Effects of a combination of heat and hypobaric hypoxia on cognitive performance.

Driven by technological advancements, the role of the pilot within the
fifth-generation air force is shifting from platform-driven to strongly
information-driven operations. New technology will more and more support and
supplement the human operator*s perception and decision-making. Nevertheless,
the human operator must still be able to perform his tasks given these expanded
capabilities and availability of information. Moreover, fifth-generation pilots
need to perform these tasks in a new role of information manager, under
mentally and physically demanding circumstances that are intrinsic to military
operations. Research program V1917 is funded by the Dutch Ministry of Defense
to acquire knowledge on the effects of internal and external operational
conditions on the physical and cognitive capabilities of the pilot. The main
program objective is to gain knowledge on the effect of (a combinations of)
physical and cognitive stressors on aircrew performance. This knowledge can be
applied to improve simulation environments used for training of aircrew, and to
develop human models that predict operator performance in adverse operational
conditions, such as related to hypoxia, heat, spatial disorientation and
information overload.
Based on several interviews with experts about relevant scenarios, use-cases,
stressors and associated performance measures, two physical stressors (heat and
hypoxia) have been chosen for this study. This study focuses on simulating an
aircrew-mission (transport helicopters) in a warm climate. During such missions
crew regularly fly at an altitude between 10.000 - 13.000 ft without the use of
supplementary oxygen mask, after being exposed to heat load in the cockpit
during ground procedures and flight preparation. During these missions, aircrew
wear a military flight suit with underneath it a fire-resistant Nomex shirt and
pants. This can lead to an insulation layer on the body, which causes an extra
thermal burden.

We examine how a combination of these two physical stressors affect cognitive
performance and (subjective) feelings of cognitive (over)load, and which
mechanisms are associated with the anticipated decline in performance. Although
effects of heat and hypobaric hypoxia stressors on cognitive performance have
been studied in isolation (Martin et al., 2019), little is known about the
possibly interacting effects of the combination of these stressors on cognitive
performance, or about the potentially underlying mechanisms of these effects.

Research questions:

A. What are the effects of hypobaric hypoxia on cognitive performance?
B. What are the effects of heat load on cognitive performance?
C. What are the effects of the combination of these two stressors on cognitive
performance?

Questions pertaining possible underlying (physiological) processes:
D. What are the effects of hypobaric hypoxia and heat load, as well as their
combined effect, on blood oxygen saturation, heart rate, mean body temperature,
skin temperature, visual perception, and self-reported mental effort?

Participants will visit the test center on four separate days. Both the
stressors *hypobaric hypoxia* (sea level vs. hypobaric hypoxia) and heat load
(normal temperature vs. heat load) have a within-subjects (2x2) design. The
participants will be exposed to these stressors in a counterbalanced design for
the following four conditions:
• Condition 1: sea level + no heat load
• Condition 2: sea level + heat load
• Condition 3: hypobaric hypoxia + no heat load
• Condition 4: hypobaric hypoxia + heat load

Because the stressors will be noticeable for the participants, it is not
possible to do (double-)blind research. The four conditions will take place in
a (incomplete) Latin-square crossover design (block of 4 x 7). On each test
day, 3 subjects will be tested at once. This means that a total of 7 possible
sequences can be used (for a total of 21 subjects).

The exposure to a single condition takes a total of 105 minutes, where the
first 60 minutes simulate the *flight preparation/ground procedures part* (with
potential heat load stimuli) and the next 45 minutes the *actual flight* (with
potential hypobaric hypoxia). In order to simulate hypoxia, participants will
be exposed to hypobaric hypoxia in the RNLAF hypobaric chamber at the Centre
for man in Aviation in Soesterberg. Heat load will be induced by 35 degrees
Celsius air temperature, radiant heat from an artificial sun (<1000W/m2 from
infrared heat lamps), and by wearing a flight suit and vest. After the first 60
minutes in the heat load condition, the temperature will be decreased to normal
temperatures of about 25-30 degrees Celsius, while the heat lamps remain on
(simulating sun radiation). During the no heat load condition, a normal air
temperature of about 20-25 degrees Celsius will be used.

Burden on test subjects will not be very high, aspects of the study are quite
standard and od not pose high risks. Participants will visit the CML on four
different days with at least seven-day washout between each test day. Each test
day will take approximately 3 hours of testing and participants will be exposed
to four conditions:
• Condition 1: sea level + no heat load
• Condition 2: sea level + heat load
• Condition 3: hypobaric hypoxia + no heat load
• Condition 4: hypobaric hypoxia + heat load

Exposure to these conditions is divided into two separate phases during a test
day, so that exposure to heat and hypobaric hypoxia will not occur
simultaneously. The research focuses on cognitive performance and which
physiological processess underlie maintaining or loss of performance. The
emphasis of this research is not on health effects.

Prior to taking part in the study a medical (heat- and hypoxia related)
questionnaire is filled in by the participant and approved by the medical
doctor related to this study. In case the medical doctor does find
contraindications, the participant is excluded from participation in this
study. We will monitor the participant during the experiment thoroughly on the
parameters given chapter 5 (core temperature, saturation and heartrate). In
addition, we will regularly observe and communicate with the participant, and a
medical doctor will be available on call. Based on the physiological
parameters, stop criteria (see chapter 5; stop criteria) will be maintained.
Participants are instructed to indicate if they are not feeling well. In that
case, the experiment will be paused or even terminated. In case one participant
in the hypobaric hypoxia condition (3 or 4) has to stop the experiment, all
other participants at that moment have to stop as well.

Counter measures:
A. Participants are screened by a medical doctor using a medical screening
checklist;
B. Participants will have a cardiovascular screening (ECG) assessed by a
medical doctor;
C. During the experiment a medical doctor is available on call at the location;
D. Back-up oxygen bottles are present in the hypobaric chamber;
E. Participants will be monitored continuously (core temperature, heart rate
and saturation) and stop criteria are maintained.
F. After the experiment, participants can drink water.

Different studies focus on the effects of hypobaric hypoxia and heat load in
isolation on cognitive- and physiological responses. However, the combination
of heat and simulated altitudes is less clear. The results of this study can
help to improve simulation environments used for training of aircrew, and to
develop human models that predict operator performance in adverse operational
conditions.