Effect of Volume History on Measurements of Respiratory Mechanics Using the Interrupter Technique

Abstract

ABSTRACT. The importance of the viscoelastic properties of the tissues of the respiratory system has recently been recognized, and lung models have been produced to describe the resistive and viscoelastic properties of the lung. The pulmonary mechanics of 10 rabbits were studied using the interrupter technique to assess the effect of volume history on the resistive and viscoelastic elements of the respiratory system. The influence of the tone of the muscles of respiration was also studied. In healthy lungs, the resistive and viscoelastic elements of the lung are dependent on the volume history of the respiratory system and are significantly lower if these elements do not reach a resting position before expiration. The chest wall made a significant contribution to the resistive and viscoelastic elements of the respiratory system, which was also dependent on the lung volume history. The tone of the muscles of respiration had no effect on the resistive or viscoelastic elements of the respiratory system. (Pediatr Res 33: 261-266, 1993) Abbreviations R1, resistance of respiratory system RZ, dissipative properties of lung or chest wall El, static elastance of respiratory system E2, elastic properties ET, endotracheal FRC, functional residual capacity Pao, airway opening pressure Pes, esophageal pressure Pdiff, static recoil pressure of respiratory system Pinit, resistance pressure drop across airways and chest wall Rinit, Newtonian flow resistance of airways and chest wall Rrs, flow resistance of the respiratory system ANOVA, analysis of variance RE=, endotracheal tube resistance Recently, the importance of the viscoelastic properties of the tissues of the respiratory system has been recognized (1-10). The two-compartment model for the lung that best represents experimental data consists of a single alveolar compartment surrounded by a viscoelastic tissue compartment (1 1), and models have been produced to describe the resistive and viscoelastic properties of the lung. This model can be represented by springs 26and dashpots as shown in Figure 1, where R1 represents the airway resistance and any Newtonian component of tissue resistance that is in parallel with another three elements (El, E2, and R2) in the form of the Kelvin body, an elastic element in parallel with a series elastance-resistance. El represents the static elastance of the respiratory system and E2 and R2 the dissipative and elastic properties of the tissues of the lung and chest wall (12). If the two bars at either end of the model are moved relative to each other to represent the changes in volume during respiration, the properties of R1, El, R2, and E2 determine the behavior of the model. If the bars are stopped abruptly, simulating a flow interruption, the "energy dissipation" in R I and El will stop immediately; however, some time will be required for R2 and E2 to reach their resting position. This model allows a better description of the changes in Pao observed after rapid airway occlusions during passive expiration than the traditional one-com...

Different contributions from lungs and chest wall to respiratory mechanics in mice, rats, and rabbits

“…However, changes in lung tissue mechanics following alveolar recruitment/derecruitment, interstitial edema, and/or parenchymal remodeling may be masked by an unknown and potentially variable chest wall component. Indeed, our study confirmed the substantial contribution of the chest wall to total respiratory damping and elastance for rabbits (16) and a proportionally smaller, but still important, contribution for rats (31). These chest wall contributions appear to bias the assessments of lung mechanical changes significantly (as much as 2-fold) when they are inferred from parameters reflecting the total respiratory system mechanics [Supplemental Fig.…”

“…Measurement of the difference between airway opening and esophageal pressures (P es ) as a surrogate of transpulmonary pressure offers the possibility to separate the mechanical properties of these two compartments. This approach has been successfully applied to humans (7, 10 -12, 14, 29), dogs (5,20,27), cats (17), rabbits (1,16), and rats (22,24,31). However, no such measurements have been performed in mice despite the rapidly increasing importance of this animal model in a wide variety of respiratory diseases.…”

Measurements of respiratory system resistance by the interrupter technique in healthy and asthmatic children

“…Although expiration is passive and inspiration is influenced by inertance and muscular drive, R int FV i was always lower than R int FV e , and muscular activity during the time of occlusion seems improbable. Freezer et al noted in their study 30 that the volume history of the lung may be important in determining the stresses distending the intrapulmonary air spaces. They observed in healthy, anesthetized, mechanically ventilated rabbits higher resistance of the respiratory system during passive expiration when performing an endinspiratory occlusion before the expiratory occlusion than when omitting it.…”

Respiratory Mechanics During Sevoflurane Anesthesia in Children With and Without Asthma

“…This was done to avoid the confounding effect of comparing respiratory mechanics during spontaneous breathing prior to intubation, with measurements taken during positive pressure ventilation postintubation. We would not expect our results to have been different if muscle relaxants had been used (16).…”