NEW YORK (Reuters Health) – In chronic obstructive pulmonary disease (COPD), vertebral deformities often contribute to excess height loss with aging – which in turn may lead to misinterpretation of patients’ lung function tests, say researchers from Norway.

Therefore, the investigators advise, “For COPD patients with height reduced more than normal for age, one might use recalled tallest height or height calculated from arm span in the calculation of predicted values.”

In an online article published January 28 by the European Respiratory Journal, lead author Dr. Aina Kjensli, from Glittreklinikken in Hakadal, and colleagues explain that because height is used for calculating reference values for pulmonary function tests, predicted values may be underestimated and lung function overestimated in patients with excessive height loss.

The investigators studied 465 COPD patients (mean age 63, 50% female) and 462 controls (mean age 65, 50% female) to compare height reductions and vertebral deformities and to see how lung function is affected by height reduction in COPD.

There were no significant differences in height between patients and controls. On average, current measured height was 2.3 cm lower than recalled tallest height and 2.5 cm lower than height determined by arm span (Parker algorithm) (p < 0.0001 for each). The reduction in recalled tallest height averaged 0.2 cm more among patients vs controls. The COPD group had a higher rate of vertebral deformities (30% vs 21%, p = 0.002) and more deformities per person (0.8 vs 0.5, p = 0.001). Height reduction was correlated with spinal deformity index in both groups (p < 0.0001), with no significant difference between groups. Only the COPD patients had pulmonary function tests done. The effects of height reduction on actual vs predicted values were smallest for tests of forced expiratory volume in 1 second and vital capacity, and most pronounced for total lung capacity and residual volume, the authors report. However, pulmonary function did not differ based on number of vertebral deformities per se. When estimating pulmonary function, Dr. Kjensli’s group makes two recommendations. First, for COPD patients with normal age-related height reduction, reference values should be based on measured standing height. Second, for patients with height reduction of 4 cm or more, pulmonary function tests should be compared to predicted values based on patients’ recalled tallest height or height according to arm span. They also advise that patients with increased height reduction be evaluated for coexisting vertebral deformities and osteoporosis. Reference:
Eur Respir J 2010.