MEASUREMENT OF RESPIRATORY IMPEDANCE BY FORCED OSCILLATION - COMPARISON OF THE STANDARD AND HEAD GENERATOR METHODS

Physiological and clinical studies have shown that the standard method of measuring respiratory impedance by forced oscillation leads to les s efficient control of the upper airway shunt effect than the head gen erator method. To test the effects of these two techniques in epidemio logical studies, we compared, in a sample of 73 French agricultural wo rkers, the values obtained with each method for five forced oscillatio n parameters: resistance, frequency dependence of resistance, inertanc e, compliance and resonant frequency. For these comparisons, subjects were classified according to four respiratory status factors: smoking status, cough, expectoration and airway obstruction assessed from the maximum expiratory flow volume curve. Logistic regression models using the set of four forced oscillation parameters (excluding resonant fre quency, which is derived from compliance and inertance) were then used to analyse the ability of each method to classify the subjects in eac h group. Significant differences between the two methods were observed for the mean values obtained for all five parameters. However, when e ach parameter was considered separately, the correlations between the values for each method were significant. Each method possessed the nec essary ability to separate subjects into our group classification, but the significant relationships were not always found for the same para meters. Finally, logistic regression models showed that the two method s led to almost the same classification of the subjects. According to our results, the standard method of applying forced oscillation at the mouth seems an acceptable device for measuring respiratory impedance for epidemiological purposes.