Lung volume predictions are likely to be inaccurate in elderly patients because the equations were derived using data from younger subjects, Spanish researchers report.
Their findings, the investigators say, "underscore the importance of using prediction equations appropriate to the age and height characteristics of the population" when screening for pulmonary function problems.
Dr. Francisco Garcia-Rio and colleagues at Hospital Universitario La Paz, Madrid, came to this conclusion after measuring lung volume in 321 healthy subjects, ages 65 to 85 years, who never smoked. Standard spirometry and lung volume determinations by plethysmography and by the multibreath helium equilibration method were employed.
In the December 1st issue of the American Journal of Respiratory and Critical Care Medicine, they report that values for all lung volumes were higher with plethysmography than with the dilutional methods. "The differences obtained between plethysmography and helium dilution are notable," the authors write.
In almost all cases, reference equations overpredicted true lung volumes in their elderly subjects.
For instance, between 17.9% and 62.5% of women were classified as having a total lung volume below the normal lower limit. For men, the corresponding value was between 12.5% and 42.2%.
In contrast, the report indicates, only 0.6% to 1.7% of the women and 0.1% to 0.3% of the men were above the upper limit of normal when residual volume was measured with plethysmography.
Based on their findings, Dr. Garcia-Rio and colleagues have developed their own more age-appropriate reference equations that take into account not just standing height, as in younger individuals, but other factors as well, including age, body surface area, body mass index, and weight.
Their equations "may be used for the prediction of lung volumes in white patients 65 to 85 years of age with standing heights for women between 144 and 174 cm and men between 152 and 181 cm."
"The use of our reference equations beyond these age and height limits may lead to inaccuracies," they add.
Am J Respir Crit Care Med 2009;180:1083-1091.
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