Altered cardiac β1 responsiveness in hyperthermic older adults

Area of Science:

• Cardiovascular Physiology
• Gerontology
• Thermoregulation

Background:

• Passive heating impairs cardiac output increase in older adults compared to younger adults.
• This impairment may stem from reduced stroke volume maintenance via ionotropic or chronotropic mechanisms.
• Understanding age-related cardiac responses to heat stress is crucial for public health.

Purpose of the Study:

• To investigate the combined effects of aging and hyperthermia on cardiac responsiveness to dobutamine.
• To determine if older adults have impaired inotropic or chronotropic responses to beta-adrenergic stimulation during heat stress.

Main Methods:

• Eleven young and eight older adults underwent normothermic and hyperthermic trials.
• Dobutamine was administered intravenously at two doses (5 and 15 µg/kg/min) during both thermal conditions.
• Cardiac function was assessed using echocardiography, measuring parameters like peak systolic mitral annular velocity (S').

Main Results:

• Heart rate responses to dobutamine were similar between age groups in both normothermic and hyperthermic conditions.
• While normothermic, the increase in S' (left ventricular systolic function index) with dobutamine was similar between groups.
• During hyperthermia, the increase in S' in response to dobutamine was significantly attenuated in older adults.

Conclusions:

• Healthy older individuals demonstrate attenuated inotropic responsiveness to dobutamine during hyperthermia.
• Chronotropic responsiveness to dobutamine is maintained in older adults even during hyperthermia.
• Older individuals have a diminished capacity to enhance cardiomyocyte contractility via beta-1 adrenergic mechanisms when exposed to heat stress.