Web-HUMAN short lab

Heat Loss Due to Sweating
(version 4/29/04c)


Recall (see the Thermal Stress Experiment) that maintenance of a constant body temperature in a homeotherm requires that all heat gains be balanced by an equal amount of heat loss (i.e. that heat balance be maintained). Further recall that losses and gains in a simplified thermal model are largely each representable by heat fluxes (e.g. cal/min.) that are dependant both on the temperature gradient between the organism and the environment and the thermal conductance of that particular route of heat flux.


In most mammals and in web-HUMAN, one of the routes available for heat loss is sweating. Users can monitor the sweating heat flux (SWETC), the sweat volume (SWETV) and the salt concentration of the sweat (SWETNA) (check the variables list for units of each). They can also keep track of body temperature (TEMP, TEMPF) and hypothalamic target temperature (TEMSET).


Also note that the lower critical temperature (i.e. bottom of the thermoneutral zone) in humans (and in the model) is about 27 deg. C.. Below this environmental temperature heat production increases to defend body temperature.


Design an experiment in which you

1) Monitor (via Tables) the following variables:
Sweat heat flux

Sweat volume

Sweat sodium concentration

Ambient temperature

Body temperature

Target temperature

2) Change the ambient temperature on consecutive runs from 5 degrees C to 40 degrees C in steps of approximately 5.0 degrees. Be certain to also include a run at thermoneutral temperature (27 deg. C.).
3) In each of these runs run the model for 1hour (1H) with 15 min. between printouts.
4) Record the value for sweating heat loss at one hour vs. ambient temperature. This constitutes your basic data (a hand written table will suffice).
5) Repeat this design (Back button-> change ambient temperature) for the range 5-40 deg. C.. (be sure to include 27 deg. C also).
            You should now have data for one hour's sweating heat loss as a function of ambient temperature.
6) In Excel, construct a table of Sweat Calories Lost at hour 1as a function of Ambient Temperature. Plot this data as Sweat Calories Lost (Y axis) vs. Ambient Temperature (X axis).



A)    Characterize very briefly the nature of the relationship.






            B) The model quite clearly sweats rather steeply at and well below its thermoneutral temperature. In terms of heat balance (losses and gains) account briefly for why it already does so at 27 degrees despite the fact that the environment is at a lower temperature (by 10 degrees) than the body temperature and web-HUMAN must therefore be losing heat passively by routes other than sweating.