Introduction

 

            The
lungs, which are a major component of the respiratory system, are a very vital
organ to the human body, having many functions that enable us to sustain life (1).

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Some of the lungs main functions are breaking down and filtering harmful
substances, and acting as a holding site for blood (1). However, the
lungs are importantly responsible for the site of the exchange of gases, such as
the movement of oxygen and carbon dioxide from the air into and out of the
lungs, which is also known as ventilation, and throughout the respiratory
system and blood (1).  What drives
ventilation on a physiological level are chemoreceptors, which ensure that we
breathe to maintain proper blood oxygen and carbon dioxide levels, as well as
pH (2).  

            Gas
exchange of carbon dioxide and oxygen during ventilation relies on a mechanism
called diffusion, which and depends on the surface area of the membrane of the lung,
the pressure difference across the lung, and the thickness of the membrane of
the lung (1). This is known as Fick’s law of diffusion. Moreover, detrimental
actions on the 3 variables of Fick’s law of diffusion can leave harmful impacts
on the lungs and respiratory system, and can ultimately inhibit normal lung
function (1). Diseases of the lungs would leave this type of negative
effect on the respiratory system and hinder the 3 variables of Fick’s Law of
diffusion.

            There
are two main categories of diseases that can affect the lungs, which are
obstructive diseases and restrictive diseases (3). These lung
diseases can have detrimental effects on the lung because they can result in decreased
airway size, swollen or loss of alveolar sacs, and ultimately reduced gas
exchange (3). Lung diseases, as well as the overall function of the
lung can be evaluated using a method known as spirometry (4).

Spirometry is a tool used to evaluate the breathing mechanisms of a patient and
allow doctors to detect pulmonary diseases in patients displaying abnormal lung
function (4). Spirometry can consist of static and dynamic tests to
measure variables such as vital capacity, which is the highest volume of air
that can be exhaled out of the lungs after taking the largest inspiration
possible, as well as forced vital capacity (FVC), which is the amount of gas
that is expelled out of the lungs as fast and hard as possible after the
greatest possible inspiration (3).

            The
main purpose of this lab is to study pulmonary function through static and dynamic
testing such as slow breathing, forced vital capacity and maximum voluntary
ventilation, and identify how resting and dynamic lung values may differ under
normal and obstructed breathing circumstances. Moreover, control of ventilation
will be studied as well to determine how the length of breath holding may
change during resting, hyperventilating, and exercise procedures. We
hypothesize that resting and dynamic lung values will be greater under normal
breathing conditions and decreased during obstructed airway conditions since
the flow of air into and out of the lungs would be altered. We also hypothesize
that breath holding will be the greatest after hyperventilation due to
decreased amounts of carbon dioxide in the blood, and the least after
exercising due to the body’s new high demand for oxygen.

 

Methods

Subject
Characteristics and Environmental Conditions

There was
a total of four participants in this lab. For the static and dynamic lung
testing regarding resting lung volumes, forced vital capacity, and maximum
voluntary ventilation, 2 subjects participated in these breathing exercises. The
first subject was a 20-year-old moderately active male who was 68 kilograms in
weight and 163 centimetres in height. The second subject was a 20-year-old moderately
active female who was 50 kilograms in weight and 171 centimetres in height. Subjects
3 and 4 that completed the different breath hold procedures were a 20-year-old
female and a 20-year-old male respectively. Additionally, the temperature of
the room was 22.5 degrees Celsius and the barometric pressure of the room was
744 mmHg. It is also noted that subject 2 had a history of recurring bronchitis
over the past 5 years. A handheld spirometry system was used to record
breathing, as well as a software called winspiroPRO to document all spirometry
data.

Static
and Dynamic Lung Testing

            Subject
1 started the lab with static lung testing, and began by breathing normally
into the mouthpiece with a nose clip on, facing away from the computer screen
to not influence any breathing patterns. Once a normal breathing pattern
ensued, subject 1 inhaled his largest possible breath and exhaled as much air
as he could to end the trial. The same trial was repeated an additional two
times. Subject 1 then proceeded to complete the dynamic lung testing, the first
test being forced vital capacity (FVC). For the forced vital capacity
procedure, subject 1 began by breathing normally into the mouthpiece, again
with a nose clip, then inhaled his largest breath possible and held it for one
second, followed by a forceful and rapid exhale that lasted about 5 seconds.

This test was performed a total of three times and all data was recorded. For
the final dynamic lung test of maximum voluntary ventilation, subject 1 breathed
as deeply and as rapidly as possible into the mouthpiece for 15 seconds while
giving maximal effort. The data was recorded and the test was repeated once
more, as well as having a break in between the two trials to ensure the subject
did not feel too light headed. Subject 1 then completed the same static and
dynamic tests again, however, this time he completed the same tests as above
with a flow restricting stopper that was placed in the mouthpiece to simulate an
obstructed airway. Once subject 1 completed his tests, subject 2 performed the
same static and dynamic lung tests above; first under normal breathing
circumstances and then under obstructed breathing circumstances.

 

Breath-holding
Procedures

            Subjects
3 and 4 began to prepare for the 3 breath-holding procedures. In a seated
position, participants 3 and 4 took their deepest breath and held it for as
long as possible for the resting breath hold procedure. While doing so, they
ensured to keep their noses plugged so no ventilation was done whatsoever.

Their breath-hold times were recorded. The second breath-hold procedure
consisted of subjects 3 and 4 voluntarily hyperventilating for 1 minute,
followed by holding their breath for as long as possible. Their breath hold
times were recorded once again. Lastly, participants 3 and 4 cycled for 90 seconds
at a cadence between 75 and 85 rpm against a resistance of 200W. Directly after
cycling, participants 3 and 4 tried to hold their breath as long as they could
once again, and their breath hold times were recorded.

 

Results

During
static lung testing, it was observed that normal breathing patterns into the
spirometer resulted in higher resting lung volumes (Figure 1). Obstruction in
breathing caused a decrease in all resting lung volumes by roughly 0.15 to 0.5
litres in subject 1(Figure 1). Similar results were seen in subject 2, however
subject 2 had a slightly higher tidal volume of 1.3 L with obstructed breathing
when compared to 0.89 L during normal breathing (Figure 2). Subject 1 had a
forced vital capacity of 3.37 litres during normal breathing, and only 3.1
litres during obstructed breathing (Figure 3). Subject 2 had a higher forced
vital capacity during normal breathing as well (3.05 L) compared to 2.85 litres
during obstructed breathing. For the forced expiratory volume at one second
values, subject 1 and 2 had nearly identical results, with roughly 3 L expired
at one second during normal breathing, and roughly 2.5 litres expired at one
second during obstructed breathing (Figure 4) There was a slight reduction in
forced expiratory volume percentage from normal breathing to obstructed
breathing in both subjects. However, the percentage values for both subjects
and both breathing conditions remained above 80% (Figure 5). For subject 1, his
peak expiratory flow decreased from 4.01 L/s during normal breathing, to 2.88
L/s during obstructed breathing, and for subject 1, her peak expiratory flow
decreased from 6.48 L/s during normal breathing, down to 2.77 L/s during
obstructed breathing (Figure 6). Obstruction also reduced FEF25-75 in both
subjects as well compared to normal breathing conditions (Figure 7). Furthermore,
almost identical results were seen during the maximum voluntary ventilation
test between subjects 1 and 2. Both subjects had a MVV of about 112 L/min
during normal breathing, and a drastically lower MVV during obstructed breathing
of around 70 L/min (Figure 8).

It was
observed that between both subjects 3 and 4, breath holding lasted the longest
after hyperventilating voluntarily for 1 minute; subject 3 lasted 55 seconds
after hyperventilating and subject 4 lasted 120 seconds after hyperventilating
(Figure 9). Breath holding lasted the shorted duration after exercising at 200
watts for 90 seconds for both subjects, subject 3 only able to hold their
breath for 6 seconds and subject 4 able to hold their breath for 7 seconds
(Figure 9).

 

 

 

                                                                                                          

                                                   

 

Discussion

 

            The
results indicate that the hypotheses made were able to be validated by the data
collected in this experiment. In the static lung volume tests, variables such
as inspiratory and expiratory reserve volumes and vital capacity all decreased
during obstructed breathing compared to normal breathing in both subjects 1 and
2, as to be expected. This is due to the reduction of airflow because of airway
swelling and compression, which alters and limits the flow of air into and out
of the lungs (3). Tidal volume appeared to decrease in obstructed
breathing when compared to normal breathing in subject 1, and increased during
obstructed breathing for subject 2. However, tidal volume is said to not change
drastically in the case of an obstructive lung disease since tidal volume
refers to the air that is inhaled or exhaled during normal shallow breathing,
not during maximal effort breathing, therefore having a less noticeable change (3).

 Moreover, forced vital capacity, a
dynamic lung test, decreased in both subjects during obstructed breathing when
compared to normal breathing, which again was to be expected due to increased
challenge to expire entirely. Studies show that in patients who demonstrate an
obstructive pulmonary disease, they generate a smaller flow of air upon expiration
after trying to take a maximum exhalation (5). The time it takes for
expiration to occur while breathing with an obstruction is inadequate to empty
lung volume due to decreased flow, therefore when an obstruction in breathing
is placed, not the entire amount of air will be exhaled out during an
expiration that lasts roughly 5 seconds in a dynamic lung test (5). Additionally,
the dynamic lung variable FEF25-75 is expected to decrease as a result of airway
obstruction, which was seem in both subjects 1 and 2 when compared to normal
breathing (4). Lastly, results indicate that maximum voluntary
ventilation was seen to decrease during obstructed breathing testing when
looked at next to normal breathing testing. Frequency of breathing as well as
volume is expected to decrease due to the added challenge of breathing with an
obstruction, which results in a decreased flow rate (3). If flow is
decreased, volume of air that is inhaled per minute will inevitably be
decreased as well (3). This demonstrates that normal and expected
results were seen in static testing, forced vital capacity and maximum
voluntary ventilation testing.

            Expected
results were seen in subjects 3 and 4 during the breath holding procedures. Breath
holding duration increased after voluntarily hyperventilating for 1 minute, and
decreased drastically after exercising at 200 watts for 90 seconds. It is
expected for breath holding durations to increase in length almost twice after hyperventilation,
due to high oxygen and low carbon dioxide conditions of the body since the
drive for respiration is decreased (7). However, the opposite is
true for breath-holding after exercise. Ventilation needs to increase during and
after exercise to fulfill the body’s needs for oxygen, which is why subjects 3
and 4 were not able to hold for very long after exercising at a relatively high
power output (1). The signals that chemoreceptors send are what is
responsible for our ability to hold our breath for certain periods of time (1).

Chemoreceptors respond to changes in blood pH and carbon dioxide levels (1).

When exercising, the body’s need for oxygen increases, and gets fulfilled by
increasing ventilation. Chemoreceptors in the muscle and lung act upon this
need for oxygen and are activated so this demand is fulfilled (1).

During breath holding after hyperventilation, chemoreceptors are inhibited due
to the body’s sufficient oxygen levels, and are activated later to stimulate
ventilation when the subjects couldn’t hold their breath any longer (1).

Additionally, the role of chemoreceptors is also seen in obstructive lung
diseases as well. In patients with obstructive lung diseases, their partial
pressure and saturation of oxygen are typically lower and their carbon dioxide
concentrations are higher due to decreased air flow, so the body stimulates
chemoreceptors to try to increase ventilation to increase blood oxygen levels (3).

            Furthermore,
obstructive lung diseases as well as restrictive lung diseases both have a
negative impact on gas exchange. When there is an obstruction in the airway,
there is a decreased amount of air into the lung and to the alveoli,
potentially causing the alveoli to die, which decreases surface area in the
lung (3). Alveoli can also become swollen and filled with thick
mucus, which causes a greater distance between the alveoli and the blood, as
well as increases thickness of the sheet (3). Additionally, if the
airway becomes swollen in a patient with an obstructive pulmonary disease, the
pressure difference decreases as well (3). These are all negative
affects on Fick’s law of diffusion, and therefore resulting in reduced
diffusion and gas exchange. Furthermore, in restrictive lung diseases, there is
evidence that alveoli become scarred and lungs become very stiff, making it
more difficult to inhale or exhale a high volume of air at a certain time (6).

This inevitably leads to hypoxia and reduced gas exchange as well (6).

Conclusion

            Overall,
the results of this experiment could be supported by the hypotheses that were
made. The purpose of this lab was to study pulmonary function testing and to
see how resting lung values and dynamic lung values may differ under normal and
obstructed breathing circumstances. Expected results were seen in static lung
testing, forced vital capacity and maximum voluntary ventilation tests. Normal
breathing always yielded higher resting and dynamic lung values when compared
to obstructed breathing. Moreover, breath holding durations were evaluated
after 3 different exercises, and it is concluded that hyperventilation can
improve breath holding duration, whereas exercise will decrease breath holding
duration. To conclude, this lab greatly outlines the importance of the
pulmonary system to our health and how detrimental a lung disease can be, but
also how important pulmonary function testing is to detect problems of the lung
when they arise.

·      Obstructive
lung disease can alter flow into and out of the lungs, interfering with all 3 components
of Fick’s for diffusion, ultimately hindering diffusion and gas exchange in the
respiratory system.

·      Breath
holding can be held for a much longer duration after voluntary hyperventilation
due to the body’s hyperoxic conditions, whereas breath holding can only be held
for a short duration after exercise due to the body’s need to ventilate to
fulfil its needs for oxygen.