Informative value of simple multibreath nitrogen washout measurements for clinical and research purposes

Some simple multibreath nitrogen washout indexes quantifying inspired gas distribution and ventilatory efficiency were obtained in a group of patients with mild to advanced chronic obstructive pulmonary disease (COPD) and studied in their relationships with routine pulmonary function tests. The indexes (lung clearance index (LCI), mixing ratio (MR) and data obtained by graphic analysis of the washout curve) were correlated with spirometric, pulmonary mechanics and arterial blood gas measurements, but only 8-38% of the interindividual variation in these indexes was explained by the above routine tests. An additional 5-13% of the variation was explained by the washout tidal volume (VT); this finding may reflect changes in gas distribution with VT and/or the influence of the dead space on ventilatory efficiency. Our data indicate that, in patients with COPD, nitrogen washout indexes tend to change in parallel with routine pulmonary function tests, reflecting the severity of the disease; these indexes also contain specific information (in addition to that provided by routine physiologic tests), presumably related to the distribution and efficiency of ventilation. Nitrogen washout measurements may thus represent a helpful adjunct to routine pulmonary function testing; LCI and MR appear to be particularly convenient for practical purposes because of their simplicity, and an informative content comparable with that of more complex indexe

Effects of bronchodilators on the behavior of pulmonary resistance and dynamic compliance as functions of respiratory frequency

The effects of bronchodilator treatment (intravenous atropine or inhaled metaproterenol) on the behavior of pulmonary resistance (RL) and dynamic compliance (Cdyn) as functions of respiratory frequency were studied in patients with chronic obstructive pulmonary disease and in apparently normal smokers. No systematic changes in the frequency-dependent behavior of RL and Cdyn were observed after bronchodilator treatment; the degree of frequency dependence increased in some subjects, and decreased or remained unchanged in others. The present results suggest that the effects of bronchodilators on the relationships between lung mechanical properties and respiratory frequency are not based on a single mechanism, but probably reflect the interaction of multiple factors possibly associated with the bronchodilator treatmen

Reproducibility of multibreath nitrogen washout measurements

The reproducibility of data obtained from the analysis of the pulmonary nitrogen clearance during oxygen breathing was studied in a group of normal subjects and in patients with chronic obstructive pulmonary disease. As shown by statistical analysis, the reproducibility of some relatively simple measures of gas distribution inequality and ventilatory efficiency (lung clearance index and mixing ratio) was found to be satisfactory; the intrasubject variation of data obtained from the graphic analysis of the nitrogen washout curve according to a multicompartment lung model was found to be greater than that of the lung clearance index and mixing ratio, but tolerable for most of these data. The results indicated that the intrasubject variability of the nitrogen washout measurements analyzed in the present study, although acceptable, is not negligible and should be taken into account when assessing the significance of experimental nitrogen clearance changes

Pulmonary resistance and dynamic compliance as functions of respiratory frequency

The behavior of pulmonary resistance (RL) and that of dynamic compliance (Cdyn) as functions of respiratory frequency (f) were compared in normal subjects and in patients with chronic obstructive pulmonary disease (COPD). Although both RL and Cdyn varied with f in most COPD patients and in some normal subjects, Cdyn appeared to be more sensitive than RL to variations of frequency; no significant changes in RL could be demonstrated in subjects in whom Cdyn was frequency dependent. The degree of frequency dependence of Cdyn was correlated with the severity of respiratory impairment (as quantified by conventional pulmonary function tests); in contrast, RL was not detectably frequency dependent in some subjects with advanced COPD. Compared with Cdyn, RL was more commonly nonlinearly related to respiratory frequency, often increasing at high breathing rates. Our results indicate that changes in RL with frequency are less predictable and more difficult to detect than the corresponding changes in Cdy