oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
See also separate article Spirometry.
The EMIS predicted peak flow calculation used within its clinical systems is based on a published revision to the original Nunn and Gregg equation in 1973. The revised Nunn and Gregg equation is as below and applies to ages 15-85 years.
Loge(PEF)= 0.544 x loge(age) - 0.0151 x(age) - 74.7/(height) + 5.48
Loge(PEF)= 0.376 x loge(age) - 0.0120 x (age) - 58.8/(height) + 5.63
The paediatric calculation (for ages below 15 years) is taken from Lung Function by J E Coates (Fourth Edition):
PEF = 455 x (height/100)-332
In 2004 the Department of Health initiated a change to PEF meters to align to those that met a new EC standard. The new scale resulted in a conversion being required for PEF recorded using the conventional Wright McKerrow scale to the new European standard.
A conversion equation was developed by Clement Clarke™ that allows conversions of readings from the Wright McKerrow scale to EN 13826 scale.
EU = 50.356 + (0.4 x W) + (0.0008814 x W2) - (0.0000001116 x W3)
It is therefore necessary that when using one of the three equations above for male, female, or paediatric predicted peak flow, the value obtained should be converted to the EU scale. The clinical systems use an array of values to look up old values against the EU value. Alternatively, the above equation can be applied to achieve the same result.
This calculator uses an algorithm derived from healthy adult lifetime non-smokers in Australia.
|Measurements made in Spirometry|
|VC (SVC)||Vital capacity (slow vital capacity)||Maximal amount of air exhaled steadily from full inspiration to maximal expiration (not time-dependent). It should be >80% of predicted, reduced in restrictive disease.|
|FVC||Forced vital capacity||Volume of lungs from full inspiration to forced maximal expiration. It is reduced in restrictive disease, and in obstructive disease if air trapping occurs.|
|FEV1||Forced expiratory volume in one second||Volume of air expelled in the first second of a forced expiration. Reduced in both obstructive and restrictive disease.|
|FEV1% (FER)||Forced expiratory ratio (FEV1/FVC)x100||Percentage of FVC expelled in the first second of a forced expiration.
Normal in restrictive disease - reduced in obstructive disease.
|FEF 25-75%||Forced expiratory flow between 25-75%||Average expiratory flow rate at the middle part of forced expiration. It is a more sensitive indication of what is happening in the middle/lower airways, but is not as reproducible as FEV1. Normal in restrictive disease.|
|PEFR||Peak expiratory flow rate||Maximum rate of airflow achieved during expiration.|
Further reading & references
- Nunn AJ, Gregg I; New regression equations for predicting peak expiratory flow in adults. BMJ. 1989 Apr 22;298(6680):1068-70.
- Marks GB; Are reference equations for spirometry an appropriate criterion for diagnosing disease and predicting prognosis? Thorax. 2012 Jan;67(1):85-7. doi: 10.1136/thoraxjnl-2011-200584. Epub 2011 Aug 8.
- Olofson J, Bake B, Tengelin MN, et al; COPD 'diagnosis' based on spirometric reference equations. Clin Respir J. 2008 Oct;2(4):214-9. doi: 10.1111/j.1752-699X.2008.00065.x.
- Gore CJ, Crockett AJ, Pederson DG, et al; Spirometric standards for healthy adult lifetime nonsmokers in Australia. Eur Respir J. 1995 May;8(5):773-82.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Huw Thomas
Dr Hayley Willacy
Dr Colin Tidy