RESPIRATORY CYCLE Introduction Three primary functions of the respiratory system are to provide oxygen for the body's energy needs, provide an outlet for C0 2 and help maintain the ph of the blood plasma. The respiratory cycle serves these multiple purposes in conjunction with the circulatory system. The mechanics of the respiratory cycle consists of alternating processes of inspiration and expiration. During inspiration, skeletal muscles (such as the diaphragm and external intercostals) contract, thereby increasing volume within the thoracic cavity and lungs. The increased volume creates less pressure within the lungs than the atmosphere, so air rushes into the lungs. During resting expiration, the inspiratory muscles relax, causing the volume of the thoracic cavity and the lungs to be reduced. This reduction forces gas back into the atmosphere. Normally, unlabored expiration at rest is a passive event determined by relaxation of inspiratory muscles. During exercise or during forced exhalation, e.g., coughing, expiration becomes an active event dependent upon contraction of expiratory muscles that pull down the rib cage and compress the lungs. During inspiration, oxygen drawn into the lungs, diffuses to the pulmonary capillaries and is transported to cells via erythrocytes (red blood cells). The cells use oxygen to supply energy for metabolic processes. When producing energy, these cells then release carbon dioxide as a waste product. Some of the carbon dioxide reacts with water in the body to form carbonic acid, which then dissociates to H + and bicarbonate. The erythrocytes transport C0 2 and H + back to the lungs. Once in the lungs, the H + and HCO 3 recombine to form water and C0 2 (Fig.1). Figure 1 The respiratory cycle Many factors are involved in the regulation of ventilation, the rate and depth of breathing. The basic rhythm of breathing is established by inspiratory and expiratory respiratory centers in the medulla.the inspiratory center initiates inspiration via activation of the inspiratory muscles. During normal, quiet breathing at rest (eupnea), the average respiratory rate (RR) is 12-14 cycles/minute. The inspiratory center always acts to produce an active inspiration. In contrast, the expiratory center acts to limit and then inhibit the inspiratory center, thereby producing a passive expiration.this basic breath pattern is affected by: a) Higher centers in the brain. b) Feedback from peripheral and central chemoreceptors in the arterial system and medulla, respectively. c) Stretch receptors in the lungs. d) Other sensory receptors in the body.
For example, cerebral control of the medullary respiratory centers is observed when a subject attempts to thread a needle. The cycle temporarily ceases in order to minimize body movement so that the needle may be threaded more easily. Cerebral control is also evident during speech, which requires expiratory air to pass over the vocal cords. The separate chemoreceptors sense 0 2, C0 2 levels in the blood and in the cerebrospinal fluid of the medulla. In hyperventilation, the breathing rate and depth is increased so that the lungs rid the body of carbon dioxide faster than it is being produced. Hydrogen ions are removed from body fluids and the ph becomes elevated. This tends to depress ventilation until normal carbon dioxide and hydrogen ion levels are restored. The temporary cessation of breathing after voluntary hyperventilation is known as apnea vera. In hypoventilation (shallow and/or slow breathing) the lungs gain carbon dioxide in body fluids (hypercapnia) since the lungs fail to remove carbon dioxide as rapidly as it is being formed. The increased formation of carbonic acid results in a net gain of hydrogen ions, lowering ph in body fluids. The chemoreceptor feedback causes ventilation to increase until carbon dioxide levels and extracellular fluid ph return to normal. We are more sensitive to changes in C0 2 levels than to changes in 0 2 levels in the blood. The central medullary chemoreceptors are exposed to the cerebrospinal fluid (CSF). Because the CSF is unbuffered, in contrast to the blood, changes brought about by the dissociation of C0 2 are more pronounced. One condition stimulated by low 0 2 levels occurs at high altitudes in some individuals. The low levels of 0 2 stimulate increased ventilation, which decreases C0 2 and H+. This causes ph to increase (respiratory alkalosis). One simple treatment for the effects of respiratory alkalosis is to have the person breathe into a bag. As the person inhales, the elevated levels of C0 2 restore the ph balance of the blood. In this lesson, you will measure ventilation by recording the rate and depth of the breathing cycle using a pneumograph transducer. This transducer converts changes in chest expansion and contraction to changes in voltage, which will appear as a waveform. One respiratory cycle will then be recorded as an increasing voltage (ascending segment) during inspiration and a decreasing voltage (descending segment) during expiration. You will also record the temperature of the air flowing in and out of one nostril with a temperature probe. The temperature of the air passing by the temperature probe is inversely related to the expansion or contraction of the Subject's chest. During inspiration (when the chest expands) the Subject breathes in relatively cool air (compared to the Subject's body temperature). The air is warmed in the body. During expiration (when the chest contracts) the warmer air is compressed out of the lungs and out the respiratory passages. I. Experimental objectives 1) To record and measure ventilation utilizing pneumograph and air temperature transducers. 2) To show how ventilation relates to temperature changes in airflow through one nostril. 3) To observe and record chest expansion and contraction and modifications in the rate and depth of the breathing cycle due to cerebral influence and chemoreceptor influence on the medullary control centers. II. Materials BIOPAC Respiratory Transducer SS5LB (or older SS5LA or SS5L) BIOPAC Temperature Transducer SS6L (Fast Response Thermistor) Single-sided (surgical) tape (TAPE1) Computer system Biopac Student Lab 3.7 BIOPAC data acquisition unit.
III. Procedure A. Set Up 1. Turn the computer ON. 2. Make sure the BIOPAC MP3X unit is turned OFF. 3. Plug the equipment in as follows: RespiratoryTransducer (SS5LB) CH 1 Temperature Transducer [Thermistor] (SS6L) CH 2 Figure 2 The equipment preparation 4. Turn the MP3X Data Acquisition Unit ON. 5. Attach the respiratory transducer (SS5LB) to the Subject (Fig.3). The Temperature Transducer is used to measure air flow. Each inhale brings cooler air across the transducer, and each exhale blows warmer air across the transducer. The transducer records these temperature changes, which are proportional to the air flow output. This indirect method is efficient when rate and relatively amplitude measurements are sufficient; a direct air flow measurement requires a complex scaling procedure. Attach the respiratory transducer around the chest below the armpits and above the nipples (Fig. 3). The correct tension is critical. The respiratory transducer must be slightly tight at the point of maximal expiration. The transducer can be worn over a thin shirt, such as a T-shirt. Figure 3 Location of respiratory transducer 6. Attach the temperature transducer [thermistor] (SS6L) to the Subject (Fig. 4). The thermistor should be firmly attached so it does not move and should be positioned below the nostril and not touching the face. It s usually best to make a small loop in the cable about 2 from the temperature probe (tip) and tape the loop to the Subject s face. Figure 4 Location of temperature transducer
7. Start the Biopac Student Lab Program 8. Choose lesson 8; type in your filename, click OK. B. Calibration The Calibration procedure establishes the hardware s internal parameters (such as gain, offset, and scaling) and is critical for optimum performance. Calibration steps are: 1. Subject should sit in a relaxed state, breathing normally. 2. Click Calibrate; the calibrate button is in the upper left corner of the Setup window. 3. Wait two seconds, then breathe deeply for 1 cycle, then breathe normally. The program needs a reading of your maximum volume and temperature changes to perform an autocalibration. 4. Wait for the Calibration to stop. The Calibration will run for 8 seconds and then stop automatically, so let it run its course. 5. Check your calibration data. At the end of the 8-sec calibration recording, your screen should resemble Fig. 5. Figure 5 Calibration data Note: The top channel displays data from the temperature transducer that is positioned under the Subject s nose. The channel is labeled airflow because the temperature at the nostrils is inversely proportional to the airflow in and out of the nostril. If similar, proceed to the Data Recording section. If different, Redo Calibration. C. Recording lesson data You will record airflow on one channel and chest expansion on another channel with the subject under four conditions: normal breathing, hyperventilation and recovery, hypoventilation and recovery, and coughing and then reading aloud. Hints for obtaining optimal data: a) Subject should stop hyperventilation or hypoventilation if dizziness develops. b) The respiration transducer should fit snugly around the chest prior to inspiration. c) The temperature transducer should be firmly attached so it does not move. The transducer thermistor should be positioned below the nostril and not touching the face. d) The Subject should be sitting for all segments. e) The recording should be suspended after each segment so that the Subject can prepare for next recording segment. 1. Prepare for recording; the subject sit down and relax. 2-3. When you click Record, the recording will begin and an append marker labeled Seated and relaxed will automatically be inserted. Subject should be sitting in a chair, breathing normally (seconds 0-15).
4. Click Suspend. The recording should halt, giving you time to review the data and prepare for the next recording segment. Figure 6 First segment recording (seconds 0-15) Review the data on the screen. If correct, go to next step for the next recording segment. The data would be incorrect if: a) The pneumograph (respiration) data has plateaus instead of waveforms. If there are plateaus, adjust the pneumograph and repeat from Set Up Step 8(file name). b) The waveforms in the temperature (airflow) data are not offset from the respiration data. If there is no offset, adjust the respiration transducer and repeat from Set Up Step 8. c) The temperature thermistor moved and is no longer directly under the nostril. d) The pneumograph slipped. e) The Suspend button was pressed prematurely f) Any of the channels have flat data, indicating no signal. If incorrect, you should redo the recording by clicking Redo and repeating Steps. Note that once you press Redo, the data you have just recorded will be erased. 5. When you click Resume, the recording will continue and an append marker labeled hyper-ventilation and recovery will be automatically inserted. 6. Subject hyperventilates for 30 seconds, then recovers from hyperventilation for 30 seconds. Then, resume breathing nasally until a normal breathing pattern is reestablished. Seconds 15-45 is hyperventilation Seconds 45-75 is recovery Figure 7 Hyperventilation and recovery Recorder needs to record both hyperventilation and the initial recovery period. The recording should halt, giving you time to review the data and prepare for the next recording segment. If all went well, your data should look similar to Fig. 7 and you can proceed to Step 7. Use the horizontal scroll bar to look at different portions of the waveform. The data would be incorrect for the reasons in Step 5. If incorrect, you should redo the recording by clicking Redo and repeating steps. Note that once you press Redo, the data you have just recorded will be erased. Important: Subject should NOT do the next section until breathing has returned to normal. 7. When you click Resume, the recording will continue and an append marker labeled hypoventilation and recovery will be automatically inserted.
8. To hypoventilate (insufficient ventilation), Subject should breathe slowly and shallowly through the mouth for a maximum of 30 seconds. Then, resume breathing nasally until a normal breathing pattern is reestablished. Recorder needs to record both hypoventilation and the initial recovery period. Seconds 75-105 is hypoventilation Seconds 105-135 is recovery The recording should halt, giving you time to prepare for the next recording segment. Figure 8 Hypoventilation and recovery 9. Review the data on the screen. If correct, go to next step. If all went well, your data should look similar to the Fig. 8 and you can proceed to Step 10. Use the horizontal scroll bar to view different portions of the data segment. If incorrect, click Redo. 10. When you click Resume, the recording will continue and an append marker labeled Cough, then read aloud will be automatically inserted. The recording should halt. 11. Have subject cough once and then begin reading aloud 12. Click suspend 13. Review the data on the screen. If correct, go to Step 14. Figure 9 Cough once then read aloud If incorrect, you should redo the recording by clicking Redo and repeating Steps 10-12. Note that once you press Redo, the data you have just recorded will be erased. 14. Click on Done. A pop-up window with options will appear. Make your choice, and continue as directed. If choosing the Record from another Subject option: a) Attach the respiration transducer and temperature transducer per Set Up Steps 5 and 6, and continue the entire lesson from Set Up Step 9. b) Each person will need to use a unique file name 15. Remove the respiration and temperature transducers. D. Data analysis Enter the review saved data mode from the Lessons menu. Note Channel Number (CH) designation: Channel Displays CH 2 Airflow CH 40 Respiration
The data window should come up the same as Fig. 10. Figure 10 The final data Set up the measurement boxes as follows: Channel Measurement CH 40 ΔT CH 40 BPM CH 40 p-p CH 2 p-p ΔT: The Delta Time measurement is the difference in time between the end and beginning of the selected area. BPM: The Beats Per Minute measurement first calculates the difference in time between the end and beginning of the area selected by the I-Beam tool (same as ΔT), and divides this value into 60 seconds/minute. Because the BPM only uses the time measurement of the selected area for its calculation, the BPM value is not specific to a particular channel. p-p: finds the maximum value in the selected area and subtracts the minimum value found in the selected area. Note: The selected area is the area selected by the I-beam tool (including the endpoints). Zoom in on a small section of the Segment 1 data. Zoom in far enough so that you can easily measure the intervals between peaks, approximately four cycles. Using the I-Beam cursor, select the area of inspiration. The respiration channel data [CH 40] in the following figure shows an example of selecting an inspiration segment. The ΔT measurement gives the duration of inspiration. Figure 11 Selected area of inspiration Select the area of expiration. The following figure shows an example of selecting an expiration segment. The ΔT measurement gives the duration of expiration. Figure 12 Selected area of expiration
Repeat the above inspiration and expiration measurements for two additional cycles in data Segment 1. Select an area within Segment 1 data from the beginning of one cycle to the end of the same cycle (this is the total duration). The following figure shows an example of selecting the total duration of one cycle. The ΔT measurement displays the total duration and BPM indicates the breathing rate of the selected cycle. Figure 13 Repeat steps on each of the three remaining data segments. Select three individual cycles in each of the four data segments and determine the respiration amplitude for each. The selected area should start at the middle of the descending wave and end at the middle of the next descending wave to capture the min and max amplitudes. The p-p measurement will display the amplitude. The following figure shows an example of selecting an area in the cycle that captures the minimum and maximum amplitude values. Note: Segment 4 (cough) only requires one measurement. Figure 14 Using the I-beam cursor, select the interval between the maximal inspiration and max temperature change in each data segment.select the interval in each of the four data segments. Record the ΔT (time interval) between the two peaks and the p-p [CH 2] (temperature amplitude).