The summer thunderstorm is great theater. Lightning seems like it might have been hurled by the hand of an angry god. If it's close, we're treated to the sharp crack of thunder that makes us jump and the dog hide. And if it's far away, there's that heavy kettledrum rumble.
Of course all this presumes we're viewing the proceedings from somewhere inside. Being outside, with the thunder and lightning, can be perilous — and very, very wet. But even if you stay indoors, thunderstorms are associated with some adverse health effects. Researchers have documented thunderstorm-related outbreaks of asthma, and there are hints that storms could cause lung and sleep apnea problems.
Lightning is the most obvious threat of a summer thunderstorm, but here are some associated hazards that may not be as familiar.
Reports of thunderstorm-related asthma go back to 1985 to a report in The Lancet about a sudden spike in asthma patients in Birmingham, England, after a July thunderstorm. There have been reports since from Australia and Canada. Researchers in Georgia investigated the relationship between the 564 thunderstorms recorded at the Atlanta airport between 1993 and 2004 and over 200,000 asthma-related emergency department visits at hospitals in the area. They found a real, if modest, 3% increase in asthma-related visits on days following thunderstorms.
The people affected by thunderstorm asthma almost invariably have seasonal allergies — otherwise known as hay fever — which means they're prone to having an allergic reaction to pollen, fungal spores, or both. And the episodes of thunderstorm asthma have been associated with high pollen and spore counts.
How might thunderstorms increase pollen and spore counts
Thunderstorms are created by updrafts of warm, humid air. When that rising air cools off at the higher altitudes and the humidity condenses into rainfall or hail, it creates downdrafts and outflows of cool, dry air that race ahead of the storm and the rainfall. Most of us have experienced that ominous drop in temperature and the gusts of wind that signal the approach of a thunderstorm. According to one theory, those gusts whip pollen off of grass and trees. Another, more elaborate explanation is that pollen (and possibly spores also) first gets swept up into the storm clouds where moisture ruptures the pollen grains into smaller fragments, which then get transported down to ground level by cool downdrafts and outflows. The electrical activity associated with thunderstorms may also play a role in breaking up the pollen into smaller pieces. This explanation takes into account the assertion that whole pollen grains aren't likely to cause asthma because they are too large to get down into the narrow airways of the lungs. It also explains why some people claim that they can tell a thunderstorm is coming by the worsening of their asthma symptoms.
A lung collapses when air gets into the space between the lungs and chest wall and pushes on the lung so it loses its shape. The medical term for the pocket of air is pneumothorax. Anything that punctures or tears the lung — a broken rib, for example — can cause a collapsed lung. But often there's no obvious violation of the lung. These spontaneous collapsed lungs often occur because weak spots in the wall of the lung give way, allowing air from the lungs to escape.
Researchers have documented that hospital cases of spontaneous collapsed lungs occur in clusters. And it's understood that a large air pressure change outside the body from, say, scuba diving or airplane travel can trigger a spontaneous collapsed lung. So a handful of researchers have investigated whether much smaller, weather-related decreases in air pressure might be associated with collapsed lungs. If air pressure is low, air trapped inside the alveoli of the lung might expand and put pressure on the lung wall.
Searching for the cause
The results of these investigations have been mixed. In 2000, Dutch researchers found no connection between falling air pressure and spontaneous collapsed lungs in Amsterdam. Italian researchers who conducted a similar study in Bologna, Italy, more recently did. But both groups saw a pattern of thunderstorms occurring on days just before the clusters of collapsed lungs. One explanation is that asthma brought on by thunderstorms might cause collapsed lungs. The humidity and wind of thunderstorms may also bring about changes in the lungs (mucus retention, bronchiolar spasm, cough) that add up to make spontaneous collapsed lung more likely.
People with sleep apnea repeatedly stop breathing for short periods while they're asleep. Serious cases put a strain on the cardiovascular system and increase the risk of heart attack and stroke. In 2010, researchers reported the results of a study of 537 apnea patients at the University of Washington Medicine Sleep Institute in Seattle. They checked apnea patterns of the patients while they were in the overnight sleep clinic against barometer readings during those stays, and found that the number of obstructive sleep apnea "events" — instances when breathing was interrupted — increased on the nights when atmospheric pressure was lower. Thunderstorms weren't part of this study, but falling atmospheric pressure is a common feature of most storms.
Obstructive sleep apnea is usually caused by soft tissue in the back of the throat relaxing and blocking the normal flow of air. Atmospheric pressure may help hold those tissues open a little bit, so when pressure falls, they relax and interfere with breathing.