- Dick M Goedhart: Cardialysis B.V., Westblaak 92, 3012 KM Rotterdam, The Netherlands.
In the literature, different statistical methods to evaluate bronchodilator studies are used. These approaches are all based on the absence of residual heterogeneity and on baseline independency of the parameter under analysis. A database containing the lung function values of newly referred patients was used to assess these assumptions as function of the underlying diagnosis (asthma, bronchitis and emphysema) and to chart the characteristics of analysis of covariance, which (partly) deals with these drawbacks. Bronchodilator data of 709 asthmatics, 522 bronchitic and 126 emphysema patients were used. It was shown that, in asthma, for almost all lung function parameters, bronchodilation was indeed dependent on baseline values, which was less strong in bronchitis and even weaker in emphysema. A negative effect of age on bronchodilation was found, which is strong in asthma and almost absent in emphysema, rendering the use of bronchodilation as a diagnostic tool less useful. The conclusion is that analysis of covariance is a good way to evaluate bronchodilation studies in obstructive lung disease, particularly in asthma. For bronchitic or emphysema patients, difference-based approaches may suffice. The assumptions underlying the other methods were not met.