As part of our first newsletter, I thought I would write a short piece on the underlying physiological changes happen as we age, and why this makes over 65s more susceptible to heat stress. I won’t cover all risk factors or detail the underlying processes of these changes. Instead, I will briefly touch on key factors you may already have some understanding of, related to body temperature regulation, heart function, fluid regulation and temperature sensitivity – all of which change as we get older.
First, let’s get familiar with how the body removes heat. Heat is transferred between our body and the environment through several pathways. These are convection, radiation, conduction, and evaporation. Usually in the context of heat stress, the body primarily relies on the evaporation of sweat to remove heat into the environment. The heat stored in the body’s core is transferred through dilated blood vessels to the skin where warm blood can be cooled by the evaporation of sweat.
So, what happens as we age? Several key biological functions change, lessening our ability to remove excess heat. For example, sweat glands don’t produce as much sweat, meaning less heat can be removed through evaporation. We also have changes in our circulatory system which influence how well our blood vessels work. These changes include loss of vessel elasticity (making it harder for blood vessels to dilate) and reductions in the automatic control of blood pressure and blood flow to the skin. Additionally, changes in the heart cause less blood volume to be pumped from each heartbeat. Because of the stress high temperatures put on our bodies, the body sends most of our blood to vital organs to maintain function, instead of the skin’s surface to cool down.
Finally, we see changes in kidney function, making it harder for our body to hold onto water. Paired with a lowered ability to feel thirsty, becoming dehydrated is more likely. Thermal sensitivity to the heat is also blunted for the very old, meaning those people can be at risk without realising.
Because of these kinds of age-related changes, the Ethos Project is trying to prevent heat illness and injury of older persons in their own homes. Our understanding of the principles in which heat can be best removed from the body will allow us to individualise alerts and cooling strategies for restoring the ability of older persons to keep cool.
