Metrics details. However, the nature of this dependence is uncertain. Spirometry is the fundamental diagnostic method in obstructive lung diseases because it is easy and inexpensive to perform, and thus it can be used as a screening test. Evaluation of forced spirometry results begins with analysis whether bronchial airflow capacity quantified by means of the forced expiratory volume in one second FEV1 corresponds to the lungs size estimated with the forced vital capacity FVC or is too small.
According to the present recommendations, the relationship between FEV1 and FVC is quantified by means of the ratio of these indices, i. Accurate matching of the equation is essential since an incorrect equation may lead to either the abandonment of a sick individual or the diagnosis of a non-existing disease and unnecessary treatment of healthy individuals.
Unfortunately, the present equations proposed by various authors differ significantly in predictions, especially for more advanced age, i. Therefore, the following doubt might appear: is it possible that the age-dependence of this index is an accidental effect of its calculation method not matched to the nature of the true relationship between FEV1 and FVC?
To test this hypothesis, a direct statistical analysis of the relationship in healthy individuals was performed. The nature - whether mathematical or physiological - of troublesome dependence of an index that is calculated not measured on some factors may be very important: if the nature is mathematical then another, better mathematical index could be proposed, which is the additional aim of this work.
With the permission of the Local Ethics Committee, the authors utilized the database of that project in the analysis of the relationship between FEV1 and FVC that is presented in this paper. It should be noted that the same database was utilized in our other works related to different matters: prediction equations of a novel form [ 7 ] and an index for quantitative assessment of correctness of the flow-volume curve [ 16 ]. That project involved spirometry screening for obstructive lung diseases in Poland.
With a mobile laboratory, the examinations were performed at 93 sites: both large cities and small towns as well as villages throughout Poland. All examinations were performed and analyzed by the same group of six qualified employees performing routinely spirometry in the Central Clinical Hospital of the Polish Ministry of National Defense.
Like during elaboration of prediction equations, only data for healthy subjects were taken into account. The final selection was performed by the authors taking into account both medical and technical criteria. Consequently, the results for females and males were used in the analysis.
Table 1 presents details concerning these groups. The strength of the relationship between FEV1 and FVC was described quantitatively with the fraction of explained variance R 2 and the correlation coefficient r. As the correlation coefficient appeared very high, the relationship could be described accurately with a linear equation. Age was used as an additional independent variable of the regression to examine a possible increase in R 2 suggesting age influence on the relationship between FEV1 and FVC.
The values of the coefficients A and C for males and females are shown in Table 2. R 2 increased very little when age was added as the second independent variable in the regression of FEV1 Table 2 , which means that the relation between FEV1 and FVC is practically age-independent.
Although age and height significantly influence both FEV1 and FVC, they have a very insignificant influence on the relationship between them Figure 1. Thus, the main result of the work could be expressed as follows: in healthy subjects FEV1 depends on FVC without respect to the other factors, including age and height. If FVC for an individual is known, the expected value of FEV1 can be estimated with the formula 1 using the coefficients from the Table 2.
If, however, a patient is suffering from an obstructive lung disease, the difference between the measured and expected values of FEV1 should be significant. Figure 2 shows graphical interpretation of the above. Direct analysis of this relationship confirmed the linearity formula 1 , however the correlation between FEV1 and FVC appeared to be surprisingly high. The relationship between FEV1 and FVC can be described precisely by means of a linear equation with the constant term C different from zero.
Neither original data used by other authors [ 8 , 11 — 14 ] could be utilized to verify the existence of the constant term being different from zero nor their equations could be used in the formula 3 because those equations had forms being physiologically uninterpretable.
Note that all the curves in Figure 3 suggest the x-intercept different from zero, despite that some of these curves are not appropriate for the population analyzed here. Comparison of the relationship between values predicted with old ECSC equations [ 11 ] thin continuous lines in Figure 3 with the relationships between FEV1 and FVC for subjects in this study as well as predicted with more recent equations the other lines in Figure 3 suggests movement of the relationship to the right in comparison with ECSC a possible reason: less restrictive criterion for the forced expiration time in the past causing underestimation of FVC [ 7 , 8 , 18 ].
Light gray dots — the studied material. It should be noted that Burrows et al. You may also need different treatments to make it easier for you to go about your….
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See also separate article Spirometry. 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. Normal in restrictive disease - reduced in obstructive disease. Normal in restrictive disease. Are you protected against flu? Further reading and references. Marks GB ; Are reference equations for spirometry an appropriate criterion for diagnosing disease and predicting prognosis?
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