Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties

Jonson, B; Beydon, L.; Brauer, Kerstin; Månsson, Cecilia; Valind, Sven; Grytzell, H.

doi:10.1152/jappl.1993.75.1.132

Cited by 95 publications

(88 citation statements)

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“…The Pel,dyn points indicate the presence of hysteresis, but no apparent quasi-static hysteresis was observed. The same behaviour for the viscoelastic characteristics were observed in every infant, a finding which is consistent with a similar conclusion for the viscoelastic characteristics by JOHNSON et al [8].…”

Section: Resultssupporting

confidence: 91%

Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis

et al. 2001

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The elastic pressure/volume (P/V) curve obtained by the multiple linear regression (MLR) technique using a new model, was compared with the quasi-static P/V points obtained by the rapid airway occlusion technique.Seven infants were studied during mechanical ventilation using a pressure controlled mode. The resistive pressure was subtracted from airway opening pressure, thus determining the elastance related pressure, which was then plotted against the volume to make an MLR-elastance curve. Quasi-static P/V curves of the rapid occlusion technique were constructed by plotting the different inspiratory and expiratory volumes against the corresponding values of the quasi-static airway pressure.The calculated MLR-elastance curves closely fit the experimental quasi-static P/V points obtained by the occlusion technique. There were, however, some discrepancies due to the viscoelastic behaviour of the respiratory system.Although slightly altered by these discrepancies, the multiple linear regressionelastance curves did fit the observed quasi-static pressure/volume characteristics for use in clinical practice. Respiratory system elastance has been shown to exhibit a negative lung volume dependence due to the curvilinear character of static pressure/volume [1 -3] (P/V) curves. During mechanical ventilation, the lungs are frequently inflated to the nonlinear level on the P/V curve. It is generally accepted that a graphic presentation of the P/V relationship at a given respirator setting can provide great insight regarding whether or not lung overdistension occurs.The static P/V relationship, as a parameter for the elasticity of the respiratory system, can be determined by various methods. The super syringe technique is a continuous procedure of step-by-step inflation and deflation using a large syringe while the patient is disconnected from the ventilator [4]. The interrupter technique consists of rapid occlusions within a single breath cycle [5,6] or of interrupting airways at different inflation and deflation volumes [7 -9]. All occlusion data can then be plotted on a P/V diagram. The constant flow technique is performed during volume controlled mechanical ventilation using a very slow constant inflation flow of 3 L?min -1 or 9 L?min -1 , and thus pressure consumed by the flow resistance in the airway is not considered to be of any clinical relevance [10,11]. These techniques are sometimes not practical to perform or require the presence of a trained investigator and the respirator settings may need to be changed. With the increasing availability of computer-based data acquisition systems, high speed data collection and analyses are now possible using the computerized least-squares multiple regression analysis technique [12]. Using a multiple linear regression (MLR) analysis to analyse the flow and pressure changes at the airway opening during mechanical ventilation, permits dynamic mechanics to be measured noninvasively without interfering with the ventilation pattern being employed. An MLR analysis also allows...

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Section: Resultssupporting

confidence: 91%

Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis

et al. 2001

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“…Using the iso-V' MB method and a modified MB method, D'ANGELO et al [4] and JONSON et al [19], respectively, determined the viscoelastic constants of the total respiratory system in normal subjects under similar experimental conditions to those of the present study. The values obtained were not significantly different to those presently reported.…”

Section: Discussionmentioning

confidence: 69%

Bedside assessment of respiratory viscoelastic properties in ventilated patients

Antonaglia¹,

Peratoner²,

Simoni³

et al. 2000

Eur Respir J

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Viscoelasticity represents an important component of respiratory mechanics, being responsible, in some cases, for most of the pressure dissipated during breathing. Hitherto the methods available for determining the viscoelastic properties have been simplified, but are still time-demanding and depend on a great deal of calculation. In this study, a simple means of determining respiratory viscoelastic properties during mechanical ventilation was introduced.The viscoelastic constants of the respiratory system, modelled as a Maxwell body, were studied in 17 normal subjects and seven patients with acute lung injury (ALI) using two end-inspiratory occlusions; one with a short inspiratory time (tI) to determine the elastic component of viscoelasticity and the other with a long tI to assess the resistive component of viscoelasticity.The results were reproducible and similar to those provided by the previously described multiple-breath method (MB) Viscoelasticity represents an important component of respiratory mechanics, being responsible, in some cases, for most of the pressure dissipated during breathing. In order to study the viscoelastic behaviour of the respiratory system, it is necessary to assess the pressure developed by the viscoelastic components. Direct measurement of the viscoelastic inspiratory pressure can be performed by the technique of rapid end-inspiratory airway occlusion and the viscoelastic behaviour interpreted according to a Maxwell body. This linear viscoelastic model has been shown to provide an accurate description of the time-dependency of resistance and elastance of the respiratory system observed in normal animal [1] and human lungs [2] In this model, the viscoelastic properties which impact such time-dependency can be characterized by two parameters, the theoretical maximal viscoelastic resistance (R2) and elastance (E2). A third useful variable, the viscoelastic time constant (t2), can also be obtained from R2/E2 [3]. Using the technique of rapid airway occlusion (RAO) during constant-flow (V') inflation, it has been possible to determine the values of these viscoelastic constants for the lung, chest wall and total respiratory system in normal mechanically ventilated humans [3±5] and experimental animals [1,6], based on either of the following functions:where Pvisc(t) is the viscoelastic pressure (Pvisc) dissipated within the lung, chest wall or both during constant-V' inflation started from the relaxed volume of the respiratory system, t is time during lung inflation and DRrs is viscoelastic resistance, obtained by dividing both sides of Equation 1 by V' [3]. This analysis, however, is timeconsuming and technically complex because it requires either a series of isovolumic inflations with different inspiratory V' , or multiple iso-V' inflations with different volumes [3,6]. As a result, the above analysis has been used only in a limited number of studies on normal subjects [3±5] and patients [7±9]. Recently, a single-breath method was proposed for assessing the viscoelastic prope...

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“…Flow measured in the inspiratory and expiratory circuits within the ventilator included flow that did not reach the animal. In order to obtain airway flow rate (V' aw ), measured flow rate was corrected for the compliance in the tubings by subtraction from each flow sample the product between compliance and rate of pressure change (7). The expiratory flow signal was normalized so that, at steady state, expired V T equaled inspired V T (7).…”

Section: Discussionmentioning

confidence: 99%

“…In order to obtain airway flow rate (V' aw ), measured flow rate was corrected for the compliance in the tubings by subtraction from each flow sample the product between compliance and rate of pressure change (7). The expiratory flow signal was normalized so that, at steady state, expired V T equaled inspired V T (7). Volume relative to end-expiratory volume (V) was calculated by integration of V' aw .…”

Section: Discussionmentioning

confidence: 99%

“…Studies in various mammals, healthy and diseased humans validate such a model as long as tidal volumes are not large (6,7,(17)(18)(19). The model did not incorporate viscoelastic properties, as such properties are particularly difficult to measure (7,20). Experimental validation is necessary to evaluate the adequacy of the simple model, the analysis leading to the physiological profile and the simulation program.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Computer‐aided ventilator resetting is feasible on the basis of a physiological profile

Uttman

Jonson

2002

Acta Anaesthesiol Scand

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Background: Ventilator resetting is frequently needed to adjust tidal volume, pressure and gas exchange. The system comprising lungs and ventilator is so complex that a trial and error strategy is often applied. Comprehensive characterization of lung physiology is feasible by monitoring. The hypothesis that the effect of ventilator resetting could be predicted by computer simulation based on a physiological profile was tested in healthy pigs. Methods: Flow, pressure and CO 2 signals were recorded in 7 ventilated pigs. Elastic recoil pressure was measured at postinspiratory and post-expiratory pauses. Inspiratory and expiratory resistance as a function of volume and compliance were calculated. CO 2 elimination per breath was expressed as a function of tidal volume. Calculating pressure and flow moment by moment simulated the effect of ventilator action, when respiratory rate was varied between 10 and 30 min ª1 and minute vol-

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Mechanics of respiratory system in healthy anesthetized humans with emphasis on viscoelastic properties

Cited by 95 publications

References 0 publications

Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis

Monitoring of nonlinear respiratory elastance using a multiple linear regression analysis

Bedside assessment of respiratory viscoelastic properties in ventilated patients

Computer‐aided ventilator resetting is feasible on the basis of a physiological profile

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