Understanding How Your Blood Reacts To Cold Can Save Your Life

By Lizzie Bennett

Every winter we are bombarded by information about the cold and how to protect ourselves from it and from health issues associated with it.

Wrap up warm, keep one room heated to a minimum 18°C, avoid hypothermia by…, eat and drink warm food, get the boiler serviced to avoid carbon monoxide poisoning, turn off the Christmas tree lights to avoid fire. It’s endless.

Every winter in the UK upwards of 20,000 extra deaths occur that are attributed in one way, or another to the cold. These are referred to as ‘excess deaths from all causes’ on the official statistics. Now that wording makes it sound like the medics record which deaths are caused by the cold. In some cases they do, but in most they don’t the figure is derived by taking the figure for the deaths recorded during non-winter months and taking it away from the winter months total, the number left is the excess deaths from all causes figure.

Now, some things that happen in winter are fully understandable and clearly lead to more deaths than would occur in drier warmer weather. Road accidents, domestic boiler incidents, house fires, drowning from falling through ice, asthma, pneumonia, falls, influenza and so on all have a higher incidence level in winter than at any other time of year.

There are however other deaths that occur, that are directly attributable to cold weather that never even get a mention as weather related. We are all aware that heavy duty snow shovelling can cause a person to keel over with a heart attack, but this is not the main cause of heart attacks during cold weather. Heart attack and strokes, or to give them their proper names, cardiac arrest and cerebo-vascular accident are responsible for thousands of cold weather deaths each year. They are listed on the statistics as exactly what they are, but as a heart or brain does not have ‘packed up due to cold weather’ stamped on it at autopsy it’s hard to absolutely say the death was caused by the weather.

Even though they were.

These two conditions are entirely different but they do have one thing in common…blood. Both conditions are caused by a clotting of, or restriction of, the flow of blood through an organ, namely the heart and the brain, and this is blood supply comes in.

Although blood is a liquid, it’s viscous, it has a stickiness to it that some fluids, such as water, don’t have. Like motor oil, blood becomes more viscous if its left in the open air, and it becomes more viscous when it is cooled, and less viscous when it’s warmed. So, when it’s trundling around in your blood vessels, for the most part all is well, it’s warm and fluid and goes on it’s way doing it’s thing.

In some parts of your body blood vessels are far nearer the surface than you might think, look at the inside of your wrists, your jugular vein that you may see pulsing in your neck, the veins visible at your temples, and in the case of newborns under the thin skin of their scalp. Here the blood dissipates heat far more readily than it does from other parts of your body. When it cools, it becomes a little stickier, a little more viscous. Cool it further still, like on a really cold day, and it becomes even more viscous. Sticky blood cells stick together and form tiny clumps, which turn into bigger clumps quite quickly, certainly within a couple of hours.

So. Lets have an example. We’ll call him John. John has a desk job in the city, he travels by train as the congestion charge is exorbitant.

He is fit, going to the gym three times a week and plays football on a weekend. That and running around after his three kids is enough he feels. He gets up, showers has a healthy breakfast of whole wheat cereal and fruit, a glass of orange juice and sets off.

He drives to the station, parks and makes his way to the platform. He is wearing a shirt, suit and tie and thick overcoat. He realises when he is standing on the open platform that he’s shivering, he has left his gloves and scarf in the car and doesn’t have time to fetch them.

Still the train is hopefully running on time and will be here soon. The blood travelling around John’s’ body is cooling as it moves past his unprotected wrists and up to his unprotected neck, a shirt and tie is not that warm, and on to his unprotected head. As it moves back down into the protected areas of his body it warms and becomes more fluid again.

He is shivering which increases his heart rate, making the blood move faster, so more blood is passing the exposed areas more often and passing through the warm areas at a faster rate. After a few minutes his blood is slightly more sticky than it was when he arrived on the platform. He continues to shiver. A couple of blood cells have agglutinated, clumped together in one of his veins.

He doesn’t know this has happened, he feels nothing, but the process leading to John’s’ possible demise has begun. The longer he stands there in the cold the more cells will bump into the still microscopic clump and stick to it, increasing its size.

At this point there are several scenarios:

1. The clot increases in size lodges in his brain, blocks the flow of blood and he has a stroke.

2. The clot increases in size lodges in his lungs and he has a pulmonary embolism

3. The clot increases in size, lodges in his heart, blocks the flow of blood and he has a cardiac arrest.

4. The train comes, John warms up before the clot increases in size and he survives this particular encounter.

Today is not John’s lucky day. The train is late. The thing with clots is the bigger they get the more blood cells bump into and stick to them. By the time John gets on the train fifteen minutes later the clot is no longer microscopic, but it is stuck in place for now. John feels a touch off colour but has put it down to the shivering and shaking he has been doing for 20 minutes.

He gets of the train and makes his way to his office, glad to be in the warm at last. As he settles at his desk, he warms up, his blood gets less sticky and starts moving at its proper rate around his body. The clot in his vein gets less sticky also, the clot becomes less stable as his blood warms.

John doesn’t feel too good, he’s a bit pale, his chest is a little tight, the fingers on his left hand feel odd, his left arm is tingling. These sensations pass almost as quickly as they arrived so he has another cup of coffee and settles down to get some work done.

Looking out of the window John can see it’s started to snow. An hour later it’s snowing faster and at 4pm he decides to head home, an hour before he usually does but the weather is worsening.

Predictably his train is delayed. Standing on the draughty platform because the waiting rooms are all full of other like-minded individuals, he pulls up his collar and stamps his feet to stay warm. Just as it did in the morning his blood starts to get a bit sticky, it’s not flowing as well as it usually does due to the cold.

The train comes and an hour later he is in his car heading home. It’s only a short journey from the station so the car doesn’t get that warm.

The back wheels of his car spin a bit as he drives up the small incline of his drive. The snow is six inches deep and shows no sign of slowing. He will need the car tomorrow and so decides to play with the kids for half an hour and then clear it off, putting down some rock salt and grit so that’s it’s clear for the morning.

This time he is prepared for the cold and puts on full cold weather gear. Hat, scarf, gloves and windproof coat. Within minutes he is sweating and feels a little dizzy. His warm blood has destabilized the clot and bits of it are breaking off. With no warning his chest tightens, he tries to shout for help but hasn’t got the breath to do so. Feeling like a huge weight is crushing him he falls sidewards, hitting the car, setting of the alarm. By the time his wife comes outside to see why the car alarm is going off John is dead. He was 39 years old.

Many people die each year of cold related strokes, heart attacks and pulmonary emboli. Even wrapped up, some people with conditions that make them prone to sticky blood will still die, but many thousands more would survive if they dressed in weather appropriate clothing.

It’s not rocket science that the colder it gets the more we need to wrap up. Cover your head neck and wrists when out in extreme cold. The ankles also have vessels near the surface so socks are a must, and boots in snow or when trouser legs are likely to get soaked exposing the skin to excessive cold. Wearing several layers means you can take something off if you get too hot and makes managing your temperature far easier.

Do you remember your mother shouting:

Don’t forget your hat, scarf and gloves or you’ll catch your death?

She had a point. Don’t become a weather related statistic, stay safe this winter

Contributed by Lizzie Bennett of Underground Medic. Lizzie Bennett retired from her job as a senior operating department practitioner in the UK earlier this year. Her field was trauma and accident and emergency and she has served on major catastrophe teams around the UK. Lizzie publishes Underground Medic on the topic of preparedness.