Obstructive Sleep Apnea Explained Clearly – Pathophysiology, Diagnosis, Treatment


well welcome to another MedCram lecture
we could talk about obstructive sleep apnea and specifically we’re going to
get into the pathophysiology the risk factors the diagnosis and the treatment
for obstructive sleep apnea ok let’s talk a little bit about the
pathophysiology thought the physiology is the basically how do things go wrong
so what is obstructive sleep apnea it’s basically literally when you stop
breathing because of an obstruction and if you were to look at somebody’s cross
section of their face and I’ll just kind of draw I’m not a very good artist but
you can kind of see what it is that I am talking about here and this is the nose
here this is the person lying on their back and this is the airway going down
kind of a simple drawing yes but gets the point across and here’s the tongue
basically in this area so you’ve got two areas where air can travel they can go
into the nose and it can go into the mouth the problem is is back here in
this area here this is where the back of the tongue is and this is where fat gets
stored and it’s in this area specifically that you can have tissues
so big because of fat storage that you can actually get an obstruction in that
area so typically what will happen is is that when you’re awake you can breathe
through this area but when you go to sleep your muscles go to sleep and when
your muscles go to sleep they become flexible this is not like a PVC pipe
it’s not rigid and especially with gravity lying on your back your tongue
muscle can actually fall back and this area becomes flabby and finally it can
become obstructed so your lungs which are of course connected down here and of course you’ve got the diaphragm
which is contracting in this direction causing the lungs to expand okay that’s
going to cause air to try it again and so you’ve got a negative pressure that’s
going to try to suck air in but because this area here is blocked you’re not
going to have any airflow there’s a blockage of airflow and that’s basically
the pathophysiology of obstructive sleep apnea you’re basically sleeping and when
you’re sleeping the lungs are breathing on their own because they’re getting
input from the medulla oblongata of the brain but because of the tissues here in
the back of the throat no air can get in because of the obstruction now as this
happens since no air is getting in of course your pulse ox your o2 saturation
starts to drop and the resistance starts to increase what that does is it sends a
signal up to the brain that says there’s a problem and then what does that do it
causes the brain to arouse out of its sleep sometimes completely waking up and
what that does is it sends a signal down to these areas to tighten up and then
air starts to go in again when the air starts to go in that sympathetic
response from the lungs is stopped the brain goes back to sleep and this area
once again becomes flabby and it closes off and so what you see in terms of
oxygen saturation is the cyclical type of a vent where the oxygen drops because
there’s an obstruction and then the brain becomes aroused out of its mental
state and as it does as the brain becomes a rounds out of its sleepy state
the airway becomes open again and air starts to go back in again as it comes
back up the brain goes back to sleep again as the brain goes back to sleep
again the muscles become flabby and they close off and the oxygen starts to drop
and so you’ll see this type of a wavy oxygen pattern
unless the patient gets into a position where there’s not any sleep apnea or the
patient goes into and two different types of sleep now the problem here is
that and we’ll talk about this over and over again is that there are things that
can make this area worse and these are risk factors for sleep apnea we’ll talk
about that but though two that I’ll bring up here that’s related to sleep
and we’ll talk about this later is anything that makes that obstruction
worse is going to make your sleep apnea worse and there’s two things that I want
you to be aware of that can make that area worse the first one is being
supplied now this doesn’t happen in all patients but in some patients being
supine can make it worse and this is reasonable if you think about someone’s
tongue so one’s tongue can fall back and make this area closed off so being
supine is one the second one is being in REM sleep now REM stands for rapid eye
movement but there’s something very important about REM sleep and REM sleep
you dream and as a result of that the body has a defense mechanism where you
become paralyzed which is very important because if you weren’t paralyzed you
would act out your dreams so most of the muscles in your body are paralyzed and
that includes these muscles that are trying to keep your airway open so REM
sleep can really make obstructive sleep apnea much worse so so being so pine and
being in REM sleep can make this worse so this is the pathophysiology of
obstructive sleep apnea okay let’s talk about the risk factors so what are
things that make this condition more likely well one of the big ones that
we’ll talk about is mail this doesn’t mean that women can’t have it but let me
put it to you this way in terms of the prevalence in the population for men in
terms of the prevalence now of actually stopping breathing
not necessarily having the syndrome of sleep apnea but just stopping breathing
at night more than five times per hour it’s 24% of men do that when we look at
women it’s 9% now if we actually look and see how many have the syndrome this
is where they stop breathing more than five times per hour and in addition to
that they have excessive daytime sleepiness because they’re not getting
good sleep at night because they keep getting aroused then it drops down to
about 4% for men and 2% for women so that’s the syndrome there that we’re
talking about so how many people in the population have obstructive sleep apnea
and have the syndrome associated with it it’s about on average about 3% and
that’s in the general population that’s not in your clinic population or in your
hospital population or in your sick population it’s much higher for that and
we’ll talk about that the other thing about male I should tell you is that men
tend to store fat more in the neck the other thing I should tell you is that
women catch up to men after menopause so after the age of 40 50 55 for women
and women catch up with men in terms of their of their risks
what about obesity obviously this is a big thing some people think that only
obese people get obstructive sleep apnea that’s that’s not the case but it is a
big risk factor now if you’ve got obesity it increases your risk by about
10 to 14 times you’ll see in patients with obesity that it’s usually recent
weight gain and just to give you an idea about how little this can can be if if
you have just a 10% increase in weight that can be about a six times increase
over 6 fold increase over four years so the things that we’re looking for there
is the BMI the neck size and something called the waist to hip ratio interestingly race also plays a role in
we have white non-white and the prevalence is about 4.9 percent in white
and in non-white it’s 16.3% now in Asians it also is it increased risk so
if you have these patients in your population think about this as well the
other risk factors that I would remember is nasal obstruction so think of things like allergic
rhinitis this may be this the case where medication for the allergic rhinitis may
actually improve sleep apnea and then finally the last respecter which we’ll
talk about is genetic factors so if you have a first-degree relative that
increases the prevalence from 22 percent to about 86 percent that’s a huge
increase so first-degree relatives that would be
like mother fathers brothers sisters that would increase the risk of
obstructive sleep apnea there is actually one other risk factor that I
think is important to go over and that is age and it basically if you were to
look at a graph it kind of goes up with age until it reaches about 50 or 60 and
then it kind of just Peters off and stops so the maximum prevalence is in
the 50 to 59 age group and it just stops kind of about there but in the part
before it there is a definite increase in incidence some things that also
increase it acromegaly testosterone makes it worse hypothyroidism has no
connection and then we talked about menopause it’s kind of like the
equalizer for women good so let’s talk about the diagnosis how do we go about
diagnosing it we will talk about that in the next lecture as well as the
treatment for obstructive sleep apnea thanks for joining us you