Dynamics of expiration and gas trapping in rabbits during mechanical ventilation at rapid rates

Jj, Pérez Fontán; Gp, Heldt; Rc, Targett; Mm, Willis; Ga, Gregory

doi:10.1097/00003246-198601000-00010

Cited by 14 publications

(7 citation statements)

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“…THE POSSIBILITY THAT GAS TRAPPING may occur during high-frequency oscillatory ventilation (HFOV) has been a source of concern for many years. This concern has been heightened by perceived similarities with conventional mechanical ventilation, where it is well recognized that gas trapping can occur at high ventilator rates (17,18,20).…”

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“…During conventional mechanical ventilation (CMV), the time required for pressure to equilibrate between the alveolar space and the patient's airway, and thus for inspiration or expiration to be complete, is determined by the time constant, which is the product of compliance (C) and resistance (R) of the respiratory system. Because expiratory resistance is commonly up to fourfold greater than inspiratory resistance (17), application of rapid ventilator rates during CMV may easily compromise expiration. Gas trapping results, with elevation of alveolar pressure above airway pressure at end expiration, in a phenomenon commonly referred to as inadvertent positive end-expiratory pressure (3,17,20).…”

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confidence: 99%

“…Because expiratory resistance is commonly up to fourfold greater than inspiratory resistance (17), application of rapid ventilator rates during CMV may easily compromise expiration. Gas trapping results, with elevation of alveolar pressure above airway pressure at end expiration, in a phenomenon commonly referred to as inadvertent positive end-expiratory pressure (3,17,20). To minimize the risk of this problem occurring during CMV at rapid rates, inspiratory-to-expiratory time (I/E) ratios of at least 1:2 are commonly employed.…”

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Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation

Pillow

Neil

Wilkinson

et al. 1999

Journal of Applied Physiology

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This study investigated factors contributing to differences between mean alveolar pressure (PA) and mean pressure at the airway opening (Pao) during high-frequency oscillatory ventilation (HFOV). The effect of the inspiratory-to-expiratory time (I/E) ratio and amplitude of oscillation on the magnitude of - Pao (Pdiff) was examined by using the alveolar capsule technique in normal rabbit lungs (n = 4) and an in vitro lung model. The effect of ventilator frequency and endotracheal tube (ETT) diameter on Pdiff was further examined in the in vitro lung model at an I/E ratio of 1:2. In both lung models, fell below Pao during HFOV when inspiratory time was shorter than expiratory time. Under these conditions, differences between inspiratory and expiratory flows, combined with the nonlinear relationship between resistive pressure drop and flow in the ETT, are the principal determinants of Pdiff. In our experiments, the magnitude of Pdiff at each combination of I/E, frequency, lung compliance, and ETT resistance could be predicted from the difference between the mean squared inspiratory and expiratory velocities in the ETT. These observations provide an explanation for the measured differences in mean pressure between the airway opening and the alveoli during HFOV and will assist in the development of optimal strategies for the clinical application of this technique.

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Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation

Pillow

Neil

Wilkinson

et al. 1999

Journal of Applied Physiology

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“…Each of these factors has an impact on τE. Furthermore, under mechanical ventilation τE is not simply the product of resistance and compliance of the patient's respiratory system, but also depends on additional resistive elements, such as the endotracheal tube (ETT), ventilator tubing and the expiratory valve [7,8]. Since ETT resistance (RETT) is markedly flow-dependent [9,10], τE must be expected to be flow-dependent, also.…”

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Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients

Guttmann¹,

Eberhard²,

Fabry³

et al. 1995

Eur Respir J

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T Ti im me e c co on ns st ta an nt t/ /v vo ol lu um me e r re el la at ti io on ns sh hi ip p o of f p pa as ss si iv ve e e ex xp pi ir ra at ti io on n i in n m me ec ch ha an ni ic ca al ll ly y v ve en nt ti il la at te ed d A AR RD DS S p pa at ti ie en nt ts s The mean values of τE for each volume slice did not differ significantly throughout expiration, averaging 690±218 ms (mean±SD of five slices and 12 patients). We show that the flow-dependent resistance of the endotracheal tube (RETT) is mainly responsible for the observed time constant homogeneity.We conclude that in ARDS patients during uninterrupted mechanical ventilation the time constants of passive expiration are markedly modified by the flow-dependent resistance of the endotracheal tube (RETT), and also by the external resistance of tubing and ventilator (REX). RETT and REX render τE about three times larger than the time constant of the patient's respiratory system alone.

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“…4 x Nevertheless, careful review of the literature reveals that the decelerating flow pattern offered some advantage in each study evaluating that pattern. Interpreting or comparing studies on this topic is difficult because of a variety of confounding variables, such as the use of "shunt tubes," 37 a failure to control all the relevant parameters (particularly T1 311 • 39 ) , and comparisons of only two or three of the four or five waveforms commonly usedY-47 Also, many types of lungs and models have been used: healthy adult lungs,:J>< 40 injured and diseased human lungs, 41 · 45 injured animal lungs, 13 · 15 • 47 lung models, 37 · 39 · 42 -44 computer models, 4 h and an electrical analog model.…”

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confidence: 99%

Pressure-preset Ventilation

Blanch

Jones²,

Layon³

et al. 1993

Chest

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Dynamics of expiration and gas trapping in rabbits during mechanical ventilation at rapid rates

Cited by 14 publications

References 0 publications

Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation

Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation

Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients

Pressure-preset Ventilation

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