The amount of air that is breathed in is dependent on the combined actions of the diaphragm, abdominal and intercostal muscles. During exercise impulses received from the brain tell these muscles to contract or relax with greater depth, leading to greater changes in the cavity of the chest. The higher the pressure changes in the lungs the greater the movement of air in and out of the lungs.
Central Controlling Area
The respiratory centre located in the lower part of the brain stem, in the medulla oblongata in the area responsible for controlling breathing. This region has both "inspiratory neurones" and "expiratory neurones” which are active at different times of breathing. These neurones automatically maintain the rhythmic cycle of inspiration and expiration. These neurones can be controlled by higher brain functions and afferent information from the body.
Afferent Supply
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Central chemoreceptor – these are a group of cells that respond to changes in pH. Cells in the fourth ventricle (brain stem) respond to the acidity of the cerebrospinal fluid (CSF). The normal pH of the body is 7.4; any changes to this value will be sensed by the chemoreceptors resulting in a change in the rate of respiration. If the pH falls below 7.4 (acidic) the cells cause hyperventilation, whereas an alkaline pH (above 7.4) causes inhibition of the respiratory centre. During exercise when the carbon dioxide level in the blood increases, there is a corresponding rise in the CSF (as well as hydrogen ions and bicarbonate). This results in a lowered pH in the CSF and as a result hyperventilation.
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Peripheral chemoreceptors – chemoreceptors are also found in the carotid artery and aortic branch. Both of these chemoreceptors will respond to oxygen and carbon dioxide levels in the blood. Information from the carotid body passes along the glossopharyngeal nerve (the ninth cranial nerve) and information from the aortic body is along the vagus nerve (the tenth cranial nerve), to the respiratory centre. If the arterial blood reaching the carotid body has a partial pressure of oxygen of 10kPa (80mmHg) or a carbon dioxide partial pressure greater than 5kPa, (40mmHg), then there is an immediate and marked increase in breathing.
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Stretch receptors - There are various receptors in the lung that modify breathing. Receptors in the wall of the bronchi respond to irritant substances and cause coughing, breath holding and sneezing. In the elastic tissues of the lung and the chest wall are receptors that respond to stretch.
There are also stretch receptors in the blood vessels in the lung. If these are stretched, as in heart failure, the response is to hyperventilate. The information from these receptors in the lung is carried to the respiratory centre along the vagus nerve.
Null hypothesis
There will be no significant difference in the tidal volume or breathing rate of a subject between rest and exercise
Hypothesis
The tidal volume and breathing rate of a subject will be higher under periods of exercise than compared to rest.
Variables
Safety precautions
No more than 5 breaths should be taken from the apparatus due to the build up of carbon dioxide. If continued breaths are taken after this it could result in hypoxia and loss of consciousness.
Ethical issues arising from the experiment-
There are no ethical issues in this experiment
Equipment:
- As listed in the NEC Booklet.
The method:
- As listed in the NEC Booklet.
Results
The graph shows an increase in the number of breaths per minute as the intensity of the exercise is increased.
A mathematical calculation can be carried out on this experiment to see if there is a correlation between the temperature and one of the readings in the results; transmission or absorbency. If there is then it is possible to accept or reject our original hypothesis. For this calculation I will be using transmission, as it is an easier figure to use being larger, the average data will be applied to the calculation to get a more accurate result. The hypotheses remain the same from the main experiment found earlier in the report.
Data Table: Spearman's Rank Correlation
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Calculate the coefficient (R) using the formula below. The answer will always be between 1.0 (a perfect positive correlation) and -1.0 (a perfect negative correlation).
When written in mathematical notation the Spearman Rank formula looks like this :
Now to put all these values into the formula.
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d² = 0 multiplying this by 6 gives 0
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n=4, therefore n3 – n = 43-4 = 64 – 4 = 60
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R = 1 - (0/60) which gives a value for R:
= 1 - 0
= 1
The R value of 1 suggests perfect negative correlation relationship.
A further technique is now required to test the significance of the relationship.
The R value of 1 must be looked up on the Spearman Rank significance table below as follows:
Degrees of freedom = number of pairs -2 = 4-2 = 2
The Spearman Rank test shows that there is a positive correlation between exercise intensity and the rate of respiration. It also suggests that that the null hypothesis can be rejected with 95% confidence. This means that there is a significant difference between the rate of respiration and the level of exercise intensity.
This graph shows that the volume of air breathed into the lungs is greater at times of exercise compared to that consumed at rest. As you can see from the graph there is little difference between the volumes of breath when comparing the experiments at rest. This can also be said for exercise. If the intensity of the exercise is kept the same the body responds by increasing ventilation to the same rate as shown in the graph.
The mean value for both experiments (red) and for individual experiments show that the air consumed during exercise is greater than that consumed at rest. The means of the experiments conclude that there is a 40% increase in the tidal volume between periods of rest and exercise.
The t-test demonstrates that the p value is >0.01, showing that the null hypothesis can be rejected with more than 99% confidence. This experiment shows that there is a significant difference between the tidal volume at rest and during exercise.
Conclusion
As the humans move from a period of rest to exercise, there is an increase in the demand for oxygen. To meet this demand the rate of respiration and the amount of oxygen taken into the lungs is increased.
Discussion
When we breathe oxygen is brought into the lungs. It is this that is used in final step of respiration to create ATP. As the intensity of exercise increases the demand for energy by our muscles also increases. This means that more oxygen needs to be supplied to the muscles so they can perform respiration. To do this the rate and quantity of oxygen that is breathed into the body needs to be increased.
All of the oxygen that is brought into the lungs does not reach the alveoli (gas exchange region of the lungs). It is only the air that travels past the dead space into the alveoli that contributes to the gas exchange. As a result the alveoli ventilation is much less than the total ventilation – and this is the volume that passes oxygen to the blood and the body beyond.
The alveolar oxygen concentration determines the amount of oxygen concentration in the blood. The concentration of oxygen in the blood during exercise is maintained (at least close too) the oxygen concentration at rest. Despite the demand for oxygen being ten times that at rest. This can only be maintained if the ventilation of the alveoli is increased proportionally to supply that demand.
The increase in ventilation to the lungs is brought about through physiological changes in the body as a direct result of exercise. One of the exercised induced challenges to the body is a lowering of the body’s pH level (acidic). Firstly to increase the energy available to the muscles the body increases its oxidation of fats and carbohydrates. During the oxidative phosphorylation of these compounds hydrogen molecules are removed to link with oxygen to produce energy.
For example, glucose: C6H12O6 + 6O2 → 6H2O + 6CO2. As the concentration of carbon dioxide in the blood increase the concentration of [H+] ions also increase (via the Bohr shift). For the [H+] ions concentration to be kept as low as possible carbon dioxide needs to exhale at the same rate as it is produced.
During moderate exercise ventilation increases with proportion to the rate of metabolism maintaining the level of carbon dioxide and as a result the concentration of [H+] is kept close to rest. At higher levels of intensity the body’s acidity level can only be maintained if the carbon dioxide in the blood is reduced. To compensate for this the body increases ventilation proportionally to carbon dioxide production.
When we participate in less strenuous exercise the extra energy that we need is provided for by an increase in the tidal volume. However during strenuous exercise, tidal volume can only increase to a maximum of 50-60% of the vital capacity, about 2.5-3L (in an average man). The increase in tidal volume comes as an expense of inspiratory reserve volume. The frequency of breathing may increase to 40 to 50 breaths per minute in a healthy individual. The increase of tidal volume (VT) during exercise occurs as a result of both an increase in end-inspiratory and a decrease in end-expiratory lung volume, and the work of breathing during exercise is sustained by activity of both inspiratory and expiratory muscles. When exercising the Tidal Volume increases because your breathing at a faster rate and your muscles are using up the oxygen at a quicker rate hence a need for more oxygen hence you body increasing the Tidal Volume to allow more oxygen to be consumed and meet the muscles oxygen demands.
The increase in ventilation during exercise could, theoretically, be accomplished by an infinite variety of depths (tidal volumes) and number (breathing frequency) of breaths per minute. Very deep and slow breathing requires extra effort because the thorax, and in particular the lungs, become very stiff at high volumes. Rapid shallow breathing, on the other hand, mostly ventilates the dead space. The spontaneously-chosen pattern is typically the one which most effectively combines low breathing effort with a high fraction of the breaths reaching the alveoli. Consequently, most people initially increase ventilation predominantly by increasing tidal volume up to a certain optimal maximum; higher ventilatory demands are then achieved predominantly by increasing breathing frequency.
The results of this experiment fit with the literature, that the main mechanism for reducing the level of [H+] ions in the blood that are produced by the increase in carbon dioxide is through an increase in ventilation rate and depth.
One way to improve this method is too use a device called a spirometer. It can be used to measure expired and inspired volumes of air over a timed period. From the results it can be calculated how fast the lungs can be filled and empted as well as the volume of air moving in or out of the lungs.
In the above example the first 15 seconds of the trace show the normal breathing rate of the subject. During this period 3 full breaths were taken this means that the resting breathing rate of the subject is 12 breaths min-1. Each breath at rests consumes 0.67dm3 of air. This equates to a minute volume of (12 x 0.67 = 8.04 dm3min-1. When a subject is breathing normally at rest they will never fully expire all of the air from the lungs. The volume of air that is kept in the lungs is termed the expiratory reserve volume. Even during forced ventilation the lungs will never be fully devoid of air this is known as the residual volume. To measure the vital capacity of the lungs the subject first breaths out to force as much air from the lungs. The subject then breaths in as deeply as possible and then forces as much air from the lungs as possible. Vital capacity is the amount of air that can be forced out of the lungs after a maximal inspiration.
A spirometer can be used to see the changes that occur in the lungs after a period of exercise. The first thing that occurs on the example shown is an increase in the both the rate of respiration and the depth of breathing. These two effects are explained by the increase in carbon dioxide in the blood as a result of raising respiration in the muscle cells. The increase in carbon dioxide in the blood lowers the pH of the blood activation chemoreceptors in the aortic arch and carotid arteries. This activates neurones in the cardiac centre of the medulla to send impulses to the diaphragm and intercostal muscle to increase the rate and depth of breathing.
The spirometer can also be used to identify the physiological effects that occur after a period of exercise. As shown in the trace following exercise the tidal volume and rate of respiration decrease until they reach resting values. From concluding exercise to reaching normal resting values a period of 7 seconds elapses. This period of time is due to a phenomenon known as oxygen debt. During exercise the body needs as much energy as possible being delivered to the working muscles. To do this much of the glucose consumed during respiration is converted to lactic acid. The extra oxygen needed following exercise is required to remove the lactate and convert it back to pyruvate.
Evaluation
Although the results fit with the literature, they are as reliable as they could be. This experiment was only conducted on one individual. To improve the accuracy of the results the number of subjects, age, sex and the number of times that this experiment was carried out.
Textbook of work physiology: physiological bases of exercise By Per-Olof Åstran
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Expiratory Flow Limitation Roger S. Mitchell Lecture , MD 10.1378/chest.117.5_suppl_1.219S-a CHEST May 2000 vol. 117 no. 5 suppl 1 219S-223S
UCI 205340050507X Candidate Number 0507 NEC student number SS121598 Page
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nealparkes (student)
