Physiology of the Respiratory System

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1 Biology 212: Anatomy and Physiology II Physiology of the Respiratory System References: Saladin, KS: Anatomy and Physiology, The Unity of Form and Function 8 th (2018). Required reading before beginning this lab: Chapter 22 INTRODUCTION: As discussed in the previous lab exercise on the anatomy of the human respiratory system, pulmonary ventilation is the movement of air in and out of the lungs, exchanging atmospheric air which is rich in O 2 and low in CO 2 with the air in our lungs which is low in O 2 and rich in CO 2. This movement of air is caused by changing the size of the thoracic cavity, which in turn changes the pressures within the lungs. During quiet breathing, the diaphragm and intercostal muscles produce most of this movement. However, during heavy breathing accessory muscles of respiration in the neck, thorax, and abdomen may also be involved as shown in Figure of your Saladin text. The volumes of air that move into and out of the lungs are shown in Figure We will be using a spirometer to measure some of these respiratory volumes, but others such as residual volume and total lung capacity can not be as easily measured. Learning Objectives: Upon completion of this exercise students will: Understand the relationship between the pressure and the volume of air during respiration Be able to explain the functions of principle respiratory muscles and accessory respiratory muscles of the human Be able to explain tidal volume, inspiratory reserve volume, expiratory reserve volume, vital capacity, residual volume, total lung capacity, minute respiratory volume, and forced expiratory volume in one second. Understand the use of spirometry to measure respiratory volumes From a spirometry tracing, be able to calculate tidal volume, inspiratory reserve volume, expiratory reserve volume, vital capacity, minute respiratory volume, and forced expiratory volume in one second. Exercise 1. Review of Respiratory Anatomy: Quickly review the structure of the thoracic cavity on the torso models and the position of the lungs within it. Observe how the costal surface of each lung lies against the ribs and intercostal muscles, the diaphragmatic surface of each lung lies immediately superior to the diaphragm, and the mediastinal surface of each lung faces toward the heart and mediastinum. 1

Review how each lung is surrounded by a double-layered membrane called the pleura. The visceral layer of the pleura is firmly attached to the surface of the lung and moves with it as you breathe.

surrounding the heart. Between the visceral and parietal layers of the pleura around each lung is a pleural cavity.

2 Review how each lung is surrounded by a double-layered membrane called the pleura. The visceral layer of the pleura is firmly attached to the surface of the lung and moves with it as you breathe. The parietal layer of the pleura is firmly attached to the inner surface of the ribs and intercostal muscles, to the superior surface of the diaphragm, and to the parietal layer of the pericardium surrounding the heart. Between the visceral and parietal layers of the pleura around each lung is a pleural cavity. A small amount of pleural fluid fills this cavity and is important for reducing friction between lung and thoracic wall, as well as for maintaining a slight vacuum within the pleural cavity as you breathe. Exercise 2. The Relationship Between Volume and Pressure Air only moves into and out of your lungs when there is a difference in pressure. Air will flow into the lungs if the pressure there is lower than the pressure of the atmospheric air, and air will flow out of the lungs if the pressure there is higher than the pressure of atmospheric air (Figure 22.16). If those two pressures are equal, no air will flow in either direction. You can change the pressure of the air in your lungs because of something called Boyle s Law, which says that the pressure of a gas (or, in our case, the mixture of gases that we call air) is inversely proportional to its volume. When you inhale, you increase the volume of your lungs which decreases the pressure of the air they contain. When you exhale, you decrease the volume of your lungs which increases the pressure of the air they contain. We can do a simple demonstration to show this with a small (5-10 ml) syringe half filled with air. Under resting conditions, the pressure of the air inside the syringe is equal to the pressure of the atmospheric air outside the syringe, so you see that no air moves in either direction. Plug the end of the syringe with your finger and pull back on the plunger, thus increasing the volume of the syringe. You can feel the suction (more correctly, a negative pressure ) created by the decreased pressure of the air at the larger volume. If you remove your finger which is plugging the end, the higher atmospheric pressure will force air to flow into the syringe until the two pressures are again equal. Plug the end of the syringe again with your finger, and now push down on the plunger. You can feel the increased pressure of the air caused by the decreased volume within the syringe. Remove your finger, and you can feel that increased pressure forcing air out of the syringe until it is again equal with the atmospheric pressure. You should be able to correlate what happens in the syringe with what happens in your lungs. Half-way through a breath, stop and hold it for 5 seconds. You should not feel any air moving because the pressure of the air in your lungs is equal to the pressure of the atmospheric air. Take a deep breath, Inhaling slowly. You can feel the volume of your thoracic cavity increasing, and you can feel air moving into your respiratory system because of the lower pressure that creates in the air of your lungs. Exhale slowly. You can feel the volume of your thoracic cavity decreasing, and you can feel air moving out of your respiratory system because of the higher pressure that creates in the air of your lungs. 2

3 Exercise 3. The Muscles of Ventilation As we have discussed, pulmonary ventilation the movement of air into and out of the lungs - is achieved by using muscles of your thorax, neck, and abdomen to rhythmically change the volume in the thoracic cavity. Changes in this volume will change the pressures according to Boyle's law, and air flows between the lungs and the atmosphere along its pressure gradient, always moving from wherever there is a higher pressure to wherever there is a lower pressure unless you block that flow. Examine Figure in your Saladin text and label the muscles you use for inhaling (inspiration) and exhaling (expiration) on the diagram below. Circle the principle respiratory muscles you use for normal, quiet breathing, and place a rectangle around the name of each accessory respiratory muscles you use for deep breathing. Remember that the parietal layer of the pleura is firmly attached to the superior surface of your diaphragm and to the internal surfaces of your ribs. Therefore, when these structures move they pull that parietal layer with them, thus changing the pressures within the pleural cavity (Figure 22.16) Questions for discussion based on your reading of Chapter 22 before lab: Which nerve on each side innervates your diaphragm and causes it to contract? From which levels of the spinal cord (see Figure 13.14) does this nerve arise? Which nerves on each side innervate your internal and external intercostal muscles and cause them to contract? 3

4 Exercise 4. Review and Calculation of Respiratory Volumes Review Figure in your Saladin textbook and be sure you understand what tidal volume, inspiratory reserve volume, expiratory reserve volume, vital capacity, residual volume, and total lung capacity are. Have your lab partner sit quietly and breathe normally while you place your hands gently on the sides of his or her ribs. You should be able to feel his/her chest move with each breath. Have your lab partner place a hand on the superior part of her or his abdomen she/he can feel the abdominal organs being pushed out as the diaphragm contracts. Count the number of your lab partner s breaths for 60 seconds: breaths/minute With your hands still in the same position, have your lab partner Inhale normally, then take a deep breath, pulling in as much air as he or she can. Feel how the outward movement of both the thoracic and abdominal walls is more pronounced. Have your lab partner breathe normally for about one minute, then force as much air as possible out of her or his lungs. You can feel the contractions of both the thoracic and abdominal walls. Again, have your lab partner breath normally for about one minute, then breathe as hard as she or he can, forcing as much air as possible in and out for two or three breaths. You can feel the contractions of both the thoracic and abdominal walls. Questions for discussion based on your reading of Chapter 22 before lab: Which one of the volumes listed in Figure was your lab partner using during normal quiet breathing? This volume in normally how large in a normal, healthy adult? Which one of the volumes listed in Figure did your lab partner use when she/he inhaled deeply? Is this volume the same, more, or less than the previous one? This volume in normally how large in a normal, healthy adult? Which one of the volumes listed in Figure did your lab partner use when he/she exhaled deeply? Is this volume the same, more, or less than the previous two? This volume in normally how large in a normal, healthy adult? What is the total volume of air called (from Figure 22.17) that your lab partner moved in and out of her/his lungs when he/she was both inhaling and exhaling as much as possible? This volume in normally how large in a normal, healthy adult? There are a number of respiratory volumes which can not be observed and measured directly, but can be calculated. These include the residual volume, which is typically about 25% of the vital capacity in a healthy individual, and total lung capacity which is calculated by adding the residual volume of the lungs to the vital capacity. A bit later in this laboratory exercise, we will also calculate the minute respiratory volume by multiplying resting breathing rate by the tidal volume, and we will calculate the maximum amount of air which can be exhaled in one second (Forced Expiratory Volume, or FEV 1). 4

5 Exercise 5. Measuring Respiratory Volumes (Spirometry) Your instructor will now lead you through a demonstration of how to measure various respiratory volumes on a member of the class. While you do not need to know how to set up the instrumentation to do this, you should pay attention to how it is done. The spirometer measures the flow of air through a metal screen in a respiratory mouthpiece, changing it into an electrical signal which can be recorded. It also measures pressure differences on either side of the screen. The computer then uses this information to calculate and display the respiratory volumes as they change over time. 1. Select a volunteer who does not currently have a respiratory infection. Obtain a clean mouthpiece from the beaker containing alcohol, rinse it in water, and dry it with a paper towel. Obtain a new blue filter and attach it to the clear hose, then attach the mouthpiece to the blue filter. Obtain a noseplug. 2. If you are the volunteer, you should breathe normally through the mouthpiece while wearing the nose plug to force all of the airflow through your mouth. You will automatically modify your respiratory rate and pattern if watching the spirometer screen, so you should be facing away from the display and, if possible, should close your eyes while listening to the instructions given by your lab instructor. Be sure to maintain a good seal around the mouthpiece so air can not escape. 3. The instructor will start the recording, then instruct you to a) breath quietly for seconds to measure breathing rate and tidal volume. These will later be multiplied to calculate the minute respiratory volume. b) inhale as deeply as possible to demonstrate your inspiratory reserve volume, then breathe normally for seconds. c) exhale as deeply as possible to demonstrate your expiratory reserve volume, then breathe normally for seconds. d) inhale as deeply as possible, then exhale as quickly and as completely as possible to measure the vital capacity. This will also be used to calculate forced expiratory volume in one second (FEV 1). The residual volume cannot be determined by spirometric recordings. However, in a healthy individual it is typically about 25% of vital capacity Compare this spirometric recording to Figure in your text. While it should demonstrate the same volumes, it will not be as smooth and will be more spread out along the X-axis showing time. Your instructor will demonstrate how to measure certain intervals on that tracing, then you will do these calculations on the tracings which are attached. Exercise 6. Calculation of Respiratory Volumes Two respirometry tracings are attached at the end of this exercise. Note that the horizontal ( X ) axis of each graph shows time in minutes, and the vertical ( Y ) axis shows changes in the volume of air, in liters, as the person was breathing. On each graph you should be able to identify normal tidal volume breathing, the inspiratory reserve volume (inhaling as much as possible), the expiratory reserve volume (exhaling as much as possible), and vital capacity. Although these graphs look very different, once again you can refer back to Figure in your Saladin textbook to identify these if necessary. Pick one of those two graphs to make the following measurements with your lab group. Be sure everyone in the group understands these calculations and can do them correctly. 5

6 You will need to use a small millimeter ruler to measure two things: - The distance on the horizontal ( X ) axis of the graph equal to one minute ( a below), and - The distance on the vertical ( Y ) axis of the graph for one liter of air inhaled or exhaled ( c below) You will then use those measurement to calculate various respiratory volumes. a) Making the first measurement: Time. If the horizontal ( X ) axis of your graph shows an entire minute, measure that distance directly with the millimeter ruler. If it does not show an entire minute, measure half a minute and multiply by 2, or measure one-third of a minute and multiply by 3. Be careful: Notice that the beginning of the tracing you are measuring is not the starting time of 0. Record the distance (in mm) on the horizontal axis of your graph which equals one minute millimeters (mm) per minute b) Resting Breathing Rate: We can use that measurement you just did to calculate the approximate resting breathing rate, in breaths per minute, for the individual from whom this spirometry recording was made. Since resting breathing rate includes only tidal-volume breaths, the tracings of breathing using inspiratory reserve volume and expiratory reserve volume will interfere with your count and you will need to use only the section of the graph showing tidal volume breathing. Identify a region of the graph showing four consecutive tidal-volume breaths, and use the millimeter ruler to measure the horizontal distance of three of them, from the peak of the first to the peak of the fourth. Record that distance here: millimeters (mm) per three breaths If you divide that by the number of millimeters you calculated for one minute in a above and then do a bit of simple math you can calculate the resting breathing rate as the number of tidal volume breaths per minute. For example (obviously, your measurements will be different than this example) If: you measured in a that 200 mm on the horizontal axis equals one minute, and you calculated in b that three tidal-volume breaths covered 50 mm, then x = = 200 mm 3 breaths 600 breaths 12 breaths 1 minute 50 mm 50 minutes minute Do the measurements on the graph you are using and use those numbers to calculate the resting breathing rate. We ll set it up for you to fill in your measurements and calculations: mm x 3 breaths breaths breaths = = 1 minute mm minutes 1 minute Record your answer here. You will need it for a later calculation. Resting Breathing Rate = breaths per minute 6

7 c) Making the second measurement: 1 Liter of Air. Use the millimeter ruler to measure the distance on the vertical or Y axis of your graph that the tracing would move if the person inhaled or exhaled exactly one liter of air. You can do this by measuring the distance from -1 to 0, or from 0 to 1, but it will be more accurate if you measure a larger distance. I recommend that you measure the distance on the vertical axis for a total of 4 liters, from -2 to +2, and then divide by 4 to get the distance for just one liter For example (obviously, your measurements will be different than this example) If: You measure the distance for four liters of air, between +2 L and -2 L, to be 60 mm, Then: 60 millimeters per 4 liters (60 mm / 4 L) equals 15 millimeters per one liter (15 mm / 1 L) Record or calculate the distance on the vertical axis of your graph which equals one liter of air millimeters (mm) per liter of air You will use this for many of the calculations below. d) Tidal Volume. Measure the height in millimeters of three tidal-volume (TV) breaths. Be sure you measure the entire breath, not just the part above 0 on the graph. For each one, divide that measurement by your calculated distance per liter from c above to calculate the tidal volume of that breath. For example (obviously, your measurements will be different than this example) If: You calculated that 15 mm on the vertical axis equals one liter of air, and You measure the height of the breaths as 12 mm, Then, for this example: x = = = 12 mm 1 liter 12 liters 0.8 liters 800 milliters 1 TV breath 15 mm 15 TV breaths TV breath TV breath Do the measurements on the graph you are using and use those numbers to calculate the volumes of each of the three tidal volume breaths you measured. For the second (and final) time we ll set it up for you to fill in your measurements and calculations: x = = = mm 1 liter liters liters milliters 1 TV breath mm TV breaths 1 TV breath 1 TV breath Record your answers here for each of the three breaths you measured Breath #1: milliliters (ml) of air per tidal volume breath Breath #2: milliliters (ml) of air per tidal volume breath Breath #3: milliliters (ml) of air per tidal volume breath Average those three to determine an average volume of a tidal volume breath You will need this for a later calculation. Tidal volume = ml of air per breath 7

8 STOP! Before you go any further, be sure you understand those calculations you just did. You will need to set up and solve similar equations for the measurements and calculations below, so you will need to figure out which fractions you need to use for each one. We have not set them up for you. e) Inspiratory Reserve Volume: Measure the vertical distance in mm of the inspiratory reserve volume (IRV) and use the same type of equation to calculate that volume. Record your answer here: Inspiratory Reserve Volume = ml of air f) Expiratory Reserve Volume: Measure the vertical distance in mm of the expiratory reserve volume (ERV) and use the same type of equation to calculate that volume. Record your answer here: Expiratory Reserve Volume = ml of air g) Vital Capacity: Measure the vertical distance in mm of the vital capacity (from the top of the IRV peak to the bottom of the ERV) and use the same type of equation to calculate that volume. Record your answer here: Vital Capacity = ml of air h) Residual Volume: You can not directly measure residual volume from these graphs, but in a healthy individual it is approximately 25% of the vital capacity. Calculate the approximate residual volume for the person from whom this graph was made: Record your answer here: Residual Volume = ml of air 8

9 i) Total Lung Capacity: You also can not directly measure total lung capacity from these graphs, but you can calculate it from the other measurements and calculations you have made. What measurements do you need to add together to calculate total lung capacity? Calculate the approximate total lung capacity for the person from whom this graph was made: Record your answer here: Total Lung Capacity = ml of air j) Minute Respiratory Volume: A clinically important calculation is the volume of air which you inhale and exhale per minute, called the minute respiratory volume. This is calculated by multiplying the tidal volume you calculated in d above times the resting breathing rate you calculated in b above. Calculate the minute respiratory volume for the person from whom this graph was made: Record your answer here: Minute Respiratory Volume = ml of air per minute k) Forced Expiratory Volume In One Second: Another clinically important calculation, and the last measurement we will make in lab today, is the maximum volume of air you can exhale in a short period of time such as one second. This is called the forced expiratory volume in one second, abbreviated FEV 1. An example is given below. o o o o o Locate the tracing of the FEV 1 on the spirometry graph you are evaluating (you may also have used this tracing to calculate the vital capacity). Return to the measurement you did in a above to calculate the distance (in mm) which the tracing moved in one minute, then divide that by 60 to determine the distance (still in mm) which the tracing moved in one second. Mark the point at the top of the tracing where the person began exhaling as quickly as possible. Measure over the distance equal to one second, and mark where the tracing crosses that point. Measure the vertical distance the graph moved in that one second You can now use that distance along with your calculation in c above of the vertical distance per liter of air to calculate the volume of air exhaled in one second. 9

10 Here s an example. This graph was taken from a different spirometry tracing, and it is not copied here to the same scale. The measurements were taken on the original tracing. We calculated that 27 mm on the vertical axis represented one liter of air, and that the tracing of the FEV 1 moved 82 mm vertically in one second. The numbers for your graph, of course, will be different. FEV 1 was then calculated as 82 mm x 1 liter 82 liters 3.04 liters = = 1 second 27 mm 27 seconds second Questions for discussion based on your reading of Chapter 22 before lab: Normal values for tidal volume, inspiratory reserve volume, expiratory reserve volume, vital capacity, residual volume, and total lung capacity are given in Table 22.2 of your Saladin text, and the normal values for minute respiratory volume and FEV 1 are discussed on the previous page. Compare the measurements and calculations you did for those respiratory volumes. Were they close? If not, why are the values you measured and calculated different from normal values? Exercise 7. Repeating Calculations of Respiratory Volumes A second spirometry tracing is attached to this exercise. Repeat your measurements on this one at home or during open lab to be sure you understand how to do it. 10

11 Volume of Air (Liters) 11

12 12

Respiratory Physiology

Respiratory Physiology Background Information: When inspiring, the pleura attached to the internal chest wall is pulled outward as the thoracic cavity expands. The pleural cavity [space between the outer