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Forced oscillation assessment of respiratory mechanics in ventilated patients.

Navajas D, Farré R - Crit Care (2000)

Bottom Line: As the FOT requires a minimal modification of the conventional ventilation setting and does not interfere with the ventilation protocol, the technique is potentially useful to monitor patient mechanics during invasive and noninvasive ventilation.Applying FOT at different frequencies may allow the physician to interpret patient mechanics in terms of models with pathophysiological interest.The current methodological and technical experience make possible the implementation of portable and compact computerised FOT systems specifically addressed to its application in the mechanical ventilation setting.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unitat de Biofisica i Bioenginyeria, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi Sunyer, Universitat de Barcelona, Spain. dnavajas@medicina.ub.es

ABSTRACT
The forced oscillation technique (FOT) is a method for non-invasively assessing respiratory mechanics that is applicable both in paralysed and non-paralysed patients. As the FOT requires a minimal modification of the conventional ventilation setting and does not interfere with the ventilation protocol, the technique is potentially useful to monitor patient mechanics during invasive and noninvasive ventilation. FOT allows the assessment of the respiratory system linearity by measuring resistance and reactance at different lung volumes or end-expiratory pressures. Moreover, FOT allows the physician to track the changes in patient mechanics along the ventilation cycle. Applying FOT at different frequencies may allow the physician to interpret patient mechanics in terms of models with pathophysiological interest. The current methodological and technical experience make possible the implementation of portable and compact computerised FOT systems specifically addressed to its application in the mechanical ventilation setting.

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Related in: MedlinePlus

Respiratory resistance (Rrs) and reactance (Xrs) during inspiratory (●) and expiratory (▲) pauses (Figs 3 and 4) in a paralysed and mechanically ventilated patient with chronic obstructive pulmonary disease.
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Figure 5: Respiratory resistance (Rrs) and reactance (Xrs) during inspiratory (●) and expiratory (▲) pauses (Figs 3 and 4) in a paralysed and mechanically ventilated patient with chronic obstructive pulmonary disease.

Mentions: One advantage of measuring Rrs and Xrs during inspiratory and expiratory pauses in a given patient is to quantify the dependence of respiratory mechanics on lung volume or transpulmonary pressure. Indeed, as shown in Fig. 5, Rrs and Xrs computed from the measurements in Figs 3 and 4 show that in this patient with chronic obstructive pulmonary disease (COPD), impedance was considerably greater during expiratory than inspiratory pauses, particularly at the lower frequencies. Rrs during the expiratory pause was considerably dependent on frequency over the whole frequency band. By contrast, Rrs during the inspiratory pause was much less dependent on frequency (Fig. 5). Xrs also was also different during inspiratory and expiratory pauses, particularly at more than 1 Hz. This pattern of frequency dependence has been interpreted in terms of increased peripheral resistance due to airway closure at end-expiration [5,7]. This interpretation is in keeping with the observations in Fig. 6, namely that Rrs at end-expiration progressively and considerably decreased as transpulmonary pressure (PEEP) increased. The values of Rrs and Xrs provided by FOT can be compared with the resistance and elastance indices derived from the application of the airway occlusion technique, which has been used extensively to assess airway mechanics in ventilated patients [6,7]. Indeed, FOT data are obtained from small-amplitude oscillations at the extreme points of a conventional inflation (end-expiration and end-inspiration), whereas data from the occlusion manoeuvres are obtained from a high-amplitude excursion across those extreme points. Such a comparison sheds some light on the mechanisms determining the nonlinear properties of the respiratory system in patients and might be useful for predicting the relationship between pressure, flow and volume during mechanical ventilation.


Forced oscillation assessment of respiratory mechanics in ventilated patients.

Navajas D, Farré R - Crit Care (2000)

Respiratory resistance (Rrs) and reactance (Xrs) during inspiratory (●) and expiratory (▲) pauses (Figs 3 and 4) in a paralysed and mechanically ventilated patient with chronic obstructive pulmonary disease.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC137264&req=5

Figure 5: Respiratory resistance (Rrs) and reactance (Xrs) during inspiratory (●) and expiratory (▲) pauses (Figs 3 and 4) in a paralysed and mechanically ventilated patient with chronic obstructive pulmonary disease.
Mentions: One advantage of measuring Rrs and Xrs during inspiratory and expiratory pauses in a given patient is to quantify the dependence of respiratory mechanics on lung volume or transpulmonary pressure. Indeed, as shown in Fig. 5, Rrs and Xrs computed from the measurements in Figs 3 and 4 show that in this patient with chronic obstructive pulmonary disease (COPD), impedance was considerably greater during expiratory than inspiratory pauses, particularly at the lower frequencies. Rrs during the expiratory pause was considerably dependent on frequency over the whole frequency band. By contrast, Rrs during the inspiratory pause was much less dependent on frequency (Fig. 5). Xrs also was also different during inspiratory and expiratory pauses, particularly at more than 1 Hz. This pattern of frequency dependence has been interpreted in terms of increased peripheral resistance due to airway closure at end-expiration [5,7]. This interpretation is in keeping with the observations in Fig. 6, namely that Rrs at end-expiration progressively and considerably decreased as transpulmonary pressure (PEEP) increased. The values of Rrs and Xrs provided by FOT can be compared with the resistance and elastance indices derived from the application of the airway occlusion technique, which has been used extensively to assess airway mechanics in ventilated patients [6,7]. Indeed, FOT data are obtained from small-amplitude oscillations at the extreme points of a conventional inflation (end-expiration and end-inspiration), whereas data from the occlusion manoeuvres are obtained from a high-amplitude excursion across those extreme points. Such a comparison sheds some light on the mechanisms determining the nonlinear properties of the respiratory system in patients and might be useful for predicting the relationship between pressure, flow and volume during mechanical ventilation.

Bottom Line: As the FOT requires a minimal modification of the conventional ventilation setting and does not interfere with the ventilation protocol, the technique is potentially useful to monitor patient mechanics during invasive and noninvasive ventilation.Applying FOT at different frequencies may allow the physician to interpret patient mechanics in terms of models with pathophysiological interest.The current methodological and technical experience make possible the implementation of portable and compact computerised FOT systems specifically addressed to its application in the mechanical ventilation setting.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unitat de Biofisica i Bioenginyeria, Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi Sunyer, Universitat de Barcelona, Spain. dnavajas@medicina.ub.es

ABSTRACT
The forced oscillation technique (FOT) is a method for non-invasively assessing respiratory mechanics that is applicable both in paralysed and non-paralysed patients. As the FOT requires a minimal modification of the conventional ventilation setting and does not interfere with the ventilation protocol, the technique is potentially useful to monitor patient mechanics during invasive and noninvasive ventilation. FOT allows the assessment of the respiratory system linearity by measuring resistance and reactance at different lung volumes or end-expiratory pressures. Moreover, FOT allows the physician to track the changes in patient mechanics along the ventilation cycle. Applying FOT at different frequencies may allow the physician to interpret patient mechanics in terms of models with pathophysiological interest. The current methodological and technical experience make possible the implementation of portable and compact computerised FOT systems specifically addressed to its application in the mechanical ventilation setting.

Show MeSH
Related in: MedlinePlus