Physiologically interpretable prediction equations for spirometric indexes

Abstract

The need for ethnic-specific reference values of lung function variables (LFs) is acknowledged. Their estimation requires expensive and laborious examinations, and therefore additional use of results in physiology and epidemiology would be profitable. To this end, we proposed a form of prediction equations with physiologically interpretable coefficients: a baseline, the onset age (A0) and rate (S) of LF decline, and a height coefficient. The form was tested with data from healthy, nonsmoking Poles aged 18-85 yr (1,120 men, 1,625 women) who performed spirometry maneuvers according to American Thoracic Society criteria. The values of all the coefficients (also A0) for several LFs were determined with regression of LF on patient's age and deviation of patient's height from the mean height in the year group of this patient. S values for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow, and maximal expiratory flow at 75% of FVC (MEF75) were very similar in both sexes (1.03+/-0.07%/yr). FEV1/FVC declines four to five times slower. S for MEF25 appeared age dependent. A0 was smallest (28-32 yr) for MEF25 and FEV1. About 50% of each age subgroup (18-40, 41-60, 61-85 yr) exhibited LFs below the mean, and 4-6% were below the 5th percentile lower limits of normal, and thus the form of equations proposed in the paper appeared appropriate for spirometry. Additionally, if this form is accepted, epidemiological and physiological comparison of different LFs and populations will be possible by means of direct comparison of the equation coefficients.

A mathematical reason for FEV1/FVC dependence on age

“…Since both FEV1 and FVC depend on a common factor that is age [7,8,11-14], one may expect some statistical correlation between FEV1 and FVC. Moreover, assuming that dependence of FEV1 and FVC on age in middle-aged and elderly healthy subjects is linear [7,11], also the relationship between FEV1 and FVC should be linear.…”

“…Moreover, assuming that dependence of FEV1 and FVC on age in middle-aged and elderly healthy subjects is linear [7,11], also the relationship between FEV1 and FVC should be linear. Direct analysis of this relationship confirmed the linearity (formula 1), however the correlation between FEV1 and FVC appeared to be surprisingly high.…”

“…Direct analysis of this relationship confirmed the linearity (formula 1), however the correlation between FEV1 and FVC appeared to be surprisingly high. In particular, regression of FEV1 on FVC produced R 2 being much higher than R 2 obtained during regression of FEV1 or FVC on age for the same sample of the Polish population [7]. …”

“…where: FEV1 0 is the mean value of FEV1 for the left end of this age range, S FEV1 and S FVC are the decline rates of FEV1 and FVC, respectively (S FEV1  = 1.070%/year and S FVC =0.992%/year in Polish females, S FEV1  = 1.098%/year and S FVC =0.968%/year in males [7]).…”

“…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.…”