Effect of expiratory flow limitation on respiratory mechanical impedance: a model study

Peslin, R; Farré, Ramón; Rotger, M.; Navajas, Daniel

doi:10.1152/jappl.1996.81.6.2399

Cited by 30 publications

(18 citation statements)

References 27 publications

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“…the imaginary part of total input impedance) measured by a forced oscillation technique (FOT). Similar behaviour was observed in a simplified mechanical model of the respiratory system when a flow-limiting segment was included [8] and in mechanically ventilated rabbits [9] after intravenous methacholine infusion. This phenomenon occurs because the linear velocity of gas passing through flow-limiting segments (choke points) equals the local speed of wave propagation [10].…”

supporting

confidence: 73%

Detection of expiratory flow limitation in COPD using the forced oscillation technique

et al. 2004

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Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present.To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean¡SD forced expiratory volume in one second was 36.8¡11.5 % predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited.Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (DXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2. Unlike healthy subjects who do not develop expiratory flow limitation (EFL) even during exhaustive exercise [1], many chronic obstructive pulmonary disease (COPD) patients are flow-limited (FL) at rest [2]. These patients can only increase their expiratory flow rate during exercise by allowing their end-expiratory lung volume (VL) to rise, an energetically inefficient strategy that is accompanied by severe dyspnoea that reduces exercise duration [3,4]. The severity of dyspnoea in COPD is better predicted by the presence of EFL during tidal breathing than by the forced expiratory volume in one second (FEV1) [5,6]. Thus, a simple method of detecting EFL during tidal breathing would be a potentially useful clinical tool. Several noninvasive methods have been proposed to detect tidal EFL in COPD patients, but each has its limitations and, to the best of the authors9 knowledge, to date none has been tested against any form of "gold standard" in spontaneously breathing patients.In 1993, PESLIN et al. [7] reported that some COPD patients during mechanical ventilation developed large negative swings in the respiratory system input reactance (Xrs, i.e. the imaginary part of total input impedance) measured by a forced oscillation technique (FOT). Similar behaviour was observed in a simplified mechanical model of the respiratory system when a flow-limiting segment was included [8] and in mechanically ventilated rabbits [9] after intravenous methacholine infusion. This phenomenon occurs because the linear velocity of gas passing through flow-limiting segments (choke points) equals the local speed of wave propagation [10]. Normally the reactance reflects the elastic and inertial properties of the respiratory system but when flow limitation is present, the oscillatory signal cannot pass through the choke points and reach the alveoli, producing a ...

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supporting

confidence: 73%

Detection of expiratory flow limitation in COPD using the forced oscillation technique

et al. 2004

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“…However, the improvement seen in the agreement between methods when the NEP data were averaged suggests that much of the variance lies in how the NEP are interpreted. Bronchodilator drugs would be expected to modify the degree of EFL, and this has been proposed as an explanation of the reduced end-expiratory lung volume during exercise that usually [24,25], but not always [26], follows bronchodilator treatment in COPD. However, studies to date have been disappointing, with no change in NEP score after the administration of high-dose bronchodilators to patients with severe COPD at rest [6].…”

Section: Detection Of Flow Limitation By Fot and Nep Rl Dellacà Et Almentioning

confidence: 99%

Expiratory flow limitation detected by forced oscillation and negative expiratory pressure

Dellacà¹,

Duffy²,

Pompilio³

et al. 2006

Eur Respir J

110

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The within-breath change in reactance (DXrs) measured by forced oscillation technique (FOT) at 5 Hz reliably detects expiratory flow limitation in chronic obstructive pulmonary disease (COPD). The present study compared this approach to the standard negative expiratory pressure (NEP) method.In total, 21 COPD patients were studied by applying both techniques to the same breath and in 15 patients the measurements were repeated after bronchodilator. For each patient and condition five NEP tests were performed and independently scored by three operators unaware of the FOT results.In 180 tests, FOT classified 53.3% as flow limited. On average, the operators scored 27.6% of tests flow limited and 47.6% non-flow limited, but could not score 24.8%. The methods disagreed in 7.9% of cases; in 78% of these the NEP scores differed between operators. Bronchodilation reduced NEP and DXrs scores, with only the latter achieving significance. Averaging the operators9 NEP scores, a threshold between 24.6-30.8% of tidal volume being flow limited by NEP produced 94% agreement between methods.In conclusion, when negative expiratory pressure and forced oscillation technique were both available they showed good agreement. As forced oscillation technique is automatic and can measure multiple breaths over long periods, it is suitable for monitoring expiratory flow limitation continuously and identifying patients9 breathing close to the onset of expiratory flow limitation, where intermittent sampling may be unrepresentative.

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“…However, the data from DELLACÀ et al [9] suggest that Xrs could be a more suitable index than Rrs to assess respiratory mechanics during EFL. The results of these authors also indicate [12,13] that averaging the impedance data over the whole breathing cycle, which is the most common procedure [15], could result in data misinterpretation when FOT is applied in COPD patients. Accordingly, tracking the impedance data along the breathing cycle or, at least, separating inspiratory and expiratory data could improve the performance of FOT in evaluating the respiratory mechanics of COPD patients [9,12,13].…”

mentioning

confidence: 93%

“…[11] when studying mechanically ventilated COPD patients, and the hypothesis was more specifically substantiated in a controlled analog model [12] and animal studies [13]. However, the usefulness of the FOT for detecting EFL in spontaneously breathing COPD patients was not studied in detail before the work of DELLACÀ et al [9] published in this issue of the ERJ.…”

mentioning

confidence: 99%

Assessment of expiratory flow limitation in chronic obstructive pulmonary disease: a new approach

Farré¹,

Navajas²

2004

Eur Respir J

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Patients with severe chronic obstructive pulmonary disease (COPD) usually experience expiratory flow limitation (EFL) during spontaneous breathing at rest [1]. As EFL reduces the effectiveness of expiration, it results in dynamic hyperinflation with consequent dyspnoea, which is one of the major complaints of patients with COPD. In these patients, the consequences of EFL are markedly increased during exercise [2]. Bearing in mind that EFL is a good predictor of dyspnoea in COPD patients [3,4], simple methods for detecting EFL without perturbing normal breathing are of clinical interest. In 1995 KOULOURIS et al. [5] proposed a method to detect EFL based on the external application of a negative pressure at the mouth during tidal expiration (negative expiratory pressure (NEP)). EFL is detected by comparing the magnitude of expiratory flow before and after application of NEP: in case of EFL, the expiratory flow does not rise when increasing the driving pressure. More recently, NINANE et al.[6] proposed the estimation of EFL during spontaneous breathing with a similar approach. To increase the driving pressure during expiration, these authors applied a positive abdominal pressure by manual compression of the patient9s abdominal wall. When compared with the NEP technique, this approach has the advantage of instrumental simplicity, but suffers from the drawbacks of applying abdominal pressure of uncontrolled magnitude and lack of automatisation. Both procedures can be applied during breathing at rest as well as during exercise [7,8].In this issue of the European Respiratory Journal (ERJ), DELLACÀ et al.[9] present interesting novel data showing that the forced oscillation technique (FOT) can be useful for noninvasively detecting EFL during spontaneous breathing. The FOT, which was proposed in the 1950s [10], is based on applying a small-amplitude oscillation pressure at the mouth. Using the FOT the patient9s respiratory mechanics can be determined by simply recording the oscillatory pressure and flow signals at the mouth, provided that the oscillation frequency is much higher than the breathing rate. The relationship between the pressure and the flow oscillation is the impedance of the respiratory system, which has two components: respiratory resistance (Rrs) and reactance (Xrs). In a simple interpretation, Rrs is attributed to airways and tissue resistances, whereas Xrs is determined by the inertial and compliant properties of the respiratory system. The rationale of using FOT for assessing EFL is that under this flow regime the forced oscillation applied at the mouth cannot reach the alveoli given the fact that the choke point shifts upstream of the lung during EFL. Therefore, the effective impedance viewed from the FOT device corresponds to only a fraction of the respiratory system: from the mouth to the choke point. According to this hypothesis, the associated decrease in the effective respiratory compliance results in a reduction of the measured Xrs during expiration when compared with the non flow-limited inspi...

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Effect of expiratory flow limitation on respiratory mechanical impedance: a model study

Cited by 30 publications

References 27 publications

Detection of expiratory flow limitation in COPD using the forced oscillation technique

Detection of expiratory flow limitation in COPD using the forced oscillation technique

Expiratory flow limitation detected by forced oscillation and negative expiratory pressure

Assessment of expiratory flow limitation in chronic obstructive pulmonary disease: a new approach

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