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Discussion

            Measurements
from the resting lung values decreased mostly for both subjects when an
obstructive disease was mimicked vs. normal conditions. This decrease is
expected as the flow of gas is reduced by the stopper placed in the spirometer
which decreased the diameter of the hole both subjects were breathing through.

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As a result, not only is air from the environment to the respiratory zone
affected, but the same can be said when air is travelling in the opposite
direction. For this reason, we see a decrease in the VT, VC, IC, IRV, ERV, FRC
and TLC in both subjects, except for subject two in which the recorded VT was
higher in the obstructed condition vs. normal conditions. A reason to why this occurred
is that the subject may not have been taking the same size of tidal breaths
during the normal conditions compared to the obstructed conditions. Breath’s
may have been deeper allowing for more air to enter, leading to a higher VT. With
regards to the RV of both subjects, values remained the same. This is
unexpected as VT is thought to increase due to gases in the lungs being trapped
as the airflow out the body restricted4. A reason to why no change is observed
could be that the RV in the obstructed state was calculated and not physically
measured. In order to get an accurate reading, subject would take either a gas
dilution test or a body plethysmography to measure their RV3.

The
same decrease is also seen in both subjects when evaluating their dynamic lung
volumes. Since the dynamic tests fully consisted of the subjects expiring,
measurements are expected to decline as well because of the reduction in
efficiency during expiration, which is caused by the increased resistance from
the airways due to the reduction in diameter.

With
regards to the MVV, the concept of a decrease in flow of gases during
inspiration and expiration mentioned before is used to explain the significant
decline in values in obstructed vs. normal conditions. An overall decrease in
flow in both directions meant that less volume of air was being inspired and
expired per breath, leading to the decrease in MVV.

            In
breath holding experiments, subjects three and four displayed similar patterns
after performing different tasks, with all times being expected. Chemoreceptors
are present in the carotid artery and are responsible for providing feedback to
the brain regarding levels of oxygen (O2) and CO2.

Although, the body is more sensitive to the levels of CO2 in
comparison to O21. When both subjects hyperventilated,
carbon dioxide (CO2) in their bodies decreased leading to a condition called
hypocapnia, which causes inspiratory neurons to be inhibited2. As a
result, there is a lower tendency to breathe when the body is in a hypocapnic
condition, which was seen in both subjects as they were able to hold their breaths
longer.

In
contrast, when there are high levels of CO2 in the body or when the
body is hypercapnic, the chemoreceptors send signals to the brain which cause
almost all of the respiratory neurons in the brainstem to be stimulated,
forcing individuals to ventilate3. When both subjects exercised,
their bodies had increased levels of CO2 due to production of CO2
from cellular metabolism. As mentioned, this causes the respiratory neurons to
fire which leads to an increase in the tendency to ventilate, which was seen in
both subjects as both couldn’t hold their breath for a long period of time.

If
both these subjects were to repeat the experiment while imitating as if they
had an obstructive lung disease, the time they will be able to hold their
breath after the different conditions is expected to decrease compared to
normal conditions. By looking at the results of subject one and two, it is
clear that the amount of air inspired and expired is reduced by the presence of
the flow stopper. If this is the case for subject’s three and four, then
theoretically this means that not only will both be inspiring less O2, but more
importantly expiring less CO2 meaning that both these subjects will have a
greater CO2 buildup in their body compared to normal conditions. Therefore, in
the obstructive state, levels of CO2 after rest, hyperventilation and exercise
is greater due to a decrease in efficiency in expiring air out. It is previously
mentioned that increased CO2 levels in the body provoke the nerves that
stimulate ventilation, and if this were the case then it is expected for
subjects three and four to hold their breath for a shorter period of time.

            As
previously mentioned, obstructed diseases decrease the flow of air to and from
the lungs, decreasing the total amount of inspired and expired air. The other category
of respiratory diseases, referred to as restrictive diseases, again is characterized
by a decrease in the amount of air in the lungs because it cannot expand to its
maximum potential5.

According to Fick, the efficiency in which gases diffuse through tissues are
dependent on three variables. It is proportional to both the surface area and
the pressure difference across the tissue, and inversely proportional to the thickness
of across the tissue6.

Under normal conditions, the PO2 and PCO2 in the lungs is 100 mmHg and 40 mmHg
respectively. In the body, PO2 coming from the systemic veins is 40 mmHg with
PCO2 being roughly around 46 mmHg7. With these pressures, gas exchange is
favourable due to the large pressure difference of gases between the systemic
veins and the alveoli’s. Compared
to healthy individuals, those who are diagnosed with either of these diseases
will have a decrease in the pressure difference between the circulatory and
respiratory system as not only do their body’s transfer less O2 to the lungs
but expelling CO2 from the lungs becomes more difficult. This as a result decreases the PO2 and increases PCO2 in the lungs,
leading to a smaller pressure gradient between the lungs and blood, which
ultimately leads to a decrease in efficiency of gas exchange.

·      Obstructive
lung disease is characterized by a decrease in flow of gases in and out of the
lungs, while restrictive lung diseases fully prevent lungs from expanding to
its full capability. Both cause a decrease in the partial pressure of O2 in the
lungs, which in turn reduce the efficiency of gas exchange.

·      Chemoreceptors
present in the carotid artery sense the levels of O2 and CO2 in the body. When
either of these two are disturbed from their normal levels, chemoreceptors send
signals to the brain to change ventilation in order to get levels back to their
standard levels. 

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