Ignite Creation Date:
2024-05-06 @ 2:34 PM
Last Modification Date:
2024-10-26 @ 1:33 PM
Study NCT ID:
NCT04353076
Status:
COMPLETED
Last Update Posted:
2021-08-18
First Post:
2020-04-13
Brief Title:
Physiological Responses in Young and Older Adults During a Prolonged Simulated Heatwave
Sponsor:
University of Ottawa
Organization:
University of Ottawa
Study Overview
Official Title:
Understanding and Managing the Limits of Physiological Tolerance in Heat Vulnerable Canadians During Rest and Physical Exercise
Status:
COMPLETED
Status Verified Date:
2021-08
Last Known Status:
None
Delayed Posting:
No
If Stopped, Why?:
Not Stopped
Has Expanded Access:
False
If Expanded Access, NCT#:
N/A
Has Expanded Access, NCT# Status:
N/A
Acronym:
HW1
Brief Summary:
Climate change not only affects the planets natural resources but also severely impacts human health An individuals ability to adequately cope with short- or long-term increases in ambient temperature is critical for maintaining health and wellbeing Prolonged increases in temperature heatwaves pose a serious health risk for older adults who have a reduced capacity to efficiently regulate body temperature However information regarding the impact of age on body temperature regulation during prolonged exposure to extreme heat is lacking as is research on the effectiveness of interventions aimed at reducing heat strain in such situations This project will address these important knowledge gaps by exposing healthy young and older adults to a prolonged 9 hour heat exposure with conditions representative of heatwaves in temperate continental climates An additional cohort of older adults will complete the same heatwave simulation but will be briefly 2 hours exposed to cooler conditions 22-23C mid-way through the session akin to visiting a cooling centre or cooled location The investigators will evaluate age-related differences in the capacity to dissipate heat via direct air calorimetry a unique device that permits the precise measurement of the heat dissipated by the human body and their effect on the regulation of body temperature The investigators anticipate that older adults will exhibit progressive increases in the heat stored in the body throughout the simulated heatwave resulting in progressive increases in body core temperature Further older adults exposed to brief-mid day cooling will rapidly gain heat upon re-exposure to high ambient temperatures As a result by the end of exposure body temperatures will be similar to the group not removed from the heat
Detailed Description:
OBJECTIVES Intervention 1 Evaluate the effect of age on whole-body heat storage body core temperature and the development of cardiovascular strain and acute inflammation during day-long 9 hours exposure to simulated heatwave conditions
Intervention 2 Determine whether short-duration exposure 2 hours to an air-conditioned environment following extreme heat exposure results in lasting reductions in physiological strain in older adults upon return to the heat
Hypotheses Intervention 1 Older adults will experience greater heat storage throughout the 9-hour simulated heatwave compared to the younger participants Consequently body core temperature will be greater in the older adults and between-group differences will be exacerbated as exposure progresses We will also explore the secondary hypothesis that differences in body temperature will be paralleled by greater alterations in cardiovascular variables and acute circulatory and intracellular inflammation in the older adults
Intervention 2 Body heat storage will be exacerbated in the older adults exposed to the cooling centre intervention upon return to the heat hours 5-6 compared to the older adults from Intervention 1 who remained in the heat Consequently body core temperature will be comparable statistically equivalent between groups by the end of exposure
Methods Participants A total of 20 young age 18-31 years and 40 older age 64-80 years adults will be recruited for the proposed project with an approximately even distribution of men and women in each intervention arm Young n 20 and older n 20 adults will complete Intervention 1 and a separate cohort of older adults n 20 will complete Intervention 2 Participants will be homogenous for anthropomorphic characteristics as well as habitual physical activity levels as verified via standardized questionnaires
Experimental Design Pre-trial instructions All participants will be asked to avoid strenuous physical activity and alcohol for 24 hours prior to all preliminary and experimental sessions and to eat a light meal 2 hours before the start of each session Participants will also be asked to consume a minimum of 500 ml of water the night before and morning of each session to ensure adequate hydration Adequate hydration will be verified upon arrival to the laboratory urine specific gravity 1025 For all sessions participants will wear athletic shorts and a sport top for women
Preliminary screening All participants will complete one preliminary evaluation a minimum of 7 days before the first experimental session During this session they will be familiarized with all procedures and measurement techniques and will complete the Get Active Questionnaire GAQ and the American Heart Association Pre-participation screening Questionnaire to assess their eligibility to participate The GAQ will also be used to assess habitual activity levels along with the Kohl Physical Activity Questionnaire Participants will also provide verbal and written informed consent at this time Body height and mass will be determined via a physician stadiometer and a high-performance weighing terminal respectively and from these measurements body surface area will be calculated
Experimental Protocol Intervention 1 Each session will commence at 0700-0900 Upon arrival to the laboratory the participant will provide a urine sample for the assessment of urine specific gravity after which a measurement of nude body mass will be obtained Participants will then insert a temperature probe for the continuous measurement of rectal temperature Thereafter participants will be instrumented for the measurement of skin temperature and 5-lead echocardiogram Baseline cardiovascular parameters will be evaluated via a brief 45 min cardiovascular test battery performed as follows Brachial arterial systolic and diastolic pressures reconstructed from arterial pressure waveforms measured at the right middle finger volume clamp technique and 5-lead echocardiogram recordings will be collected for 10-min while the participant rests quietly spontaneous breathing Immediately thereafter arterial systolic and diastolic pressures will be measured in triplicate via manual auscultation 30 sec between measures after which forearm and calf blood flows on the right side of the body will be measured via automated venous occlusion plethysmography Throughout the test battery the participant will be seated with both feet on the floor except for during the measurements of limb blood flow where the instrumented limbs will be elevated to facilitate venous drainage Finally a venous blood sample and body mass measurement will be obtained
Participants will then be transferred to the whole-body direct calorimeter chamber regulated to 40C and 10-15 humidity These conditions were chosen to simulate peak temperatures experienced during heatwaves and are similar to peak conditions in recent heatwaves in North America in 2018 Ottawa Ontario 34C and 58 heat index 41C and Europe in 2003 Paris France 38C and 25 heat index 38C The participant will rest quietly for 3-hours hours 1-3 within the calorimeter chamber while whole-body heat production and exchange are measured continuously At the 3-hour mark the participant will exit the calorimeter and the brief cardiovascular test battery will be performed again followed by a measurement of body mass Hours 4-6 will be spent resting in the heat in the thermal chamber adjacent to the calorimeter During this time participants will be allowed to consume a light self-provided lunch with low water content Tap water will be provided ad libitum via a self-service insulated water cooler located in the thermal chamber Another cardiovascular battery will then be performed followed by a measurement of body mass The participant will then re-enter the calorimeter where the final 3 hours will be spent hours 6-9 At the end of this period the participants will undergo a fourth and final cardiovascular test battery and a final venous blood sample and body mass measurement will be procured
Statistical analysis and sample size calculations Primary and secondary variables will be evaluated using linear mixed-effects models Time will be modelled as a repeated within-subject fixed effect and age-group will be modelled as a between-subject fixed effect Pre-heat exposure values of the outcome variable participant sex and self-reported weekly physical activity minweek as assessed via the GAQ will be included as covariates Participant identification will be modeled as a random effect in all analyses Akaikes information criterion will be used to determine random effect and variancecovariance structures
Post hoc multiple comparisons will be made on model estimated marginal means Given the small number of comparisons for each variable multiplicity corrections will not be employed Homoscedasticity will be evaluated for all models by visual assessment of residual plots Approximate normal distribution of residuals will be assessed via visual inspection of histograms and Q-Q plots Data will be log-transformed in the event that the distribution of residuals meaningfully deviates from normality For all analyses alpha will be set at 0050 Descriptive statistics will be presented as means and standard deviations Comparisons between groups andor time-points will be presented as means and 95 confidence intervals lower limit upper limit
An a priori power analysis determined that a total sample size of 19 young and 19 older adults was required to detect a difference in the rate of whole-body heat storage between groups at the end of each calorimeter session ie hours 3 and 9 with 80 statistical power In lieu of clinically meaningful data ie what would be considered a clinically meaningful change in whole-body heat storage the standardized effect size Cohens d106 was calculated based on the difference in the rate of whole-body heat storage between young and older adults over the final 30-min of a 3-hour heat exposure protocol young -2 26 kJhour older 43 54 kJhour in our previous work
Experimental Protocol Intervention 2 Experimental design The protocol for Intervention 2 is identical to that of Intervention 1 except that after the first calorimeter session and subsequent cardiovascular battery participants will exit the thermal chamber and spend 2 hours hours 5-6 resting in an air-conditioned room 23C 50 relative humidity Similar to Intervention 1 participants will be allowed to eat a small self-provided lunch during this time and consume water tap ad libitum The third cardiovascular battery will also be performed in the cooled environment As in Intervention 1 participants will then re-enter the calorimeter for the final 3 hours where they will rest in the heat for the remainder of the experimental session
Statistical analysis and sample size calculations Statistical analysis for Intervention 2 will be performed to assess whether mid-day exposure to a cooled room results in greater body heat storage following exposure such that physiological responses are similar to those of the non-cooled group by the end of the 9-hour heatwave simulation Cumulative whole-body heat storage will be evaluated using a linear mixed-effects model with experimental group modelled as a between-subject fixed effect Cumulative heat storage over the first three hours of the 9-hour exposure will be included as a covariate to account for the influence of any inter- or intra-individual factors eg sex physical activity levels measured or unmeasured impacting whole-body heat exchange and storage Comparisons of heat storage between groups will be made using model estimated marginal means
Body core temperature as estimated by rectal temperature primary outcome will be analyzed with a linear mixed effects model with experimental group two levels cooling and no-cooling modelled as a between-subject fixed effect and time as a repeated within-subject fixed effect 0- 1- 2- and 3-hours post-cooling intervention Like the model for heat storage rectal temperature at the end of the first calorimetry session ie hour 3 of the 9-hour exposure will be included as a covariate to account for the influence of any measured or unmeasured inter- or intra-individual factors impacting the body temperature responses to resting heat exposure
The effect of cooling on rectal temperature will then be assessed via two one-sided tests performed on the mixed-effects model derived estimated marginal means at each timepoint Equivalence bounds will be set to 03C which corresponds to the typical day-to-day variation of core temperature and has been suggested to reflect a meaningfuldetectable change in body temperatures in a recent study assessing the influence of cooling strategies on physiological strain in young adults Secondary variables will be similarly evaluated The level of significance will be set at P 0050 Descriptive statistics will be presented as mean standard deviation and comparisons between groups will be presented as mean 95 confidence interval
An a priori power analysis determined that a total sample size of 18 older adults in each group 36 participants total is required to confirm whether between-group differences in rectal temperature are equivalent within upper and lower bounds of 03C and -03C respectively with 80 power This corresponds to an effect size Cohens d of 10 based on the pooled-standard deviation of 03C determined from published data from our laboratory demonstrating a 02C SD 03 difference in core temperature between young and older adults and a 00C SD 03 difference in core temperature between older adults with and without type 2 diabetes following 3 hours of rest in a hot environment
Intervention 2 Determine whether short-duration exposure 2 hours to an air-conditioned environment following extreme heat exposure results in lasting reductions in physiological strain in older adults upon return to the heat
Hypotheses Intervention 1 Older adults will experience greater heat storage throughout the 9-hour simulated heatwave compared to the younger participants Consequently body core temperature will be greater in the older adults and between-group differences will be exacerbated as exposure progresses We will also explore the secondary hypothesis that differences in body temperature will be paralleled by greater alterations in cardiovascular variables and acute circulatory and intracellular inflammation in the older adults
Intervention 2 Body heat storage will be exacerbated in the older adults exposed to the cooling centre intervention upon return to the heat hours 5-6 compared to the older adults from Intervention 1 who remained in the heat Consequently body core temperature will be comparable statistically equivalent between groups by the end of exposure
Methods Participants A total of 20 young age 18-31 years and 40 older age 64-80 years adults will be recruited for the proposed project with an approximately even distribution of men and women in each intervention arm Young n 20 and older n 20 adults will complete Intervention 1 and a separate cohort of older adults n 20 will complete Intervention 2 Participants will be homogenous for anthropomorphic characteristics as well as habitual physical activity levels as verified via standardized questionnaires
Experimental Design Pre-trial instructions All participants will be asked to avoid strenuous physical activity and alcohol for 24 hours prior to all preliminary and experimental sessions and to eat a light meal 2 hours before the start of each session Participants will also be asked to consume a minimum of 500 ml of water the night before and morning of each session to ensure adequate hydration Adequate hydration will be verified upon arrival to the laboratory urine specific gravity 1025 For all sessions participants will wear athletic shorts and a sport top for women
Preliminary screening All participants will complete one preliminary evaluation a minimum of 7 days before the first experimental session During this session they will be familiarized with all procedures and measurement techniques and will complete the Get Active Questionnaire GAQ and the American Heart Association Pre-participation screening Questionnaire to assess their eligibility to participate The GAQ will also be used to assess habitual activity levels along with the Kohl Physical Activity Questionnaire Participants will also provide verbal and written informed consent at this time Body height and mass will be determined via a physician stadiometer and a high-performance weighing terminal respectively and from these measurements body surface area will be calculated
Experimental Protocol Intervention 1 Each session will commence at 0700-0900 Upon arrival to the laboratory the participant will provide a urine sample for the assessment of urine specific gravity after which a measurement of nude body mass will be obtained Participants will then insert a temperature probe for the continuous measurement of rectal temperature Thereafter participants will be instrumented for the measurement of skin temperature and 5-lead echocardiogram Baseline cardiovascular parameters will be evaluated via a brief 45 min cardiovascular test battery performed as follows Brachial arterial systolic and diastolic pressures reconstructed from arterial pressure waveforms measured at the right middle finger volume clamp technique and 5-lead echocardiogram recordings will be collected for 10-min while the participant rests quietly spontaneous breathing Immediately thereafter arterial systolic and diastolic pressures will be measured in triplicate via manual auscultation 30 sec between measures after which forearm and calf blood flows on the right side of the body will be measured via automated venous occlusion plethysmography Throughout the test battery the participant will be seated with both feet on the floor except for during the measurements of limb blood flow where the instrumented limbs will be elevated to facilitate venous drainage Finally a venous blood sample and body mass measurement will be obtained
Participants will then be transferred to the whole-body direct calorimeter chamber regulated to 40C and 10-15 humidity These conditions were chosen to simulate peak temperatures experienced during heatwaves and are similar to peak conditions in recent heatwaves in North America in 2018 Ottawa Ontario 34C and 58 heat index 41C and Europe in 2003 Paris France 38C and 25 heat index 38C The participant will rest quietly for 3-hours hours 1-3 within the calorimeter chamber while whole-body heat production and exchange are measured continuously At the 3-hour mark the participant will exit the calorimeter and the brief cardiovascular test battery will be performed again followed by a measurement of body mass Hours 4-6 will be spent resting in the heat in the thermal chamber adjacent to the calorimeter During this time participants will be allowed to consume a light self-provided lunch with low water content Tap water will be provided ad libitum via a self-service insulated water cooler located in the thermal chamber Another cardiovascular battery will then be performed followed by a measurement of body mass The participant will then re-enter the calorimeter where the final 3 hours will be spent hours 6-9 At the end of this period the participants will undergo a fourth and final cardiovascular test battery and a final venous blood sample and body mass measurement will be procured
Statistical analysis and sample size calculations Primary and secondary variables will be evaluated using linear mixed-effects models Time will be modelled as a repeated within-subject fixed effect and age-group will be modelled as a between-subject fixed effect Pre-heat exposure values of the outcome variable participant sex and self-reported weekly physical activity minweek as assessed via the GAQ will be included as covariates Participant identification will be modeled as a random effect in all analyses Akaikes information criterion will be used to determine random effect and variancecovariance structures
Post hoc multiple comparisons will be made on model estimated marginal means Given the small number of comparisons for each variable multiplicity corrections will not be employed Homoscedasticity will be evaluated for all models by visual assessment of residual plots Approximate normal distribution of residuals will be assessed via visual inspection of histograms and Q-Q plots Data will be log-transformed in the event that the distribution of residuals meaningfully deviates from normality For all analyses alpha will be set at 0050 Descriptive statistics will be presented as means and standard deviations Comparisons between groups andor time-points will be presented as means and 95 confidence intervals lower limit upper limit
An a priori power analysis determined that a total sample size of 19 young and 19 older adults was required to detect a difference in the rate of whole-body heat storage between groups at the end of each calorimeter session ie hours 3 and 9 with 80 statistical power In lieu of clinically meaningful data ie what would be considered a clinically meaningful change in whole-body heat storage the standardized effect size Cohens d106 was calculated based on the difference in the rate of whole-body heat storage between young and older adults over the final 30-min of a 3-hour heat exposure protocol young -2 26 kJhour older 43 54 kJhour in our previous work
Experimental Protocol Intervention 2 Experimental design The protocol for Intervention 2 is identical to that of Intervention 1 except that after the first calorimeter session and subsequent cardiovascular battery participants will exit the thermal chamber and spend 2 hours hours 5-6 resting in an air-conditioned room 23C 50 relative humidity Similar to Intervention 1 participants will be allowed to eat a small self-provided lunch during this time and consume water tap ad libitum The third cardiovascular battery will also be performed in the cooled environment As in Intervention 1 participants will then re-enter the calorimeter for the final 3 hours where they will rest in the heat for the remainder of the experimental session
Statistical analysis and sample size calculations Statistical analysis for Intervention 2 will be performed to assess whether mid-day exposure to a cooled room results in greater body heat storage following exposure such that physiological responses are similar to those of the non-cooled group by the end of the 9-hour heatwave simulation Cumulative whole-body heat storage will be evaluated using a linear mixed-effects model with experimental group modelled as a between-subject fixed effect Cumulative heat storage over the first three hours of the 9-hour exposure will be included as a covariate to account for the influence of any inter- or intra-individual factors eg sex physical activity levels measured or unmeasured impacting whole-body heat exchange and storage Comparisons of heat storage between groups will be made using model estimated marginal means
Body core temperature as estimated by rectal temperature primary outcome will be analyzed with a linear mixed effects model with experimental group two levels cooling and no-cooling modelled as a between-subject fixed effect and time as a repeated within-subject fixed effect 0- 1- 2- and 3-hours post-cooling intervention Like the model for heat storage rectal temperature at the end of the first calorimetry session ie hour 3 of the 9-hour exposure will be included as a covariate to account for the influence of any measured or unmeasured inter- or intra-individual factors impacting the body temperature responses to resting heat exposure
The effect of cooling on rectal temperature will then be assessed via two one-sided tests performed on the mixed-effects model derived estimated marginal means at each timepoint Equivalence bounds will be set to 03C which corresponds to the typical day-to-day variation of core temperature and has been suggested to reflect a meaningfuldetectable change in body temperatures in a recent study assessing the influence of cooling strategies on physiological strain in young adults Secondary variables will be similarly evaluated The level of significance will be set at P 0050 Descriptive statistics will be presented as mean standard deviation and comparisons between groups will be presented as mean 95 confidence interval
An a priori power analysis determined that a total sample size of 18 older adults in each group 36 participants total is required to confirm whether between-group differences in rectal temperature are equivalent within upper and lower bounds of 03C and -03C respectively with 80 power This corresponds to an effect size Cohens d of 10 based on the pooled-standard deviation of 03C determined from published data from our laboratory demonstrating a 02C SD 03 difference in core temperature between young and older adults and a 00C SD 03 difference in core temperature between older adults with and without type 2 diabetes following 3 hours of rest in a hot environment
Study Oversight
Has Oversight DMC:
None
Is a FDA Regulated Drug?:
False
Is a FDA Regulated Device?:
False
Is an Unapproved Device?:
None
Is a PPSD?:
None
Is a US Export?:
None
Is an FDA AA801 Violation?:
None