Pediatric Pulmonology 9:86-90 (1990)
Peak Expiratory Flow Measured With the Mini Wright Peak Flow Meter in Children Jose Sanz, MD, Antonio Martorell, MD, Rosa Saiz, MD,Vicente Alvarez, MD,and Jose 1. Carrasco, MD Summary. We established pediatric reference values for peak expiratory flow rate (PEFR), using the Mini Wright Peak Flow Meter. The study was based on 1,566 Mediterranean white children, aged 7 to 14 years from Valencia (Spain) schools. Height was the biometric variable with the greatest correlation to PEFR in both sexes; significant differences were noted between males and females. Prediction equations and percentile tables are presented for each sex. The performance of the Mini Wright Peak Flow Meter was compared with that of a spirometer. Pediatr Pulmonol 1990; 9:86-90. Key words: Comparison with spirometry; multiple and simple regressions, percentiles, by sex.
INTRODUCTION
Measurements of peak expiratory flow rate (PEFK) alone or in conjunction with other pulmonary function tests have been found useful in assessing airway obstruction. PEFK, although a less sensitive measurement than others, correlates well with measurements of forced expiratory volume in 1 second (FEV,).lP4 The standard Wright Peak Flow Meter (WPFM) is a simple and reliable instrument that has been used for many years. In 1978 a smaller and less expensive version, the Mini Wright Peak Flow Meter (MWPFM) was developed by Wright.' This instrument's popularity has been due partly to its portability and simplicity." Normal values for the MWPFM are not presently available for children, and the WPFM values are used instead. Kotes et al.7 in 1984 concluded that standard and Mini Wright scores are not equivalent and therefore may not confidently be interchanged. In accordance with the European Coal and Steel Society (ECSS), results obtained by different equipment are not always comparable; therefore further studies are recommended.' This study was designed to establish normal values for the Mini Wright Peak Flow Meter in Mediterranean white children, and to evaluate the performance of the MWPFM in comparison with a spirometer. MATERIALS AND METHODS
This work was carried out in conjunction with a spirometric study of 1,566 Mediterranean white children (792 males, 774 females), aged 7 to 14 in Valencia city schools.
o 1990 Wiley-Liss, Inc.
The subjects were selected at random from different elementary and secondary schools. To homogenize the sample according to the school population (ages 7 to 14), a stratified randomized sampling approach was used by sex and age group. Testing consisted of the administration of the summary ATS-DLD children's Respiratory Symptom Questionnaire,' anthropometric and PEFR measurements by spirometry, and by MWPFM. The selection of the reference population was carried out according to the healthy child criteria of the GAP Committee." Each student was tested with the MWPFM and the spirometer by the same trained technician. We used the adult model of the MWPFM as calibrated by the manufacturer (Clement-Clarke International Ltd., London, England), for peak expiratory flow rates ranging from 60 to 800 L/min. Each child was instructed to take a deep breath, secure the mouthpiece by the teeth, make a tight seal with the lips, and blow out quickly and forcefully into the instrument. Proper positioning included holding the mouthpiece horizontally and avoiding obstruction of the airway by flexing the neck. All tests were carried out standing, wearing a nose clip, and each
From the Pediatrics Service (Allergy Section), University General Hospital, Valencia, Spain. Received July 17, 1989; (revision) accepted for publication February 20. 1990. Address correspondence and reprint requests to Dr. J. Sanz, Avda. Tres Cruces sin, Hospital General Universitano, Servicio de Pediatria, 46018 Valencia, Spain.
Peak Expiratory Flow With the Mini Wright
87
MALE
110 115 120 125 130 135 140 145 150 155 160 165 170 175 180
Fig. 1. Percentile table for the PEFR obtained with the Mini Wright in males.
For the simple regression analysis we studied three subject was allowed a minimum of three attempts. The highest reading was taken as the PEFR for the s ~ b j e c t . ~mathematical regression equation models (linear, power, The PEFR was also measured by a Spirotrac I1 Sys- and exponential); the biometric variable used was that tem, consisting of a Vitalograph dry bellows spirometer with the greatest correlation coefficient. Mathematical fit (Vitalograph Ltd., Buckingham, England) interfaced was studied using the same approach as in the simple with an Apple computer. Spirometric testing was used regression analysis. according to the standardized method recommended by The normal limits of the reference values were deterthe ATS-DLD 11. A portable 1-liter precision calibration mined by the confidence intervals. l3 For the intraindisyringe was used for periodic checking of the spirometer. vidual analyses of the spirometer and MWPRM data we The intraindividual analyses of the MWPFM and applied Student's t-test for paired series. spirometer values were carried out on 30 randomly chosen children on different days. Statistical Analysis
The Statistical Package for the Social Sciences (SPSSX) was used for the statistical analysis of the data.'* The Pearson correlation coefficient was obtained, determining the correlation coefficients between the biometric variables and MWPFM values. In establishing the regression equations we employed the routine regression, multiple regression technique contained in the SPSS-X, using a stepwise selection of variables.
RESULTS
Out of a total sample of 1,566 children, 325 (20.7%) were excluded; 27 1 (17.3%) according to GAP Committee criteria and 54 (3.4%) because of incomplete questionnaires. Thus, I ,241 children comprised the reference population. In the intraindividual analyses of MWPRM we obtained a high correlation coefficient (r = 0.92), with a mean difference of 8.5 Limin (1.83%), standard deviation, 8.92 L/min (1.92%), and standard deviation of the
88
Sanz et al.
FEMALE
110
115 120
125 130 135 140 145 150 155 160 165 170 175
Fig. 2. Percentile table for the PEFR obtained with the Mini Wright in Females.
TABLE 1. Multiple and Simple Regression Equations for PEFR (L/min) Obtained by the Mini Wright Peak Flow Meter Sex
Eauation
r ~~
Multiple model M + F M F Simple model
M F
1.96 H 3.36 H 1.30 H
+ +
+
13.94 A 11.73 A 15.70 A
+ 72.68 BSA + -
+
10.42 S 240.06 103.68 BSA - 128.05
4.99 H 5.20 H
-
346.59 386.58
-
164.33
~
SEE ~
0.84Y 0.840 0.858
41.41 41.62 41.06
0.825 0.826
43.38 45.12
H, height (cm); A, age (yr); BSA, body surface area (m2); S, sex (M: 1, F:O); r, correlation coefficient; SEE, standard error of estimate.
mean, 1.62 L/min; no significant differences were observed. Height presented the greatest Pearson correlation for MWPFM values (r = 0.82 for both sexes), whereas weight showed the poorest correlation (r = 0.73). The biometric variables (weight, height, age, and body surface area) were in good correlation in both sexes. The multiple regression analysis incorporated height
as a biometric variable in both sexes at the first place, followed by age and body surface area. Analyses of variance (ANOVA) presented a significance under 0.01, without satisfying the null hypothesis of a horizontal regression line; MWPFM could thus be predicted from the biometric variable (Table 1). Significant differences by sex were observed, as shown on introducing this functional variable according
Peak Expiratory Flow With the Mini Wright
t 15
125
135
145
155
165
89
175
Fig. 3. Regression line of PEFR obtained with the MWFM for all subjects in our study in comparison with results by Godfrey et al.” with the standard WPFM.
to the stepwise method in the multiple regression equation for the reference population (Table l ) . In the simple regression analysis with height as the predictive variable, no differences were observed in mathematical fit between the three models (linear, power, and exponential); therefore we propose the linear model for simplicity (Table 1). Figs. 1 and 2 show percentile curves for males and females. The paired t-test between MWPFM and spirometric values yielded a highly significant difference between the two methods. Hence, a simple regression analysis was carried out to determine their relationship. The following prediction equation was obtained:
dards for PEFR have been obtained with the standard Wright Peak Flow Meter. Correlations reported previously between PEFR values recorded with the MWPFM and the standard WPFM range from 0.94 to 0.98.’4-’7 Intraindividual analyses showed that Mini Wright values are not equivalent to standard Wright scores and, therefore, are not reliably interchangeable.7 , 1 8 The mean MWPFM values of our study were somewhat higher (between 25 and 33 L/min) than those obtained by G ~ d f r e y with ’ ~ the WPFM (Fig. 3). When we compared the values obtained by MWPFM and by spirometry we obtained a high correlation (r = 0.81 in both sexes). This good correlation was maintained at low and high flows; thus we were unable to Spirometer - PEFR = 0.665 X MWPFM who found that at high confirm the results by Hsu et PEFR + 67.249 flows (over 325 L/min) the values obtained by WPFR were lower than by spirometry, and higher at flows unr = 0.817 325 L/min. der SEE = 36.528 In conclusion, we present the first reference equations for PEFR children, obtained with the adult model of the DISCUSSION Mini Wright Peak Flow Meter. For quick reference we A search of the literature failed to yield normal values provide percentile tables by sex. Comparing PEFR defor MWPFM in children. Presently used reference stan- termined by the MWPFM and Vitalograph spirometer a
90
Sanz et al.
high correlation was observed, and a simple regression equation is presented for correcting values obtained by these types of equipment. REFERENCES 1. Brown LA, Sly RM. Comparison of Mini-Wright and standard
Wright Peak Flow Meters Ann Allergy. 1980; 45:72-74. 2. Wright BM, McKerrow CB. Maximum forced expiratory flow rate as a measure of ventilatory capacity. Br Med J. 1959; 2: I04 1-1 047. 3. Shephard RJ. Some observations on peak expiratory flow. Thorax. 1962; 17:39-48. 4. Lebowitz HD, Knudson RJ, Robertson G, Burrows B. Significance of intraindividual changes in maximum expiratory flow volume and peak expiratory flow measurements. Chest. 1982; 8 11566-570. 5 . Wright BM. A miniature Wright peak-flow meter. Br Med J. 1978; 2~1627-1628. 6. Hsu KHK, Jenkins DE, Hsi BP, Bourhofer E, Thompson V, Hsu FGF, Jacob SC. Ventilatory functions of normal children and young adults, Mexican-American, white and black. 11. Wright peak flowmeter. J Pediatr. 1979; 95:192-196. 7. Kotes H, Harver A, Creer TL. An intraindividual comparison of standard and Mini-Wright scores. Ann Allergy. 1984; 52:419422.
8. Quanjer PH, Tammeling GJ. Standardized lung function testing. Eur PhysioPathol ResPir. 1983; 19:1-95. 9. Ferris Jr. Epidemiology standardization project. Am Rev Respir Dis. 1978; 118:l-89. 10. Taussig LM, Chernick V, Wood R, Farrell P, Mellins RB. Standardization of lung function testing in children. J Pediatr. 1980; 971668-676. 11. American Thoracic Society. Standardization of spirometry-1987 update. Am Rev Respir Dis. 1987; 136:1285-1298. 12. Norusis MJ. Basic Statistics and Operations. SPSSr Introductory Guide. Chicago: McGraw-Hill, 1982. 13. Zellner A. An Introduction to Bayesian lnference in Econometrics. New York: John Wiley & Sons, 1971. 14. Perks WH, Tams IP, Thompson DA, Prowsw K . An evaluation of the Mini-Wright peak flow meter. Thorax. 1979; 34:79-81. 15. Oldham HG, Bevan MM, McDermott M. Comparison of the new miniature Wright peak flow meter with the standard Wright peak flow meter. Thorax. 1979; 34307-809. 16. Burns KL. An evaluation of two inexpensive instruments for assessing airway flow. Ann Allergy. 1979; 43:246-249. 17. Godfrey S , Kamburoff PL, Nairn JR. Spirometry, lung volumes and airway resistence in normal children aged 5 to 18 years. Brt J Dis Chest. 1970; 64:15-24. 18. Harver A, Kotses H, Creer TL. On comparing the Mini- and standard Wright peak flow meter. Am Rev Respir Dis. 1983; 127:135 (Suppl.).
Peak Expiratory Flow Measured With the Mini Wright Peak Flow Meter in Children Jose Sanz, MD, Antonio Martorell, MD, Rosa Saiz, MD,Vicente Alvarez, MD,and Jose 1. Carrasco, MD Summary. We established pediatric reference values for peak expiratory flow rate (PEFR), using the Mini Wright Peak Flow Meter. The study was based on 1,566 Mediterranean white children, aged 7 to 14 years from Valencia (Spain) schools. Height was the biometric variable with the greatest correlation to PEFR in both sexes; significant differences were noted between males and females. Prediction equations and percentile tables are presented for each sex. The performance of the Mini Wright Peak Flow Meter was compared with that of a spirometer. Pediatr Pulmonol 1990; 9:86-90. Key words: Comparison with spirometry; multiple and simple regressions, percentiles, by sex.
INTRODUCTION
Measurements of peak expiratory flow rate (PEFK) alone or in conjunction with other pulmonary function tests have been found useful in assessing airway obstruction. PEFK, although a less sensitive measurement than others, correlates well with measurements of forced expiratory volume in 1 second (FEV,).lP4 The standard Wright Peak Flow Meter (WPFM) is a simple and reliable instrument that has been used for many years. In 1978 a smaller and less expensive version, the Mini Wright Peak Flow Meter (MWPFM) was developed by Wright.' This instrument's popularity has been due partly to its portability and simplicity." Normal values for the MWPFM are not presently available for children, and the WPFM values are used instead. Kotes et al.7 in 1984 concluded that standard and Mini Wright scores are not equivalent and therefore may not confidently be interchanged. In accordance with the European Coal and Steel Society (ECSS), results obtained by different equipment are not always comparable; therefore further studies are recommended.' This study was designed to establish normal values for the Mini Wright Peak Flow Meter in Mediterranean white children, and to evaluate the performance of the MWPFM in comparison with a spirometer. MATERIALS AND METHODS
This work was carried out in conjunction with a spirometric study of 1,566 Mediterranean white children (792 males, 774 females), aged 7 to 14 in Valencia city schools.
o 1990 Wiley-Liss, Inc.
The subjects were selected at random from different elementary and secondary schools. To homogenize the sample according to the school population (ages 7 to 14), a stratified randomized sampling approach was used by sex and age group. Testing consisted of the administration of the summary ATS-DLD children's Respiratory Symptom Questionnaire,' anthropometric and PEFR measurements by spirometry, and by MWPFM. The selection of the reference population was carried out according to the healthy child criteria of the GAP Committee." Each student was tested with the MWPFM and the spirometer by the same trained technician. We used the adult model of the MWPFM as calibrated by the manufacturer (Clement-Clarke International Ltd., London, England), for peak expiratory flow rates ranging from 60 to 800 L/min. Each child was instructed to take a deep breath, secure the mouthpiece by the teeth, make a tight seal with the lips, and blow out quickly and forcefully into the instrument. Proper positioning included holding the mouthpiece horizontally and avoiding obstruction of the airway by flexing the neck. All tests were carried out standing, wearing a nose clip, and each
From the Pediatrics Service (Allergy Section), University General Hospital, Valencia, Spain. Received July 17, 1989; (revision) accepted for publication February 20. 1990. Address correspondence and reprint requests to Dr. J. Sanz, Avda. Tres Cruces sin, Hospital General Universitano, Servicio de Pediatria, 46018 Valencia, Spain.
Peak Expiratory Flow With the Mini Wright
87
MALE
110 115 120 125 130 135 140 145 150 155 160 165 170 175 180
Fig. 1. Percentile table for the PEFR obtained with the Mini Wright in males.
For the simple regression analysis we studied three subject was allowed a minimum of three attempts. The highest reading was taken as the PEFR for the s ~ b j e c t . ~mathematical regression equation models (linear, power, The PEFR was also measured by a Spirotrac I1 Sys- and exponential); the biometric variable used was that tem, consisting of a Vitalograph dry bellows spirometer with the greatest correlation coefficient. Mathematical fit (Vitalograph Ltd., Buckingham, England) interfaced was studied using the same approach as in the simple with an Apple computer. Spirometric testing was used regression analysis. according to the standardized method recommended by The normal limits of the reference values were deterthe ATS-DLD 11. A portable 1-liter precision calibration mined by the confidence intervals. l3 For the intraindisyringe was used for periodic checking of the spirometer. vidual analyses of the spirometer and MWPRM data we The intraindividual analyses of the MWPFM and applied Student's t-test for paired series. spirometer values were carried out on 30 randomly chosen children on different days. Statistical Analysis
The Statistical Package for the Social Sciences (SPSSX) was used for the statistical analysis of the data.'* The Pearson correlation coefficient was obtained, determining the correlation coefficients between the biometric variables and MWPFM values. In establishing the regression equations we employed the routine regression, multiple regression technique contained in the SPSS-X, using a stepwise selection of variables.
RESULTS
Out of a total sample of 1,566 children, 325 (20.7%) were excluded; 27 1 (17.3%) according to GAP Committee criteria and 54 (3.4%) because of incomplete questionnaires. Thus, I ,241 children comprised the reference population. In the intraindividual analyses of MWPRM we obtained a high correlation coefficient (r = 0.92), with a mean difference of 8.5 Limin (1.83%), standard deviation, 8.92 L/min (1.92%), and standard deviation of the
88
Sanz et al.
FEMALE
110
115 120
125 130 135 140 145 150 155 160 165 170 175
Fig. 2. Percentile table for the PEFR obtained with the Mini Wright in Females.
TABLE 1. Multiple and Simple Regression Equations for PEFR (L/min) Obtained by the Mini Wright Peak Flow Meter Sex
Eauation
r ~~
Multiple model M + F M F Simple model
M F
1.96 H 3.36 H 1.30 H
+ +
+
13.94 A 11.73 A 15.70 A
+ 72.68 BSA + -
+
10.42 S 240.06 103.68 BSA - 128.05
4.99 H 5.20 H
-
346.59 386.58
-
164.33
~
SEE ~
0.84Y 0.840 0.858
41.41 41.62 41.06
0.825 0.826
43.38 45.12
H, height (cm); A, age (yr); BSA, body surface area (m2); S, sex (M: 1, F:O); r, correlation coefficient; SEE, standard error of estimate.
mean, 1.62 L/min; no significant differences were observed. Height presented the greatest Pearson correlation for MWPFM values (r = 0.82 for both sexes), whereas weight showed the poorest correlation (r = 0.73). The biometric variables (weight, height, age, and body surface area) were in good correlation in both sexes. The multiple regression analysis incorporated height
as a biometric variable in both sexes at the first place, followed by age and body surface area. Analyses of variance (ANOVA) presented a significance under 0.01, without satisfying the null hypothesis of a horizontal regression line; MWPFM could thus be predicted from the biometric variable (Table 1). Significant differences by sex were observed, as shown on introducing this functional variable according
Peak Expiratory Flow With the Mini Wright
t 15
125
135
145
155
165
89
175
Fig. 3. Regression line of PEFR obtained with the MWFM for all subjects in our study in comparison with results by Godfrey et al.” with the standard WPFM.
to the stepwise method in the multiple regression equation for the reference population (Table l ) . In the simple regression analysis with height as the predictive variable, no differences were observed in mathematical fit between the three models (linear, power, and exponential); therefore we propose the linear model for simplicity (Table 1). Figs. 1 and 2 show percentile curves for males and females. The paired t-test between MWPFM and spirometric values yielded a highly significant difference between the two methods. Hence, a simple regression analysis was carried out to determine their relationship. The following prediction equation was obtained:
dards for PEFR have been obtained with the standard Wright Peak Flow Meter. Correlations reported previously between PEFR values recorded with the MWPFM and the standard WPFM range from 0.94 to 0.98.’4-’7 Intraindividual analyses showed that Mini Wright values are not equivalent to standard Wright scores and, therefore, are not reliably interchangeable.7 , 1 8 The mean MWPFM values of our study were somewhat higher (between 25 and 33 L/min) than those obtained by G ~ d f r e y with ’ ~ the WPFM (Fig. 3). When we compared the values obtained by MWPFM and by spirometry we obtained a high correlation (r = 0.81 in both sexes). This good correlation was maintained at low and high flows; thus we were unable to Spirometer - PEFR = 0.665 X MWPFM who found that at high confirm the results by Hsu et PEFR + 67.249 flows (over 325 L/min) the values obtained by WPFR were lower than by spirometry, and higher at flows unr = 0.817 325 L/min. der SEE = 36.528 In conclusion, we present the first reference equations for PEFR children, obtained with the adult model of the DISCUSSION Mini Wright Peak Flow Meter. For quick reference we A search of the literature failed to yield normal values provide percentile tables by sex. Comparing PEFR defor MWPFM in children. Presently used reference stan- termined by the MWPFM and Vitalograph spirometer a
90
Sanz et al.
high correlation was observed, and a simple regression equation is presented for correcting values obtained by these types of equipment. REFERENCES 1. Brown LA, Sly RM. Comparison of Mini-Wright and standard
Wright Peak Flow Meters Ann Allergy. 1980; 45:72-74. 2. Wright BM, McKerrow CB. Maximum forced expiratory flow rate as a measure of ventilatory capacity. Br Med J. 1959; 2: I04 1-1 047. 3. Shephard RJ. Some observations on peak expiratory flow. Thorax. 1962; 17:39-48. 4. Lebowitz HD, Knudson RJ, Robertson G, Burrows B. Significance of intraindividual changes in maximum expiratory flow volume and peak expiratory flow measurements. Chest. 1982; 8 11566-570. 5 . Wright BM. A miniature Wright peak-flow meter. Br Med J. 1978; 2~1627-1628. 6. Hsu KHK, Jenkins DE, Hsi BP, Bourhofer E, Thompson V, Hsu FGF, Jacob SC. Ventilatory functions of normal children and young adults, Mexican-American, white and black. 11. Wright peak flowmeter. J Pediatr. 1979; 95:192-196. 7. Kotes H, Harver A, Creer TL. An intraindividual comparison of standard and Mini-Wright scores. Ann Allergy. 1984; 52:419422.
8. Quanjer PH, Tammeling GJ. Standardized lung function testing. Eur PhysioPathol ResPir. 1983; 19:1-95. 9. Ferris Jr. Epidemiology standardization project. Am Rev Respir Dis. 1978; 118:l-89. 10. Taussig LM, Chernick V, Wood R, Farrell P, Mellins RB. Standardization of lung function testing in children. J Pediatr. 1980; 971668-676. 11. American Thoracic Society. Standardization of spirometry-1987 update. Am Rev Respir Dis. 1987; 136:1285-1298. 12. Norusis MJ. Basic Statistics and Operations. SPSSr Introductory Guide. Chicago: McGraw-Hill, 1982. 13. Zellner A. An Introduction to Bayesian lnference in Econometrics. New York: John Wiley & Sons, 1971. 14. Perks WH, Tams IP, Thompson DA, Prowsw K . An evaluation of the Mini-Wright peak flow meter. Thorax. 1979; 34:79-81. 15. Oldham HG, Bevan MM, McDermott M. Comparison of the new miniature Wright peak flow meter with the standard Wright peak flow meter. Thorax. 1979; 34307-809. 16. Burns KL. An evaluation of two inexpensive instruments for assessing airway flow. Ann Allergy. 1979; 43:246-249. 17. Godfrey S , Kamburoff PL, Nairn JR. Spirometry, lung volumes and airway resistence in normal children aged 5 to 18 years. Brt J Dis Chest. 1970; 64:15-24. 18. Harver A, Kotses H, Creer TL. On comparing the Mini- and standard Wright peak flow meter. Am Rev Respir Dis. 1983; 127:135 (Suppl.).
