It starts with a cough, or a wheeze. Soon, your chest feels tight.
它开始于一阵咳嗽，或是一阵喘息。不久后，你会觉得胸口发紧。
Your breathing speeds up and gets shallower, making you feel short of breath.
呼吸速度加快并且呼吸变浅，这让你感到喘不上气。
These are common symptoms of an asthma attack.
这些都是哮喘的典型症状。
Around the world, more than 300 million people suffer from asthma, and around 250,000 people die from it each year.
全世界有超过3亿人患有哮喘病，每年约25万人因此丧生。
But why do people get asthma and how can this disease be deadly?
为什么人们会患上哮喘，它又为何如此致命？
Asthma affects the respiratory system, particularly the smaller airways, such as the bronchi and bronchioles.
哮喘影响人们的呼吸系统，尤其是小的气道，例如支气管和细支气管。
These airways have an inner lining called the mucosa that's surrounded by a layer of smooth muscle.
这些气道内部分布着一层黏膜，它们被一层平滑肌所包裹。
In people with asthma, the airways are chronically inflamed, which can make them hyper-responsive to certain triggers.
患有哮喘的人的气道会慢性发炎，这使得他们对于某些诱因高度敏感。
Some of the many asthma triggers include tobacco smoke,
这些诱因包括香烟、
pollen, dust, fragrances, exercise, cold weather, stress, and even the common cold.
花粉、灰尘、香水、体育锻炼、寒冷天气、压力，甚至是普通感冒。
When people with asthma are exposed to these triggers, an asthma attack, or exacerbation, can occur.
当哮喘病人接触这些要素，哮喘病症就会发作。
But how exactly do such everyday factors lead to an asthma attack?
这些日常因素如何导致哮喘病发作呢？
If an asthmatic is exposed to a trigger,
当哮喘病人接触这些触发因素时，
the smooth rings of muscle that circle the small airways in their lungs contract and become narrow.
肺里包裹气道的一圈平滑肌就会收缩变得更加狭窄。
Simultaneously, the trigger worsens inflammation,
同时，触发因素会加剧炎症，
causing the mucosal lining to become more swollen and secrete more mucus.
使得气道黏膜变得更加肿胀从而分泌更多粘液。
Under normal conditions, the body uses this mucus to trap and clear particles, like pollen or dust,
在通常情况下，粘液可以捕捉和清除小颗粒，例如花粉和灰尘，
but during an asthma attack, it blocks the narrowed airways, making it even harder to breathe.
但是哮喘发作时，它会堵住狭窄的气道，使得呼吸变得更加困难。
These effects lead to this symptoms of asthma.
这就导致了哮喘发作时的症状。
Smooth muscle constriction results in the feeling of chest tightness.
平滑肌收缩导致了胸口紧张的感觉。
Excess mucus and increased inflammation can cause coughing. And the wheezing noise?
过量的粘液和恶化的炎症会导致咳嗽。喘息声是哪里来的？
That happens because as the airways constrict, air whistles as it passes through the narrowed space.
是由于随着气道收缩，空气经过狭窄空间会发出哨音。
These symptoms may make a person feel like they're running out of air.
这些症状会使人喘不上气。

Yet counterintuitively, during an asthma attack, the inflammation can make it harder to exhale than inhale.
但与直觉相反，哮喘发作时，炎症会让呼气变得比吸气更加困难。
Over time, this leads to an excess of air in the lungs, a phenomenon known as hyperinflation.
之后，这会导致肺里的空气过量，这称为过度充气。
The trapping of air inside the lungs forces the body to work harder to move air in and out of them.
肺里的大量空气会迫使身体更努力地进行排气。
Over time, this can lead to reduced oxygen delivery to the body's organs and tissues.
这会导致运输到身体各器官和组织的氧气减少。
Sometimes, in untreated severe asthma attacks, the body can't keep up, which can lead to death from lack of oxygen.
有时候，严重哮喘在不及时医治的情况下，身体就会无法继续维持，这最终会导致缺氧死亡。
So how do we prevent these uncomfortable and potentially fatal attacks in people who have asthma?
哮喘病人该如何预防令人不适且有潜在生命威胁的病情发作呢？
One way is to reduce the presence of triggers.
方法之一是减少接触触发因素。
Unfortunately, the world is an unpredictable place and exposure to triggers can't always be controlled.
可惜的是，我们生活的世界无法预知，接触触发因素与否并不总是可控的。
This is where inhalers, the primary treatment for asthma, come in.
这时就需要吸入器的帮助了，它也是治疗哮喘的主要方法。
These medications help asthmatics both control and prevent their asthma symptoms.
这种药物帮助哮喘病人控制和预防病症发作。
Inhalers transport medication along the affected airways
吸入器将药物运送到出现问题的气道，
using a liquid mist or fine powder to treat the problem at its source.
通过液体喷雾或是细密的粉末从源头上解决问题。
They come in two forms. There are reliever medications, which treat symptoms immediately and contain beta-agonists.
吸入器有两种。一种是平缓性药物，它可以直接缓解症状并含有β-受体激动剂。
Beta-agonists relax constricted muslces, allowing the airways to widen so more air can travel into and out of the lungs.
β-受体激动剂可以使紧张的肌肉放松，使得气道变得更加通畅，更多的空气可以出入肺部。
The other form of inhalers serve as preventive medications,
另一种吸入器则是预防性药物，
which treat asthma symptoms over the long term, and contain corticosteroids.
可以达到长期治疗哮喘病的作用，它通常包含糖皮质激素。
Corticosteroids reduce airway sensitivity and inflammation, so asthma can be kept under control.
糖皮质激素可以减轻气道的敏感性和炎症，从而使哮喘病症得到控制。
They're also crucial in preventing long-term damage from chronic inflammation, which can cause scarring of the airways.
这在预防慢性炎症所带来的长期伤害方面也有重要作用，因为慢性炎症会带来气道创伤。
Inhalers are known to be very effective, and have helped many people live better lives.
吸入器是非常有效的，并且已经帮助了众多人更好地生活。
Although we've come a long way in improving how we treat and diagnose asthma, we still don't know its exact causes.
虽然我们花费了很长时间在改进哮喘病的诊断和治疗，我们仍然不能确定其明确的发病原因。
We currently believe that a combination of genetic and environmental factors play a role, potentially acting during early childhood.
目前我们已知基因和环境因素共同会导致这种疾病，并且在幼儿早期就会有潜在影响。
Recent research has even linked poverty to asthma incidents.
最近的研究发现了哮喘病和贫穷的关联。
This may be due to reasons ranging from exposure to additional pollutants and environmental irritants to difficulties in obtaining medical care or treatment.
其原因可能在于对污染物和环境刺激物的过量接触，以及难以获取医疗救治。
As our understanding of asthma improves, we can continue to find better ways to keep people's airways happy and healthy.
随着我们对哮喘病的理解加深，我们可以找到让气道健康和舒适的更好方式。