Heat Stress, Physiological Stress
Conditions
Keywords
Indoor overheating, Indoor temperatures, Heat wave, Thermoregulation, Heat strain, Heat vulnerability, Hyperthermia, Elderly, Thermal comfort, Clothing, Activity
Brief summary
While an upper limit of 26°C has been shown to be protective for heat-vulnerable older occupants (DOI: 10.1289/EHP11651), this recommendation did not consider the added heat burden associated with increases in internal heat production accompanying activities of daily living or the restriction to heat loss caused by clothing insulation. To safeguard the health of older adults, health agencies worldwide recommend the remain in cool space indoors, avoid strenuous activity, wear lightweight clothing, and drink cool water regularly throughout the day. However, older adults do not sense heat as well as their younger counterparts. Consequently, they may not take appropriate countermeasures to mitigate physiological strain from indoor overheating. This may include overdressing despite high indoor temperatures. In other cases, individuals may wear insulated clothing in hot weather to observe cultural or religious modesty requirements, which serve as expressions of faith and identity rather than a tool for thermoregulation. Further, individuals may be unaware of the consequences of increases in physical activity on heat gain and may therefore not adjust their normal day-to-day activity levels to prevent potentially dangerous rises in body temperature. Consequently, this may necessitate a lowering of recommended upper indoor temperature limit during hot weather. To address these important considerations, on separate occasions the investigators will assess the change in body temperature and cardiovascular strain in older adults (65-85 years) exposed for 8 hours to the recommended indoor temperature upper limit of 26°C and 45% relative humidity equivalent humidex of 29 (considered comfortable) while they A) perform seated rest dressed in light clothing (t-shirt, shorts and socks), B) perform light exercise (stepping exercise to simulate activities of daily living, 4-4.5 METS) every hour (except during lunch hour period) dressed in light clothing, C) perform light exercise (4-4.5 METS) every hour (except during lunch hour period) dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants) and D) perform seated rest dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants). With this experimental design, investigators will assess the effects of added clothing insulation and light activity, representative in activities of daily living on physiological strain and identify whether refinements in the recommended 26°C indoor temperature limit may be required.
Interventions
Older adults exposed to an 8-hour simulated exposure.
Sponsors
University of Ottawa
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
SINGLE (Outcomes Assessor)
Eligibility
Sex/Gender
ALL
Age
65 Years to 85 Years
Healthy volunteers
Yes
Inclusion criteria
* Non-smoking. * English or French speaking. * Ability to provide informed consent. * with or without a) chronic hypertension (elevated resting blood pressure; as defined by Heart and Stroke Canada and Hypertension Canada), b) type 2 diabetes as defined by Diabetes Canada, with at least 5 years having elapsed since time of diagnosis
Exclusion criteria
* Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness). * Serious complications related to your diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy). * Uncontrolled hypertension - BP \>150 mmHg systolic or \>95 mmHg diastolic in a sitting position. * Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.). * Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable. * Cardiac abnormalities identified during screening
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Core temperature (Peak) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Profiles of Mood States (POMS) during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Potential changes in mood (7 subscales of mood: tension, anger, depression, fatigue, confusion, vigor and esteem related affect). The POMS-40 is a validated, self-administered questionnaire that examines seven distinct aspects of mood state across two positive subscales (Esteem-Related Affect, and Vigor) and five negative subscales (Fatigue, Tension, Confusion, Anger, and Depression), which are described across 40 distinct adjectives. For each individual item, participants were asked to describe "how you feel right now" by responding using a 5-point Likert scale (0 = "Not at all", 1 = "A little", 2 = "Moderately", 3 = "Quite a lot", or 4 = "Extremely"). The values of items associated with a specific subscale (e.g., Fatigue) were summed to calculate its score. |
| Environmental Symptoms Questionnaire (ESQ) during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Self-reported environmental reactions and medical symptomatology associated with prolonged heat exposure. The ESQ-IV is a validated 68-item, self-administered questionnaire that has been used successfully in identifying symptomatology during exposure to a wide variety of environmental conditions, including heat exposure \[24, 25\]. Participants are asked to assess and described "how you have been feeling today" by responding to each item using a 6-point Likert scale (0 = "Not at all", 1 = "Slight", 2 = "Somewhat", 3 = "Moderate", 4 = "Quite a bit", or 5 = "Extreme"). Total Symptom Score was calculated from this data by taking the sum of the intensity ratings from all 68 individual items using reverse scores for the three positive items from the list ("I Felt Good", "I Felt Alert", and "I Felt Wide Awake"). |
| Activity levels during daylong exposure to indoor overheating | End of 8 hour daylong exposure | Activity levels assessed via a wearable monitor (Actical) containing an accelerometer worn on the wrist and hip. |
| Hydration status during daylong exposure to indoor overheating | At the start (hour 0) and end of 8 hour daylong exposure | Hydration status measured via assessing the urine specific gravity of a urine sample. |
| Perceived exertion scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Perceived exertional assessed via a visual analog scale ("How hard are you working?") ranging from "no exertional at all" to "maximal exertion" |
| Feel good scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Feel good assessed via a visual analog scale ("How good do you feel?") ranging from "very good" to "very bad"(midpoint: neutral) |
| Orthostatic intolerance symptoms assessment during daylong exposure to indoor temperature limit. | At end of 8 hour daylong exposure. | Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance during the lying to standing tests. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort". |
| Thermal sensation 2 scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Thermal sensation assessed via a visual analog scale ("How do you feel?") ranging from "hot" to "cold"(midpoint: neutral) |
| Thermal sensation scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Thermal sensation assessed via a visual analog scale ("How hot do you feel?") ranging from "extremely hot" to "neutral"(midpoint: hot) |
| Arousal scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Felt arousal scale assessed via a visual analog scale ("How worked up are you?") ranging from "high arousal" to "low arousal". |
| Thirst sensation scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Thirst sensation assessed via a visual analog scale ranging from "very, very thirsty" to "not thirsty at all". |
| Thermal comfort scale during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from "very uncomfortable" to "comfortable". |
| Change in plasma volume during daylong exposure to indoor temperature limit. | At end of 8 hour daylong exposure. | Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of each exposure using the technique by Dill and Costill. |
| Fluid loss during daylong exposure to indoor temperature limit. | At end of 8 hour daylong exposure | Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption). |
| Fluid consumption during daylong exposure to indoor temperature limit. | At end of 8 hour daylong exposure | Average hourly fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure (normalized to the exposure duration). |
| BTrackS Balance Assessment during daylong exposure to indoor temperature limit (postural stability). | At the start (hour 0) and end of 8 hour daylong exposure | To assess postural stability, participants will be asked to stand on a BTracks force plate with their feet spread out to shoulder width while looking straight ahead. The assessment will comprise of one trial lasting 120 seconds in length. Center of pressure (COP) vector data along vertical (y) and horizontal (x) axes will be summed for the total path excursion length (cm) during each trial. |
| CDC 4-Stage Balance Test during daylong exposure to indoor temperature limit (postural stability). | At the start (hour 0) and end of 8 hour daylong exposure | To assess postural stability, participants hold a tablet to their chest, then auditory cues guide participants through four consecutive stances, feet side by side, instep of one foot touching the big toe of the other foot, tandem stand with one foot in front of the other, heel touching toe, and stand on one foot. The balance assessment will be evaluated based on movement detected by an accelerometer integrated into the hardware of the tablet device (Sway Medical Inc). |
| Impulse control during daylong exposure to indoor temperature limit (cognitive function). | At the start (hour 0) and end of 8 hour daylong exposure | Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of impulse control. Participants will be asked to respond to both "go" and "no-go" visual cues. In response to the "go" cue, participants will initiate a movement of the device. |
| Reaction time during daylong exposure to indoor temperature limit (cognitive function). | At the start (hour 0) and end of 8 hour daylong exposure | Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of reaction time. Participants will be asked to initiate a movement of the device in response to a visual cue. |
| Rate pressure product during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate. |
| Diastolic blood pressure during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Diastolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures). |
| Systolic blood pressure during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Systolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures). |
| Systolic response to standing from supine during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Systolic blood pressure response to standing evaluated as the difference in blood pressure measured between the standing and supine. Standing systolic blood pressure will be taken as the lowest value of those measured after 60 and 120 seconds of standing. Systolic response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest). |
| Cardiac response to standing from supine (30:15 ratio) during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Cardiac response to standing evaluated as the ratio between the highest R-wave to R-wave interval (lowest heart rate) measured at the 30th heart beat after standing from supine (+/- 5 beats) and the lowest R-wave to R-wave interval (highest heart rate) measured at the 15th heart beat after standing (+/- 5 beats). Cardiac response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest). |
| Heart rate variability: SDNN during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the supine position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of supine rest). |
| Heart rate variability: RMSSD during daylong exposure to indoor temperature limit. | At the start (hour 0) and end of 8 hour daylong exposure | Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the supine position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of supine rest). |
| Heart rate end of daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Heart rate measured at hour 8 of exposure to indoor temperature limit (15-min average). |
| Heart rate (AUC) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Areas under the curve (AUC) of heart rate during the 8 hour exposure to the simulate indoor temperature upper limit. |
| Heat rate (Peak) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Peak heart rate (15 min average) during exposure. Heart rate is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit. |
| Mean skin temperature end of daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Mean skin temperature measured over 7 body regions at hour 8 of exposure to indoor temperature limit (15-min average). |
| Mean skin temperature (AUC) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Areas under the curve (AUC) of mean skin temperature as calculated over 7 body regions during the 8 hour exposure to the simulate indoor temperature upper limit. |
| Mean skin temperature (Peak) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Peak mean skin temperature (15 min average) during exposure. Mean skin temperature as calculated from skin temperature measured across 7 body regions is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit. |
| Core temperature end of daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Rectal temperature measured at hour 8 of exposure to indoor temperature limit (15-min average). |
| Core temperature (AUC) during daylong exposure to indoor temperature limit. | End of 8 hour daylong exposure | Areas under the curve (AUC) of rectal temperature during the 8 hour exposure to the simulate indoor temperature upper limit. |
| Sleep quality and quantify assessment during daylong exposure to indoor temperature limit. | At start of 8 hour daylong exposure. | The Pittsburg Sleep Quality Index will be administered to provide an overview of the sleep quantity and quality of individuals over the previous month. |
Countries
Canada
Contacts
CONTACTGlen P Kenny, PhD
PRINCIPAL_INVESTIGATORGlen Kenny, PhD
University of Ottawa
Outcome results
None listed