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Summary. The variability (coefficient of variation of five consecutive measurements), reproducibility (difference of results at 1 h and 24 h), and interobserver difference (independent reading of the tracings by two observers) of airways resistance (Raw) and static lung volumes (residual volume, functional residual capacity, total lung capacity) using a body plethysmograph were assessed in 14 healthy subjects and in 25 patients with various respiratory disorders. The variability was low for TLC (4–5%), moderate for FRC (74%) and high for Raw (28%). No significant changes of Raw or lung volumes were found for the groups at 1 h and 24 h. Between observers, a slight difference existed for FRC and Raw in normal subjects; the difference was higher (4·5% for FRC and 11 % for Raw) and became significant in patients. The overestimation of Raw by observer 2 as compared to observer 1 was more important at larger values. The present findings call for caution when pooling results obtained by several observers in large-scale studies, or when comparing figures obtained by different technicians in the pulmonary function laboratory.

Ventilatory function--forced vital capacity (VC)--forced expiratory volume (in 1-sec forced expiratory flows) static lung volumes, closing volume, and phase III slope (single-breath N2 test) were compared in 94 children with and 436 children without a history of recent mild acute respiratory infection. Their age ranged from 10 to 16 years; subjects with symptoms on the day of the study were excluded. We found no difference in lung function between the two groups, with the exception of a slight (inconsistently significant) increase in closing volume (CV) and the CV/VC ratio. Although the influence of a persistent increase in interstitial lung pressure leading to early small airways closure cannot be ruled out, this isolated functional abnormality probably represents a spurious positive result, arising by chance when a large number of statistical tests are done.

Density dependence variables (helium-to-air difference in forced expiratory flows at 50 and 25% vital capacity and volume of isoflow) were compared with spirographic performance (vital capacity, FEV 1.0) in 76 men aged 33-56 years. The group included nonsmokers, asymptomatic smokers, subjects with chronic expectoration, but normal ventilatory function and subjects with chronic expectoration and minimal obstructive ventilatory impairment. Low-level correlations were found (coefficients of less than 0.3) between delta He25% or volume of isoflow on one side and FEV1.0 or FEV1.0/VC. Some possibly confounding factors for these correlations are discussed. We conclude that density dependence variables are not consistently related to the FEV1.0 in subjects 'at risk' or with minimal airflow limitation.

Summary. The variability, short-term (1 hour) and long-term (2 weeks) reproducibility of the variables derived from the single-breath N2 test were evaluated in a group of 56 healthy children aged 10 to 16 years with a computerized system. The variability was low for vital capacity and total lung capacity (coefficient of variation less than 3%), moderate for residual volume and phase III N2 slope (9 and 13%) and very high for closing volume (more than 50%). A closing volume could not be identified by the computer algorithm in 18.3% of the trials. The reproducibility of the variables was satisfactory both at 1 hour and at 2 weeks, with the exception of the closing volume, whose increase at 2 weeks seemed to be due to methodological factors. We conclude that reliable results of static lung volumes and phase III N2 slope, but not of closing volume, may be obtained in children by a computerized system in epidemiological studies.

Detailed pulmonary function studies were carried out on 11 workers of middle age, who had been exposed for 7 to 11 years to moderate concentrations of cadmium oxide. Minor abnormalities of lung volumes, intrapulmonary mixing and lung compliance were found in a few cases; no airway obstruction was present. The lung diffusing capacity and the blood gases were normal. The chest roentgenogram showed a normal vascular pattern at the periphery of the lung. It is concluded that emphysema was absent in the group studied.

Pulmonary function was investigated in four men one month after onset of acute histoplasmosis. Restrictive ventilatory impairment was found in one. Seven months later, his pulmonary function became normal. In the other three patients, a slight ventilation-perfusion unevenness was probably present.

Intrapulmonary gas distribution was studied in 18 patients with conglomerate silicosis using the standardized single-breath O2 test. To avoid the influence of chronic bronchitis and emphysema only patients without obstructive ventilatory impairment were tested. An increased N 2 gradient was found in 10 patients; the mean value in patients was highly significantly greater than that of normal subjects of similar age and smoking habits. The pathogenesis and physiological consequences of this ventilation unevenness are discussed.

The authors report the results obtained by routine utilization of inhalation tests with allergens in perennial asthma. One hundred seventy-five subjects from 230 consecutive asthmatic adults were submitted to inhalation tests. Both clinical observation and a simple spirographic recording (FEV 1.0 ) were used to assess the bronchial responses. The results are discussed from the point of view of clinical practice. It was found that a very suggestive anamnesis, supported by positive skin tests, was always associated with positive inhalation tests. In contrast, a somewhat suggestive anamnesis, with positive skin test to the incriminated allergen, was accompanied in only 23 per cent of the patients by a positive inhalation test to this allergen. Negative skin tests lowered considerably the incidence of positive inhalation tests. Allergens not indicated by anamnesis never determined a positive inhalation test, irrespective of the skin reaction. The authors support the view that inhalation tests are the only method available for an accurate etiological diagnosis in perennial asthma.

Currently, there is much interest in measuring fractional exhaled nitric oxide (FE NO ) in populations. We evaluated the reproducibility of FE NO in healthy subjects and determined the number of subjects necessary to carry out a longitudinal survey of FE NO in a population containing smokers and non-smokers, based on the assessed reproducibility. The reproducibility of FE NO was examined in 18 healthy smokers and 21 non-smokers. FE NO was assessed once at 9 AM on five consecutive days; in the last day this measurement was repeated at 2 PM. Respiratory symptoms and medical history were assessed by questionnaire. The within- and between-session repeatability of FE NO and log-transformed FE NO was described. The power of a longitudinal study based on a relative increase in FE NO was estimated using a bilateral t-test of the log-transformed FE NO using the between-session variance of the assay. FE NO measurements were highly reproducible throughout the study. FE NO was significantly higher in males than females regardless of smoking status. FE NO was positively associated with height (p < 0.001), gender (p < 0.034), smoking (p < 0.0001) and percent FEV1/FVC (p < 0.001) but not with age (p = 0.987). The between-session standard deviation was roughly constant on the log scale. Assuming the between-session standard deviation is equal to its longitudinal equivalent, either 111 or 29 subjects would be necessary to achieve an 80% power in detecting a 3% or a 10% increase in FE NO respectively. The good reproducibility of FE NO is not influenced by gender or smoking habits. In a well controlled, longitudinal study it should allow detecting even small increases in FE NO with a reasonable population size.