Excessive height reduction may reduce lung function test accuracy in COPD
MedWire News: Excessive height reduction may reduce the accuracy of lung function assessments in patients with chronic obstructive pulmonary disease (COPD), researchers warn.
“In Caucasians, height reduction of about 1 cm per decade occurs during the 40s and 50s and accelerates after age 60 in both sexes,” explain Aina Kjensli (Glittreklinikken, Hakadal, Norway) and team.
They add: “Vertebral deformities are prevalent in COPD patients, and may lead to height reduction beyond what is normally expected with age.
“As height is used for calculating reference values for pulmonary function tests, larger than normal height reduction could cause overestimation of lung function.”
To investigate, the researchers studied 465 COPD patients and 462 controls from the general population who were aged 50–80 years.
The participants’ height and weight were measured, and their arm span height (ASH) – body height estimated from arm span – was calculated by algorithms. They were also asked to recall their tallest lifetime height.
Radiographs were used to assess vertebral deformities in both groups, and those with COPD underwent comprehensive lung function tests.
Height reduction was frequent in both groups, with a “true loss” reduction of more than 2 cm in 55% of patients with COPD and 61% of the control group using recalled tallest height (RTH) as baseline, and 56% of patients with COPD when using ASH as baseline.
The researchers found that the percentage-point difference in pulmonary function tests increased with increasing height reduction, irrespective of whether RTH or ASH was used as baseline, with the effects smallest for FEV1 and forced vital capacity (FVC), and largest for total lung capacity (TLC) and residual volume (RV).
The proportion of COPD patients in whom the pulmonary function test differences exceeded a clinically-significant 5% increased with greater height reduction.
In men, the differences in FEV1 and FVC exceeded 5% for a height reduction of at least 4 cm, and differences in TLC and RV exceeded 5% for a height reduction of at least 2 cm. In women, the differences in FEV1 exceeded 5% with height reductions of at least 6 cm, and differences FVC, TLC and RV exceeded 5% in all height reduction categories.
Height reduction increased with the number and severity of vertebral deformities in both groups.
Kjensli and team conclude in the European Respiratory Journal: “When using current measured height, lung function may be overestimated in a large proportion of COPD patients at relatively modest height reductions.”
They add: “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. These patients should be further evaluated for coexisting vertebral deformities and the possibility of having osteoporosis.”
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By Mark Cowen