Keeping with a theme of being a safe, and effective global health responder.

Dr. Davis returns to explain how the human body responds to different environmental

stressors, and just how vulnerable we are to extremes of ecosystems, especially,

if one comes unprepared.

After the lecture, he'll be joining us in the studio for

a short question and answer session.

>> For aspiring global health workers

you need to be aware that traveling to these far-flung places in the world.

There tremendous amount of variability in the type of environment,

cold environments, hot environments, high altitude environments.

And that can be really harsh on your own physiology.

So, we'll be covering what it'll take to stay healthy

in all of those types of environments.

The first environment we want to talk about,

is the hot environment, and that can be temperatures, up to 120 degrees.

We obviously are trying to keep our bodies at 98.6,

and that is quite the physical challenge.

So, we gotta harken back to some high school science here, and

there are four ways that we actually, cool ourselves.

There's evaporation, there's conduction, there's convection, and

then there's radiation.

But right now, the sun is sort of beating down on me a little bit, and

so I'm getting heat from the sun, and I'm accepting that heat.

And I have to figure out a different way to actually dissipate it.

Humans actually use evaporation to a large extent,

and that's what sweating is all about.

So, we sweat under our skin, it comes out obviously, as a liquid, and

as that evaporates, that's stealing heat away from the actual skin itself, and

that's how we're cooling ourselves.

And then, there's conduction and convection.

And convection is a much bigger deal, that's why, a cool breeze feels so good.

And conduction would probably, be the least relevant of these concepts, but

that would be sort of, sitting against a cool rock, that sort of thing.

So, in the hot environment, as in most of these harsh environments, prevention, and

preparedness is absolutely critically.

So, hottest part of the day, 10 am to about 3 pm.

If you can stay out of the direct sun during those times that's,

that's absolutely critical.

If you are working during those types of day, try to be in the shade.

In the hottest environment, we're sweating a tremendous amount, and

to keep up with that fluid loss, we may have to drink up to 10

to 12 Quarts of liquid a day, you'll also need a little bit of salt, as well.

Even the type of clothing that you, that you're wearing has some importance.

If you can stick with light, even cotton

clothing that reflects some of that heat from the sun, you'll be ahead of the game.

Again, those behavioral things can really go a long way in preventing heat illness.

So, for doing hard vigorous physical activity.

We want to do that early morning or late in the afternoon, and

take that siesta in the middle of the day, in that hottest part of the day.

Again, wearing light color, colored clothing, staying hydrated, and

then really being in the shelter.

Getting some sort of, shade between 10 and 3 pm.

The next concept we want to cover is this idea of heat acclimatization, and

like any acclimatization, this takes time.

What you all need to remember is that, it will take a week or

more until your bodies are really ready to work in that higher, hot environment, and

we do that in two different ways.

One, we sweat more in a hot environment, and that takes time to establish.

And two, the salt content of our sweat also changes, and

that allows us to stay a little bit more hydrated.

So, how hot is hot?

So, we know, of course, hot temperatures mean, hot environment,

that's not the whole story.

We've got to think about the humidity as well, and 110 degrees in a dry heat

is not the same as 95 degrees with 70% humidity.

And really that Heat Index, that's what that is.

It's the combination of a humid environment with a hot environment,

that is sabotaging our ability to cool ourselves through evaporation.

And so, again it's those hot humid environments that are more dangerous

than that hot dry environment.

The other thing we need to talk about for the hot environment, is sunburn and

sunburn prevention.

So, what causes sunburns?

Sunburns are caused by ultraviolet rays that are getting through our atmosphere,

notably the ozone ra, layer.

And when we get enough exposure of those ultraviolet rays,

it can cause an actual burn.

So, we can block that with sunscreen.

The type of ultraviolet or UV ray that causes sunburn is usually UVB.

Where we are in the world is going to determine our risk for

sunburn, and the higher we are, the more exposure we have to ultraviolet rays.

For every 1000 feet that we go up in altitude,

we're exposed to 5% more ultraviolet rays.

What does SPF mean?

It's a silly acronym that means Sun Protection Factor.

So, if you had an SPF of one, that's the time that it takes for

you to get sunburned.

When we add SPF 15, that means that it takes 15 times longer for

a given sun exposure to get that sunburned.

What's interesting is after about ESP 15, we're not really getting a lot of bang for

our buck, so you don't need to go rush out there, and get SPF 100,

that's probably a waste of your money.

So, clothing does provide some protection from the sun, but

maybe not as good as an actual sunscreen.

Your average cotton white t-shirt has an SPF of about five, so the takeaway

message there is that you can still get sunburned through your clothing depending,

again on the color, and how tight the weave is.

There's two flavors of heat illness we need to talk about.

There's heat exhaustion on one end of the spectrum,

and there's heat stroke on the other end of the spectrum.

Heat exhaustion feels like a bad hangover, you've got a headache,

you feel dizzy, you feel a little, kind of sick to your stomach, but

our temperature stays the same at 37 degrees Celsius.

So, treatment for that is getting out of the heat, not doing vigorous physical

activity, getting hydrated, and then cooling ourselves as best we can.

That could be jumping into a cooler stream,

it could be soaking that cotton t-shirt, putting it back on.

It all depends on the environment that you're in.

On the other end of the spectrum, we have heat stroke, and

this disease is far more dangerous.

Couple of things you need to know about heat stroke.

Our temperature doesn't stay at 37 degrees, it creeps up to 40, 41, and

42 degrees.

That's in counter distinction to heat exhaustion,

where a temperature stays the same.

What defines heat stroke is an alteration in our mental status.

What does that mean?

Means, we might be confused, slurring our words, stumbling around,

that is what defines heat stroke.

And I think, there's sort of, a wives tale out there, where you can't be hot and

sweaty, and have heat stroke, that's unfortunately not true.

So, if you have a confused, stumbling,

mumbling person in a hot environment, you gotta think about heat stroke, and

you have to cool them as rapidly as you can, by any means that you can.

Again, dumping them in a cold stream, getting them in the shade,

getting their clothing wet, and just taking advantage of that aper,

evaporation, that's the treatment for heat stroke.

On the other end of the spectrum, we have the cold or the cool environment, and

this doesn't have to be the South Pole, it doesn't have to be Greenland.

Some of the most challenging environments are those that are really hot

during the day, and then cool off at night.

So, a good example of this would be a high desert, and

this is where it can be 35, or 40 degrees centigrade during the day, and

it can drop down close to freezing at night, very difficult to prepare for.

So, how do we prepare for the cold environment?

So, what kind of clothing is appropriate for the cold environment?

Well, in the hot environment cotton can be appropriate, but

cotton kills is the saying, in the cold environment.

You need a wicking fabric in a cold environment, and that takes moisture

away from the skin without actually, losing heat through evaporation.

So, the other types of clothing that we need to have in the cold environments

are an insulating layer, and a wind or rain layer.

So, that insulating layer, we want to keep dry at all times.

That's your down, or your synthetic puffy jacket.

Keep that in a garbage bag, or in a stuffed sack that's waterproof.

Again, that's your backup layer.

The other thing that we have to have is that wind, or rain layer to

keep us warm and dry in those wind storm, and to limit the effect of wind chill.

So, just as we saw with the Heat Index,

the absolute temperature isn't the whole part of the story.

With wind chill, we can have cold temperatures, and then, if we have high

winds as well, that's going to steal away heat from our skin, through convection.

So, what does wind chill do?

So, if it's below freezing Centigrade, and we have 15, or 20 knot winds,

that's going to drop our effective temperature, 10, or 15 more degrees.

So, the high altitude environment, this can be a very challenging environment,

often because it's combined with either a hot environment, and a cold environment.

Depends where you are in the world, so some basic science.

So, we often hear that there's less oxygen up in the high altitude environments, and

that's not really true.

So, a fraction of oxygen stays the same, but

what happens is, we have less barometric pressure.

And it's that pressure,

that pushes that oxygen across our lungs into our blood, and when we

don't have that pressure less oxygen effectively gets into our blood stream.

So, for example, we're in the Denver area at 5, or 6,000 feet.

There's 8 to 10% less pressure, and

that results in 8 to 10% less oxygen in our bloodstream.

If we go up to 18,000 feet,

we have half the available pressure, therefore, half the available oxygen.

When we're on the top of Mount Everest,

it's a third of the available pressure, and a third the available oxygen.

Now, if you pluck me, and put me on the top of Everest from where I am right now,

I'm going to die within minutes, I haven't had the ability to acclimate.

So, how does a acclimatization work?

Firstly, it takes time, nobody goes to Everest for

the weekend, and expects to make it to the summit.

That can takes weeks, and weeks, and weeks.

There's really two main parts to a acclimatization, or

adaption to high altitude.

So, the first step to acclimating to the high altitude environments is

breathing more.

So, there's less available oxygen, so we have to breathe faster.

There are limits to this, we are breathing off carbon dioxide, and that's an acid.

We have to keep our pH neutral, so it takes time for

our kidneys to adapt to that, and we spill base in the form of bicarb into our urine,

that takes a period of several days.

The second part of acclimatization takes place over several weeks, and

we make more red blood cells, so we can carry more oxygen in our blood.

If we go up too high, or too fast, we can get altitude illness.

The most common form of this, is acute mountain sickness.

Most people liken this to a very bad hangover, it's the headache,

it's the nausea, vomiting, dizziness.

Feeling like you might have the flu, or, again, the worst hangover of your life.

So, acute mountain sickness is what we call self-limited.

That means, it gets better on its own as long as we stay put and

don't go any higher.

So, what is a safe ascent rate?

Well, guidelines say, that we really shouldn't be going, or

sleeping higher than 500 meters each night, and

after about three nights of that we should take an extra rest day.

So, the take away message here is that our bodies can do amazing things, and

surviving even thrive, and all these harsh in a stir environments around the world.

So, again, these take away message is if you're in a high altitude environment,

don't go too high,

too fast, no more than 500 meters each night in that hot environment.

Stay away from those hot,

hot temperatures in the middle of the day from 10 am to 3 pm.

In the cold environments, have that insulating layer, have that rain layer,

fight that wind chill, and as your mom would always say, wear sunscreen.

>> Chris Davis, thanks for joining us in the studio.

That was great.

I think, on of the key concepts of this course to be

proficient global health responders that think about situational awareness.

And I think you really hit upon that

knowing our body's vulnerabilities particularly, when we travel.

The thing that comes to mind for me is, when Westerners go to the tropics, and

I see this all the time in have some personal experience with it,

where it's March in Boston.

You get off the plane, you take off your overcoat, and you get to work, and

you don't realize that the humidity is skyrocketing, the sun's much stronger and

it's 90 degrees outside.

And at the end of the day, you're sick, you're dehydrated, and you're sunburned.

It's a very common thing, would, would you agree that this is something that

we need to, you know, a savvy traveler needs to be very aware of?

>> A, absolutely, that, the fact of the matter is,

is that we're not born savvy travelers, and then-.

>> Some point-.

>> It takes time, and experiencing, with that, with that old axiom of,

you know, good judgment comes from experience, which comes from bad judgment.

And certainly, we internalize those lessons,

where things might have gotten uncomfortable in the past.

And that's, you know, that's a good definition there, or

a good example there would be a bad sunburn.

You're like, well, gosh, I really screwed that one up.

>> Yeah. >> Let's at least for

the rest of the season, that lesson is fairly fresh.

So, absolutely.

So, we can think about this in, in terms of almost the, the Swiss cheese risk

model, where again, getting into these uncomfortable scenarios,

usually it's not just one mistake, it's many, and

they're all lining up in sort of this horrible highway of bad luck.

But what we want to do is, is, again, try, and

mitigate, the risk of those things happening.

And, and that, you can get some of that by book learning, but

a lot of it comes from just your experience.

>> I remember the story where, a traveler got caught in a snow storm, who was, I

think, they were from Asia, but they were experiencing extreme weather in the US.

And the highway got snowed in, and rather than staying with the car,

I've been waiting for help to come, which is by far the safest thing to do.

They the father went out into blazing snow storm with just an overcoat,

and no gloves or anything, and ended up perishing,

getting lost, and perishing from from exposure.

>> Yeah, I, I think that can be particularly

relevant when you're visiting such a big country like the US, or

a big country like India, and you're there for weeks, or even months.

And maybe you're there in a climate that you're very familiar with, but

you have the weekend, or a week off, and you're going someplace that, perhaps, you,

you're cutting on weight, and you don't have those supplies.

But you certainly want to understand the season, understand

the weather, and when we have this sort of, this climate instability that we've

seen over the last several decades that can certainly get us into trouble.

And, and another, again speaking on snow storms, I mean this,

this horrible tragedy in Nepal in this past climbing season.

When people who were familiar with trekking, and were, theoretically,

knew exactly, what to expect, and we're traveling tea house to tea house but,

you know, a huge blizzard comes in, and a lot of people, a lot of people died.

>> Yet, it brings up a good point that we to think about group risk assessment,

and how in groups, which is often how people are going to be traveling,

risk assessment gets warped by this sense of mission.

And we see this a lot in the altitude world, where we know that

firm rules to say, if someone's sick, you stop ascending because

you don't want to succumb to, to lethal entities [INAUDIBLE] the altitude illness.

Can you just talk a little bit about that, sort of, your experience with how group

mentalities can warp sort of our ability to, to stay healthy?

>> Oh, absolutely.

The, the group I guess, group decision making has a number of pitfalls,

and I get in, I think we're still understanding some of those heuristics,

and it's a bit of a, a black box.

But certainly,

when there's already a defined hierarchy because you're involved in the mission, or

the mission and, and the purpose of your, your travel that's easier to fit into.

But again, that, that's an area of, hey, that week that you're traveling

afterwards, and it's your buddies, and no one's really in charge.

And so, who's packing the first aid kit, and

who's checking the weather, and who's making sure tha,

that you're prepared for, for what you're, even if you're, a vacation.

But you're prepared for the environment you're going to often that can get you,

just get kit lefted on the wayside.

>> Yeah.

>> I guess, [INAUDIBLE] again, none of us are born savvy travelers,

and and you know, a lot of us are fond of these sort of,

scary memories, and, and I'm not trying to romanticize them at all.

Only just to say that when we're young perhaps,

our decision making isn't the best.

I remember, traveling with was my girlfriend,

my now wife on the cusp end of the monsoon season in Thailand,

and having to get back to the airport, and monsoon season came in early.

And we were just in this little fishing boat trying to get back to the mon,

to the main land in truly in the middle of the monsoon, and

we were scared out of our wits, and

talking about, you know, if this boat goes down, how are we going to swim to shore?

I mean, ideally, we never would've been in that situation at all.

We would've checked the weather, left a day early.

That's not the fun, or popular thing to do but certainly, it could keep you safe.

>> Yeah, I wonder if, the best advice we can give for

to be a savvy traveler is to ask the locals.

>> I think, that's solid advice.

>> Chris Davis, thanks for joining us.

>> My pleasure.

28 - Chris Davis - Physiologic Vulnerability

Foundations for Global Health Responders

Meet the Instructors