Study design: A cross-over single-blinded treatment design will be used. Participants will undergo 4 different conditions: (1) low air flow and 23°C, (2) low air flow and 35°C, (3) high air flow and 23°C, and (4) high air flow and 35°C. Participants will be blinded to the air quality level; however, it is not possible to blind them to the temperature condition, as they will be able to perceive it as different.

Study population: The population consists of healthy young and middle-aged adults of both sexes between 18 and 40 years.

Intervention (if applicable): Each participant undergoes 4 conditions in randomized order. Two conditions consist of poor air quality defined as 3,000 ppm carbon dioxide and 23°C or 35°C temperature, respectively.

Objective: This study aims to examine the effect of indoor air quality and temperature on human cognitive performance. The main research objective of this study is to examine how indoor air quality and temperature affects cognitive performance, respectively. As a secondary objective, it will be examined if a higher temperature of 35°C compared to 23°C amplifies the negative effect of low air flow vs. high air flow on cognitive performance. It will also be examined if human perceive the air quality as less pleasant under the higher temperature, even if the air quality itself does not change in terms of carbon dioxide concentration. Also, the physiological reaction towards poor air quality and elevated temperature will be examined in isolation and interaction.

Main study parameters/endpoints: The main study parameters are the achieved scores of the cognition test, mainly derived from the Cambridge Neuropsychological Test Automated Battery (CANTAB) and the Cognitive Ability Task. As secondary outcome, the physiological response will be examined. Specifically, it will be investigated how the air quality and temperature affect the following physiological parameters: Capillary blood CO2 and pH level, salivary cortisol and a-amylase and serum cytokine response, lung function, heart rate, respiration rate, skin temperature, core temperature, blood pressure, physical activity, and metabolic rate.

Primary Objective: The main research objective of this study is to examine how poor indoor air quality in terms of low air flow compared to high air flow and elevated temperature of 35°C compared to 23°C affect cognitive performance, respectively.

Secondary Objective(s): The following secondary objectives will be investigated in this study:

1. It will be examined whether the decline in cognitive performance is greater when low air quality to high air quality compared to when temperature levels are increasing from 23°C to 35°C.
2. It will be examined whether a higher temperature of 35°C compared to 23°C amplifies the negative effect of poor air quality.
3. It will be examined whether participants perceive the air quality as less satisfactory if temperature levels are higher indoors, even when the air quality is unchanged. It will be also examined to which physiological reactions poor air quality and elevated temperature lead. Specifically, the following objectives will be investigated:
4. It will be examined whether metabolic rate is affected under poor air quality conditions or higher temperature indicated by a change in CO2 production and oxygen consumption.
5. It will be examined whether poor air quality or higher temperature levels are associated with a stress response defined by a higher heart rate, higher respiration rate, higher blood pressure, higher alpha-amylase and cortisol levels, and a higher rate of non-exercise activity thermogenesis through increased physical activity.
6. It will be examined whether lung function in terms of forced expiratory volume and forced vital capacity are reduced when participants are exposed to poor air quality in combination with a higher temperature of 35°C.
7. It will be examined whether blood capillary carbon dioxide concentration and blood pH level are elevated under worse air quality in combination with a higher temperature of 35°C.

Inclusion Criteria:

• Adults between 18 to 40 years old
• Western-European background
• Generally healthy
• No medication which may influence the outcome parameters. This will be determined on a case-by-case basis. Contraceptive uses for women are allowed and will be verified through a questionnaire.
• Non-smokers or persons who quit smoking more than five years ago

Exclusion Criteria:

Participants, who do not want to be informed about unexpected medical findings, or do not wish that their treating physician will be informed, cannot participate in this study

• Individuals with a diagnosed physical or mental disability or attention deficit hyperactivity disorder (ADHD) or depression
• Any medication or medical condition that might interfere with the physiological outcome parameters or in some regards impair cognition
• Unstable body weight (weight gain or loss >3kg in the past three months)
• Participation in another biomedical study within 1 month prior to screening visit
• Shift workers
• Colour blindness
• Pregnancy
• People with a low haemoglobin or haematocrit concentration
• Not having visited or resided in a warm country in the last 3 months
• Participants with asthma or restricted lung function due to allergies

Open Access upon request of fully anonymized data after initial analysis

Open Access upon request of fully anonymized data after initial analysis