PEFR meters

Sorry but I was just wondering if anyone knew what the normal limits are for PEFR meters, are they between 80% and 120% of the estimated values, ie. taking height and weight into consideration or do they change with the severity of asthma?

I noticed reading my notes that different allergies can affect the severity of asthma. Could I ask anyone reading this comment who suffers from asthma if they are aware of this and if they have had an allergy test done which can identify which trigger it may be. I witnessed one in a hospital the other day and noticed that it seemed very helpful in the treatment of asthma.

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Hi Petebrads,

Do you mean the range of values around the predicted value that can still be considered to be normal? The Mini-Wright website (peakflow.com/top_nav/home/i... - a very useful site, as it also includes a calculator for predicted values) states that a value of upto 100 L/min less than predicted, for a man, and 85 L/min less than predicted, for a woman, may still be considered to be normal. With lung function tests in general, 80% of predicted or over is often considered to be within the normal range.

It's worth bearing in mind, though, that peak flow is a very individual thing, and that there will always be outliers who have peak flows that are a lot higher or lower than predicted, but still perfectly normal for them and not indicative of respiratory disease. This is why it's important to consider peak flow in the context of several readings a day over the course of a few weeks, when making a diagnosis - a one-off reading, whether normal, low or high, is not particularly useful in making a diagnosis. People who have chronic or severe asthma also may never achieve their predicted value, and will usually have a good idea of what is 'normal for them'.

In terms of your question about allergy testing - many of us have had this done as part of an asthma work-up. It can be done as skin prick tests - where a small amount of a solution of the allergen is put on the skin, which is then scratched with a small needle - the resulting wheal is measured to assess the degree of allergy. Blood tests can also be used - the RAST test for specific IgE levels to a particular allergen. Neither test is perfect, and it is possible to be allergic to something and not have a positive RAST, for example. Highly atopic individuals can find that they will react to everything on a skin prick test, whether or not they are actually specifically allergic to it in terms of symptoms. The results of these tests always have to be interpreted with caution by a doctor who has knowledge of the patient's general condition and history. Having said that, if used in the right context, allergy testing can be very helpful - and indeed life-saving - to some asthmatics.

Hope this helps

Em H

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Hi there, I appear to be on a roll for questions at the moment

Would someone who participates in regular sport/fitness have higher peak flow readings/better lung function than someone who is less fit?

I ask as Jaydens best peak flow is 50 l/min higher than predicted on the EU meter. When he is in hospital/A&E they always use the predicted value to assess lung function even though they are aware his best is higher. Is there a reason for this? Admittedly his average at present is around 75% predicted and has been since the summer despite steroids.

Just another query from a confused mum.

Nikki

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Hi koolkat,

I know that Olympic athletes have been shown in studies to have tidal volumes (the volume that you breath with normal breathing) far in excess of normal, and their lung capacities are usually on the high side too. I would assume from this that their peak flows would be increased too. It's not known, though, whether this increased lung capacity is a consequence of their training or part of the reason why they became Olympic atheletes in the first place.

I don't really know what effect more normal levels of exercise would have on peak flows, but there are various 'respiratory training devices' on sale which claim to improve respiratory capacity, and there is no good evidence that I am aware of that they have any effect. I would deduce from this that more conventional exercise probably doesn't have much effect on peak flow. It probably does help your blood carry oxygen more efficiently, and your muscles use it more efficiently, being physically fit, so it would help you to perform better on the same peak flow. I also think that when I was able to exercise in between attacks and was physically fitter, I coped with attacks better.

I will do more research, though - it's a really interesting subject. Actually, thinking about it, Alex has an interest in Sports medicine and human adaptation to different environments and challenges, so I might make him do the research!

Take care

Em

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I'd be interested to see if you turn up anything about that - my predicted PEFR is about 430, I think, but I should usually be about 510-540 on a good day. I'd always (with a completely non-medical head on) assumed this might be due to the fact that I always did loads of sport as a child and through my teens - especially swimming. Be interesting to see if there's any scientific basis for it.