PHYSICAL ASPECTS OF HUMAN BIOCLIMATOLOGY* 
By KONRAD J. K. BUETTNER 
Randolph Field, Texas 
According to the classical definition by Humboldt 
[50], the term climate designates all changes in the 
atmosphere that noticeably affect human physiology. 
With this definition, upon which the present article is 
based, the meteorological elements must be evaluated 
in a manner different from that used, for instance, in 
connection with an airway meteorological service or 
with plant geography. Thermal elements of the climate 
become the most decisive, specific radiations come next, 
whereas pressure, wind direction, and similar basic 
weather data play only an indirect role. 
HEAT BALANCE 
Heat Production. The body gains the energy 
necessary for maintaining its internal temperature by 
combustion of converted food. This energy is given off 
by conduction, convection, radiation, and evaporation 
from the skin, as well as by advection to, and evapora- 
tion from, the respiratory organs. A maximum of 20 per 
cent of the heat produced (less basal metabolism) may 
be used for external work. The excretion of stool, urine, 
ete., merely presents a decrease in the body’s heat 
capacity. Unfortunately, metabolism, which is essential 
for the life of every cell, takes place in both hot and 
cold environments; however, it cannot be regulated 
beyond certain limits. 
An adequate oxygen supply to the blood through 
diffusion in the lungs’ surface requires a certain partial 
pressure of oxygen in the lungs. This partial pressure 
is determined almost exclusively by the atmospheric 
pressure because the fraction of oxygen in the air is 
very nearly constant. Pressure variations caused by 
weather, however, are too small to be significant in this 
relation. Consequently, only the well-known variation 
of pressure with altitude needs to be considered. 
The combustion end products, CO. and HO, are 
removed by breathing and metabolism. Excessive CO2 
content of the inspired air is harmful; it occurs only 
near volcanoes and in artificial climates (crowded rooms, 
submarines, etc.), but in such cases the coexistent 
sultriness is often more important than the presence of 
COs. 
The base value of heat production (at rest, “‘com- 
fortable” climate) is about 40 Cal m~ hr *. Exercise, 
fever, or cold increase this value up to a rate larger 
by more than one order of magnitude. 
If, starting with “comfortable” conditions, the room 
temperature decreases by 10C, the heat production of 
the body increases by about one half. This heat produc- 
tion would have to double if the skin temperature were 
to remain constant. Actually, however, the latter de- 
creases by about 7C because of a decrease in the ad- 
vection of warm blood to the skin, particularly to that 
* Translated from the original German. 
of the extremities whose temperature then drops almost 
to that of the air. The thermal conductance (taken be- 
tween the interior of the body and the average skin) 
decreases from about 50 to 10 Cal m~ hr (deg C)—. 
On the other hand, it may rise to 120 Cal m~ hr (deg 
C)- for portions of the skin heated separately and may 
drop almost to zero for cold extremities [7, 19, 84]. This 
complex of phenomena corresponds to variations in 
blood circulation which, in both extremes, constitute a 
severe load on the heart: since the temperature gradient 
between heart and skin is small in the case of warm sur- 
roundings, the heart must pump large quantities of 
blood to the periphery in order to rid the body of the 
heat it produces. In the case of cold surroundings, on the 
other hand, the necessary heat must be produced by 
arduous muscular activity which, again, strains the 
heart. 
Rapid variations of the thermal environment pro- 
duce temperature fluctuations first in the skin, then in 
larger portions of the body, until a new equilibrium is 
established. This involves a stock-piling of heat, using 
the body’s heat capacity. The values of specific heat 
are: 
Skkinielcnd.c oma be we doodle $8 0.77 Cal kg (deg C)- 
CT reeeeney ic Reo ere es 6. coc 0.55 oe 
IMiiscle tate ncaa casera tes 0.91 ce 
Roughly, the entire body can lose j Cal m ~ without 
discomfort if its heat metabolism amounts to 7 Cal 
m hr — [8]. The corresponding drop in the true body 
temperature is composed of 65 per cent core temper- 
atures (rectum) and 35 per cent skin temperature 
[24]. This ratio may vary; nevertheless, the mean body 
temperature is usually not equal to the rectal temper- 
ature. 
Heat Loss by Convection. In the simplest case, the 
temperature of a room may be used as a measure of its 
climate. However, thermal environments are rarely as 
simple as that; usually wind, radiation, and humidity 
act simultaneously. The total rate of heat loss can be 
determined only synthetically from these weather ele- 
ments. 
The known laws of heat transfer by convection have 
successfully been applied to the human body [13, 16, 
19, 49]. The skin is’ surrounded by a laminar boundary 
layer several millimeters thick (in the case of calm 
air). At the inner portion of this layer, heat transfer 
takes place by pure conduction. A steady transition 
to turbulent austausch takes place towards the outside. 
The dependence of surface conductance h, on wind 
velocity v, diameter d, and density of the air p is 
expressed by the following formula: 
had 
i CU", (1) 
1112 
