What is hypercapnia?

In November 22, 2015, a woman felt uncomfortable while she was driving through Highway No.3 in Nantou, Taiwan. Because her daughter was fainted in the same vehicle, she called the police.

When the police arrived, they found that she did not turn on the air-conditioning. She switched to circulation, which did not allow fresh air to come in.

I often found it curious why our car has a setting "circulation". Although it can prevent bad smell coming from outside to enter our car, but it also prevent fresh air from coming in. If we drive for a long time and leave the setting on "circulation" (like this woman did), you may suffer from hypercapnia.

What is hypercapnia?

The prefix hyper-, we is from Lesson 6-1, meaning above.

The prefix capn- is introduced in Lesson 17-1, meaning carbon dioxide. It can also be written as capno-, depending on what letter connecting to it.

The suffix -ia is introduced in Lesson 16-4, meaning condition.

Putting them together, hypercapnia is a condition of abnormally elevated carbon dioxide (CO₂) levels in the blood.

According to Wikipedia, hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, for example as a contributory factor in sudden infant death syndrome.

Symptoms and signs of early hypercapnia include flushed skin, full pulse, tachypnea (abnormally rapid breathing), dyspnea (difficult in breathing), extrasystoles (a heartbeat outside the normal rhythm), muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure. According to other sources, symptoms of mild hypercapnia might include headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmias.

Recently, a research paper suggested if the carbon dioxide in the ocean keeps rising, the fish will also suffered from hypercapnia too!

Source: Wikipedia

Hypercapnia is also called carbon dioxide toxicity. It will happen within 30 minutes when the concentration of carbon dioxide reach 6%.

Next time when you are going for a long ride with your family, please remember to check the air-conditioner's setting!

Reference :

民視新聞。2015/11/22。國道驚魂!車內只開循環 女副駕缺氧昏厥。

Wikipedia. Hypercapnia.

Ben I. McNeil & Tristan P. Sasse. 2016. Future ocean hypercapnia driven by anthropogenic amplification of the natural CO2 cycle. Nature. 529, 383–386

高碳酸血症（hypercapnia）

2015年11月22日的新聞提到，一位婦人開車行經國道3號南投名間路段時，突然女兒在副駕駛座上暈倒，加上她自己也感到不舒服，趕緊報警，後來警方才發現，原來車內沒開冷氣，只開車內循環。

汽車空調的車內循環設定，我很好奇為何有這個設定呢？雖然可避免把外面的臭味引入，但卻會使得車內空氣不流通，長期可造成高碳酸血症（hypercapnia）。

hypercapnia這個字是由三個部分所組成的，hyper- ，capn- ，與 -ia。

其中hyper-請參考第六課（一），是高（above）的意思；

而capn- 請參考第十七課（一），是二氧化碳（carbon dioxide）的意思，也可寫作capno-，看後面連接的字而定；

最後的-ia 請參考第十六課（四），是狀況（condition）的意思。

所以加起來就是「高二氧化碳（碳酸）的狀況」，用來形容血液裡的碳酸過多。

當血液中二氧化碳(CO₂)水平異常升高時，會引發增強呼吸以接觸氧氣等等反應，例如：如果正在睡覺時，會忽然覺醒與頻頻轉頭。如果無法進行這類反應，將有可能致命。

高碳酸血症又稱為二氧化碳中毒，如果空氣中二氧化碳達到6%，在小於30分鐘內即可發生。

圖片來源：wiki

所以，開車時（尤其是長途）千萬要記得，別把空調設定到「車內循環」喔！

2016.1.24 更新：最近的研究發現，如果海洋裡的二氧化碳繼續升高，海裡的魚兒在本（21）世紀中期，也會因為罹患高碳酸血症，在海裡迷路喔～

參考資料：

民視新聞。2015/11/22。國道驚魂!車內只開循環 女副駕缺氧昏厥。
Wikipedia. Hypercapnia.
Ben I. McNeil & Tristan P. Sasse. 2016. Future ocean hypercapnia driven by anthropogenic amplification of the natural CO₂ cycle. Nature. 529, 383–386 doi:10.1038/nature16156