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So now
let's talk about the physiology of pregnancy.
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So here's a case.
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Jennie is a 25 year old gravida 1 para 0
female at 34 weeks of gestation.
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She reports increased difficulty
in taking deep breath.
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She did not shortness of breath on exertion
and no chest pain.
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Her pregnancy has been uncomplicated
and she has no medical problems.
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What is the most likely cause of her difficulty
in breathing?
And we'll think about this
as we go throughout the lecture.
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So when we think about the changes, physiology
that happen in pregnancy,
there are eight systems that we want to focus on.
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First cardiovascular.
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Next hematologic.
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Next respiratory.
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Then the.
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The gastrointestinal system.
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Then the renal system.
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Metabolic, endocrine and anatomic changes
that we see throughout the pregnancy.
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So let's start with the cardiovascular system.
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First, there are some anatomical changes
that we need to talk about.
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The heart is displays left and upward
and is rotated on its long axis in pregnancy.
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This is important because where you listen for
heart sounds is a little different than
in the non-pregnant patient.
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So now
let's think about the physiologic changes
within the cardiovascular system.
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So we know that the systemic vascular
resistance changes.
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So how do you think it changes?
Does it increase?
Does it decrease?
Well, in fact, it decreases.
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And this is the reason in the first
and the second trimester,
we notice that the blood pressure also decreases.
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Well, when we think about the main arterial
pressure, what do you think happens there?
Does it increase?
Does it decrease?
It in fact, decreases as well.
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Our heart rate also changes in pregnancy.
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What do you think?
Does it increase or does it decrease?
The heart rate also increases in pregnancy.
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And lastly, cardiac output.
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Do you think it increases or decreases?
You probably guessed right. It increases.
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In fact, it increases to almost 15 to 40%
in the first trimester
and even more during the labor process.
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So now let's moved
to the hematologic system
that also changes in pregnancy.
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First,
we noticed that the blood volume increases to 40
to 45% above the non-pregnant patient.
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This is mostly because of increase in erythrocytes
and in plasma.
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And we noticed that pregnant women have
a physiologic anemia because of this increase.
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So what else changes?
Well,
our iron requirements also increase in pregnancy.
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Some of that can be met in the diet,
but in some pregnant women,
they require iron supplementation
to meet that increase demand.
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Now our immune system also changes in pregnancy.
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While pregnancy does not cause a true, generalized immunodeficient state,
alterations in the immune system do occur.
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Cytotoxic immunity appears to decrease, while the regulatory adaptive immune response is upregulated.
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It is important to note that pregnancy is associated with increased susceptibility
or severity of certain infections, such as urinary tract infections,
influenza, and toxoplasmosis.
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Now lastly,
but most importantly in the hematologic system.
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Pregnant women are hypercoagulable.
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That means their blood is thickened.
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And because of that,
there are increased risk for deep vein thrombosis
as well as pulmonary embolism.
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This is important to think about as
this can be a huge cause of maternal mortality,
especially in light of patients
that undergo C-section.
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Surgery,
we know, increases our risk of DVT and pregnancy
because it is a hyper collateral state,
also increases that risk.
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So we need to be sure to watch out for that.
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So now moving on to the respiratory system,
there are some anatomic as well as physiologic
changes in that system as well.
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First is the change in the diaphragm.
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We notice that that rises by four centimeters.
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Can you think of why that may be?
Well, let me tell you,
the uterus is increasing during that time.
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As the uterus gets larger,
the diaphragm gets pushed up as well.
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So how does that affect our physiologic changes
within the respiratory system?
Well, the functional residual capacity decreases.
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And again,
that's just because the diaphragm is pushing up.
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So that residual capacity decreases.
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The total lung volume, however, does not change
our expiratory residual volume
and our residual volume also decrease.
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And then when we think about our tidal volume
and our ventilate
ventilation, they both increase.
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So this is a nice diagram
that puts all those things
that I just told you into one big location.
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So I would make sure that you go through this
in a lot of detail to make sure you understand
those changes in the long volume,
as we previously discussed.
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So let's move on to a question.
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During pregnancy, which of the following
physiologic changes happen within the pulmonary
system?
A Because of compression from the uterus,
the total lung capacity decreases.
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B Because of compression from the uterus,
there is rotary capacity decreases.
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C Because of compression from the uterus,
the residual volume decreases.
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R. D None of the above. What do you think?
Well,
the answer is C because of the compression
from the uterus.
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And remember, that also causes the diaphragm
to decrease by four centimeters.
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The residual volume also decreases.