Introduction

Geriatric Essentials

• The elderly are particularly susceptible to hyperthermia and hypothermia; either can develop even when elderly people stay indoors.
• Many commonly used drugs predispose the elderly to hyperthermia or hypothermia.
• Hyperthermia and hypothermia increase risk of death from serious comorbidities, and the more severe a comorbidity, the greater the risk of death from hyperthermia or hypothermia.

Aging and temperature regulation: Under usual environmental conditions, convection and radiation account for 65% of heat loss; evaporation from skin and lungs contributes another 30%. The hypothalamus regulates heat loss through neuroendocrine and autonomic mechanisms; heat causes blood vessels in the skin to dilate, and sweating increases as a result of cholinergic discharge. Vasodilation, in turn, reflexively increases heart rate and cardiac output.

When ambient temperature exceeds body surface temperature, heat is no longer lost through convection and radiation but is absorbed instead. Evaporation of sweat is the last mechanism by which heat can be lost, but increased humidity can prevent cooling by this mechanism.

Aging appears to reduce sweat volume (from up to 2 L/h of fluid and 10 to 100 mEq/L of Na in younger adults). In elderly people, sweating appears to cool the body less effectively. Initiation of sweating requires a higher core body temperature. Also, many sweat glands become fibrotic, and connective tissue around sweat glands becomes less vascular. As a result, each sweat gland produces less sweat.

Increased ambient heat can greatly increase the demand for cutaneous blood flow and thus increase cardiac output. Thus, increased ambient heat and humidity appear to exacerbate heart failure; the lower the cardiac reserve, the less a person is able to withstand high ambient temperatures.

With aging, perception of cold diminishes. Thermoregulatory responses to cold--shivering, which increases metabolic heat production, and peripheral vasoconstriction, which decreases body heat loss--also decrease because responsiveness to endogenous catecholamines decreases. Shivering is less efficient in producing heat because lean body mass is decreased.

Disorders due to heat: Environmental heat can cause hyperthermia, which, depending on its severity, may be accompanied by heat edema, heat cramps, heat exhaustion, or heatstroke. Heat cramps are muscle cramps that occur during or shortly after intense physical activity done during hot, humid weather. They usually affect people who can produce large quantities of sweat; thus, they tend to occur in young, fit people and do not often occur in the elderly.

Disorders due to cold: Environmental cold can cause chilblains, frostnip, frostbite, immersion foot, or hypothermia.

This topic was last updated February 2006.