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so now let's talk about the physiology
of pregnancy so here's a case Ginny is a
25 year old
gravity' one pair of zero female at 34
weeks of gestation she reports increased
difficulty in taking deep breaths
she did not shortness of breath on
exertion and no chest pain her pregnancy
has been uncomplicated and she has no
medical problems what is the most likely
cause of her difficulty in breathing and
we'll think about this as we go
throughout the lecture so we think about
the changes of physiology that happen in
pregnancy there are eight systems that
we want to focus on first cardiovascular
next hematologic next respiratory then
digit the gastrointestinal system then
the renal system metabolic endocrine and
anatomic changes that we see throughout
the pregnancy so let's start with the
cardiovascular system first there are
some anatomical changes that we need to
talk about the heart is displaced left
and upward and it's rotated on its own
axis in pregnancy this is important
because where you listen for heart
sounds is a little different than in the
non pregnant patient so now let's think
about the physiologic changes within the
cardiovascular system so we notice that
the systemic vascular resistance changes
so how do you think it changes does it
increase does it decrease well in fact
it decreases and this is the reason in
the first and the second trimester we
notice that the blood pressure also
decreases well when we think about the
mean arterial pressure what do you think
happens there does it increase does it
decrease it in fact decreases as well
our heart rate also changes in pregnancy
what do you think does it increase or
does it decrease the heart rate also
increases in pregnancy and lastly
cardiac output do you think it increases
or decreases you probably guessed right
it increases in fact it increases to
almost 15 to 40 percent in the first
trimester and even more during the
labour process so now let's move to the
human logic system that also changes in
pregnancy firm
we notice that the blood volume
increases to forty to forty-five percent
above the non pregnant patient this is
mostly because of increase in the rhythm
sites and in plasma and we notice that
pregnant women have a physiologic anemia
because of this increase so what else
changes well our iron requirements also
increase in pregnancy some of that can
be met in the diet but in some pregnant
women they require iron supplementation
to meet that increased demand now our
immune system also changes in pregnancy
we're not exactly sure why that happens
but we do know that the immune system is
blunted in pregnancy making pregnancy an
immunodeficient state now lastly but
most importantly in the hematologic
system pregnant women are
hypercoagulable that means their blood
is sickened and because of that they're
at increased risk for deep vein
thrombosis as well as pulmonary embolism
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 surgery
we know increases our risk of DVT and
pregnancy because it is a
hypercoagulable state also increases
that risk so we need to be sure to watch
out for that so now moving on to the
respiratory system there are some
anatomic as well as physiologic changes
in that system as well first is the
change in the diaphragm we notice that
that rises by four centimeters can you
think of why that may be well let me
tell you the uterus is increasing during
that time as the uterus gets larger the
diaphragm gets pushed up as well so how
does that affect our physiologic changes
within the respiratory system
well the functional residual capacity
decreases and again that's just because
the diaphragm is pushing up so that
residual capacity decreases the total
lung volume however does not change our
expert ory residual volume and our
residual volume also decrease and then
when we think about our tidal volume and
our minute ventilate ventilation they
both increase so this is a nice diagram
that puts all those things that I just
told you into one big location so I
would make sure that you go through this
in a lot of detail to make sure you
understand those
in the lung volume as we previously
discussed so let's move on to a question
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 be because of
compression from the uterus the
inspiratory capacity decreases see
because of compression from the uterus
the residual volume decreases our D none
of the above what do you think well the
answer is C because of the compression
from the uterus and remember that also
causes the diaphragm to decrease the 4
centimeters the residual volume also
decreases total lung capacity
inspiratory capacity those volumes do
not change because of pregnancy
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