How well do ECCS/ERS predictions fit?
If the ECCS/ERS prediction equations (see reference below) fit the reference population (lifelong non-smokers, no chronic respiratory symptoms in the past) well, then the differences between observed and predicted values should on average be close to 0. This is not the case:
| Gender | Average FEV1 (L) | FEV1 measured - predicted (L) | Average FVC (L) | FVC measured - predicted (L) |
| Females | 2.96 | 0.22 | 3.71 | 0.52 |
| Males | 4.49 | 0.30 | 5.65 | 0.60 |
The differences between measured and predicted values correlate with standing height, and as regards FEV1 also with age, but the explained variance is very small (1 to 2.2%). In a person of average age (50 yr) and height (1.68 m in women, 1.78 m in males) predicted valus for FEV1 are about 8% too low in males and females, 10% too low for FVC in males, and 15% too low for FVC in females (in agreement with another large Dutch study). Therefore, in the SpirXpert software package a set of adjusted predicted values is made available in addition to the original ECCS predictions. The resulting difference between actual spirometric index and adjusted predicted value is now (RSD: standard deviation about the predicted mean according to ECCS):
| Gender | FEV1 measured - predicted (L) | SD FEV1 measured - predicted | FVC measured - predicted (L) | SD FVC measured - predicted |
| Females | 0.00 | 0.40 (0.38) | -0.04 | 0.48 (0.43) |
| Males | 0.01 | 0.51 (0.51) | -0.03 | 0.61 (0.61) |
After
the adjustment there is good agreement between actual and
predicted values. The residuals (measured – predicted
values) in males are unrelated to height and age; in females
there is still a ‘statistically very significant’
relationship with age, but biologically this is irrelevant
as the difference comes to only a few mL over the entire age
range.
As shown in the graph, in women the adjusted predicted equation appears to be valid up to about 80 yr. This also holds for males (not shown).
ECCS and ERS
In the revised version (1993) of the 1983
report (Quanjer PhH (ed.) Standardized lung function testing.
Bull Eur Physiopathol Respir 1983; 19 suppl. 5: 45-51) of
the European Community for Coal and Steel (ECCS), published
in 1993, predicted values of lung indices were unchanged.
They are almost universally applied in Europe. The 1993 report
was officially adopted by the European Respiratory Society
(ERS).
The following chapter deals with spirometry, predicted values
and bronchodilator responsiveness:
Quanjer PhH, Tammeling GJ, Cotes JE, Pedersen OF, Peslin R,
Yernault JC. Lung volumes and forced ventilatory flows. Eur
Respir J 1993; 6 suppl. 16: 5-40.