Aging, Heat Stress
Conditions
Brief summary
This study will test the hypothesis that the drugs propranolol and metoprolol will result in greater increases in core body temperature during 3 hours of extreme heat exposure in older adults.
Detailed description
Older individuals are more likely to die or become ill during heat waves. During the 1995 Chicago heat wave, there was 35% increase in hospital admissions for individuals older than 65 years of age. Moreover, adults over the age of 65 have a heat-related death rate that is more than double any other age group. Therefore, with an increasing elderly population that is expected to rise by 60% (to 78 million) by 2035, the causes of this excess mortality must be understood to better protect the ageing United States population. It is notable that selective and non-selective beta blocker drugs are commonly prescribed to older individuals with cardiovascular diseases. In younger individuals exposed to a heat stress, beta blocker administration reduced whole-body sweat rate and skin blood flow responses resulting in greater increases in core body temperature. Notably, nothing is known regarding the effects of beta blockers on thermoregulatory responses during heat exposure in older individuals. This project will evaluate core body temperature responses to selective and non-selective beta blocker drugs during simulated heat wave exposure in older individuals.
Interventions
OTHERAmbient Heat
Subjects will spend 3-hours in a heat chamber at 41°C and 40% humidity.
Sponsors
University of Texas Southwestern Medical Center
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
BASIC_SCIENCE
Masking
DOUBLE (Subject, Investigator)
Masking description
Neither the participants nor the researchers will know whether the participant received the placebo or one of the beta blocking drugs. Masking will be performed by the research nurse who will know which drug the participant received.
Intervention model description
We will first collect participant demographics, medical history, anthropometrics (body mass, height and composition). Individuals will be exposed to 3 hours in a hot environmental condition after receiving the placebo, propranolol, or metoprolol. Prior to entering the environmental chamber, baseline data will be collected while resting in a thermoneutral environment. Drug or placebo will be administered. Participants will then enter the environmental chamber and will be seated in a semi-recumbent position on a chair with breathable fabric to minimize impediments to heat dissipation. Periodically throughout the simulated heat-wave participants will lightly exercise to simulate metabolic heat production associated with activities of daily living (\ 3 metabolic equivalents; METS). Throughout the heat-wave simulation trials we comprehensively evaluate the thermoregulatory and cardiovascular responses.
Eligibility
Sex/Gender
ALL
Age
65 Years to No maximum
Healthy volunteers
Yes
Inclusion criteria
* Healthy and free of any significant medical problems * Normal resting electrocardiogram * 65+ years of age * Controlled cholesterol of less than 200 mg/dl * Controlled blood pressure of less than 140/90 mmHg
Exclusion criteria
* Known diseases or other chronic conditions requiring regular medical therapy including cancer, diabetes, neurological diseases, uncontrolled hypertension, and uncontrolled hypercholesterolemia * Serious abnormalities detected on routine screening * Taking prescribed medications or over-the-counter medications that have known influences on either cardiac function or sweating * Current smokers, as well as individuals who regularly smoked within the past 3 years * body mass index ≥31 kg/m2
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Internal temperature | Continuously throughout the 3-hour heat exposure. | The change in internal temperature to the 3-hour heat exposure will be measured. |
| Whole body sweat rate | Nude body mass will be measured before and after the 3-hour heat exposure. | Whole body sweat rate will be measured via changes in pre/post nude body mass. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Arterial blood pressure | Continuously throughout the 3-hour heat exposure. | Systolic and diastolic arterial blood pressures will be measured via a brachial blood pressure cuff. |
| Heart rate | Continuously throughout the 3-hour heat exposure. | Heart rate will be measured via electrocardiogram. |
Countries
United States
Contacts
Primary ContactErin Harper, MS
Backup ContactCourtney Kirby, RN
Outcome results
None listed