Mitigating Heat-induced Physiological Strain and Discomfort in Older Adults Via Lower Limb Immersion and Neck Cooling

Aging Clinical Trial

Official title:

Evaluating the Efficacy of Lower Leg Immersion With and Without Neck Cooling for Limiting Heat Strain in Elderly Adults During Extreme Heat Events

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT05601713
• Other study ID #: H-11-20-6234
• Status: Completed
• Phase: N/A
• Start date: September 28, 2022
• Est. completion date: May 4, 2023

Study information

• Verified date: May 2023
• Source: University of Ottawa
• Contact: n/a
• Is FDA regulated: No
• Study type: Interventional

Clinical Trial Summary

The incidence and severity of hot weather and extreme heat events (heat waves) is increasing. As such, there is an urgent need to develop heat-alleviation strategies that can provide targeted protection for older adults who are at an elevated risk for heat-induced illnesses or death due to impaired body temperature and cardiovascular regulation. While air-conditioning provides the most effective protection from extreme heat, it is inaccessible for many individuals and cannot be used during power outages (e.g., heat-related rolling blackouts). Immersion of the lower limbs in cold water and/or the application of cold towels to the neck have been recommended as simple and sustainable alternatives to air-conditioning. However, empirical data to support the efficacy of these interventions for mitigating physiological strain and discomfort in older adults is lacking. To address this knowledge gap, this randomized crossover trial will evaluate the effect of lower limb immersion with and without application of cold towels to the neck on body core temperature, cardiovascular strain and autonomic function, dehydration, and thermal comfort in adults aged 65-85 years exposed to simulated heat wave conditions (38°C, 35% relative humidity) for 6 hours.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 18
• Est. completion date: May 4, 2023
• Est. primary completion date: May 4, 2023
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: All
• Age group: 65 Years to 85 Years

Eligibility

Inclusion Criteria:

• Male or female adults.
• Aged 65-85 years.
• Non-smoking.
• English or French speaking.
• Ability to provide informed consent.

Exclusion Criteria:

• Physical restriction (e.g., due to disease: 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 (e.g., medications increasing risk of heat-related illness; beta blockers, anticholinergics, etc.)
• Cardiac abnormalities identified via 12-lead ECG during an incremental exercise test to volitional fatigue (performed for all participants).
• Peak aerobic capacity (VO2peak), as measured during an incremental exercise test to volitional fatigue, exceeding the 50th percentile of age- and sex-specific normative values published by the American College of Sports Medicine (ACSM).

Related Conditions & MeSH terms

• Aging
• Heat Stress
• Heat Stress Disorders
• Hyperthermia
• Sprains and Strains
• Syncope

Intervention

Other:
• No cooling (control)
Participants are exposed to 38°C, 35% relative humidity for 6 hours without cooling interventions (control condition). Drinking water is available ad libitum.
• Lower limb immersion
Participants are exposed to 38°C, 35% relative humidity for 6 hours. For the last 40 min of each hour, participants lower limbs are immersed in cool water (~20°C) up to the level of mid calf. Drinking water is available ad libitum.
• Lower limb immersion + neck cooling
Participants are exposed to 38°C, 35% relative humidity for 6 hours. For the last 40 min of each hour, participants lower limbs are immersed in cool water (~20°C) up to the level of mid calf. During limb immersion, a towel soaked in cool water (~20°C) is placed around the participants neck. The towel is re-wet half way through the 40-min limb immersion. Drinking water is available ad libitum.

Locations

Country	Name	City	State
Canada	University of Ottawa	Ottawa	Ontario

Sponsors (1)

Lead Sponsor	Collaborator
University of Ottawa

Country where clinical trial is conducted

Canada, 

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	Core temperature	Rectal temperature measured as an index of core temperature (15 minute average)	End of heat exposure (hour 6)
Secondary	Heart rate	Heart rate derived from 3-lead electrocardiogram (15 minute average)	End of heat exposure (hour 6)
Secondary	Systolic blood pressure	Systolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)	End of heat exposure (hour 6)
Secondary	Diastolic blood pressure	Diastolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)	End of heat exposure (hour 6)
Secondary	Rate pressure product	Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.	End of heat exposure (hour 6)
Secondary	Heart rate variability: SDNN	Standard deviation of normal-to-normal RR intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).	End of heat exposure (hour 6)
Secondary	Heart rate variability: RMSSD	Root mean squared standard deviation of normal-to-normal RR intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the seated position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of seated rest).	End of heat exposure (hour 6)
Secondary	Cardiac response to standing from supine (30:15 ratio)	Cardiac response to standing evaluated as the ratio between the highest RR interval (lowest heart rate) measured at the 30th heart beat after standing from supine (+/- 5 beats) and the lowest RR 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).	End of heat exposure (hour 6)
Secondary	Systolic response to standing from supine	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).	End of heat exposure (hour 6)
Secondary	Integrated baroreflex sensitivity (sit-to-stand maneuvers)	Determined from beat-to-beat arterial pressures and heart rate (volume-clamp technique) during 5 min of sit-to-stand maneuvers performed at 0.05 Hz (3 cycles per min; 15 total cycles).	End of heat exposure (hour 6)
Secondary	Fluid consumption	Cumulative fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure.	End of heat exposure (hour 6)
Secondary	Fluid loss	Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption)	End of heat exposure (hour 6)
Secondary	Change in plasma volume	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.	End of heat exposure (hour 6)
Secondary	Thermal comfort	Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from extremely uncomfortable to extremely comfortable (midpoint: neutral).	End of heat exposure (hour 6)
Secondary	Orthostatic intolerance symptoms assessment	Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance during the last 1-2 hours (including the lying-to-standing and sit-to-stand 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".	End of heat exposure (hour 6)