Creating health and resilience by a dynamic indoor climate

Van Marken Lichtenbelt, Pallubinsky, & Kramer studied the effects of dynamic interior climate on metabolic health.

Introduction

Our indoor environment is typically regulated to ensure that it is comfortable for the ordinary individual. However, a growing body of research suggests that routine exposure to temperatures outside the thermal neutral zone may have important positive effects on metabolism. Heat and cold exposure both have a favorable impact on our metabolism and cardiovascular system, as well as ‘training’ our resistance to high temperatures (heat waves or cold spells). Importantly, mild cold and mild warm surroundings can already have positive benefits on health without having to be exposed to high temperatures. It’s crucial to understand that exposure to excessive heat or cold is not necessary. First, acclimatization leads to higher comfort ratings during medium-term (days to weeks) temporal excursions outside the thermal comfort zone. Second, exposure to low or high temperatures for brief periods of time (minutes to hours) in a dynamic thermal environment may be regarded as tolerable or even pleasant (evoking so-called thermal alliesthesia). Another benefit is the ability to significantly lower energy use in the built environment by allowing indoor temperatures to fluctuate within a broad range and applying seasonal changes to this range.

Goal of this study

Even now, while designing the indoor climate, comfort and health are still seen as being synonymous. The person’s comfort is given a lot of attention, which has led to strictly regulated interior air temperatures. As a result of regular exposure to temperatures outside the thermal neutral zone, the findings indicate, there may be significant health advantages. Our metabolism and cardiovascular system benefit from exposure to cold and heat, and it also “trains” us to withstand extremely cold and hot conditions (heat waves and cold spells). It’s important to note that moderate cold and mild warm conditions can already have favorable effects on health. They don’t even need to be exposed to high temperatures. The idea of dynamic interior environments is produced by transferring these findings to the physical environment.

Methods

van Marken Lichtenbelt , W., Pallubinsky, H., & Kramer, R. have undertaken several laboratory research over the past two millennia to identify the physiological and metabolic impacts of brief excursions outside of the thermal neutral zone (see below) and the thermal comfort zone. In order to understand the impact of a chilly environment without shivering, it was first necessary to investigate the effects of mild cold on human energy metabolism and metabolic health. In-depth research on the so-called non-shivering thermogenesis resulted in the identification of adult humans’ brown adipose tissue. Later, the researchers began examining the impact of modest heat exposure on the cardiovascular system, metabolic health, and energy metabolism. The measurements in the respiration/climate chambers were crucial to the success of the experiments.

Study design

The Room calorimeters

Although each of the 20 lab spaces can be adjusted for climate, five of them are specifically made climate-controlled respiration chambers (room calorimeters). These airtight chambers allow for the measurement of O2 consumption and CO2 production under controlled conditions over a time span of 12 hours to 7 days, allowing researchers to analyze human energy expenditure and substrate oxidation. This implies that measurements of people can be made in rather typical living situations.

The subjects can carry out regular daily activities including sleeping, eating, working from home, etc. despite being restricted to the room. The rooms (18 m3) can be furnished with a bed, sink, toilet, desk with computer, TV, and DVD player. The study can be utilized as a bedroom, living room, or office, depending on the study. The compartments have a deep-freeze toilet for feces collection; bottles are used to collect pee separately. For the exchange of food, the gathering of urine, and the sampling of blood, three air locks are available. The subjects’ physical exercise can be carried out on a treadmill, stepping platform, or cycle ergometer. Overall, extensive research may be done on the energetics, metabolic characteristics, and subjective experiences of human volunteers. An automatic information system constantly regulates and keeps an eye on the climate. The temperature can be set to 10 to 45 degrees Celsius, and the relative humidity can range from 20% to 80%. An LED lighting system from Philips called SkyRibbon is installed in the rooms. With corresponding color temperatures ranging from 2000 K to 10000 K and a maximum intensity of 1600 lux, the latter enables customizable white light (under 4000 K). The participants can also alter the temperature and light levels within predetermined ranges. The enclosed compartment’s air conditioning unit circulates air throughout it. As a result, a circulation rate between 200 and 800 m3/h is permitted. Using mixing or displacement ventilation are the two options for supplying the air.

Combining technology (MOX Accelerometers)

During the respiration chamber research, various sensors are employed to evaluate a range of physiological characteristics. Telemetric tablets are used to assess core temperature (VitalSense, EquivitalTM, UK, or CoreTemp, HT150002; HQ, Inc. Palmetto, FL, USA). Wi-Fi iButton dataloggers are used to measure skin temperatures (DS-1922 L, Maxim, USA). A three-axial accelerometer (MOX, Maastricht Instruments, NL or Actigraph, wGT3X-BT, USA) applied to predetermined skin sites measures physical activity. Various cardiovascular indicators are measured depending on the study, including heart rate (HR) using a Polar H10 chest belt and blood pressure (Omron M6 Comfort IT, Omron Healthcare, JPN). Additionally, Qsweat (WR Medical Maplewood, USA) and laser doppler flowmetry are frequently used to evaluate sweat rate and skin blood perfusion, respectively (PeriFlux System 5000, Perimed, SE). Additional cellular and metabolic factors are frequently discovered using muscle biopsies and blood samples. Participants complete the following surveys regarding their thermal experiences: A continuous visual analogue scale (VAS) is utilized to measure thermal comfort and the standard 7-point ASHRAE thermal scale is used to evaluate subjective thermal experience. Subjective thermal preference and local thermal sensation by ASHREA 7-point scale are two additional frequently utilized questionnaires.

Results

Not many studies connect thermophysiology and comfort with heat. The thermal neutral zone (TNZ) is a traditional physiological indicator for the thermal comfort range. The thermo-physiological characteristics of metabolic rate and sweat production in physiology define the TNZ. Sweating is produced above the TNZ to cool the body down while non-shivering and shivering thermogenesis boost metabolic rate below the TNZ to give the body with additional heat. Although there is significant individual variation, the TNZ significantly influences thermal comfort and has considerable overlap with the thermal comfort zone.

The study has demonstrated that, in response to cold exposure slightly beyond the TNZ, non-shivering thermogenesis (NST) enhances body heat generation. This is consistent with several earlier research. This indicates that in mild cold settings, the human energy balance can be changed without obvious shivering or significant discomfort. In fact, we have experimentally demonstrated that progressive temperature fluctuations are accepted by both young adults and the elderly with little to no discomfort. The researchers also examined mild cold acclimation, finding that after ten days of consistent cold exposure, NST increased significantly, thermal discomfort decreased significantly, and the urge to change temperatures decreased significantly, all while insulin sensitivity improved significantly.

Additionally, according to the findings, NST significantly varies across individuals and between groups, being muted in obese individuals and lowered in senior individuals. Overall, their findings clearly demonstrate metabolic and cardiovascular adaptations to (moderate) cold and repeated exposure to cold, as well as increased resilience to cold. Passive and mild heat acclimation causes conventional physiological adaptation, just like other traditional, aggressive, and intense (exercise-induced) heat acclimation methods.

Regular exposure to heat and cold both show enhanced metabolic health and heightened resistance to temperature extremes, despite the fact that their underlying mechanisms appear to be distinct.

Finally, individuals and groups of people exhibit vastly different temperature reactions and experiences. It is also well known that people can tolerate a wider range of temperatures if given enough time to acclimatize and, secondly, if they have some control over their living conditions. Therefore, personal control systems, windows that can be opened, and programmable thermostats may be necessary in rooms and offices. The study demonstrated that a dynamic environment with an average daily temperature range of 8°C may produce adequate comfort. With a PCS, this comfort was significantly increased. It is significant that the PCS was created to locally modify body temperature without losing the benefits of the dynamic indoor climate for health.

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Whole body room calorimeters

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Creating health and resilience by a dynamic indoor climate

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