that is recorded by the PowerLab and displayed in LabChart. The volume, V, is then calculated as the integral of flow: This integration represents a summation over time; the volume traces you will see in LabChart during the experiment are obtained by adding successive sampled values of the flow signal and scaling the sum appropriately. The integral is initialized to zero every time a recording is started. A complication in the volume measurement is caused by the difference between ambient temperature and the air exhaled from the lungs, which is at body temperature. Gas expands with warming; therefore, if the ambient temperature is cooler than body temperature, you will breathe out a larger volume of air because the air is warmed in the body. The volume of air expired can also be increased by humidification, which happens in the alveoli. Since you breathe out a larger volume of air than you breathe in, the volume data trace drifts in the expiratory direction. Computer software corrections used in the Extension can reduce drift but cannot eliminate it. allows many components of pulmonary function to be visualized, measured, and calculated (Figure 3). Respiration consists of repeated cycles of inspiration followed by expiration. During the respiratory cycle, a volume of air is drawn into and then expired from the lungs; this volume is the tidal volume (VT). In normal ventilation, the breathing frequency (ƒ) is approximately 15 respiratory cycles per minute. This value varies with the level of activity. The product of ƒ and VT is the expired minute volume (VE), the amount of air exhaled in one minute of breathing. This parameter also changes according to the level of activity. Even when a person exhales completely, there is still air left in the lungs. This leftover air is the residual volume (RV), which cannot be measured by spirometry. Figure 3. Lung Volumes and Capacities

3 Lab 6: Cardiovascular Physiology Page 3 Terms with Which You Should Familiarize Yourself: Term Abbreviation/ Units Symbol Respiratory Rate RR Breaths/min (BPM) Expired Minute Volume VE = RR x VT L/min Lung Volumes Tidal Volume VT L Inspiratory Reserve Volume IRV L Expiratory Reserve Volume ERV L Residual Volume RV (predicted) L Lung Capacities Inspiratory Capacity IC = VT + IRV L Expiratory Capacity EC = VT + ERV L Vital Capacity VC = IRV + ERV + VT L Functional Residual Capacity FRC = ERV + RV L Total Lung Capacity TLC = VC + RV L Pulmonary Function Tests Peak Inspiratory Flow PIF L/min Peak Expiratory Flow PEF L/min Forced Vital Capacity FVC L Forced Expired Volume in One Second FEV1 L %FVC Expired in One Second FEV1 / FVC x 100 % Required Equipment LabChart software with Extension PowerLab Data Acquisition Unit Spirometer Pod Respiratory Flow Head (1000 L/min) with connection tubes Clean-bore Tubing & Tubing Adapter Disposable Filters Reusable Mouthpieces Nose Clips Tape measure or wall chart for measuring height Reading material Medical tape Sharpened pencil Procedure If you are suffering from a respiratory infection, do not volunteer for this experiment. Equipment Setup 1. Make sure the PowerLab is turned off and the USB cable is connected to the computer. 2. Connect the Spirometer Pod to Input 1 on the front panel of the PowerLab (Figure 4). Turn on the PowerLab.

4 Lab 6: Cardiovascular Physiology Page 4 Note: Since the Spirometer Pod is sensitive to temperature and tends to drift during warm-up, it is recommended the PowerLab (and therefore the Spirometer Pod) is turned on for at least 10 minutes before use. To prevent temperature drift, place the Spirometer Pod in a shelf or beside the PowerLab, away from the PowerLab power supply to avoid heating. Figure 4. Equipment Setup for PowerLab 26T 3. Connect the two plastic tubes from the Respiratory Flow Head to the short pipes on the back of the Spirometer Pod. Attach Clean-bore Tubing, a Filter, and a Mouthpiece to the Flow Head (Figure 4). Note: A clean Mouthpiece and Filter should be supplied for each volunteer. The Mouthpiece can be cleaned between uses by soaking it in boiling water or a suitable disinfectant. Exercise 1: Familiarize Yourself with the Equipment In this exercise, you will learn the principles of spirometry and how integration of the flow signal gives a volume. Calibrating the Spirometer Pod The Spirometer Pod must be calibrated before starting this exercise. The Flow Head must be left undisturbed on the table during the zeroing process. 4. Launch LabChart and open the settings file Airflow and Volume Settings from the Experiments tab in the Welcome Center. It will be located in the Respiratory Airflow and Volume folder. 5. Select Spirometer Pod from the Channel 1 Channel Function pop-up menu. Make sure the Range is 500 mv and the Low Pass is 10 Hz; then select Zero. When the value remains at 0.0 mv, have the volunteer breathe out gently through the Flow Head, and observe the signal (Figure 5). If the signal shows a downward deflection (it is negative), you can return to the Chart Window. If the signal deflects upward, you need to invert it. Click the Invert checkbox once.

5 Lab 6: Cardiovascular Physiology Page 5 Figure 5. Spirometer Pod Dialog with Downward Deflection Note: The signal can also be inverted by reversing the orientation of the Flow Head or by swapping the connections to the Spirometer Pod. The Invert checkbox is more convenient. Using the Equipment 6. Have the volunteer put the Mouthpiece in their mouth and hold the Flow Head carefully with both hands. The two plastic tubes should be pointing upward. 7. Put the nose clip on the volunteer s nose. This ensures that all air breathed passes through the Mouthpiece, Filter, and Flow Head (Figure 6). 8. After the volunteer becomes accustomed to the apparatus and begins breathing normally, you are ready to begin. Figure 6. Proper Positioning of the Flow Head 9. Start recording. Have the volunteer perform a full expiration and then breathe normally. Record the volunteer s tidal breathing for one minute. At the end of one minute, have the volunteer perform another full expiration. Observe the data being recorded in the Flow channel. Stop recording. The volunteer can stop breathing through the Flow Head and can remove the Nose Clip.

6 Lab 6: Cardiovascular Physiology Page 6 Setting Up the Extension The Extension processes the raw voltage signal from the Spirometer Pod, applies a volume correction factor to improve accuracy, and displays calibrated Flow (L/s) and Volume (L) traces. It takes over from Units Conversion. The trace you recorded in this exercise will provide reference points for the Extension that allow it to calculated and perform corrections on the trace. 10. Drag across the Time axis at the bottom of the Chart Window to select the data you recorded. Select Spiro. Flow from the Channel 1 Channel Function pop-up menu. Make sure the settings are the same as those in Figure 7. Figure 7. Flow Dialog 11. Select Spiro. Volume from the Channel 2 Channel Function pop-up menu. Make sure Channel 1 is selected in the Flow Data pop-up menu. Click the Apply Volume Correction checkbox to turn it on. Then select Apply to allow the extension to use the volume correction ratio that is has calculated from your data (Figure 8). The Chart Window should now appear with calculated volume data on Channel 2. Figure 8. Volume Dialog 12. Select Set Scale from the Scale pop-up menu (small downward triangle; Figure 9) in the Amplitude axis for the Flow channel. Make the top value 15 L/s and the bottom value -15 L/s.

7 Lab 6: Cardiovascular Physiology Page 7 Figure 9. Set Scale menu indicated by red arrow Understanding the Importance of Volume Correction 13. Drag across the Time axis to select data from both channels, and open Zoom Window. Note the relation between Flow and Volume. When the flow signal is positive (inspiration), Volume rises; when the flow is negative (expiration), the volume trace falls. 14. In Zoom Window, find part of the recording where the flow is zero. Note that at this time, Volume does not change (it is horizontal) because integrating a zero signal does not add anything to the integral. 15. The volume trace is calculated by the extension in such a way that the displayed volumes at the end of the two full expirations equal. In subsequent recordings, the volume correction is unlikely to be exact you will notice a tendency for the volume to drift, typically 1-2 L over 1-2 minutes. To see the effect of having no correction, turn off the Volume Correction checkbox in the Spiro. Volume dialog, and examine the data trace. Remember to turn it back on again afterward. 16. Save your data. Do not close the file. Exercise 2: Lung Volumes and Capacities In this exercise, you will examine the respiratory cycle and measure changes in flow and volume. 1. Zero the Spirometer Pod again, using the same procedure as before. Remember to leave the Flow Head undisturbed during the process. 2. Have the volunteer face away from the monitor and read. This will prevent the volunteer from consciously controlling their breathing during the exercise. 3. When ready, Start recording. After two seconds, have the volunteer replace the Nose Clip and breathe normally into the Flow Head. Record normal tidal breathing for one minute. Add a comment with normal tidal breathing to the data trace. 4. After the tidal breathing period (at the end of a normal tidal expiration), ask the volunteer to inhale as deeply as possible and then exhale as deeply as possible. Afterwards, allow the volunteer to return to normal tidal breathing for at least three breaths. Stop recording when finished.

8 Lab 6: Cardiovascular Physiology Page 8 5. Position the cursor at the end of the deep breath. Right-click and select Add Comment. Add a comment with lung volume procedure at the cursor position. 6. Save your data. Do not close the file. Exercise 3: Pulmonary Function Tests In this exercise, you will measure parameters of forced expiration that are used in evaluating pulmonary function. Note that the Extension is not intended for clinical evaluation of lung function. 1. Zero the Spirometer Pod again, using the same procedure as before. Remember to leave the Flow Head undisturbed during the process. 2. Have the volunteer replace the Nose Clip and breathe normally into the Flow Head. 3. Start recording. Add a comment with the volunteer s name. 4. Prepare a comment with forced breathing. Have the volunteer breathe normally for 30 seconds; then ask the volunteer to inhale maximally and then exhale as forcefully and fully as possible until no more air can be expired. Add the comment. After a few seconds, the volunteer should let their breathing return to normal. Stop recording. 5. Repeat steps 3-4 twice more, so that you have three separate forced breath recordings (Figure 10). Figure 10. Sample Data of Forced Breaths 6. Repeat steps 1-4 for every person in your group. Replace the Filter, Mouthpiece, and Nose Clip for each student. Zero the Spirometer Pod before each student begins the exercise. Make sure you add a comment with each volunteer s name when they begin the exercise. 7. Save your data. Do not close the file.

9 Lab 6: Cardiovascular Physiology Page 9 Exercise 4: Simulating Airway Obstructions In this exercise, you will demonstrate the effects of bronchial obstructions, such as asthma, by making modifications to your equipment. 1. Remove the Filter attachment from the Mouthpiece and Clean-bore Tubing. Attach a new Filter to the Clean-bore Tubing. 2. Cover the mouthpiece end of the filter with medical tape. Use a sharpened pencil to make a hole in the tape one centimeter in diameter. Place the Mouthpiece on the Filter, as in Figure Attempt the pulmonary function tests with the obstructed airway. Repeat the entire procedure from Exercise 3, including recording from each student in the group. Analysis Exercise 2: Lung Volumes and Capacities 1. Examine the normal tidal breathing data in the Chart Window, and Autoscale (using the button or from the Commands menu) if necessary. Calculate how many breaths there are in a one-minute period (BPM). Record RR/min in Table 1, on page Determine the volume of a single tidal inspiration by placing the Marker at the start of a normal tidal inspiration. Place the Waveform Cursor at the peak (Figure 11). The value shown in the Range/ Amplitude display for Channel 2 is the tidal volume (VT) for that breath. Record this value in Table 1. Figure 11. Proper Placement of Marker and Waveform Cursor 3. Use the values for tidal volume and the number of breaths observed over a one minute period to calculate the expired minute volume (VE). Use the following equation: VE = RR x VT (L/min)

10 Lab 6: Cardiovascular Physiology Page Find the lung volume procedure comment in your data trace. Repeat steps 2-3 to determine the inspiratory reserve volume (IRV) (Figure 12) and expiratory reserve volume (ERV) (Figure 13). Note: The Marker should be placed at the peak of a normal tidal inspiration for IRV, and it should be placed at the start of a normal tidal inspiration (trough) for ERV. 5. Calculate the inspiratory capacity (IC) using the following equation: IC = VT + IRV (L) 6. Calculate the expiratory capacity (EC) using the following equation: EC = VT + ERV (L) Figure 12. Positioning of Marker and Waveform Cursor to Measure IRV Figure 13. Positioning of Marker and Waveform Cursor to Measure ERV

11 Lab 6: Cardiovascular Physiology Page Refer to the Appendix at the end of this handout, and use the tables provided to determine the volunteer s predicted vital capacity (VC). The predicted value varies according to the volunteer s sex, height, and age. 8. Calculate the volunteer s measured VC using the experimentally derived values for IRV, ERV, and VT. Use the following equation: VC = IRV + ERV + VT (L) 9. Residual volume (RV) is the volume of gas remaining in the lungs after a maximal expiration. The RV cannot be determined by spirometric recording. Using the following equation, determine the predicted RV value for the volunteer: RV = predicted VC x 0.25 (L) 10. The total lung capacity (TLC) is the sum of the vital capacity and residual volume. Calculate the predicted TLC for the volunteer using the following equation: TLC = VC + RV (L) 11. Functional residual capacity (FRC) is the volume of gas remaining in the lungs at the end of a normal tidal expiration. Use the following equation: FRC = ERV + RV (L) 12. Select an area of the Chart Window that contains normal breathing, making sure to select across complete respiratory cycles. Select Report from the menu. The Report window contains various parameters calculated by the Extension from the data selection (Figure 14). Copy the results for VE, VT, and ƒ (which is RR) into the appropriate column in Table Make sure you have entered all the values calculated into Table 1. Figure 14. Report

12 Lab 6: Cardiovascular Physiology Page 12 Table 1. Lung Volumes and Capacities Respiratory Parameter Respiratory Rate (RR) Expired Minute Volume (VE) Tidal Volume (VT) Inspiratory Reserve Volume (IRV) Inspiratory Capacity (IC) Expiratory Reserve Volume (ERV) Expiratory Capacity (EC) Predicted Vital Capacity (from table) Vital Capacity (VC) Residual Volume (RV) Total Lung Capacity (TLC) Functional Residual Capacity (FRC) 1. Comment on the differences between the experimental and predicted values for VC, FRC, and TLC in Table 1. What could cause these differences, if any? 2. In quiet breathing, muscular effort is mainly in inspiration, and expiration is largely passive, due to elastic recoiling of the lung. Can you relate this fact to the pattern of expiratory and inspiratory flow? Hint: The normal pattern of breathing is efficient in that it requires muscular effort for only a short time. 3. Explain why RV cannot be determined by ordinary spirometry.

13 Lab 6: Cardiovascular Physiology Page 13 Exercise 3: Pulmonary Function Tests 1. USE YOUR OWN DATA FOR THIS ANALYSIS. 2. In the last data block of your LabChart recording for this exercise, move the Waveform Cursor to the maximal forced inspiration in Flow. The absolute value displayed in the Range/Amplitude display is the peak inspiratory flow (PIF). Multiply the value by 60 to convert from L/s to L/min. 3. From the flow data trace, measure the peak expiratory flow (PEF) for the forced expiration. Multiply the value by 60 to convert from L/s to L/min. Disregard the negative sign. 4. To calculate the forced vital capacity (FVC), place the Marker on the peak inhalation of Volume, and move the Waveform Cursor to the maximal expiration (Figure 14). Read off the result from the Range/Amplitude display, disregarding the delta symbol and negative sign. 5. Return the Marker to its box. To measure forced expired volume in one second (FEV1), place the Marker on the peak of the volume data trace, move the Waveform Cursor to a time 1.0 s from the peak, and read off the volume value. If you find it hard to adjust the mouse position with enough precision, a time value anywhere from 0.96 s to 1.04 s gives enough accuracy. Disregard the delta symbol and negative sign. 6. Return the Marker to its box. Select data from the last recorded data block for this exercise that includes a couple of normal breaths, the forced breath, and a few more normal breaths (Figure 15). Select Data from the menu. The Data window opens, showing the locations of PIF, PEF, FVC, and FEV1. If the values are not displayed, you need to change the settings of the Extension. Refer to step 7. If the values are displayed, refer to step 8. Figure 15. Data Window, with the Locations of the Parameters 7. Select Settings from the menu (Figure 16). The default values are shown in Figure 15. You can adjust the Cycle Detection Level between 0.25% and 1.00% of the full range, and you can adjust the Forced Expiration Threshold between 1 and 2. Try different combinations until you see a Data window like the one in Figure 15.

14 Lab 6: Cardiovascular Physiology Page 14 Figure 16. Settings Dialog with Default Values 8. With the Data window open, select Report from the menu. The report lists the values calculated for the parameters in Figure 15. Add these values to the appropriate column in Table 2, on the next page. 9. Repeat this analysis until all three forced breaths have been analyzed, both manually and with the Extension. 10. Calculate the percentage ratio of FEV1 to FVC for your experimental and Extension results. Use the maximum values of FEV1 and FVC, and use the following equation: 11. Record your values in Table 2. (FEV1 / FVC) x 100 (%) 12. When your group has completed their analysis, share your results with the rest of the class. Record the values for your and the other groups subjects in Table 3 on page 16.

15 Lab 6: Cardiovascular Physiology Page 15 Table 2. Pulmonary Function Tests Your Data Normal Respiration Respiratory Parameter Peak Inspiratory Flow (PIF) Peak Expiratory Flow (PEF) Forced Vital Capacity (FVC) Forced Expired Volume in One Second (FEV1) (FEV1 / FVC) x 100

16 Lab 6: Cardiovascular Physiology Page 16 Table 3. Pulmonary Function Tests Group Members Data Normal Respiration Respiratory Parameter Group 1 Group 2 Group 3 Peak Inspiratory Flow (PIF) Peak Expiratory Flow (PEF) Forced Vital Capacity (FVC) Forced Expired Volume in One Second (FEV1) (FEV1 / FVC) x 100

17 Lab 6: Cardiovascular Physiology Page What factors do you think could contribute to differences in pulmonary parameters between the subjects? Exercise 4: Simulating Airway Obstructions 1. USE YOUR OWN DATA FOR THIS ANALYSIS. 2. Repeat the entire Analysis for Exercise 3 using your data from Exercise Record these values in Table 4, below. 4. Record the values for the other groups subjects in Table 5 on the next page. Table 4. Pulmonary Function Tests Your Data Obstructed Respiration Respiratory Parameter Peak Inspiratory Flow (PIF) Peak Expiratory Flow (PEF) Forced Vital Capacity (FVC) Forced Expired Volume in One Second (FEV1) (FEV1 / FVC) x 100

18 Lab 6: Cardiovascular Physiology Page 18 Table 5. Pulmonary Function Tests Group Members Data Obstructed Respiration Respiratory Parameter Group 1 Group 2 Group 3 Peak Inspiratory Flow (PIF) Peak Expiratory Flow (PEF) Forced Vital Capacity (FVC) Forced Expired Volume in One Second (FEV1) (FEV1 / FVC) x 100

19 Lab 6: Cardiovascular Physiology Page What values were affected by simulated airway obstruction, and why? 6. Explain the physiological events that occurred during the simulated asthma attack. Hint: Think about what it felt like and how it would affect your general state of well-being and activity level. Appendix: Vital Capacities in Healthy Individuals 1 Height (cm) Table 1. Predicted Vital Capacities for Males Height (cm) Table 2. Predicted Vital Capacities for Females 1 These tables are based on The Johns Hopkins Pulmonary Function Laboratory equations for pulmonary function.