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.

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.

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

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.