A computer-generated graphic shows how far back one nasal cavity can go. Scientists say the cavity has a complex shape that affects how we detect scents.
英国伦敦的帝国学院科学家丹尼斯·多尔利和罗伯特·施罗特尔最近在“英国生物技术生物科学研究协会”的刊物《使命》上发表文章披露，在鼻子里面的小小的鼻腔里，被吸入的空气的流动并不平静和简单，而是会形成涡流，而且流动状况非常复杂。
研究小组首先根据对一系列受试者的鼻子的CT扫描结果，用透明的物质制作了比例放大一倍的鼻子模型，这个模型准确地模拟了人的鼻腔结构。然后他们让水流过该鼻子模型，并用数码相机对流动状况进行拍摄。为了便于观察，他们还在水中加入微细的塑料颗粒，便于拍摄。由于空气在鼻腔中的流动速度很慢，从流体力学观点上看，用水代替空气是可以的。
通过调节水进入鼻腔模型的状况，科学家可以模拟从平静呼吸到打喷嚏等所有的呼吸情况，都发现水流在前进的同时还“打旋”，形成涡流。多尔利指出，鼻腔通道没有笔直的，它们的曲线也不是流线型的，这样就使气流非常复杂。他说，“大家都以为，空气绕飞机机翼的流动很复杂，其实，这一运动比空气在鼻腔中的流动还容易被人理解，而且即使在心脏中血液的流动，也比鼻腔中空气的流动来得简单。”
科学家认为，正是因为鼻腔具有复杂的结构，才使空气在鼻腔中的流动如此复杂，从而使那些吸进鼻腔的能引起嗅觉器官反应的物质，最佳地分配到所有嗅觉细胞上，保证嗅觉的灵敏。人感冒后会引起鼻黏膜肿大，这个时候嗅觉就不灵，其原因也在于这些引起嗅觉器官反应的物质，不能很好地分配到所有嗅觉细胞上。
How your nose is more complex than a 747
Study shows why you have to sniff deeply for subtle scents
Your nose may not be as big as a jumbo jet, or maybe it is — but whatever its size, your nose is more complex in one sense.
A new study of how air flows through your schnoz reveals the process to be more complicated than air coursing over a jet's wing.
The scientists figured this out by running water laced with colored beads through a model honker. Not a model's nose, but a 3-D nose model, one twice as big as lifesize. Anyway, these guys really nosed around.
This graphic traces air flow through a 3-D model of the nose, with the flow entering the nostril from the right.
"From quiet breathing to rapid sniffing, we want to know exactly what is happening," said Bob Schroter of the Imperial College London. The results clear some things up and could lead to new ways to clear up blocked nasal passages, the researchers say.
"The geometry of the nose is highly complex, with no straight lines or simple curves like an aircraft wing, and the regime of airflow is not simply laminar or turbulent," said Professor Denis Doorly, assuming laminar and turbulent are simple. (Laminar means smooth, and turbulent is, well, anything but.)
The study revealed why we have to inhale deeply sometimes to capture a subtle scent, perhaps that of a flower.
Smelling relies on getting air to the olfactory bulb, which sits somewhat inconveniently at the top of the nose, thought conveniently on the inside. The way the nose is built, you have to take in a sharp breath at high velocity to shoot faint smells up there. Something like a strong gust of wind instead of a gentle breeze. Then the nose takes over, the model showed: Its structure causes air to eddy around the bulb, lingering a bit so you can enjoy the scent, or not.
The model nose was built from transparent silicone, based on computerized scans "of anonymous patients found to be nasally healthy." The research beats examining cadavers, the scientist said. The findings could help surgeons plan nose jobs and allow drug companies to figure out better ways to get drugs straight into your bloodstream.
The research was announced Thursday and is detailed in the January issue of Business, a magazine put out by the Biotechnology and Biological Sciences Research Council.
