Thermoregulation & Hydration

Kangaroo Mouse intro

-lives in the desert

-has the same physiology as us, but does not drink water

-it only gets it’s water from metabolism

Triathlete collapsing video: what’s the issue?

-Dehydration

• So hot turned off ability to release heat

• Competition for blood between skin (to dissipate heat) and muscle (for performance); low blood=bigger competition

  • he skipped some aid stations

-Heat stroke

• push to point allow muscles to win

• cook brain so lose consciousness

-Depleted glycogen?

• but didn’t lose mental acuity w/ this

*produced a lot of heat (fastest metabolism of racers), did not rehydrate, and had low glycogen

*Interview: did not do heat training, thus was not heat adapted; genetically prone to heat injury? (ex: lower number of sweat glands)

How would you know someone is dehydrated? (what would you measure or look for?)

-Thirst

• 1st thing you should look for, but bell-shaped curve among people

-Body weight loss

• temp dif=fluid loss

-Low volume of dark (concentrated) urine

-Elevated resting HR

• lower blood volume=higher HR to maintain BP

• BP= Q x TPR; Q=HR x SV → higher HR to compensate for lower SV

-Postural hypotension

• stand up and get a head rush

• more likely if low BP to begin with

-Elevated blood osmolality

• lot of solutes in blood/high osmolality=need fluids

consequences of dehydration

-Low BP could cause syncope (blackout)

• temporary, but not a big deal

• worried if person hits their head, if old could break a hip

-Kidney stones

• concentrated urine solids precipitate out

-Impaired athletic performance due to inadequate blood flow and thermoregulation

• tradeoffs

daily water balance

*match up dehydrated vs hydrated state

Sources In

-Beverages: most

-Food

-Metabolism: water you make with O2 at end of ETC and H’s from food; soda cans worth a day

Sources Out

-Urine: most

-skin/sweat: variable; includes everyday “insensible perspiration”, but higher if exercise

-Lungs: “I can see my breath”; zero if completely humid air

-Feces: lower if constipiated, higher if diarrhea

3 general places for fluid in the body

-intracellular water (ex: inside cells)

-intercellular water (ex: interstitial space)

-intravascular water (ex: blood stream)

*exceptions: CSF, eyes

*all goes in blood to start, then distributed if hydrated; bc of kidneys want water throughout the day (otherwise need IV so into blood); kidney/urine biggest regulator of output

Body fluid compartments + amounts

-Water is added and removed from this system

-Water flows between compartments to dilute “stuff” (e.g. electrolytes like Na⁺)

Compartments

-2/3 inside cells (intracellular fluids)

-1/3 outside cells

• Interstitial fluid: most of outside portion

• Intravascular fluid

Total body mass/fluid content females vs males

-Males more fluids than females

-Body composition impacts total fluid content; fat has less water, lean tissue is more watery

-water is added to (via the GI or IV) or removed from (via kidneys) the blood

*also shows 2/3 intracellular, 1/3 extracellular (w/ 80% interstitial fluid and only 20% plasma)

hyperhydration vs euhydration vs hypohydration

-Hyperhydration=overhydration

-Euhydration=normohydration

-Hypohydration=dehydration

osmolarity (or osmolality) in the body and sweat

-concentration of “stuff” in solution

-body= ~300 mOsm/kg

-sweat= ~100 mOsm/kg (*thus less particles in sweat than inside us)

*per kg of fluid

control of hydration status via hypothalamic osmoreceptors

-When osmolality goes up (too concentrated/less fluid and more particles), hypothalamus directs the pituitary to secrete antidiuretic hormone (ADH), which preserves water in the kidneys making urine more concentrated (*so preserve fluid)

-They also stimulate thirst and thus drinking behavior. (*bell-shape curve)

*2 levers; input=thirst; output=urine

hemotherm

-warm blooded

-stay warm in a narrow range

range of normal TC (core temp)

97-100F (~37C)

-=core temperature

Core vs shell (skin) temperature + what you “feel”

-Core: measure by swallowing temp probe

-Shell/skin: widely varies; lower than core

*how feel=relative to where your brain wants to keep you at

Heat Balance equation

Heat Gain

-Metabolic heat: most energy burn (NOT external work; always going; up w/ exercise)

-Environmental heat: conduction (ex: touch hot stove), convection (ex: hot shower, hot drink), radiation; not much

Heat Loss

-Radiation: most important; things not in contact w/ each other; if warmer than room temp radiate heat (otherwise almost everything in the room is the same temp, and net radiate heat away)

-Conduction: solid warms up solid; ex: butt in chair

-Convection: liquid and solid in contact and heat transferred; ex: cold shower, windy outside

-Evaporation: last resort; fluid on skin can evaporate

Radiation

-things not in contact with each other

-ex: radiator radiates heat in room; inferred/heat sensing cameras

Conduction (+where are your temp sensors?)

-solid warms up solid

-not a powerful way of heat transfer

-towel and tile same temp (even though don’t feel like it), but the solid tile is a better conductor so grabs heat from skin faster than the rug

-no temp sensors outside body, only in skin (so don’t feel cold, only feel heat leaving skin)

*Styrofoam=bad conductor, glass=good conductor

*when baking cookies: don’t need glove entering bc pan at room temp, but need glove exiting bc blocks conduction from hot pan

Convection

-liquid and solid in contact and heat transferred

-hot air raises

maximal sweat rates + how would you ideally measure?

-maximal sweat rates=2-4L/hr

• how measure: hot and humid envionrment, no airflow, exercise, look at weight loss; want to maximize heat gain

  • everybody has a dif range

-1L=1kg; 1L=580kcal/hr

*could sweat 9lb in an hour during exercise

-Salt=3g/L sweat

• 2.3g/day recommendation, thus easy to sweat all out what consume in a day

-humidity hinders evaporation

Thermoneutral zone

-temperature regulation happens ONLY with vasomotor control (no sweating or shivering)

• just use blood vessels; blood away or towards skin

• =temp room your’e in (not your body)

*outside zone add sweating or shivering

Temperature negative feedback control

*hypothalamus

Blood warmer

-Vasodialate (ideal)

-Sweat (want only if exercise)

Blood cooler

-Vasoconstrict (ideal)

-Shiver

Energy accounting graph (for normal and humid envionrment)

In a normal envionrment during progressive exericse…

-Energy output: not all to exercise….

*energy put in; resting=60kcal/hr; we are 20% efficient

-Heat production: most energy;80% lost to heat

*how much heat stays in your body; example of a higher TC/normal response

-Total heat loss: loss a lot but don’t loss all

*next 3=dif heat loss ways

-Evaporative heat loss: most effective; sweating

-Radiative and Evaporative heat lost: don’t change much

If Humid

-red and orange same

-green and teal down

*Tc goes up; dif between what losing and gaining gets wider; why difficult to sustain exercise

relative humidity feels like bar graph

-if humid, more difficult to get rid of heat, so feel hotter

*can’t rely on evaporation/sweating as much

Exercise RT vs Hot environment: Rectal temp

-TC up both, but higher in hot

*no radiation heat lost

Exercise RT vs Hot environment: SV & HR

SV

-RT maintained

-Hot: SV lower (bc more blood in skin/less in blood and back to heart bc dehydrated)

HR

-both up, but higher in hot (so get same Q to a limit…)

Exercise RT vs Hot environment: Q

-Q roughly same for some time…

-but HR has a limit: can’t keep compensating for SV at high intensities and hot envionrment

Consequence of dehydration

-higher competition for blood between the active muscles (VO2, for work/perform) and the skin (to dissipate heat/provide fluid to sweat glands so can keep sweating)

*if muscles win=heat injury

-performance impairment starts at ~2% body weight loss

-consequences are a continuum

Heat injuries

-Heat cramps

-Heat exhaustion: more common and less challenging; put in shade, give cool towel, water

-Heat Stroke: neurological deficits bc cook thermoregulatory center in brain (hypothalamus); sweat rate and blood flow to skin goes down even though crazy hot (*ex: triathlete in video)

Fluid replacement

-Thirst mechanism not precise enough

• people need to be more rigorous with what consuming during exercise

-Weight loss a useful guide: drink 1.5 liters for each kg lost

• drink 50% more than weight you lost

  • bc kidney filters some of the blood before it can get to the cells

-Electrolytes improve hydration status (think I.V.)

-Including carbs (sports drink) benefits glycogen replacement

• water by itself dilutes blood/lowers osmoalltiy

• sport drink increases osmolality/don’t change so equilibrium; kidneys produce less urine

-Risk of overhydration and hyponatremia (*sign=light urine, low BP)

•If excessive water is replacing (salty) sweat

• low blood Na+/blood so dilute blood goes in direction too excessively; brain cells swell and neurological problems (happens if sweating a lot and replacing with just lots of water); too quick for kidneys

•Low sodium alters membrane potentials

•Hypotonic (diluted) blood causes fluid shift into cells

*pictures: limit to electrolytes

*side note: alcohol inhibits ability to hold onto water/tend to make more urine, thus drink electrolytes if hungover

“salt stick”

-measured people’s sweat and gives customized product, matches up what lost/needed

-just marketing? but good theory to replace what lost from sweat

-more than just Na+ in sweat

Hydration surrounding exercise in warm conditions (recommendations before, during, and after exercise)

-Before: show up euhydrated; ~tall glass water or 2 cups

-During: ~1 cup

-After: ~1 pint:1lb or 50% more than what lost

*ranges bc everyone not the same

*conversions to know: 8oz=1 cup; 2 cups=1 pint=1lb; 1L=1kg

24-hours hydration needs

-2L or 8 cups

-but depends largely on body size and daily sweat lost