Human respiratory impedance from 8 to 256 Hz corrected for upper airway shunt

Farre, R.; Peslin, R; Oostveen, Ellie; Suki, Bélâ; Duvivier, C.; Navajas, Daniel

doi:10.1152/jappl.1989.67.5.1973

Cited by 35 publications

(15 citation statements)

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“…Its original derivation included the entire dead space, it was greater than the measured compliance of the supraglottal airway wall (0.014 L?kPa -1 ) and it produced simulation results that did not show the correct qualitative behaviour in terms of either Rrs or Xrs. Several studies in which parameters were fitted to a similar model have resulted in estimates of a smaller value for Cbr, in the range 0.002-0.02 L?kPa -1 [33,39,40], and, hence, a value in this range (0.005 L?kPa -1 ) was used in the present simulation.…”

Section: Appendixmentioning

confidence: 99%

Use of reactance to estimate transpulmonary resistance

Johnson

Birch²,

Carter³

et al. 2005

Eur Respir J

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This study examines the relationship of respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillometry with transpulmonary resistance (RL) measured by oesophageal manometry.Simultaneous forced oscillometry using a single frequency of 5 Hz and oesophageal manometry were performed on five asthmatics during bronchoprovocation. The data obtained were used to derive prediction equations for RL from oscillometric parameters, which were tested on a further six asthmatics and 35 nonasthmatic subjects.In the first five asthmatic subjects, RL correlated more strongly with Xrs than with Rrs. In the second set of asthmatics, RL ranged 0.0005-4.57 kPa?s?L with the values measured in this set of patients. Xrs in subjects with other respiratory conditions appeared to follow the same relationship with RL as in asthmatics. Lumped element modelling suggested that the linear relationship between Xrs and RL was a consequence of the increasing contribution of central and upper airway wall shunts as peripheral airway resistance rose, and that this effect was much larger than that due to changes in static elastance.In conclusion, the reactance of the respiratory system can predict transpulmonary resistance more accurately than can the resistance of the respiratory system. KEYWORDS: Airway hyperresponsiveness, airway obstruction, forced oscillation technique, resistanceA s a pulmonary function test for measuring resistance, the forced oscillation technique (FOT) has several advantages [1]. It is a passive manoeuvre, requiring only tidal breathing from the subject, and can provide continuous measurement of the resistance of the respiratory system (Rrs), delineating within-breath changes with sub-second resolution. It also has limitations. First, as distal airways obstruction increases, there is worsening agreement of Rrs with transpulmonary resistance (RL) measured by oesophageal manometry [2]. Under these conditions, Rrs is underestimated because the upper airway wall, which acts as an impedance in parallel (or shunt) with the lower airway, becomes increasingly important. Secondly, it is less useful for diagnosis as any pathology produces a similar pattern of abnormality in oscillometric results, although differing in degree [1]. Despite these drawbacks, the FOT performs similarly to standard tests in many areas (e.g. bronchodilator reversibility [3] and bronchial challenge testing [4]). In order to guarantee its wider use, it needs to surpass current techniques or be useful in areas less well furnished with tests.The agreement between Rrs and RL can be improved by the use of a head plethysmograph [5], but this approach is cumbersome. A further recent proposal was the use of changes in admittance (the reciprocal of impedance) during bronchoprovocation [6]. Theoretically, this quantity should be independent of the effect of upper airway wall shunt, and the results obtained from standard oscillometric equipment compared with the head plethysmograph, although not identical, supported this claim. However,...

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Section: Appendixmentioning

confidence: 99%

Use of reactance to estimate transpulmonary resistance

Johnson

Birch²,

Carter³

et al. 2005

Eur Respir J

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“…This occurs when Rr~ is maximum and falling, and X~ is crossing zero. in infants, Ja~,m has a mean (SD) of 171.6 (34.8) Hz and a coefficient of variation (SD) of 9.7 (5.4)%, implying clinical measurement potential (CHALKER et al, 1992;FREY et al, 1997;FARRI~ et al, 1989).…”

Section: Recent Applications Of Fot In Paediatric Subjectsmentioning

confidence: 99%

Respiratory input impedance measurement: Forced oscillation methods

MacLeod

Birch

2001

Med. Biol. Eng. Comput.

152

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The paper reviews how forced oscillation techniques (FOT) for measuring respiratory input impedance Zrs,in have recently been used in clinical applications. Zrs,in is clinically relevant, as it provides data on both the resistive, Rrs, and nonresistive, Xrs, components of the respiratory system. Additionally, when excitatory test signals extending into low- (<4 Hz) or high-frequency (>100 Hz) ranges are used, reliable partitioning of lung tissue from airway components is feasible. Adult and paediatric studies examining the use of Zrs,in for routine lung-function assessment, sleep and mechanical ventilation are reviewed. For clinicians, Zrs,in repeatable and sensitive to airway resistance. It is helpful for assessing unco-operative and severely obstructed patients, for monitoring mechanics during artificial ventilation and for tracking airway closure during sleep studies. For paediatricians, longitudinal studies of the growth and development of the respiratory system can also be made using Zrs,in. Forced oscillation techniques, however, require further standardisation, and Zrs,in is limited by upper-airway shunt artifacts. In conclusion, measurement of Zrs,in using FOT is an important and sophisticated non-invasive lung-function test, showing good potential for future clinical applications.

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“…The occlusion impedance (Zoc) was measured on the occluded ET by the FOT [14,15]. As stated previously [13,16], this Zoc accounts both for the shunt gas compression in the measuring set-up, including the ET, and the dynamic asymmetry of the transducers [14].…”

Section: Endotracheal Tubementioning

confidence: 99%

“…In C2, pressure data were first corrected for the flow-dependent resistance of the ET (K1+K2V '), and impedance was calculated as Z2*. Next, Z2* was corrected for gas compression inside the ET by using the Zoc impedance recorded previously [13][14][15][16]. The resulting impedance Z2** was calculated as:…”

Section: Correction Algorithmmentioning

confidence: 99%

A new correction technique for measuring respiratory impedance through an endotracheal tube

Lorino¹,

Beydon²,

Mariette³

et al. 1996

Eur Respir J

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Measurement of respiratory impedance (Zrs) in intubated patients requires corrections for flow-dependent resistance and air compression inside the endotracheal tube (ET). The purpose of this study was to test a new correction technique for these effects.We therefore studied 110 patients in two conditions: breathing normally (C1), or breathing through an ET placed at the mouth (C2). In C1, we measured pressure and flow signals at the mouth, and in C2, at the ET inlet, during application of a pseudorandom forced excitation (4-32 Hz). In C1, respiratory impedance was calculated directly as Z1. In C2, pressure data were first corrected for the flow-dependent resistance of the ET, and respiratory impedance was then corrected both for gas compression inside the set-up and ET inertance (impedance Z2).Strong linear relationships were found between the reference and corrected estimates of the resistance at 6 Hz, the frequency dependence of resistance and the resonant frequency. The mean normalized distance between Z1 and Z2 observed in the patients over the 4-32 Hz frequency range was about 14% for resistance and 12% for reactance (-9% and -4%, respectively, when considering the algebraic value of the distance). This slight underestimation of both components of impedance might be due to an overcorrection of pressure for the flow-dependent resistance of the ET.We conclude that, in intubated patients, newly tested corrections for the mechanical contribution of the endotracheal tube may yield a fair estimate of respiratory impedance when pressure is measured at the inlet of the endotracheal tube. Eur Respir J., 1996Respir J., , 9, 1079 TECHNICAL NOTETo monitor respiratory mechanics of intubated patients in intensive care units, it is highly desirable to use a measurement technique which requires no special cooperation from the patient. The forced oscillation technique (FOT) allows the estimation of respiratory impedance (Zrs) by simply applying a pseudorandom airflow excitation at the airway opening of the patient. This method of Zrs measurement is based on the assumption that the mechanical behaviour of the respiratory system remains fairly linear within the flow amplitude range of the forced oscillations applied. In this respect, the presence of an endotracheal tube (ET), which introduces a nonlinear resistive component [1], makes it problematical to measure Zrs by the standard FOT, i.e. with proximal pressure and flow recorded at the ET inlet.The effects of the nonlinearities due to the flow-dependent component of the ET resistance can be limited by measuring Zrs during periods of apnoea obtained after either hyperventilation or curarization [2][3][4][5]. However, from an ethical point of view, it is not always possible to obtain periods of apnoea in spontaneously breathing patients. Theoretically, the effect of the flow-dependent ET resistance could be totally removed by measuring a distal pressure [6,7], either by using a special and rather expensive ET incorporating a lumen with an opening near the distal ...

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Human respiratory impedance from 8 to 256 Hz corrected for upper airway shunt

Cited by 35 publications

References 0 publications

Use of reactance to estimate transpulmonary resistance

Use of reactance to estimate transpulmonary resistance

Respiratory input impedance measurement: Forced oscillation methods

A new correction technique for measuring respiratory impedance through an endotracheal tube

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