Thunderstorm Asthma: How Weather Can Affect Allergens

Health Professional
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Have you ever considered that your asthma may be extremely sensitive to weather changes like thunderstorms? As a respiratory specialist, I know that weather can exacerbate asthma symptoms and instigate an asthma attack. Thunderstorms, in particular, can affect certain people.

There has been lots of discussion about extreme changes in temperature over the past decades. The fifth report of the Intergovernmental Panel on Climate Change (IPCC) indicated that global warming would result in a higher than usual number of storms. In fact, there has also been a documented increase in cases of severe asthma during thunderstorm season. This increase has been quantified and corroborated by a study conducted in Victoria, Australia, and published in the British Medical Journal in December of 2017.

Researchers measured the number of emergency medical service calls received during one day and noted over 1000 calls – which was a volume considerably higher than the average over the previous year. There was a 432 percent increase in emergency medical attendances for acute respiratory distress syndrome noted in the study. There were also large increases in demand for treatment from patients diagnosed with asthma and using bronchodilator treatment.

The findings can be attributed in part to the effects of the weather instigating respiratory disease, but other factors may be at play. In order to understand these other contributory factors, it’s important to examine the different phases of asthma after exposure to allergens. Thunderstorm asthma is really an early asthma response predominantly to the allergen grass pollen.

Different responses to an allergen

After exposure to a particular allergen or particle that elicits an allergic response, there is an “early asthmatic response" (sometimes referred to as EAR). This response occurs quickly and consists of bronchospasm (contractions of the muscles that surround the airways). This response develops within 30 to 60 minutes after allergen exposure and is rather dramatic – presenting with wheezing that frequently prompts the person to seek immediate medical attention, often in the emergency room. This phase of asthma is treated with bronchodilators, which help to relax the bronchial muscles and provide relief very quickly.

The magnitude of this early phase depends on several factors: the amount or level of allergen exposure, the degree of sensitization, and the level of airway hyper-responsiveness (AHR). These three variables are different in every person.

In some cases, when early asthmatic response is treated promptly there is complete resolution of the attack (and symptoms). However, in the case of the hypersensitive person, there is often a second phase to the asthma attack called the “later airway response.” This starts three to five hours later and it develops slowly and subtly. It is not as dramatic as early asthmatic response, but it can last for a while (eight hours or longer) and be very unpleasant.

The later airway response phase doesn’t respond to bronchodilators – corticosteroids are necessary. The underlying process is not bronchospasm, but rather inflammation of the inner mucosa of the airways, which is why it takes a while to reduce the swelling and allow the airways to fully open again.

What happens during a thunderstorm that would trigger these asthma responses?

Grass and forested areas depend on the winds to spread the pollens that maintain the environment. The highest concentration of pollen is in the center of its source area, but the pollen can spread to very far distances with the help of the wind. Most particles that leave their plant sources are large (in excess of 12 to 60 microns) and, if inhaled, get stuck in the upper airways and do not reach the airways in the lungs.

During thunderstorms several things happen. Large numbers of pollen particles are brought upwind where they are “ruptured” into smaller particles by the hypotonic cloud or rain water. In addition, these pollen particles get saturated with the surrounded moisture which makes them more sturdy and solid, capable of traveling even longer distances. These smaller particles can easily be inhaled in large quantities by people.

The people who tend to suffer the most are highly sensitve to pollen. They are suddenly exposed to these large numbers of particles, which descend deep into the airways – a rather unique situation. The persistent influx of the (pollen) allergens into the airways can account for the second later response after the early response is initially treated in the acute setting in the emergency room. The challenge is to identify thunderstorm asthma and treat early asthmatic response, but also anticipate that there may be the second LAR phase as well.

Other ways thunderstorms affect allergens

Other things occur during thunderstorms that make the associated asthma attacks more unique. When this type of weather pattern occurs, pollen particles are exposed to other pollutants, including sulfur dioxide and carbon monoxide. That exposure makes the particles more likely to perpetuate and lengthen the inflammatory reaction in the airways.

The massive changes in the humidity and temperature during the thunderstorm also has an effect on the airways, possibly prolonging the inflammation. Fungal spores and the other molds present in the air can worsen asthmatic episodes in a way that does not typically occur.

Knowing the unique elements of thunderstorms and other weather conditions, researchers and doctors have an opportunity to identify people who are at risk. Certain people with asthma could benefit from preventive measures that might limit early and later responses and prevent severe asthma attacks.

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