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Completed

NCT Number: NCT05601713

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

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.

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Key information

Conditions

Hyperthermia Aging Body Temperature Changes Heat Stress Heat Stress Disorders Heat Syncope Pathological Conditions, Signs and Symptoms Signs and Symptoms Weather; Heat Wounds and Injuries

Age range

65 year–85 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

University of Ottawa

Ottawa, Ontario, K1N6N5, Canada

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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).

Treatment and study plan

No cooling (control)

Other

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

Other

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

Other

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.

Primary outcomes

  1. Core temperature

    Time frame: End of heat exposure (hour 6)

    Rectal temperature measured as an index of core temperature (15 minute average)

Secondary outcomes

  1. Heart rate

    Time frame: End of heat exposure (hour 6)

    Heart rate derived from 3-lead electrocardiogram (15 minute average)

  2. Systolic blood pressure

    Time frame: End of heat exposure (hour 6)

    Systolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)

  3. Diastolic blood pressure

    Time frame: End of heat exposure (hour 6)

    Diastolic blood pressure measured in triplicate via automated oscillometry (~60 seconds between measures)

  4. Rate pressure product

    Time frame: End of heat exposure (hour 6)

    Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.

  5. Heart rate variability: SDNN

    Time frame: 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).

  6. Heart rate variability: RMSSD

    Time frame: 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).

  7. Cardiac response to standing from supine (30:15 ratio)

    Time frame: 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).

  8. Systolic response to standing from supine

    Time frame: 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).

  9. Integrated baroreflex sensitivity (sit-to-stand maneuvers)

    Time frame: 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).

  10. Fluid consumption

    Time frame: 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.

  11. Fluid loss

    Time frame: 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)

  12. Change in plasma volume

    Time frame: 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.

  13. Thermal comfort

    Time frame: 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).

  14. Orthostatic intolerance symptoms assessment

    Time frame: 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".

Sponsors and collaborators

Lead sponsor

University of Ottawa

Other

Registry information

Official study title

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

Important dates

Study start
2022
Primary completion
2023
Study completion
2023
First posted
Nov 1, 2022
Registry last updated
May 10, 2023

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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