by Lizzie Bennett
Medically Speaking

Recently by Lizzie Bennett: Anthrax Island

Each winter there is a myriad of articles published warning us about the dangers of hypothermia, how to spot it and what to do about it. There are articles warning about cold injuries such as frostbite, warnings to the elderly about the dangers of not keeping at least one room warm. Warnings to get the boiler serviced in case carbon monoxide builds up if its faulty. We are warned that we may need extra vitamins, warned to drive carefully, warned to take care if using candles and warned not to leave the lights on the Christmas tree switched on overnight. Not once, anywhere in this plethora of warnings have I heard the one that warns you that you are more likely to suffer a heart attack if you don't wear a warm hat in cold weather.

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 where the woolly hat comes in. Trust me, all will become clear.

Although blood is a liquid, it is 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 Joe. Joe 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 Joe'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 Joe'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, Joe warms up before the clot increases in size and lives to catch a train the next day although possibly getting a deep vein thrombosis in his leg at a later date.

Today is not Joe'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 Joe gets on the train fifteen minutes later the clot is no longer microscopic, but it is stuck in place for now. Joe 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, a lump of it breaks off and gets carried along with the liquid blood the clot lodges in Joe's heart. Joe 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. Internally more and more blood cells are backing up behind the clot, blocking the small gaps around its edges that was allowing enough blood through to keep his heart beating. As the blood supply slows, Joe's heart, starved of what it needs starts to fire off irregularly, the electrical system is failing. Joe feels a rapid tightening in his chest as the heart strains to maintain its output. It gives one last flutter before ceasing its activity. Joe Feels like his chest is going to explode, attempts to stand up and collapses. Now at this point he is not technically dead. Although not conscious of it his brain functions will continue until the oxygen in his body has been used up, but for all practical purposes Joe has died. He was 43 years old.

Many people die each year of cold related strokes, heart attacks and pulmonary emboli. Even wrapped up, some people prone to sticky blood will still die, but a great many 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"? It seems she had a point and thats the connection between woolly hats and heart attacks.

Stay safe this winter

Reprinted from Medically Speaking.