Nature Podcast：植物人状态的嗅觉测试

来源：Nature自然科研

又到了每周一次的 Nature Podcast 时间了！欢迎收听本周由Benjamin Thompson和 Nick Howe 带来的一周科学故事，本期播客片段讨论通过嗅觉测试了解知觉状况。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事。

Interviewer: Nick Howe

Imagine you’re walking in a park. It’s a beautiful sunny day with flowers everywhere and what a lovely smell.

[Inhales]

Ah… Now, I’m not just trying to keep you sane during lockdown. Humans often inhale through their nose when they smell something nice. It’s an automatic response. Now, researchers think that this sniff reflex could help doctors assess an immobile patient’s level of conscious. That’s according to a new study in this week’s Nature. I called up one of the authors, Anat Arzi, to find out more, and she started by telling me about different levels of consciousness – in particular, the difference between a vegetative and a minimally conscious state.

Interviewee: Anat Arzi

A person that is diagnosed in a vegetative state is someone that has a sleep-wake cycle and the eyes are spontaneously open. However, we have no evidence for any signs of conscious awareness for the self or to their environment, so we have no ability to communicate with this person and this person has no ability to communicate. For minimally conscious patients, they have a severe altered consciousness. However, there are subtle signs of consciousness. We have evidence that this person has some awareness of the environment.

Interviewer: Nick Howe

And why is it so important for clinicians to be able to determine between whether someone is in a vegetative state versus a minimally conscious state?

Interviewee: Anat Arzi

They have to make really hard decisions. They have to make decisions that could determine what kind of clinical treatment the patient is going to get. For example, if you think that the patient has no pain sensation, you wouldn’t give them painkillers. However, if you are mistaken, they are going to suffer. And in some countries, they’re also facing the decision about end of life about this diagnosis, so they actually determine whether the person is going to live or die.

Interviewer: Nick Howe

And in this latest work that’s being published in Nature this week, you and your team have been trying to find a new way to do that. Can you describe what it is that you are doing to try and distinguish between these vegetative and minimally conscious states?

Interviewee: Anat Arzi

Olfaction, the sense of smell, has a unique interaction with consciousness. At the neuroanatomical level, it has a direct path to the brain, which other senses like vision and audition don’t have this unique pathway. The other thing is that we have this amazing tool in the sense of smell and this is our sniff. And what do I mean? If I walk by my favourite bakery and they just bake a fresh croissant, I will take a deep inhale. However, if I walk by a public toilet, I will usually take a small inhale or even stop breathing for a few seconds, and this change in nasal airflow is our sniff response, and the sniff response is an implicit non-verbal tool for processing. I do not need to ask you whether you like the odour or not. I can just measure the respiration and actually, in a way, read your mind.

Interviewer: Nick Howe

And so, you were trying to identify if this sniff response could be used to determine between these vegetative and minimally conscious states. So, how did you do that?

Interviewee: Anat Arzi

So, every time we can came to the hospital and met the patients, we recorded their nasal respiration using a small nasal cannula. Then we explained to the patient that we are going to present a few odours. One of them was pleasant, one of them was unpleasant, and one just contained no odour. We presented each odour for about five seconds, and then after we assessed the consciousness level of the patients, whether the patient is responsive, then in the lab we tested whether the magnitude of the sniff response is different between the groups, and we found that indeed people who were in minimally conscious states had a significant change in their sniff volume when we presented an odour. However, when we presented an odour to people who were not responsive, we didn’t find any change in the sniff volume at the group level.

Interviewer: Nick Howe

How subtle of a difference was it? Is it something you could see happening or was it more something you had to measure in the lab?

Interviewee: Anat Arzi

So, there is variability between the patients. So, in some cases, you can see the modulation at the single trial level, and in some cases, you need to do a bit more of an analysis to see a statistically significant result. But what I was telling you is what we found at the group level. What we actually want is to know whether this could be informative at the single patient level. So, we wanted to know whether we can use the sniff response to know whether a person who is now unresponsive is going to recover consciousness, is going to transition into a minimally conscious state, and to do so, we had to define what is the sniff response. So, we had to define a threshold. And what we discovered after applying this threshold is that every single patient that was unresponsive but had a sniff response later on recovered consciousness and transitioned into a minimally conscious state, which was quite exciting. In addition, all the patients that did not recover and remain unresponsive during this study did not have a sniff response. So, if I need to summarise this in one sentence it’s that if you have a sniff response, you will most likely recover consciousness.

Interviewer: Nick Howe

How easy would something like this be to use for a doctor or clinician?

Interviewee: Anat Arzi

Quite simple, actually. All you need is a nasal cannula that is connected to a device that will record the pressure in the nose, and you just need to present the patient with an odour. Actually, you can use just one odour and see if they modulate their respiration. So, this could be used at the bedside and it’s affordable and accessible and quite easy to use.

Interviewer: Nick Howe

And dare I ask, what are the smells that you used?

Interviewee: Anat Arzi

So, the smell that we used for the pleasant odour was a shampoo-like odour, and for the unpleasant odour it was rotten fish, which is profoundly unpleasant, trust me. If you need a big change in respiration, you need to choose something that is really unpleasant.

Interviewer: Nick Howe

And for the doctors and people who would be using this, like you did, would they have to measure things in the lab or would they just be able to determine just from waving it under their nose that this person has a sniff response?

Interviewee: Anat Arzi

So, in some cases, you can detect it by eye, but now at the lab of Professor Noam Sobel at the Weizmann Institute, they are developing a simple tool that could be used using a simple application on your phone, so hopefully this will be available in the near future.

Interviewer: Nick Howe

That was Anat Arzi from the Weizmann Institute in Israel and the University of Cambridge here in the UK. To find out more, check out the show notes, where there’ll be a link to the paper.

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