MOST WOULD associate the word “hypothermia” with the severe form of the condition. In fact, lesser degrees of hypothermia occur when the body loses heat faster than it can produce it – something that is very common in diving. Significant drops in body temperature will affect mental activity, reasoning and cognitive function, increasing the risk of errors during diving, which may ultimately result in accidents. Inert gas exchange is also influenced by body temperature and this may contribute to decompression sickness.
Even though technical divers are usually well prepared thermally against hypothermia, other non-thermal factors have been shown to affect the body’s response to cold exposure: inert gas narcosis, hydrostatic pressure, hypoglycaemia, dehydration, age, seasickness, and finally, body size, shape and composition! So a mature thin diver (like me) might consider wearing extra layers if planning a deep or long dive.
Instead of boring you with the physiology and effects of hypothermia, I thought I could do more good by talking about a related, extremely common and often unrecognised problem. Most of the problems I see as a diving doctor are usually a result of thermal cooling of the head. Heat loss from the head in cold water can account for over half the resting metabolic heat production.
The patient is usually a sport diver diving in 15–25°C water without a hood protecting the head. Diving schools do not usually give head protection to novice divers in warm water for the initial dives as this gives a greater sense of freedom, reduces claustrophobia and enhances hearing. The reasoning is that there is then a greater chance of their booking a course for more dives. The problem is that dive schools commonly end up losing business because the diver has ear and sinus problems related to exposure.
A common scenario is a diver doing more than one dive without a hood. Thermal cooling of the head will occur even if the diver is feeling perfectly warm and comfortable, as the water is always 10 degrees or more colder than the head. This cooling induces mucus production in the air-filled cavities of the head, namely the sinuses and middle ears. These secretions may block the opening into these cavities so that sinus barotrauma or middle ear barotrauma may result. The former may produce sinus pain, sometimes with bleeding in the mask, which though dramatic in itself, is not usually a serious condition. The latter usually manifests as earache, fullness in the ear, a feeling of water in the ear, vertigo and tinnitus. If the diver persists in diving with this condition, complications like a eardrum ruptures or ear infections may result.