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Objective To provide an evidence-based review of published data regarding normal range reference values and prediction equations for measurements of respiratory impedance using forced oscillation technique (FOT) and impulse oscillometry (IOs) in adults. Methods A non-language-restricted search was performed using forced oscillation technique and impulse oscillometry as primary terms. Original research studies reporting respiratory system impedance reference values or prediction equations based on cohorts of ≥100 healthy adults were included. Publications cited in identified studies were also considered for inclusion. Results Of 882 publications identified, 34 studies were included: 14 studies of FOT, 19 studies of IOs, and one study of both techniques. Nineteen studies provided prediction equations. Most reports were from Europe (n = 20) and Asia (n = 12) and included relatively small cohorts (median = 264 subjects). Across publications, there was marked variability in performance and technique of impedance measurements. Height and sex emerged as major contributors to available prediction equations. The contribution of weight was more pronounced at the obese end of the weight spectrum. The contribution of age was less clear, and elderly were largely under-represented. Ethnicity likely plays a role, but was under-reported in currently available literature. Inclusion of current and former smokers in some studies further confound the results. Conclusions Currently available literature providing reference values and prediction equations for respiratory impedance measurements in adults is limited. Until larger-scale standardized studies are available, the choice of prediction equations should be based on datasets that best represent the target patient population and modality in use within each pulmonary physiology laboratory.

Respiratory oscillometry (also known as the forced oscillation technique) is increasingly contributing to lung function studies in clinical routine and research, as a result of its sophistication, non-invasiveness and minimal interaction with normal breathing. Oscillometry has focused traditionally on the frequency dependence of respiratory impedance (Zrs) obtained as average spectra over several respiratory cycles, and several linear models have been investigated to interpret Zrs in terms of biomechanical descriptors, such as the resistive and elastic properties of the respiratory tract. In contrast, recent advances in oscillometry address the changes in Zrs during the breathing cycle with high temporal resolution, in order to characterise the dependences of Zrs components on respiratory flow and volume and their alterations in different respiratory disorders. In the context of the development of respiratory oscillometry, this article discusses the emerging intra-breath approach and its potential in the characterisation of respiratory mechanical disorders.

This review provides the latest developments and trends in the application of fractional calculus (FC) in biomedicine and biology. Nature has often showed to follow rather simple rules that lead to the emergence of complex phenomena as a result. Of these, the paper addresses the properties in respiratory lung tissue, whose natural solutions arise from the midst of FC in the form of non-integer differ-integral solutions and non-integer parametric models. Diffusion of substances in human body, e.g. drug diffusion, is also a phenomena well known to be captured with such mathematical models. FC has been employed in neuroscience to characterize the generation of action potentials and spiking patters but also in characterizing bio-systems (e.g. vegetable tissues). Despite the natural complexity, biological systems belong as well to this class of systems, where FC has offered parsimonious yet accurate models. This review paper is a collection of results and literature reports who are essential to any versed engineer with multidisciplinary applications and bio-medical in particular.

This paper presents a theoretical basis for linking the anatomical structure, the values of the fractional order model of the impedance and the values of the fractal dimension extracted from time domain respiratory signal analysis. We employ an electrical ladder network model of the lungs which incorporates their specific morphology and anatomical structure. Measurements of 14 healthy volunteers have been used to provide the respiratory input impedance values using the forced oscillation lung function test. The results indicate that the recurrent ladder network model captures well the impedance in the 7-250Hz frequency interval. Next, we show that the time signals of the respiratory system are coupled to the recurrent ladder network values through the fractal dimension parameter evaluated from pressure-volume loops.

This paper presents the application of multidimensional scaling (MDS) analysis to data emerging from noninvasive lung function tests, namely the input respiratory impedance. The aim is to obtain a geometrical mapping of the diseases in a 3D space representation, allowing analysis of (dis)similarities between subjects within the same pathology groups, as well as between the various groups. The adult patient groups investigated were healthy, diagnosed chronic obstructive pulmonary disease (COPD) and diagnosed kyphoscoliosis, respectively. The children patient groups were healthy, asthma and cystic fibrosis. The results suggest that MDS can be successfully employed for mapping purposes of restrictive (kyphoscoliosis) and obstructive (COPD) pathologies. Hence, MDS tools can be further examined to define clear limits between pools of patients for clinical classification, and used as a training aid for medical traineeship.

The noseclip is conventionally used in lung function testing to prevent leakage via the nasal compartments. However, some subjects exhibit a velum-opening reflex which may affect results. We performed forced oscillation measurements at frequencies (8-256 Hz) that include the first antiresonance, comparing the noseclip with a cotton wool nose plug to eliminate upper airway contribution. Three sets of measurements were made in 18 adults: with and without noseclip, and with cotton wool. Velum opening during noseclip measurements was monitored using a nasal pressure transducer. A significantly greater proportion of subjects produced a characteristic distortion to the first antiresonance with the noseclip than with either no noseclip or with cotton wool. Distortion of the spectrum coincided with the transmission of oscillations into the nasal cavity. Thus, the noseclip cannot be used in high-frequency forced oscillation measurements because of the velum reflex. The cotton wool plug offers a simple alternative. This effect has unknown impact in other lung function tests.

This review discusses the history and current state of the art of the forced oscillation technique (FOT) to measure respiratory impedance. We focus on how the FOT and its interaction with models have emerged as a powerful method to extract out not only clinically relevant information, but also to advance insight on the mechanisms and structures responsible for human lung diseases, especially asthma. We will first provide a short history of FOT for basic clinical assessment either directly from the data or in concert with lumped element models to extract out specific effective properties. We then spend several sections on the more exciting recent advances of FOT to probe the relative importance of tissue versus airway changes in disease, the impact of the disease on heterogeneous lung function, and the relative importance of small airways via synthesis of FOT with imaging. Most recently, the FOT approach has been able to directly probe airway caliber in humans and the distinct airway properties of asthmatics that seem to be required for airway hyperresponsiveness. We introduce and discuss the mechanism and clinical implications of this approach, which may be substantial for treatment assessment. Finally, we highlight important future directions for the FOT, particularly its use to probe specific lung components (e.g., isolated airways, isolated airway smooth muscle, etc.) and relate such data to the whole lung. The intent is to substantially advance an integrated understanding of structure-function relationships in the lung.

Summary The aim of the present study was to investigate methodological and physiological aspects of complexrespiratory impedance measurements in calves using the impulse oscillation technique. To apply the system to animals, a tightly fitting face mask was used. The measuring system was modified by placing a flexible tube between the pneumotachograph and the loudspeaker. Complex respiratory impedance measurements were not significantly influenced by the modification. Linear correlations were found between body weight and respiratory impedance; as body weight increased, resistance decreased and reactance increased. The methodological variability of impedance measurements using the impulse technique was found to be extremely small. Diurnal variations of respiratory impedance were considered to be the main source of intea-individual variability. When comparing different animals (even when healthy and matched for age and body weight) our results suggest that inter-individual biological variability must be carefully considered.

The respiratory impedance was measured by means of the forced oscillation technique (Landser et al.) and the lung tissue compliance was measured with an oesophageal balloon in 30 patients with a wide range of values of lung tissue compliance. According to the model of respiratory impedance of Nagels et al. it is unlikely that the impedance data are markedly affected by the lung tissue compliance. This hypothesis has not been clinically tested yet.The semistatic compliance (Css) or specific compliance (Cspec) were not statistically correlated with any of the impedance data. Consequently the oscillatory respiratory measurements are not systematically influenced by the compliance of the lung tissue during quiet breathing. However, the dynamic compliance and the frequency dependence of the compliance showed a low but significant correlation with the reactance and resonant frequency (varying from r=0·41, P

Respiratory impedance measurements by means of the technique of forced oscillations together with spirometry and measurements of maximal mouth pressures were performed in 27 patients with a variety of neuromuscular disorders to assess the value of adding respiratory impedance measurements in the evaluation of lung function in neuromuscular disease. Using the technique of forced oscillations, impedance measurements are easily performed in physically disabled persons, since they require little active cooperation and no forced respiratory maneuvers. Normal respiratory impedance characteristics were found, although resistance values were somewhat higher than those found in normal subjects, signifying the absence of airflow limitation. Spirometrie values were markedly reduced, as were maximal mouth pressures. No significant correlations were found between the forced expiratory volumes in 1 s (FEV 1 ) and the impedance data. A strong curvilinear relationship was observed between PEmax and the RV/TLC ratio and a strong correlation existed between FEV 1 and PEmax. It is concluded from our study that forced oscillometry is a useful tool for the assessment or exclusion of airflow obstruction in patients with neuromuscular disorders when plethysmography is difficult to perform and forced expiratory flow-volume data reflect muscle weakness rather than airflow limitation.

The purpose of the present study was to analyze the manner in which series and parallel arrangements of respiratory muscles, contracting together, augment the forces and displacements applied to external elastic loads over those produced by a single muscle contracting alone. We first developed a series of mathematical expressions to describe the behavior of various arrangements of muscles contracting against elastic loads. We then compared the predictions of these equations with the results from experiments in which the forces and displacements produced by simple arrangements of muscles were measured. Both theoretical and experimental results indicate that, against high elastic loads, parallel arrangements of muscle strips produce greater forces and greater displacements than do single muscles; parallel arrangements do not, however, significantly increase the displacement or forced applied to low elastic loads. Conversely, series arrangements result in greater forces and greater displacement of low loads, but are no better than single muscles when contracting against high loads. Against moderate loads parallel and series arrangements of muscles appear to be equivalent in generating forces and displacements during contraction. This analysis suggests that a major determinant of the effects of contraction of various networks of inspiratory muscles is the magnitude and character of the respiratory impedance against which these muscles must work. The primary difference between series and parallel arrangemens of muscles is that muscles arranged in series are most effective against low elastic loads and muscles in parallel act most effectively against high loads.

A system for calibrating the Respitrace impedance plethysmograph was developed with the capacity to quantitatively verify the accuracy of calibration. LabVIEW software was used on a Macintosh II computer to create a user-friendly environment, with the added benefit of reducing development time. The system developed enabled a research assistant to calibrate the Respitrace within 15 min while achieving an accuracy within the normally accepted 10% deviation when the Respitrace output is compared to a water spirometer standard. The system and methods described were successfully used in a study of 10 subjects smoking cigarettes containing marijuana or cocaine under four conditions, calibrating all subjects to 10% accuracy within 15 min.

SUMMARY Marked seasonal variations were found in the total respiratory impedance of normal Shetland ponies. A large and statistically significant increase in the magnitude of impedance was seen in August, with the maximum change occurring at 22 Hz. Acute inhalation of air at -30°C had a minimal effect on the total respiratory impedance of the ponies, suggesting that changes in air temperature were not responsible for the observed variation in impedance.

Background Forced oscillation technique (FOT) measures respiratory impedance by applying external pressures to the respiratory system and makes it possible to evaluate various aspect of airway physiology including small airways. MasterScreen IOS (IOS) has been widely utilized as a FOT. Recently, a new FOT, Mostgraph, has been available in Japan. Clinical experience including reference values of FOT, especially, for Japanese children, however have not been determined and correlations of the 2 FOTs , MostGraph and IOS, are not known.

The total respiratory resistance determined by means of the forced oscillation technique during spontaneous breathing demonstates a variability which may be due (1) to variations of the resistance itself, (2) to the superposition of rapid oscillatory and slow respiratory signals, (3) to the presence in the breathing signals of harmonics the frequency of which is the same as that of the oscillations. In the present study, we investigate the importance of the third cause of variability, in a mechanical system in which causes 1 and 2 have been excluded. It is shown that the presence of high frequency components in breathing is an important source of error in the measurement of instantaneous resistance and reactance. The error is larger at higher frequency and amplitude of breathing, lower frequency and amplitude of forced oscillations, and in the presence of a high respiratory impedance. The error is likely to be negligible when the frequency of the forced oscillations is high ( e.g. 30 Hz). At lower frequencies, the influence of harmonics in breathing can be corrected by calculating average resistance or reactance values over one or more respiratory cycles.

We bench-tested a commercially available instrument for measuring respiratory impedance (Siregnost FD5: Siemens) and found that resistance (R) and phase changes were accurately recorded in models. In a single human subject, total respiratory resistance (R(l)) was closely comparable to resistance measured by the Mead-Whittenberger technique. The derived continuous variable (R(os)) was similar to R at less than 4 cmH2O . litres-1 . sec, but underestimated R at higher values. Ros was highly correlated with airways resistance by body plethysmography (R(aw)), but with a low slope and high intercept (R(os) = 1.38 + 0.59 R(aw): r = 0.89). Because of turbulence, both in model larynxes and in normal subjects, R(os) tends to rise with increases in flow in either direction. R(os) also tends to fall as lung volume rises, and vice versa, reflecting cyclic changes in airway calibre. We devised indices of expiratory narrowing of airways from the maximum flow-volume loop, and the plethysmographic alveolar pressure-flow loop, and compared them with the slope of the relation between R(os) and lung volume during tidal breathing, in nine normal subjects and 16 patients with airflow obstruction. Twelve of the 16 patients, all with abnormal flow-volume loops, had high R(os)-volume slopes, demonstrating excessive expiratory narrowing even during tidal breathing. We found no patients with normal inspiratory R(os) together with an abnormal R(os)-volume slope. Thus unstressed inspiratory calibre was never dissociated from airways narrowing on expiration.

Total respiratory resistance (Rrs), pulmonary resistance (RL), and airway resistance (Raw) of 12 male patients with chronic obstructive lung disease were measured by the partial occlusion method, intraesophageal balloon technique, and body plethysmography, respectively. Chest wall resistance (Rcw) and lung tissue resistance (Rti) were computed. Percentages of Rcw/Rrs, RL/Rrs, Raw/Rrs, Rti/ Rrs, Raw/RL, and Rti/RL were calculated. The magnitude of the components of resistance to breathing of this study and the data appearing in the literature are compared. Wide variation between the data reported by various authors was observed. The possible causes of these variations are discussed. (Chest 1989; 96:307–11) Rrs = total respiratory resistance; RL = pulmonary resistance; Raw = airway resistance; Rcw = chest wall resistance; Rti = lung tissue resistance; Ptp = transpulmonary pressure; Zrs = total respiratory impedance