Ellie Oostveen

The forced oscillation technique in clinical practice: methodology, recommendations and future developments

The forced oscillation technique (FOT) is a noninvasive method with which to measure respiratory mechanics. FOT employs small-amplitude pressure oscillations superimposed on the normal breathing and therefore has the advantage over conventional lung function techniques that it does not require the performance of respiratory manoeuvres. The present European Respiratory Society Task Force Report describes the basic principle of the technique and gives guidelines for the application and interpretation of FOT as a routine lung function test in the clinical setting, for both adult and paediatric populations. FOT data, especially those measured at the lower frequencies, are sensitive to airway obstruction, but do not discriminate between obstructive and restrictive lung disorders. There is no consensus regarding the sensitivity of FOT for bronchodilation testing in adults. Values of respiratory resistance have proved sensitive to bronchodilation in children, although the reported cutoff levels remain to be confirmed in future studies. Forced oscillation technique is a reliable method in the assessment of bronchial hyperresponsiveness in adults and children. Moreover, in contrast with spirometry where a deep inspiration is needed, forced oscillation technique does not modify the airway smooth muscle tone. Forced oscillation technique has been shown to be as sensitive as spirometry in detecting impairments of lung function due to smoking or exposure to occupational hazards. Together with the minimal requirement for the subjects cooperation, this makes forced oscillation technique an ideal lung function test for epidemiological and field studies. Novel applications of forced oscillation technique in the clinical setting include the monitoring of respiratory mechanics during mechanical ventilation and sleep.

An Official American Thoracic Society Workshop Report: Optimal Lung Function Tests for Monitoring Cystic Fibrosis, Bronchopulmonary Dysplasia, and Recurrent Wheezing in Children Less Than 6 Years of Age

Although pulmonary function testing plays a key role in the diagnosis and management of chronic pulmonary conditions in children under 6 years of age, objective physiologic assessment is limited in the clinical care of infants and children less than 6 years old, due to the challenges of measuring lung function in this age range. Ongoing research in lung function testing in infants, toddlers, and preschoolers has resulted in techniques that show promise as safe, feasible, and potentially clinically useful tests. Official American Thoracic Society workshops were convened in 2009 and 2010 to review six lung function tests based on a comprehensive review of the literature (infant raised-volume rapid thoracic compression and plethysmography, preschool spirometry, specific airway resistance, forced oscillation, the interrupter technique, and multiple-breath washout). In these proceedings, the current state of the art for each of these tests is reviewed as it applies to the clinical management of infants and children under 6 years of age with cystic fibrosis, bronchopulmonary dysplasia, and recurrent wheeze, using a standardized format that allows easy comparison between the measures. Although insufficient evidence exists to recommend incorporation of these tests into the routine diagnostic evaluation and clinical monitoring of infants and young children with cystic fibrosis, bronchopulmonary dysplasia, or recurrent wheeze, they may be valuable tools with which to address specific concerns, such as ongoing symptoms or monitoring response to treatment, and as outcome measures in clinical research studies.

Lung function and bronchodilator response in 4-year-old children with different wheezing phenotypes

Persistent wheeze is a common chronic disease in early childhood and later may progress to asthma. However, the association between pre- and post-bronchodilator lung function and the wheezing phenotype in preschool children is not known. Children 4 yrs of age involved in a prospective birth cohort study (in Antwerp, Belgium) concerning perinatal factors and the occurrence of asthma and allergies, were invited to participate in lung function measurements with the forced oscillation technique. The wheezing phenotype was assessed via (bi)annual questionnaires. Wheezing phenotype and baseline respiratory impedance data were available for 325 children, 96% of whom underwent bronchodilation tests. The baseline resistance at 4 Hz was higher in children with early transient (11.0 hPa·s·L−1, n = 127) or persistent wheeze (11.9 hPa·s·L−1, n = 54) than in children who never wheezed (10.3 hPa·s·L−1, n = 144). After bronchodilation, the resistance decreased on average by 22%. The decrease was greater among the persistent wheezers than among those who never wheezed (3.4 versus 2.3 hPa·s·L−1). The baseline lung function was poorer and the bronchodilator response was greater in 4-yr-old children with persistent wheeze than in those who never wheeze or who had early transient wheeze, implying a higher bronchomotor tone in the former group.

Pre‐ and post‐natal exposure to antibiotics and the development of eczema, recurrent wheezing and atopic sensitization in children up to the age of 4 years

Background Little data are available on the relationship between indirect antibiotic exposure of the child in utero or during lactation and allergic diseases. On the other hand, several studies have been conducted on the association with direct post‐natal antibiotic exposure, but the results are conflicting.

Respiratory impedance in healthy subjects: baseline values and bronchodilator response

Because of the minimal demand for cooperation by the subject, the forced oscillation technique is increasingly employed in routine lung function testing. However, comprehensive and device-independent values of respiratory impedance at baseline and after bronchodilation have not been established for healthy adults. The aim of this multicentre study was to collect impedance data from 4 to 26 Hz in healthy Caucasian subjects between 18 and 80 years of age. Five different devices were employed to assess baseline values and the bronchodilator response. Altogether, 368 subjects were examined. Despite adjustment for anthropometry, the impedance spectra differed in frequency dependence between the centres, and hence could not be pooled. However, resistance at all frequencies except 20 and 25 Hz, and the low-frequency (≤14 Hz) values of reactance did not exhibit a centre dependence. The regression equations for resistance reflected a greater height dependence in males and a greater weight dependence in both males and females than those published previously. Bronchodilation resulted in a statistically significant decrease (11%) in resistance and a 95th percentile equal to a 32% decrease in resistance at low frequency. We conclude that rigorous calibration procedures should be developed to ensure data compatibility. Furthermore, new reference equations based on different setups are recommended to replace those established with a single device. New prediction equations for respiratory impedance in adults have been developed based on multiple devices http://ow.ly/p9t4e

Quantification of Pharyngeal Patency in Patients with Sleep-Disordered Breathing

Many techniques are available for the assessment of pharyngeal characteristics in sleep-disordered breathing (SDB). However, most of the reported techniques are invasive to some extent and/or hard to perform during sleep studies. The focus of this concept paper is on the forced oscillation technique (FOT) to quantify pharyngeal patency in patients with SDB. In a pilot study, the potential of FOT for non-invasive and continuous assessment of pharyngeal patency during different types of respiratory events was studied in 8 patients with an established diagnosis of a sleep apnea-hypopnea syndrome. During polysomnography, FOT was applied using a 5-Hz pressure oscillation signal. The respiratory impedance was determined and considered as a marker for pharyngeal patency. The results demonstrate that FOT allows detection of the complete pharyngeal occlusion during obstructive sleep apnea. In addition, we found that central sleep apnea can be associated with pharyngeal closure. We also demonstrated that during the flow-limited breath preceding obstructive apnea, almost complete upper airway closure can occur during either the expiratory or the inspiratory phase. FOT is a suitable method to assess pharyngeal patency continuously and non-invasively during sleep. Furthermore, this technique has the potential to contribute substantially to our knowledge of upper airway physiology in SDB.

Determinants of baseline lung function and bronchodilator response in 4-year-old children.

The prolonged period required for maturation of the respiratory system makes it vulnerable to environmental exposure. This study aimed to investigate the association between early-life factors and lung function in preschool children. Children aged 4 years, who were included in a prospective birth cohort, underwent lung function testing at baseline (n=535) and after bronchodilation (n=498) by forced oscillations. Information on symptoms and exposures was collected through half-yearly questionnaires. Allergen-specific serum IgE was quantified at 1 and 4 years. Multiple linear regression analysis showed that the baseline respiratory resistance and reactance area were larger in the children with previous wheeze, those with early-onset sensitisation to inhalant allergens and those who were smaller. Furthermore, children with previous lower respiratory tract infections exhibited higher baseline resistance values. The baseline resistance was the only independent determinant of the bronchodilator-induced change in resistance, whereas current height and baseline reactance area were independently associated with the change in reactance area. In conclusion, previous lower respiratory tract infections, the timing of previous wheeze, inhalant sensitisation and current height independently influence the baseline lung function of 4-year-old children, whereas baseline lung function is the principal determinant of the bronchodilator response. Height, LRTIs, wheeze and sensitisation to inhalant allergens are determinants of lung function in preschool children http://ow.ly/x6vlH

Estimation of post-operative forced expiratory volume by functional respiratory imaging

Surgical resection is a potential curative therapy for patients with early-stage non-small cell lung cancer (NSCLC). Comorbid chronic obstructive pulmonary disease (COPD) is frequently present in these patients [1], stressing the importance of an accurate estimation of post-operative (po) forced expiratory volume in 1 s (FEV1) [2]. A predicted poFEV1 (PpoFEV1) must be calculated whenever the pre-operative FEV1 or diffusing capacity for carbon monoxide is <80% predicted [3]. The anatomic segment method (ASM) and perfusion scintigraphy (QS) are often used for this prediction [4, 5]. Both are known to underestimate the poFEV1 in a substantial fraction of patients, resulting in the possible exclusion from resection of a borderline operable patient [6, 7]. This stresses the need for a more precise tool to estimate poFEV1. Initial results indicate that FRI might better predict post-operative FEV1; confirmation in a larger trial is needed http://ow.ly/E395t

Expression of bronchodilator response using forced oscillation technique measurements: absolute versus relative

From the authors: We thank C. Thamrin and co-workers for their interest in our paper and their reflection, which continues the discussion on how to express bronchodilator responsiveness. This has been an important topic of debate for decades in the adult and the paediatric pulmonary field. In their letter, C. Thamrin and co-workers state that if a bronchodilator change is related to anthropometric factors or baseline lung function, these factors should be taken into account. The worse the baseline lung function the more room for improvement, at least for the asthmatic patient. This has been recognised and translated in the guideline that the bronchodilator response as assessed with forced expiration is …

Launching Global Lung Function Initiative reference values in Belgium: tips and tricks

Pulmonary function tests are pure physiological measurements. Spirometry allows the clinician to label lung diseases as either obstructive or restrictive, the latter requiring confirmation with static lung volume measurements. Transfer factor of the lung for carbon monoxide (TLCO) informs the clinician about the gas exchange properties of the respiratory system. A prerequisite to distinguish normal from abnormal data is the availability of accurate reference values as well as their lower and higher limits of normality. Choosing the correct set of reference values is crucial to discriminate health from disease in the individual and will influence any further medical processes. Indeed, results from one given subject may fall within the normal range using one equation while being abnormal using another [1–5]. The availability of accurate reference values is not only important in the diagnostic work-up and management of a single patient, it also leads to a better understanding of the global burden of lung disease, and allows a statistically correct estimation of the degree of impairment and disability in occupational medicine. A model consisting of a motivated working group that identified the different stakeholders to convince them, through education, over the Global Lung Function Initiative reference values has appeared to be successful in implementing these in Belgium http://ow.ly/Q21630kuE1N