Extreme Cold and the Cardiovascular System
The relationship between weather extremes and mortality rates is well documented. Extreme heat or cold increases the number of heart attacks dramatically. Just a moderate drop of 10°C in temperature raises the risk by 13% in the population of middle-aged French men. Winter is the season for heart attacks amongst all sexes and age groups in the US, with 53% more cases than during summer.
Data collected from patients fitted with heart rhythm regulators (defibrillators) gave some proof of the relationship between weather extremes and heart diseases. When scientists compared the result with climatic data obtained form the national weather service, they found that abnormal heart rhythm is more frequent on days with either very high or very low outside air temperature. Some patients reacted immediately to temperature changes, others’ reactions were delayed by 2-3 days.
While there is no more doubt that cold weather increases the risk of heart or circulatory disease, the question remained whether the link is only present in cold climate regions. Not so; ‘cold’ is relative. The mortality rate during Hawaii’s winter increases by 22%, a figure similar to some cold climate regions.
Why do the heart and the circulation react so violently to temperature drops? There is no single answer. Cold and wet weather is the time of semi-hibernation and indulgence. Unhealthy eating habits and less activity contribute to an increase in heart diseases, but aren’t the only reasons. You can blame the weather for physical changes to your blood.
Named after a French physician, the disease is a disorder that affects the blood vessels in extremities such as fingers, toes, ears, lips and nose. The vessels constrict spasmodically, thereby interrupting the blood flow to the relevant body part. In extreme cases, the blood flow almost stops. This can cause the death and decay of body tissue (gangrene).
According to a recent US survey, approximately 5-10% of the population suffer to some degree from Raynauds disease. Figures supplied from outside the US are somewhat lower. There is no argument, however, that women between the ages of 15 and 40 comprise the majority of diagnosed cases – three times as many as in the male population. The disease is not limited to regions with cold climates. While there are fewer people affected in milder climates, those who are affected experience more attacks when the weather turns cold.
Low temperatures and emotional stress are common triggers of Raynaud’s disease. But it can also manifest itself as a secondary symptom to skin disorders such as lupus and sceloderma.
The constriction of blood vessels is a natural protection against the cold. The system in patients with Raynaud’s disease, however, is too sensitive and constrictions are too intense. Severe constriction of the small arteries causes a collapse of blood circulation in the affected body part. As a consequence, the limbs undergo unwanted physical changes.
The first obvious reaction is a waxy-looking skin. If the attack continues, the lack of oxygen in the tissue turns the skin blue and the patient experiences a tingling sensation and painful throbbing. Such an attack can last for several hours. Finally, the condition fades and blood will flow back into the arteries, causing a reddening of the skin. The disease can progress further, resulting in a prolonged or permanent interruption of the blood flow. The affected body parts, most notably the fingers, become permanently thin and shiny white.
Doctors generally recommend self-help measures, such as keeping the affected body parts warm to prevent tissue damage. They recommend quitting smoking, controlling stress and exercising regularly. There is also medication available to relax the small blood vessels in the periphery.
The indoor lifestyle during cold conditions is one cause of aggravated asthma. The room is often filled with airborne allergens such as dust mites, smoke particles from wood fires, pet hair and viruses. Fresh air will dilute the particles and relieve the symptoms. But cold dry air can make matters worse. The airways tend to narrow and the mucus lining thickens, making breathing more difficult. Asthmatic children in particular display more symptoms during outdoor activities. Breathing through a scarf around the mouth is often enough to pre-warm the air.
A pity that you can’t behave like other warm-blooded creatures and feast on the delicious autumn offerings, then slumber through the cold and wet season. Wouldn’t this be great – unless you’re a diehard winter sports fanatic. Hibernating animals can drop their body temperature sufficiently to slow all their body organ activity, thus reducing their metabolism to a minimum. For a human, however, such a temperature drop can be fatal. Perhaps we are meant to live on tropical islands after all, where food is plentiful all year round – a nice dream.
But dreaming can be the first sign of hypothermia. A drop in body temperature affects your ability to think clearly and, as for a hibernating animal, slows your body functions. This makes hypothermia particular dangerous, especially if the effect is combined with alcohol or other drug intoxication. Many revellers quite happily lie down in the snow for a snooze and never wake up again.
If you fall into a fire, you are made aware of the change in temperature very quickly. Hypothermia, on the other hand, can sneak up on you. The elderly and very young can die in their sleep in cold bedrooms: the latter’s sense of the cold hasn’t yet developed and the former has lost theirs. The cause of death is often attributed to various different reasons because underlying health problems and/or drug effects can mask the real culprit.
The signs and symptoms are difficult to recognize because the victim initially behaves as if under the influence of alcohol or drugs: irrational behaviour, confusion, loss of coordination and slurred speech are some of the signs. When hypothermia progresses, the victim becomes unconscious and may not show any obvious heartbeat or pulse. Breathing is very faint. Despite appearing almost dead, most people survive with appropriate treatment. Permanent damage is likely, though, if the core temperature drops below 26.5°C. Hypothermia is a medical emergency, and is as common in summer as it is in winter.
Healthy people are actually more at risk from accidental hypothermia. Exposure to the elements during outdoor activities, such as work, commuting or travel, poses a risk. Cold water particularly drains body heat quickly – the unlucky passengers of the Titanic, immersed in icy water, probably lost consciousness within 15 minutes. Even relatively mild water of 20°C will drain body heat within a few hours and unconsciousness will set in. Wet clothing has the same effect, although it will take longer.
Hypothermia is defined as a drop in the body’s core temperature to a level that impairs normal body functions, and three stages are recognized. Mild hypothermia occurs at a core temperature above 35°C, severe when it drops below 32°C, with moderate hypothermia in-between. Controlled hypothermia is commonly used in neurosurgery and cardiac bypass surgery to slow the functions and oxygen needs of organs.
The term afterdrop is sometimes mentioned in connection with hypothermia. It occurs during rewarming of the body when the blood vessels in the periphery expand, allowing blood from the warmer core to mix with the still cooler blood of the outer layers. The cool mixture then circulates back to the body’s centre and causes another temperature drop.