Human thermoregulatory behavior and thermo-physiology before and after mild heat acclimation in healthy lean and obese subjects

Human beings are almost constantly exposed to indoor climates and in the last
decades, overheating of buildings has become an important issue. In the western
world, heating, ventilating and air-conditioning of residential, commercial and
public buildings consumes a lot of energy. In developed countries, one-third of
the primary energy supply is used for this purpose. This reveals the importance
to reduce this energy use. A lot of progress has been made towards highly
effective construction materials, which provide high standards of airtightness
and insulation. However, as a result buildings might be at risk for
overheating. Furthermore, global warming is progressing slowly but surely.
The indoor climate of a building has an important impact on human metabolism:
uncomfortable warm environments might cause sleepiness and restrict
productivity. On the other hand, building occupants influence their thermal
environment to maximize their individual comfort: they open a window or put on
a heater. Changes in skin and core temperature, as well as conscious perception
of thermal sensation and thermal comfort, seem to drive thermoregulatory
behaviour. It is difficult to predict how much energy a building will consume
in practice, which might be due to the fact that the individuality of occupancy
is not sufficiently implied in calculations. With respect to the issue of
overheating, it is desirable to improve knowledge on how human thermoregulatory
behaviour and thermophysiology can be influenced by heat acclimation, since
evidence is very limited. It is hypothesized, that prolonged exposure to mild
heat causes alterations in thermoregulatory physiology (as widely accepted),
and influences behavioural set points of thermoregulation and shifts the
perception of thermal comfort to higher ambient temperature.

1. To study thermoregulatory behavior and thermo-physiology of healthy lean and
obese subjects before and after mild heat acclimation.
2. To define categories of *temperature preference* based on thermoregulatory
behavior and thermo-physiology of healthy lean and obese subjects.
3. To study the influence of mild heat acclimation on alertness and
cardiovascular health of healthy lean and obese subjects.

The study will take place between March 2014 and December 2015. The
measurements will be conducted at the Metabolic Research Unit (MRUM) of
Maastricht University. The study will consist of 11 testing days at the
laboratory (Figure 1). Day 1 will consist of a screening. During day 2 and 3,
baseline measurements of the so-called SWITCH protocol (experimental protocol
to measure thermoregulatory behavior) as well as protocol TNZwarm and TNZcold
(thermo-neutral zone measurements) will take place. TNZwarmpre and SWITCHpre
will be carried out at the same day (day 2) and TNZcoldpre at a separate day
(day 3), followed by the first mild heat exposure. During the next 6 days,
participants will visit the laboratory for an acclimation period that consists
of 6.5h mild heat exposure per day. After completing day seven of the
acclimation, participants will undergo protocol TNZwarm (TNZwarmpost), SWITCH
(SWITCHpost) and TNZcold (TNZcoldpost) for a second time.

Mild heat exposure. The volunteers will be exposed to a mild heat temperature
(33*C) for 7 days. Day 1 consist of 4h mild heat exposure, followed by 6 days
of 6.5h mild heat exposure.

The risks of this study are low. The DEXA-scans, executed for the measurement
of body composition is a non-invasive method. The radiation dose is very low,
comparable to the radiation dose of a warm summer day or a radiation-photo
taken at a dentists. The effective radiator dose is, depending on the duration
of the scan (size of the body) between 1-7 microSievert (0,001- 0,007 mSv). We
expect the subjects to sense superior thermal discomfort during the first few
days of exposure, but this will gradually decline during the acclimation
period. The temperatures will be uncomfortable in the first place but not
harmful.