1 The Respiration System in Humans Madeline Pitman Group Members: Kathryn Hillegass Michelle Liu Noelle Owen Section 62 Danielle Cooper August 11, 2014
2 A. Introduction Experiment Goals The experiment aims to show how the lung volume can change, how the composition of gas involved in respiration can modify respiration and how exercise changes respiration in humans. Physiological Principles As the flow of air into and out of the lungs is increased and decreased, a change in the volume of air in the lungs is caused (Sheerwood, 2010, 473). The volume of an average breath, taken while resting, is referred to as the tidal volume or TV (Sheerwood, 2010, 474). The inspiratory reserve volume, or IRV, describes the additional volume of air that can be inhaled over the tidal volume. The expiratory reserve volume, or ERV, is the additional volume of air that can be expelled from the lungs by contracting the expiratory muscles more than during a normal breath. The vital capacity, or VC, is the summation of the TV, IRV, and ERV. Hyperventilation occurs when a subject breathes at a rate that exceeds the boy s needs (Sheerwood, 2010, 490). CO 2 and O 2 are absorbed through passive diffusion that is caused by differences in pressure (Sheerwood, 2010, 480). If the pressure of the O 2 in the capillary blood is greater than the capillaries surroundings, then the O 2 will diffuse away from the capillaries. During heavy exercise, the body s demand for O 2 increases and the body s need to expel CO 2 increases, which causes alveolar ventilation to increase in order to keep up with the body s need for O 2 (Sheerwood, 2010, 498).
3 Expected Results In part 1 of this experiment, it is expected that by using a spirometer the subject s tidal volume, inspiratory reserve volume, expiratory reserve volume and vital capacity will be determined (Sheerwood, 2010, 473). It is expected that during different types of breathing, the amount of CO 2 measured after breathing will remain similar (Haldane, 1905, 250). The amount of CO 2 measured during re-breathing is expected to increase from normal breathing (Haldane, 1905, 249). It is anticipated that hyperventilation, in experiment 2, will decrease the CO 2 levels measured (Sheerwood, 2010, 491). When the subject exercises, it is expected that the CO 2 production and ventilation will increase (Sheerwood, 2010, 498). It is anticipated that the length of time the subject is able to hold their breath will be determined by the amount of CO 2 present (Sheerwood, 2010, 496). B. Materials and Methods This experiment measured multiple aspects of the human respiratory system. The volumes of the subject s breathing was measured. The CO 2 content of the subject s breath was measured during different breathing situations. The subject s ability to hold their breath was measured during normal breathing, hyperventilation and re-breathing. The effects of exercise on respiration were also measured. The complete method for this experiment can be found in NPB 101L Systemic Physiology Lab Manual (Bautista, 2008, 55-63). One deviation from this method was made in Part 3, on page 61. The lab manual procedure requires an ECG to be used in Step 4 of Part 3, and this step was skipped when the experiment was preformed. C. Results Experiment 1 Measuring the Static Lung Volumes
4 In this experiment the tidal volume of the lungs was found by measuring the volume of the subject s normal breaths, and was the smallest volume found (Table 1). The subject exhaled the greatest volume of air possible from their lungs, which showed the volume of air reserved in the lungs and not used during normal breathing, as seen as the expiratory reserve volume in Table 1. As the subject inhaled as deeply as possible, the volume of air in the lungs increased to the IRV, a volume greater than the TV, as seen in Table 1. The vital capacity was found by measuring from the lowest volume of the expiration to the highest volume of the inhalation (Table 1). Table 1. The volume of air passing through the subject s lungs, was measured using a spirometer. This experiment was preformed with a female human. The data was analyzed using the Δ function of the BioPac system. The inspiratory reserve volume was measured from 98-102 seconds. The expiratory reserve volume was measured from 118-123 seconds. The tidal volume was measured from 10 cycles before the maximum inhalation at 75-77 seconds. The vital capacity was measured from 101-123 seconds. Volume (Liters) Inspiratory Reserve Volume 1.92 Expiratory Reserve Volume 0.81 Tidal Volume 0.67 Vital Capacity 3.2 Experiment 2 The Effects of Inspired Gas Composition and Lung Volume on Respiration The subject s normal CO 2 levels were measured by analyzing air that had been captured from a held breath after normal breathing (Figure 1). After the subject re-breathed air, the amount of CO 2 measured before holding their breath, increased (Figure 1). Figure 1 shows that after the subject hyperventilated the pre-breath holding measurement of CO 2 was less than the same measurement during normal breathing. As seen in Figure 1, the CO 2 levels that were measured after the subject held their breath varied, but remained similar after all three types of breathing.
5 CO 2 Before and After Holding Breath % CO2 7 6 5 4 3 2 5.25 3.75 6 5.7 5.64 3.27 %CO2 Before Breath- Hold %CO2 After Breath- Hold 1 0 Normal Breathing Re- Breathing Hyperventilation Figure 1. The amount of CO 2 expired by the subject, was measured before and after the subject held their breath. A CO 2 analyzer was used to measure the amount of CO 2 produced by the subject. A female human was used to perform the experiment. The CO 2 levels taken before the breath hold increased, from the normal breathing level, after rebreathing. The CO 2 percentage before the breath-hold decreased from the normal breathing level, during hyperventilation. The after breath holding values remained similar, and only varied 0.45% CO 2. During this experiment, the length of time the subject could hold their breath was measured. When compared to normal breathing, hyperventilation resulted in an increase in the length of the breath hold (Figure 2). After re-breathing air, the subject did not hold their breath as long as they did after normal breathing or after hyperventilating, as seen in Figure 2. 120 Duration of Breath-Hold with Different Breathing Types 110 100 Seconds 80 60 40 20 30.8 13.8 0 Normal Breathing Re- Breathing Hyperventilation
6 Figure 2. The length of time the subject could hold their breath was measured after normal breathing, re-breathing, and hyperventilation. A cell phone was used to time a female human subject. Re-Breathing caused a reduction in the length of breath held, when compared to normal breathing. After hyperventilating, the subject held their breath longer than after normal breathing or re-breathing. The subject held their breath after exhaling normally, which provided a base line for the subject s ability to hold their breath (Figure 3). After the subject inhaled as they would during a normal breath, and then held their breath, the length of the breath held increased, as seen in Figure 3. When the subject forced an inhale that was larger than their normal breathing, the time spent holding their breath was greater than after a normal inhale (Figure 3). After the subject forced an exhale larger than the exhales of their normal breathing, the time the subject held their breath decreased to a level lower than the other three types of breathing (Figure 3). Seconds 40 35 30 25 20 15 10 5 0 Duration of Breath-Hold 21.7 Normal Expiration 29.5 Normal Inspiration 37.9 Forced Inhalation 16.6 Forced Exhalation Figure 3. The length of time for which the subject could hold their breath was measured using a cell phone timer. A female human performed this experiment. The length of the breath hold increased, from the normal expiration, for both the normal inspiration and the forced inhalation. The number of seconds that the subject held their breath decreased, from the normal expiration length, to the forced exhalation length. The longest breath hold was after a forced inhalation. The shortest breath hold was after a forced exhalation. Experiment 3 Effects of Exercise on Respiration
7 This experiment increased the workload on a subject by using a stationary bike pedaled by the subject. As the workload was increased on the subject, the subject s tidal volume and respiration rate increased, as can be seen in Table 2. The tidal volume values are the average volume of four breaths. Workload (pka) Table 2. The average tidal volume was calculated using the volume of four breaths taken during the last 30 seconds of each workload. A female human was used to perform this experiment. A stationary bike was used to apply the workload. The volume of air was measured using a spirometer. The data was analyzed using the delta function of BioPac, and the values were averaged using a calculator. The respiratory rate was measured by counting the number of breaths taken during the last 30 seconds of the workload, then multiply the value by two to determine how many breaths were taken each minute. Respiratory Rate (breaths/min) Tidal Volume (Liters) 0 (Rest) 1.12 10 0 1.48 18 0.5 1.59 18 1 1.69 24 1.5 1.73 30 2 1.82 30 The minute ventilation found during the rest period was the lowest minute ventilation (Figure 4). As soon as the subject started to pedal, at 0 kilopascals (kpa), the minute ventilation began to increase, and continued to increase as the workload was increased through the rest of the experiment (Figure 4).
8 Minute Ventilation (L/min) 60 50 40 30 20 11.210 0 Minute Ventilation 26.64 28.64 40.56 51.9 Figure 4. The minute ventilation was calculated by multiplying the tidal volume by the respiration rate. The tidal volume and respiration rate were found using a female human subject exercising on a stationary bike. The minute ventilation increased from the rest period to the 2.0 kilopascals (kpa) workload. At rest, the subject did not pedal. The subject started to pedal at 0kPa. 54.6-0.5 0 0.5 1 1.5 2 2.5 Workload (kpa) During this experiment, the increase in workload changed the levels of end-tidal CO 2 (Figure 5). From the rest period to the initial start of exercise, at workload 0 kilopascals (kpa), resulted in an increase in end-tidal CO 2 (Figure 5). This initial increase continued when the workload was increased to 0.5kPa as seen in Figure 5. The increase in the workload from 0.5kPa to 1.5kPa resulted in a decrease in the percentage of end tidal CO 2 (Figure 5). This decrease stopped at 1.5kPa, and an increase occurred between the workloads of 1.5kPa and 2kPa (Figure 5).
9 %CO2 6.8 6.6 6.4 6.2 6 5.8 5.7 5.6 6.57 End Tidal CO2 6.71 6.46 Figure 5. The CO 2 content was measured using a CO 2 analyzer. A female human biked on a stationary bicycle during this experiment. The max tool of the BioPac program was used to analyze the data collected during the last 30 seconds of each woakload. The CO 2 levels increased from the rest period to a workload level of 0.5 kilopascals (kpa). From a workload level of 0.5kPa to 1.5kPa, the CO 2 levels decreased. Between the workload of 1.5kPa to 2.0kPa, the CO 2 levels increased. The subject did not pedal during the rest period. This experiment measured the minute ventilation and end tidal CO 2 levels, which were multiplied together to find the minute CO 2 values as seen in Figure 6. The minute CO 2 levels increased as soon as the workload was applied at 0 kpa after the rest period (Figure 6). The minute CO 2 continued to increase each time the workload was increased (Figure 6). 6.34 6.39-0.5 0 0.5 1 1.5 2 2.5 Workload (kpa) Minute CO2 (L CO2/min) Minute CO2 Production 4 3.5 3 2.5 2 1.5 1 0.5 0-0.5 0 0.5 1 1.5 2 2.5 Workload (pka)
10 Figure 6. The minute CO 2 production was calculated by multiplying the minute ventilation by the end tidal CO 2 values. The minute ventilation and end tidal CO 2 values were measured from a female human biking on a stationary bicycle. The minute CO 2 production increased from the rest period to the final workload of 2.0kPa. The subject began to pedal after the rest period, at 0kpa. D. Discussion Experiment 1 Measuring the Static Lung Volumes The data shows that the subject s tidal volume was 0.67 Liters (Table 1). The tidal volume was expected to be around 0.5 liters (Sheerwood, 2010, 474). The subject s tidal volume may have been larger than normal due to not being in a resting state. The subject s IRV was expected to be similar to the average IRV value of 3.0 liters, but the IRV measured was lower at 1.92 liter. The IRV of the subject may have been lower due to anticipating the breathing exercises. The IRV still demonstrates the process of contracting the diaphragm, accessory inspiratory muscles and external intercostal muscles because the IRV was greater than the TV. It was expected that the subject s ERV would be similar to the average ERV of 1.0 liter, and at a ERV of 0.81 liters the subject s ERV was close to the average. The subject s ERV is larger than the TV which demonstrates that the subject contracted the expiratory muscles more than the contractions during the resting breathing measured by the TV. The ERV of the subject may have been lower than the average because the subject was anticipating the next breathing exercise. The average VC is 4.5 liters, and the subject s VC was measured at 3.2 liters. The subject s VC, ERV and IRV may have been lower than the average because females generally have a lower lung capacity than males. Experiment 2 The Effects of Inspired Gas Composition and Lung Volume on Respiration This hyperventilation performed in this experiment was expected to lower the amount of CO 2 measured before the breath hold because the subject increased their rate of breathing beyond
11 the rate needed by the body (Sheerwood, 2010, 491). Since the subject was exhaling more CO 2 than during normal breathing, the CO 2 levels dropped as seen in Figure 1. Similar results were see in an experiment preformed by Brown (Brown et al, 1948, 334). However, Brown measured the plasma CO 2 levels, while this experiment measured the levels of CO 2 the subject exhaled. Before the breath-hold, during the re-breathing exercise, the amount of CO 2 measured increased (Figure 1). Haldane s subjects CO 2 levels also increased during re-breathing (Haldane, 1905, 249). This is because the subject were breathing in the CO 2 they produced during breathing, since the subjects air supply was restricted to a closed sample of air (Haldane, 1905, 248). The CO 2 levels taken after the breath hold remained similar through the entire experiment despite the type of breathing being preformed (Figure 1). Haldane observed a similar result when the CO 2 levels of his subjects did not change from the normal breathing to after rebreathing (Haldane, 1905, 250). This is because the P CO2 is held within a normal range, during most conditions (Sheerwood, 2010, 494). The medullary respiratory center moderates to P CO2 levels, and if they become too high it will send a signal to the respiratory muscles, through motor neurons, to increase ventilation. This is also why the subject was not able to hold their breath as long after re-breathing, and was able to hold their breath for an increased length of time after hyperventilation. Experiment 3 Effects of Exercise on Respiration This experiment showed that as the workload increased, the ventilation rate also increased (Figure 2). This was supported by the results of Clark s experiment in which he also saw higher levels of respiration in subjects that exercised with additional resistance than subjects who exercised with no additional resistance (Clark, 1968, 558). Mitchell s experiments showed
12 that as the workload placed on the subject increased, the rate respiration also increased. The same result was produced by this experiment, and as the workload applied and then increased, the respiratory rate increased (Table 2) (Mitchell et al, 1958, 1694) The increase in tidal volume and increase in respiration rate is necessary during exercise because muscles need more O 2 to continue oxidizing nutrient molecules at a rate fast enough to keep up with the bodies needs (Sheerwood, 2010, 498). As shown by Clark, it was expected that the end tidal CO 2 levels would increase as ventilation increased during exercise (Clark, 1968, 557). An increase in end tidal volume can be expected because the bodies muscles are metabolizing at a faster rate and therefore producing CO 2 at a faster rate (Sheerwood, 2010, 498). These results were seen in parts of the data, but not from workloads of 0.5 kpa 2 kpa (Figure 5). This may have been due to technical difficulties with the BioPac program. Since the minute ventilation is calculated using the tidal volume and respiratory rate, an expected increase in both should increase the minute ventilation rate, and this did happen in Figure 4. Similarly, the minute CO 2 production depends on the minute ventilation and the end tidal volume, and these values were both expected to increase. The increase seen in Figure 6 was expected.
13 E. References Sheerwood, Lauralee. Human Physiology From Cells to Systems. 8 th Edition. Belmont, Ca: Brooks/Cole, Cengage Learning, 2010. Bautista, Erwin, and Korber, Julia. NPB 101L Systemis Physiology Lab Manual. 1 st Edition. Mason, OH: Cengage Learning, 2008. Brown EB, Campbell GS, Johnson MN, Hemingway A, Visscher MB. Changes in Response to Inhalation of CO 2 Before and After 24 Hours of Hyperventilation in Man. Journal of Applied Physiology. 1948; 1(4): 333-338. Haldane JS, Priestley JG. The Regulation of the Lung Ventilation. The Journal of Physiology. 1905; 35: 225-266. Clark TJH, Godfrey S. The Effect of CO 2 on Ventilation and Breath-Holding During Exercise and While Breathing Through an Added Resistance. The Journal of Physiology. 1969; 201: 551-556. Mitchell JH, Sproule BJ, Chapman CB. Factors Influencing Respiration During Heavy Exercise. The Journal of Clinical Investigation. 1958; 37(12):1693-1701.