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

Not Applicable

Completed

• Conditions: Heat Syncope; Weather; Heat; Aging; Hyperthermia; Heat Stress
• Interventions: Other: Lower limb immersion + neck cooling; Other: Lower limb immersion; Other: No cooling (control)

• Registration Number: NCT05601713
• Lead Sponsor: University of Ottawa

Brief 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.

Detailed Description

Not available

Study Timeline

• Study Start: 2022-09-28
• Study First Submitted: 2022-10-19
• Study First Submitted QC: 2022-10-31
• Study First Posted: 2022-11-01
• Status Verified: 2023-05
• Primary Completion: 2023-05-04
• Study Completion: 2023-05-04
• Last Update Submitted: 2023-05-09
• Last Update Posted: 2023-05-10

Recruitment & Eligibility

• Status: COMPLETED
• Sex: All
• Target Recruitment: 18

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).

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Lower limb immersion + neck cooling	Lower limb immersion + neck cooling	Adults aged 65-85 years with or without type 2 diabetes and/or hypertension.
Lower limb immersion	Lower limb immersion	Adults aged 65-85 years with or without type 2 diabetes and/or hypertension.
No cooling intervention (control)	No cooling (control)	Adults aged 65-85 years with or without type 2 diabetes and/or hypertension.

Primary Outcome Measures

Name	Time	Method
Core temperature	End of heat exposure (hour 6)	Rectal temperature measured as an index of core temperature (15 minute average)

Secondary Outcome Measures

Name	Time	Method
Rate pressure product	End of heat exposure (hour 6)	Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.
Heart rate	End of heat exposure (hour 6)	Heart rate derived from 3-lead electrocardiogram (15 minute average)
Diastolic blood pressure	End of heat exposure (hour 6)	Diastolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures)
Fluid consumption	End of heat exposure (hour 6)	Cumulative fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure.
Change in plasma volume	End of heat exposure (hour 6)	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.
Orthostatic intolerance symptoms assessment	End of heat exposure (hour 6)	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".
Systolic blood pressure	End of heat exposure (hour 6)	Systolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures)
Cardiac response to standing from supine (30:15 ratio)	End of heat exposure (hour 6)	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).
Thermal comfort	End of heat exposure (hour 6)	Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from extremely uncomfortable to extremely comfortable (midpoint: neutral).
Heart rate variability: RMSSD	End of heat exposure (hour 6)	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).
Systolic response to standing from supine	End of heat exposure (hour 6)	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).
Integrated baroreflex sensitivity (sit-to-stand maneuvers)	End of heat exposure (hour 6)	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).
Fluid loss	End of heat exposure (hour 6)	Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption)
Heart rate variability: SDNN	End of heat exposure (hour 6)	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).

Trial Locations

Locations (1)

University of Ottawa; 🇨🇦 Ottawa, Ontario, Canada