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spirometer v peak flow


My asthma nurse seems to have got her hands on something called a spirometer and was keen to use it on me the other day. I was surprised when she said it showed a normal reading when i feel that i stil have asthma symptoms. She didnt seem interested that the peak flow done the same day showed a reading of 70% of my normal reading. She suggested that this was because the spirometer had tired me out. what do you think?l

5 Replies


As far as i know a spirometer measures the amount of air breathed in and out of the lungs over a specified time and i *think* that other things can be calculated from it such as breathing rate and the capcity of your lungs. I have used one once, it was part of my A-Level Biology course and my breathing rate was quite high compared to typical values of someone my height, weight and age. The teacher asked was I asthmatic or had I ever been, I replied no, as i wasnt then and she said I should check that out so I did and they tested my peak flow (which, as it always is was 400 and so was a good reading as I'm only 5ft 1"") and said it was probably just something and nothing, I didn't have any symptoms. 12 months later I started developing Asthma symptoms and was diagnosed with it, this was 14 months ago now, although my peak flow is always the same!! even when im really unwell, it only ever really drops if im having a big attack.

So all I can guess is that different things in different people can indicate whether they are or are not doing so well

Good luck!

Claire x



Thanks for that. I think it is very interesting that it was suggested that you should be checked out for asthma having been tested using the spirometer. i wonder what it is about the readings that indicate how someones asthma is. Anyway i shall ponder no more and just carry on using the meds and testing my peak flow, the old fashioned way!!




The teacher that suggested I should check it out was Asthmatic herself and had been for years, hers was quite severe as well so maybe she has used them a lot and my readings were similar to hers and so she just assumed that meant I could be Asthmatic too, but that if any other teacher had seen that, they may not have suggested it, I don't know.

Hope you're back to yourself soon anyways!!


Claire x


Hi pinky,

A spirometer simply measures your spirometry, which is one of the most basic lung function tests. Many people will be familiar with having this test done in clinic or in the lung function department.

The measurements that are obtained from spirometry are:

Peak Expiratory Flow Rate (PEFR) aka peak flow - the peak speed of air moving out of your lungs, at the beginning of expiration. Measured in litres per minute.

Forced Vital Capacity (FVC) - the total amount of air that can be blown out on forcible expiration after full inspiration. Measured in litres.

Forced Expiratory Volume in 1 sec (FEV1) - the total amount of air that you can blow out in the first second of expiration. Measured in litres.

Other measurements may be taken, but these are the main ones.

Peak flow and FEV1 can both be low in conditions where there is airflow obstruction, such as uncontrolled or symptomatic asthma. They may not necessarily correlate with each other, and they should always be taken in context with symptoms and reliever inhaler use as well. Some people feel that FEV1 is a more sensitive marker of their condition than peak flow, and others feel the converse.

FVC can be normal, slightly low or slightly high in asthma. The ratio of FEV1/FVC should be greater than 80% in normal subjects or in well controlled asthma - ie, at least 80% of the total breath is being breathed out in the first second. In obstructed airways, eg uncontrolled asthma, expiration will be delayed and the FEV1/FVC ratio will be reduced, as a smaller percentage of the breath will be breathed out in the first second.

Hope this helps explain things somewhat. I can't explain why there was such a discrepancy between your spirometry and your peak flow, but this sometimes happens. As I have said, the results should always be considered in combination with your symptoms and inhaler use.

Em H


Bumped up for Jenny H


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