Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients ADVISER Tiago António Queirós Jacinto CLASS

Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients

ADVISER Tiago António Queirós Jacinto CLASS 2

Barbosa M., Barbosa T., Brito T., Campos J., Carvalho L., Carvalho R., Costa A., Dias J., Dória M., Maciel C., Mosca A., Pires C., Silva F., Viana D. - [email protected]

Introduction to Medicine I 2009/2010

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Many respiratory diseases such as asthma and COPD can be diagnosed and also monitored using spirometry

Introduction

Research questions and aims

Methods

Results

Conclusion

It analyses how well you can breathe


Respiratory diseases can be monitored using spirometry

FEV1 is the amount of air breath out during the first second

Reference formulas convert the values of FEV1 to a percentage whose optimal value is 80 or higher


There are several reference formulas

The evolution, changes in society, as well as interpersonal differences are not taken into account

Most formulas are now obsolete


Explore the use of different reference values

Verify the differences between the four reference formulas

(Crapo, ECCS, Knudson, and Morris), in what concerns to the

predicted values (FEV1, FVC, Tiffeneau Index) in asthmatics

Interpret the cause of some misdiagnosis


Target population: Target population: Asthmatic patients from the Allergology Department of Hospital de S. João, Porto

Sampling methods: Sampling methods: 235 asthmatic people with more than 18 years old who consecutively performed spirometry in the Allergology Department of Hospital de S. João

Inclusion criteria: Inclusion criteria: The inclusion criteria are: (1) being adult, (2) being asthmatic and (3) have performed spirometry

Unit of analysis: Unit of analysis: Asthmatic participant


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DATA COLECTION METHODS

Consecutively collected

Same technique and instrument

STUDY DESIGN

Transversal


VARIABLES DESCRIPTION

IdentificationIdentification

AgeAge (in years) Gender Gender (male or female) HeightHeight (in cm)

Value from SpirometryValue from Spirometry, and Predicted value Predicted value and PercentagePercentage obtained using the reference formulas for:

FVC FVC Forced vital capacity

FEV1 FEV1 Forced expiratory volume in the first second TIFFENEAU INDEXTIFFENEAU INDEX FEV1/FVC


STATISTICAL ANALYSIS

Insert data and apply reference formulas on Microsoft® Office Excel® 2007 Reference formulas published by Crapo et al (1981), ECCS (1993), Knudson et al (1983), and Morris et al (1971)

(value collected through spirometry) / (predicted value)

Transfer to SPSS Statistics 17.0®

Recode percentages to binary code categorical

Calculate differences to FEV1 and FVC between Crapo-ECCS, Crapo-Knudson, Crapo-Morris, ECCS-Knudson, ECCS-Morris andKnudson-Morris



Variables Mean (SD) Range

Sample (n=235) [100%]Age, yr 47,3 (10,8) 18 – 70Height, cm 164,9 (5,2) 144 – 194FEV1, L 2,9 (0,8) 0,62 – 7,5FVC, L 3,9 (0,8) 1,33 – 8,94Tiffeneau index 74,9 (9,5) 33,79 – 100

Male subjects (n=32) [13,6%]Age, yr 45 (13,9) 18 – 63Height, cm 169,6 (6,3) 158 – 194FEV1, L 3,6 (1,0) 0,99 – 7,5FVC, L 4,6 (1,1) 2,93 – 8,94Tiffeneau index 76,3 (13,2) 33,79 – 100

Female subjects (n=203) [86,4%]

Age, yr 47,7 (10,2) 19 – 70Height, cm 164,2 (4,6) 144 – 165FEV1, L 2,8 (0,7) 0,62 – 4,2FVC, L 3,7 (0,7) 1,33 – 5,56Tiffeneau index 74,6 (8,9) 40,63 – 97,84

Sample description


for men

for women


Mean (SD)

2,9 (0,8) 2,8 (0,4) 2,9 (0,5) 2,7 (0,4) 2,8 (0,5)

Comparison between real and predicted FEV1 means


FEV1

FVC

for men Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients

Difference between FVC and FEV1 predicted means

for men Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients

FEV1

FVC

for women Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients

Difference between FVC and FEV1 predicted means

for women Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients

Pairs sorted by means difference, in liters, between FVC and FEV1 predicted means for men and women


FVC FEV1

Male Female Male Female

Knudson - Morris -1,76 -0,16 -1,16 0,08

ECCS - Morris -1,66 -0,29 0,06 0,06

Crapo - Morris -1,39 0,00 0,29 0,19

Crapo - Knudson 0,37 0,16 0,45 0,11

Crapo - ECCS 0,27 0,30 0,24 0,13

ECCS - Knudson -0,10 -0,14 -0,22 -0,02

> 0,2 L

Knudson Crapo Morris ECCSNormal (FEV1≥80%) 89,4 (%) 86,8 (%) 91,1 (%) 90,6 (%)Low FEV1 10,6 (%) 13,2 (%) 8,9 (%) 9,4 (%)Normal (FVC≥80%) 95,3 (%) 93,2 (%) 86,0 (%) 95,7 (%)Low FVC 4,7 (%) 6,8 (%) 14,0 (%) 4,3 (%)


Percentages of normal and low FEV1 and FVC obtained with different formulas among the sample

Reference equations Simple K Agreement K Linear Weighting

Agreement

ECCS - Morris 0,947 good 0,951 goodECCS - Knudson 0,807 good 0,916 good

Knudson - Morris 0,774 substantial 0,855 goodCrapo - Knudson 0,752 substantial 0,864 good

Crapo - ECCS 0,659 substantial 0,846 goodCrapo - Morris 0,624 substantial 0,796 substantial

Results of Simple Kappa and Kappa Linear Weighting

Agreement in FEV1 predicted values


(0-35% - very severe; 36-50%- severe; 51-60% - moderate/severe; 61-70% - moderate; 71-79% - mild; ≥80% - normal)



Agreement in the classification of the severity of the obstructive defect

Reference Equations

Concordant classifications Discordant classifications

Patients % Patients %

Crapo - Morris 218 92,8% 17 7,2%

Crapo – ECCS 219 93,2% 16 6,8%

Knudson – Crapo 223 94,9% 12 5,1%

Knudson – Morris 226 96,2% 9 3,8%

Knudson – ECCS 227 96,6% 8 3,4%

Morris - ECCS 233 99,1% 2 0,9%



Level of agreement between the equations according to age group and sex

Collen J. et al, 2008


Collen J. et al, 2010

Older reference formulas NHANES III

ECCS

All the results showed significant discrepancies between reference formulas, changing the classification of patients.

LIMITATIONS


data collected in just one hospital in a single department

demographic and social factors may influence outcomes

database includes a higher number of females compared to males

more recent equations in order to achieve more reliable and accurate results

according to these differences ,it would be a good option to make a new study only with men

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Results have significance not only statistically but also in clinical practice

need to change:


formulas must be restructured and correctly applied to each patient’s specific characteristics

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ADVISER Tiago António Queirós Jacinto CLASS 2

Barbosa M., Barbosa T., Brito T., Campos J., Carvalho L., Carvalho R., Costa A., Dias J., Dória M., Maciel C., Mosca A., Pires C., Silva F., Viana D. - [email protected]

Introduction to Medicine I 2009/2010


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Differences in the interpretation of FEV1 using four commonly used reference formulas in asthmatic patients ADVISER Tiago António Queirós Jacinto CLASS