Back in April, the hot sun but cold wind tempted Tracey and I away for a couple of nights by the sea.  When I suggested this as a treat for a birthday, bags were packed for exotic Southern European sun until I admitted we were going to Weymouth.  Talk about polar opposites – you may have guessed where the topic of hypothermia and hyperthermia is going to come in! Well, it all turned out well. The weather was fantastic and with relatively few people around, the Dorset coast rivals anywhere in the world.  Snuggled in bed on the first morning, I was informed that a sea swim was first on the day’s agenda.  Without wet suits. Or dry suits. Just swim suits.  Checked the water temperature….10 degrees Centigrade.  Hmm. But off we went, towels in hand to Preston beach where a brisk easterly was coming in off the sea. 

Oh I know cold water swimming is the thing but you really have to harden yourself off gradually.  Bit like seedlings I thought as the water rose to my neck and created a hyperventilation response.  Quite involuntarily, I gasped for breath just like Gabi Roslin in the ice with Wim Hof. Had my head been under the water, I would certainly have aspirated a lung-full.  Careful to stay in my depth, there was no problem.  Certainly not for Tracey who was breast-stroking for England through the surf and shouting at me to ‘GET IN’. 

Luckily I couldn’t answer, the effort of breathing taking away any power of speech. Eventually I regained control over my respiration and felt proud of my 5 minutes spent in the water. Not going to discuss Tracey’s 13 minutes but I must stress she regularly practises cold water immersion and so did I up until last October.  (The Outdoor Swimming Society gives good advice on the important safety aspects of cold water immersion).  Naturally, these temperature extremes bring me onto the topic of hyperthermia and hypothermia.

This episode got me thinking about two really interesting physiological topics that affect our pets (and us); control of respiration and body temperature.  We take both for granted, along with other automatic bodily functions, until something goes wrong.  Breathing hard and rapidly is a normal response to muscular exertion. An increase in carbon dioxide as a by-product of energy production causes this.  Terrestrial mammals are exquisitely sensitive to increases in CO2 that causes acid to increase (lowering pH) leading to respiratory stimulation via a brain centre. In the lungs, the acid is converted back into CO2 and expired, allowing recovery. 

The system works well providing lungs and circulation are all hunky-dory but dogs and especially cats can accumulate fluid around or inside the lungs due to heart failure, infection or trauma and this can severely compromise function.  CO2 levels increase, O2 decreases and unless lung function improves, the situation can become rapidly life-threatening.  Immediate treatment is oxygen therapy and urgent attempts to reduce the fluid, either with a diuretic or by a chest drain, depending on its location.  Long-term, effective treatments can work in some cases for months or even years, depending on the underlying cause.

So what happened to me in the cold water? Very little muscular effort involved so why the hyperventilation? Well, an initial gasp followed by uncontrolled rapid breathing is part of the cold water shock response. We think it’s due to skin temperature sensors sending a barrage of signals to the respiratory centre, bypassing the normal acid-sensitive control system.  This response can cause many human and animal deaths by drowning, almost certainly.  As I said, if my head had been underwater, I would have inhaled enough sea to be in serious trouble. 

Happily, we see very few drowning cases among dogs and cats. That said, very old animals that fall into garden ponds or swimming pools are not unknown.  My dear departed Border Terrier, Trilby, did exactly that about a year ago.  Luckily, I’d placed an inclined slab in the pond that gave him enough purchase to keep his head above water until I rescued him.  He wasn’t allowed out unsupervised again!

Cold water immersion has obvious effects on thermoregulation and control of body temperature is another critical element for all warm-blooded animals. For dogs, hypothermia is much less common than hyperthermia unless there is a specific medical problem.  Why? I guess they are covered in fur that water often fails to penetrate and working dogs are habituated to throwing themselves into cold water.  For the healthy adult dog, low temperatures are not usually a problem although toy breeds with sparse fur coats and little fat certainly can get cold as can newborn puppies and kittens. Without a regular supply of mum’s milk, the neonate’s body temperature falls quickly, making them weak and unwilling to feed.  Here’s a vicious circle that will take the lives of young animals in a few hours. Hence our advice to weigh newborn puppies and kittens daily and keep them very warm.

Hyperthermia is always a summertime issue and although I have never seen a heat-struck cat, I have seen plenty of dogs with heat-stroke.  Why is this? Cats typically don’t get locked in cars, and they avoid exercising in the midday sun.  Clearly blessed with far more intelligence, on hot days cats seek a cool corner and go to sleep.  They do have their evolutionary background of hot climates but all the same, they modify their behaviour to suit the conditions.  Very wise and a lesson for us all. The key take away? Be vigilant – hypothermia and hyperthermia can affect us all, no matter our species.