Chest
Volume 107, Issue 1, January 1995, Pages 156-161
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Clinical Investigations: Hysiology: Articles
Intraindividual Peak Flow Variability

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Objectives

To quantify intraindividual variability in peak expiratory flow (PEF) measured with peak flowmeters and to define factors affecting PEF variability.

Methods

Three hundred one healthy subjects (aged 4 to 84 years) were recruited from sites at sea level (n=220) and at 1,400 m altitude (n=81). All testing was done with the same model peak flowmeter. Each subject was actively coached through five to eight successive PEF maneuvers. Three meters of the same model were tested using a mechanical waveform simulator at three different flows at both testing altitudes (sea level and at 1,400 m).

Results

Excluding outliers, the mean PEF was 523 L/min, mean standard deviation (SD) was 22 L/min, and mean coefficient of variation (CV) was 4.6%. The upper 95th percentile for CV was 8% for adults and 10% for youths. Analyzing only the three highest peak flows for each subject, the mean PEF was 539 L/min, mean SD was 12 L/min, and mean CV was 2.4%. The upper 95th percentile for CV was 6% for adults and 9% for youths. Linear regression analysis revealed a small but statistically significant correlation (p<0.01) between mean peak flow and CV. In adults, SD correlated with sex (p<0.01) but neither CV nor SD was correlated with age, height, weight, or altitude. Meter variability defined with the mechanical waveform simulator was small. Standard deviation varied from 1.5 to 4.2 L/min and CV from 0.4 to 1.6%. When the three largest peak flows for each subject were used, 5.5% of intraindividual variance was explained by meter variance.

Conclusions

These estimates of intraindividual variability in healthy subjects are generally lower than those previously reported. Meter variability accounts for only a small part of total intraindividual variability. The 95th percentile data suggest that a fall in PEF of 6 to 8% in adults and 9 to 10% in youths would be statistically significant.

Section snippets

Materials and Methods

The study population consisted of 301 healthy volunteers between ages 4 and 84 years (141 male, 160 female) recruited for a “normal values” study from three cities located near sea level (Atlanta, mean barometric pressure 740 mm Hg; Boston, mean barometric pressure 740 mm Hg; and Hartford, Conn, mean barometric pressure 760 mm Hg) and one located at an altitude of 1,400 m (Salt Lake City, Utah, mean barometric pressure 642 mm Hg). Recruited subjects were mostly hospital employees, their

Statistical Methods

The data were analyzed using statistical software packages (Abstat, Anderson-Bell Corp, Parker, Colo, and SPSS, SPSS Corp, Chicago). The average of the three highest PEF values for each subject was calculated (high three mean). Every PEF value for each subject was then divided by the high three mean and a histogram of all measurements was created and analyzed. Based on this analysis, outliers for each individual were identified as those values deviating from the high three mean by more than 20%

Intraindividual Variability

Three hundred one subjects were tested (141 male, 160 female). All were white. Eighty-one subjects were studied at 1,400 m altitude and 220 were studied near sea level. Sixty-nine subjects were younger than 21 years old, including 36 younger than 12 years old. There were 232 subjects aged 21 years or older, including 29 elderly subjects (age >64 years). Using all acceptable values, mean population PEF1 was 522.8 L/min, mean SD1 was 22.2 L/min (95% confidence interval [CI], 20.6 to 24.1), and

Discussion

This study was limited to a single model of peak flowmeter. However, reproducibility among several of the available brands of hand-held peak flowmeters has been shown to be less than ±5% at flow rates greater than 100 L/min.23 This study was also limited to normal subjects; variance in patients with obstructive lung disease has been reported to be 64% greater than in normal subjects21 and the percentage of change in PEF measured by spirometry required for significance in patients with

ACKNOWLEDGMENTS

We thank Mark Cassidy, Mt. Sinai Hospital, Hartford, Conn, Debbie Crews, LDS Hospital, Salt Lake City, Utah, Marilyn Helgesen, Emory University Hospital, Atlanta, and Domenic Misiano, Massachusetts General Hospital, Boston, for their technical support.

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