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The
common cold. The red nose is from irritation from
tissue
and inflammation. The medicines are to treat the
symptoms.
Colds are caused by viruses, and we don’t
really
have treatments for viruses. What I don’t
understand
is the thermometer; adults with colds very
rarely
have fever. Kids usually run a fever, but not adults.
So
either this is the oldest looking child or he is worried
about
something other than a cold.
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I have noticed two things that seem to help the stuffiness I
feel with a cold. One is exercise – it always seems to open up my nasal
passages and make it easier to breathe. The rush of endorphins doesn’t hurt
either – I may not be getting better, but I don’t mind the cold as much with a good dose of endogenous opiates running through my veins.
For me, a second short-term nose opener is going outside into
the cold weather to shovel snow or chop wood. Why would being cold help a
stuffed nose? Ponder that question for a second while I vent on a common
misconception. Why do we say we catch a cold? It’s a viral infection, does
temperature have anything to do with it at all?
Sure, more people have colds in the winter – but you know
from this blog that correlation does not
imply causation. Having a cold in winter doesn’t mean that the winter
weather had anything to do with catching cold.
Your mother always told you to wear your coat outside or
you’d catch your death of cold. Your basketball coach did a hat check after
practice to make sure you didn’t leave for home with wet hair on an uncovered
head. Were there reasons for this?
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Underneath
all that winter gear is Randy Parker, Ralphie’s
little
brother from A Christmas Story. His mother, in her
time-honored
wisdom, didn’t want him to a catch cold by
being
cold. The problem was that wrapping him up just
kept
the cold from stimulating his metabolism and his
immune
system over time. Plus, he found it hard to go
through
doorways; he couldn’t put his arms down!
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When are people most often closer to other people? The
winter – people spend more time inside, heating systems recycle the air; it’s
the season for sharing. The cold weather encourages people to stay inside,
where they are more likely to receive a viral gift from someone else.
So the cold does play a role, including a slight decrease in immune function due
to changes in blood flow, and the fact that cold air holds less moisture, so
your mucosal membranes dry out and are a bit more susceptible to being invaded
by a virus. But cold is by no means the main culprit, so I propose a letter
writing campaign to rename the cold – maybe you could catch a crowd, or a doorknob, or maybe we could just call it Dennis.
O.K., now that that
issue is resolved, back to the question of how cool air and exercise can help
you breathe better when you have a “cold.” The key is a concept called nasal resistance.
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Nasal
resistance is the main way to slow air entering the
lungs.
Being slower and higher pressure keeps the lungs
from
overinflating or collapsing. The nasal vestibule (1)
squeezes
together as you inhale, the smaller space prevents
too
much air from entering. Inside is the vestibule is the
valve
(3), the narrowest region. The turbinates (5-8, superior,
middle,
and inferior) can expand slightly to decrease the
nasal
volume. There are small muscles (alae nasi) in the
vestibule
which can contract to decrease resistance as well.
Paralysis
of these muscles leads to collapse of the naostrils.
Basically,
the more stuff in the way of the air, the higher
the
resistance.
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Having a cold increases mucous production (trying to catch
viral particles before they reach your cells). A cold virus infection also
puffs up the nasal tissues due to immune inflammation reactions. These
responses increase nasal resistance and decrease airflow. It is much harder to
get the same volume of air into your lungs through your nose. This observation won’t
win me the Nobel Prize; we’ve all experienced it.
Exercise reduces nasal resistance through stimulation of the
sympathetic nervous system. Hard physical work is a lot like the fight or
flight response. Your body vasoconstricts vessels in the periphery so that more
blood can go to the big muscles. You also need more oxygen, so the alae nasi muscles in your nose relax
and the airways get bigger. Both of these actions decrease nasal resistance and
increase airflow to the lungs. During a cold this is helpful since your
ventilatory spaces are clogged with snot.
On the other hand, my sojourns into the brutal winter are
against the literature. Cold air is supposed to increase nasal resistance. Cold
air is bad for the lungs – it saps heat from the rest of the body. Therefore,
the nose anatomy functions to warm the air. When cold air enters and triggers
the TRPM8 cool sensors (there’s our first reference to the topic we have been
discussing), the alae nasi muscles contract and the blood vessels in the nasal
mucosa dilate. This swells the internal nasal tissues, increasing the surface
area and thereby transferring more heat to the air before it reaches the lungs.
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Rebreathing
is a good way to reduce nasal resistance. Just
hold
your breath for a while or breathe into a paper bag.
Increased
CO2 in blood brings vasoconstriction, so tissues will
shrink
and breathing will be easier. The same goes for changing
from
a supine (lying) position to standing or sitting. The change
in
filling of sinus vessels and nasal vessels will shrink tissues as
well
and you will breathe easier for while.
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I go out in the cold to chop wood or shovel snow - I have a
tendency to attack my work, so these activities become exercise. Upon
reflection, I now realize that it was once again exercise that was reducing my
nasal resistance and allowing me to breathe more normally, not the act of going
out into the cold. I’m caught in my own correlation-causation trap; there were
other factors that I had failed to take into account. I had too many variables
in my experiment! I never considered going out into the snow and not working hard.
Now let’s consider another cold and cough treatment, Vicks
VapoRub. The active ingredients in this concoction are menthol and camphor. We have talked recently about how menthol is a TRPM8 agonist (so mints make
everything seem colder), and that camphor is an agonist for both TRPM8 and
TRPV1, so it can induce feelings of warmth or cool, depending on the
concentration and placement.
You rub the Vicks on your chest when you have a cold. The camphor
stimulates TRPV1 and makes your trunk feel warm. The menthol vapors rise and
your breathe some in, they make your nose less stuffy. Or so it seems.
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Here
is a late 1950’s ad for Vick’s VapoRub. Which child would
you
rather have? A simple greasy rub on the chest and all the
problems
are solved. If you can read the headline, it seems that
atom tracing shows that the vapors get
into the lungs. One – is
there
anything more 1950’s than talking about atoms? Two – we
now
know that Vicks works in the nose, not the lungs.
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When you breathe in quickly and deeply, the rushing air is
colder than the air that was just hanging out in your nose. This triggers the
TRPM8 sensor, and your brain interprets it as a lot of air rushing up your nose
and to your lungs – decoding the signal means that you are breathing well and
deeply.
Now switch to the situation where you have a cold and can’t
bring in air through your nose. The menthol/camphor of the Vicks VapoRub penetrates
your nose and stimulates the TRPM8 channels there. Your brain interprets this
data just as if cool air was rushing over the TRPM8 channels. It concludes that
you are breathing well. You think you
are breathing easier, but no actual change has occurred in nasal resistance! A 2008 study showed this to be the case. Bad brain! We can’t fool Mother Nature,
but apparently she fools us all the time.
One thing that is true about the VapoRub is that it can calm
a cough. Menthol, in particular, is excellent in its anti-tussive capability. Tussive
is from the Latin tussis, meaning a
cough, although I’ve never heard anyone say, “I have a very bad tussis today.”
Likewise, does this mean that when you are coughing, you are really tussing? Do
you need to “tuss up” that ten dollars you owe me? (Yes, I am aware of the
snickering from those of you of the Cornish persuasion - look it up.)
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Developed
in 1865, Lofthouse was looking to help fisherman
with
their seasonal colds. The lozenge contains menthol and
eucalyptus,
just like Halls, but much earlier. The fisherman
liked
them so much they called them their friend. Hence the
name;
they’re still sold today. Menthol drops can calm a cough,
but
menthol is also slightly analgesic, so some throat pain can
be
reduced by them as well.
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A 2013 study went further. It assessed the anti-tussive
action of menthol in guinea pigs and showed that the effect on TRPM8 was only
effective when it was in vapor form and when it was applied to the nasal
passages. Menthol on trachea or throat TRPM8 had no effect on cough. So – when
you use Halls cough drops, it's the vapors from the dissolving drops that go
up your nose and help stop the cough – don’t chew on them and swallow! You put
them in your mouth, but they don’t act there. But don’t stuff them up your nose
either – did I need to say that?
We have considered TRPM8 in thermoregulation, nasal
resistance, and cough. Next week, let’s show some funky functions for cold
receptors – like how they can stop cancer or how they screw up opiate addiction
withdrawal.
For
more information or classroom activities, see:
Cold
viruses –
nasal
resistance –
menthol
and cough –
