J Asthma. 2013 Feb;50(1):39-44.

A curvilinear nomogram of peak expiratory flow rate for the young.

Wun YT, Chan MS, Wong NM, Kong AY, Lam TP.

Department of Family Medicine and Primary Care, The University of Hong Kong, Hong Kong. dr.ytwun@gmail.com

 

Abstract

OBJECTIVE:

Peak expiratory flow rates (PEFRs) differ among populations and between times. The new EU scale of the mini-Wright flow-meter has been introduced since 2004. This study updated the PEFR nomograms with the new scale for Chinese children and adolescents (aged 6-19 years) in Hong Kong.

METHODS:

A convenience sample was recruited from 34 primary care practices (patients’ companions/children) and four schools. Standardization workshops were run for the physicians, and the proper use of the flow-meter was demonstrated to students prior to the data collection. Brand new meters were used. For each sex, the linear regression model was used to determine the relationship between PEFR and the variables of age and body height. The open-source software PyNomo was used to generate the nomograms.

RESULTS:

After excluding 66 participants with past/current history of respiratory tract diseases, heart disease, incomplete data, and poor effort, PEFRs were collected from 798 males and 794 females. The PEFR had a linear relationship with age but a curvilinear relationship with height. The regression equations for predicted PEFR were ln(PEFR) = 1.810256*ln(height) + 0.038297*age – 3.734139 for males and ln(PEFR) = 1.525509*ln(height) + 0.033275*age – 2.368592 for females. The corresponding nomograms were constructed. They were tested with 230 patients in primary care; 9.6% (12 males and 10 females) had PEFR less than the predicted value by ≥20%.

CONCLUSION:

The body height was a stronger determinant than age for PEFR. The predicted PEFR with these determinants bear a curvilinear relationship.

PMID: 23174006

 

Supplements:

The peak expiratory flow rate (PEFR) in children was previously observed to have a linear relationship with age and body height. Age and body height were also thought to be collinear in their association with PEFR. Hence, either age or height had been used to predict PEFR. However we observe that in the present generation of children and adolescents, body height does not increase linearly with age (Fig 1).

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Fig 1. Relationship between age and body height

Age and body height are not collinear in relation to PEFR. PEFR still has a linear relationship with age but not height, for both boys and girls (Figs 2 and 3).  Hence age and height are both independent predictors of PEFR. Consequently nomograms of PEFR based on age and height are curvilinear instead of linear.

We develop PEFR nomograms for males and females aged 6-19 years in Hong Kong, using a non-linear regression model (Figs 4 and 5).

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Fig 2. Scatterplots of PEFR against age and height in the male (with smoothed 0.25, 0.5 and 0.75 percentile curves of PEFR)

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Fig 3. Scatterplots of PEFR against age and height in the female (with smoothed 0.25, 0.5 and 0.75 percentile curves of PEFR)

Wun Yuktsan-6Fig 4. PEFR nomogram for males aged 6-19 years

Wun Yuktsan-7Fig 5. PEFR nomogram for females aged 6-19 years

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