Respiratory mechanical impedances were determined during voluntary apnea in five healthy subjects, by means of 0.25- to 5-Hz pseudo/random oscillations applied at the mouth. The total respiratory impedance was partitioned into pulmonary (ZL) and chest wall components with the esophageal balloon technique; corrections were made for the upper airway shunt impedance and the compressibility of alveolar gas. Neglect of these shunt effects did not qualitatively alter the frequency dependence of impedances but led to underestimations in impedance, especially in the chest wall resistance (Rw), which decreased by 20-30% at higher frequencies. The total resistance (Rrs) was markedly frequency dependent, falling from 0.47 +/- 0.06 (SD) at 0.25 Hz to 0.17 +/- 0.01 at 1 Hz and 0.15 +/- 0.01 kPa X l-1 X s at 5 Hz. The changes in Rrs were caused by the frequency dependence of Rw almost exclusively between 0.25 and 2 Hz and in most part between 2 and 5 Hz. The effective total respiratory (Crs,e) and pulmonary compliance were computed with corrections for pulmonary inertance derived from three- and five-parameter model fittings of ZL. Crs,e decreased from the static value (1.03 +/- 0.18 l X kPa-1) to a level of approximately 0.35 l X kPa-1 at 2-3 Hz; this change was primarily caused by the frequency-dependent behavior of chest wall compliance.

Equivalent (effective) values of airway resistance were determined for total breaths, inspiration and expiration in spontaneously breathing patients by means of an off-line processing system. An improvement in the alveolar pressure determination was achieved by subtracting thermal pressure drifts of the pressure plethysmograph and by taking into account instantaneous values of the intrathoracic gas volume. Equivalent resistance values were compared with the results of several simulated routine evaluations. It was found that the equivalent resistance is best approximated by the graphical procedure using average pressure points at ± 0.5 liter/sec flow levels.

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After a period of 10 years the authors reexamined the respiratory health status of 381 dust-exposed males. Of the lung function values examined R_aw, RV/TLC%, VC, TGV and PaO₂ were found to be of significant prognostic importance. Among the radiological changes characteristic of silicosis the most serious B-C category, among the respiratory complaints dyspnoea accompanied by regular cough and expectoration, and among the physical changes extended rhonchi and rales accompanied by an emphysematous thorax are to be considered as most essential with respect to prognosis. Smoking habits significantly affected the total death rate, but did not prove to be significant with regard to respiratory death. In the development of bronchial obstruction recurrent febrile respiratory diseases proved to be more important than smoking habits and mild bronchitic complaints

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