The purpose of this study was to determine whether the forced oscillation technique is more sensitive than spirometry to detect lung function alterations in subjects with respiratory complaints.The input impedance of the respiratory system (between 2 and 24 Hz) and maximal expiratory flows and volumes were measured in 1,255 subjects referred for routine spirometry. A questionnaire concerning respiratory complaints was administered. A discriminant analysis was performed between subgroups of subjects without (137 males and 140 females), with moderate (115 males and 109 females) and with marked respiratory complaints (149 males and 132 females). A clear-cut separation was achieved by this analysis only between those subjects without and with marked complaints.Both lung volumes and flows as well as impedance parameters (mean value and frequency dependence of resistance in females, mean resistance in males) contributed to the discrimination of subjects without and with marked respiratory complaints, although there was only a moderate decrease of discriminative power when the impedance parameters were excluded. The contribution of the forced oscillation parameters to discriminative power was larger in females than in males (40 vs 19%), which may be related to the higher prevalence of asthma in our population of females. Excluding the subjects with marked functional impairment improved the share of forced oscillation parameters only slightly with respect to lung volumes and flows (females 54 vs males 23%). Considered separately, however, the sensitivity of spirometry and forced oscillation technique to detect symptomatic people appeared to be similar.We conclude that impedance measurements by forced oscillation technique and routine spirometry are both associated with respiratory complaints. Our results indicate that the information provided by impedance measurements can be complimentary to that obtained by spirometric indices. Eur Respir J., 1996, 9, 131-139. Laboratorium voor Pneumologie, U.Z. Gasthuisberg, Leuven, Belgium.Correspondence: K.P. Van The forced oscillation technique has been developed to study the impedance of the respiratory system. Although the technique has been available since 1956 [1], it is still not widely accepted in the routine lung function laboratories. One of the reasons for this is that the relevance of finding abnormal airway impedance values is unclear.Previous studies have shown that in patients with upper airway obstruction [2], lower airway obstruction (asthma, chronic bronchitis and emphysema) [3], with restrictive lung disease due to diffuse interstitial lung disease or a stiff chest wall [4,5] there is a uniform pattern of changes of resistance and reactance, i.e. an increase of respiratory system resistance (Rrs) at low oscillatory frequencies, a negative frequency dependence of Rrs and a decrease of respiratory system reactance (Xrs) at all frequencies between 2 and 32 Hz. These changes probably reflect the increase of the influence of the upper airway shunt on the ...

Supported by the Research Council of the University of Leuven (grant OT/93/12).It is known that in healthy subjects breathing through a mouthpiece results in an increase of tidal volume (VT) [1][2][3], of inspiratory (t I) [2,3] and expiratory time (t E) [2], and inspiratory drive (VT/t I) [2,4]. These changes in ventilation have been attributed to: 1) the influence of the additional dead space; 2) stimulation of the nasal and oral mucosa by the noseclip and mouthpiece; 3) shift of respiratory route from unrestricted nose to mouth.For these reasons, an alternative technique, i.e. respiratory inductive plethysmography (Respitrace) is widely used in the study of the breathing pattern to avoid the influence of the mouthpiece and occlusion of the nose.As pointed out by GILBERT et al.[1], a fourth influence which might modify the natural resting ventilation is that of registration itself, by focusing the subject's attention on his breathing. The use of any recording technique, even a noninvasive one, might modify the spontaneous breathing pattern. In the present study, we tried to evaluate this influence. Materials and method SubjectsThe study was performed on two groups of healthy volunteers: 1) 42 subjects ("younger" population), 25 females and 17 males, aged 21-26 (mean 22) yrs, who were (except for two) medical students of K.U. Leuven, Belgium; 2) 32 subjects ("older" population), 15 females and 17 males, aged 35-63 (mean 47) yrs, who were recruited from outside the hospital. All 74 subjects (younger and older population) were naive to the purpose of the study. Anonymity was ensured.Before the experiment, the subjects answered four questionnaires. One dealt with medical history, two screened the level of anxiety, and one the spontaneous complaints of the subjects. To evaluate the anxiety of the subjects, the state and trait versions of the Zelfbeoordelingsvragenlijst (ZBV-DY1, ZBV-DY2) [5], which is the Dutch Seventy four subjects (40 females and 34 males), aged 21-63 yrs, were studied under three different conditions whilst their breathing was being recorded for 5 min by means of inductance plethysmography (Respitrace): 1) subjects were misled into believing that their breathing was not being recorded but that they had to wait for 5 min whilst equipment was calibrated; 2) subjects were instructed that their breathing pattern was being recorded for 5 min; 3) the subject's breathing was recorded for 5 min with mouthpiece and pneumotachograph. The first two conditions were randomized. The Respitrace was calibrated by means of multiple linear regression carried out during the 5 min period of quiet breathing through a mouthpiece.Awareness of the recording of breathing caused prolongation of inspiratory (t I) and expiratory time (t E). Breathing through the mouthpiece resulted in an increase of t I, t E and tidal volume (VT). The breathing irregularities (sighs and end-expiratory pauses) decreased when subjects were aware of the recording of breathing and nearly disappeared when subjects breathed through the mouthpiec...

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Ankylosing spondylitis and kyphoscoliosis both alter the function of the lung by modifying the mechanical properties of the thoracic cage. The purpose of the present study was to assess the changes in total respiratory resistance (Rrs) and reactance (Xrs) in these patients and to compare these data with conventional pulmonary function tests. In 16 patients with ankylosing spondylitis and seven with kyphoscoliosis we measured lung volumes, maximal flows, diffusing capacity, airway resistance, lung compliance and Rrs and Xrs between 2-26 Hz by means of the forced oscillation technique (FOT). In the patients with ankylosing spondylitis mean total lung capacity was 83% predicted (range 60-105%). Mean values of Rrs were normal; there was a small decrease in Xrs at the lowest frequency. In the patients with kyphoscoliosis mean total lung capacity (TLC) was 41% predicted for arm span (range 26-75%). Mean Rrs was elevated with a negative frequency dependence, and mean Xrs was decreased. The observed differences in Rrs and Xrs between the two groups of patients are related to differences in severity of the restriction. There is evidence that the changes in Rrs and Xrs in both groups are mainly attributable to an increase in chest wall resistance and a decrease in chest wall compliance, while in the patients with kyphoscoliosis an increase in airway resistance and a decrease in lung compliance also intervenes.

It can be postulated that patients in early stages of pulmonary emphysema have normal values of total respiratory resistance and reactance. The purpose of this study was to investigate whether pulmonary emphysema, detected functionally by a decrease of the single breath diffusing capacity (DLCO) by at least 25% of predicted, and an increase of the static lung compliance (CLst) by at least 50% of predicted, can be accompanied by normal values of respiratory resistance (Rrs) and reactance (Xrs), measured between 2 and 24 Hz by the forced oscillation technique. In a prospective study, we determined CLst in 26 patients, who had been selected on the basis of normal values of Rrs and Xrs, and a DLCO of less than 75% of predicted. In 17 of these patients, CLst was more than 150% of predicted. Since there were only minor abnormalities on routine lung function tests and chest X-ray, it is likely that these patients presented early emphysema. In the nine other patients, CLst was within normal limits: four suffered from interstitial lung disease; the remaining five were probably in a preliminary stage of early emphysema. In conclusion, early emphysema should systematically be considered as the first diagnosis in patients with normal values of Rrs and Xrs, and a decrease of DLCO. Onset of interstitial lung disease is a possible alternative.