Most people find it hard to hold their breath for more than a minute, so imagine the extreme
self-control Stephane Misfud mustered on 8 June last year when he held his breath for 11
minutes and 35 seconds , setting a new world record for stationary breath-holding, or
"static apnoea".
Competitors float face down in a chilled pool, not to stop them cheating but to induce the
mammalian diving reflex: when your face is submerged in cold water, outer blood vessels
constrict, directing blood away from the extremities and towards the heart and brain. Your
heart rate slows, reducing the rate at which oxygen is pumped around the body. With
training, experienced breath-holders can drop their heart rate by twice that of non-divers
upon immersion in cold water.
Hyperventilation before a prolonged breath-hold is also vital. This is because the brain
monitors the amount of carbon dioxide in the blood to decide when to trigger the gasp
reflex. Purging this CO2 with rapid deep breathing increases how long you can go before the
urge to gasp becomes irresistible. Having large lungs is a natural advantage.
So have we reached the breath-holding limit yet? Not at all, says physiologist Johan
Andersson at Lund University in Sweden, who studies the effects of breath-holding in divers.
"Elite breath-hold divers expect the limit to be extended to about 15 minutes before record
-setting will level off."
They may be dicing with danger, though. Andersson found that static apnoea attempts on dry
land caused a brief 37 per cent rise in the level of a protein called S100B in the blood,
which is used as a marker for hypoxic brain damage. Andersson stresses that this rise is
"well below" the levels seen in actual hypoxia, but warns that those competing in static
apnoea events may accumulate damage in the long term.
大多数人能够屏住呼吸一分多钟已经很不容易了，那么来看看我们的超级自控能手Stephane Misfud 吧，
去年6月8号他以11分35秒的成绩创造了“水下屏息”新的世界纪录。
让选手们把脸沉浸在冰冷的水中不是防止他们作弊，而是想激起哺乳类动物本能的反应：当把脸浸在冷水
中时，血管收缩，这样血液就会由肢体末端流向心脏和大脑。这样一来心率就会减慢，同时减少了氧气向
全身扩散的机率。经过训练以后，那些有经验的选手可以在冷水中自行将心率降低到正常潜水运动员心率
的一半。
肺的换气过度在延长的屏息过程中起着至关重要的作用。这是因为大脑监督着血液里的二氧化碳量，以此
来决定什么时候进行下一次呼吸作用。迅速的深度呼吸把二氧化碳清除出去后，可以延长屏息时间直到下
一次呼吸。所以拥有大的肺活量本身就是一种优势。
那么我们人类的屏息过程已经到达极限了吗？在瑞典Lund 大学研究潜水者屏息效应的生理学家Johan
Andersson 可不这样认为。他说：在达到人类屏息极限之前，出色的潜水者有望达到15分钟。
但是他们可能面临着潜在的危险。Andersson研究发现，在陆地上的静水屏息会导致血液中的S100B蛋白质
含量升高百分之37，而这种蛋白质会对缺氧的大脑造成伤害。Andersson强调：虽然这种蛋白质数量的升
高所造成的危害远不及组织缺氧所造成的伤害，但是他提醒到，从长期来看对于水下屏息的选手造成的伤
害还是很大的。
Today's topics:
1) How long could you hold your breath?
2) Do you know the world record of holding the breath?
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