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

Abstract

Changes in lung mechanics are frequently inferred from intact-chest measures of total respiratory system mechanics without consideration of the chest wall contribution. The participation of lungs and chest wall in respiratory mechanics has not been evaluated systematically in small animals commonly used in respiratory research. Thus, we compared these contributions in intact-chest mice, rats, and rabbits and further characterized the influence of positive end-expiratory pressure (PEEP). Forced oscillation technique was applied to anesthetized mechanically ventilated healthy animals to obtain total respiratory system impedance (Zrs) at 0, 3, and 6 cmH2O PEEP levels. Esophageal pressure was measured by a catheter-tip micromanometer to separate Zrs into pulmonary (ZL) and chest wall (Zcw) components. A model containing a frequency-independent Newtonian resistance (RN), inertance, and a constant-phase tissue damping (G) and elastance (H) was fitted to Zrs, ZL, and Zcw spectra. The contribution of Zcw to RN was negligible in all species and PEEP levels studied. However, the participation of Zcw in G and H was significant in all species and increased significantly with increasing PEEP and animal size (rabbit > rat > mice). Even in mice, the chest wall contribution to G and H was still considerable, reaching 47.0 ± 4.0(SE)% and 32.9 ± 5.9% for G and H, respectively. These findings demonstrate that airway parameters can be assessed from respiratory system mechanical measurements. However, the contribution from the chest wall should be considered when intact-chest measurements are used to estimate lung parenchymal mechanics in small laboratory models (even in mice), particularly at elevated PEEP levels. NEW & NOTEWORTHY In species commonly used in respiratory research (rabbits, rats, mice), esophageal pressure-based estimates revealed negligible contribution from the chest wall to the Newtonian resistance. Conversely, chest wall participation in the viscoelastic tissue mechanical parameters increased with body size (rabbit > rat > mice) and positive end-expiratory pressure, with contribution varying between 30 and 50%, even in mice. These findings demonstrate the potential biasing effects of the chest wall when lung tissue mechanics are inferred from intact-chest measurements in small laboratory animals.

Respiratory defects in the CrtapKO mouse model of osteogenesis imperfecta

“…A previous study in normal BALB/c mice using closed versus open-chest measurements indicated that the chest wall contrib-uted~20% to G,~6% to R n , and did not affect H (53) while another study using C57BL/6 mice concluded that dynamic pulmonary mechanics in mice reflect only a minor contribution from the chest wall (28). However, a recent study on adult BALB/c mice reported that the chest wall may contributẽ 40% to G and~30% to H (55). There are no studies to date on the contribution of chest wall to respiratory mechanics in any model of OI.…”

Exosomes derived from three-dimensional cultured human umbilical cord mesenchymal stem cells ameliorate pulmonary fibrosis in a mouse silicosis model

“…The classical parameters of respiratory mechanics, resistance, and compliance are related to the resistance of air in and out of the lungs as well as the expandability of the respiratory system. These measurements are based on the analysis of pressure, volume, and flow signals obtained from the oscillating airflow waveform applied to the airway opening of the subject [ 31 , 32 ]. Exposure to the silica increased respiratory resistance (Rrs), airway resistance (Rn), and tissue damping (G) in mice.…”

Physiologically variable ventilation reduces regional lung inflammation in a pediatric model of acute respiratory distress syndrome

“…While Raw is mainly specific to the flow resistance of the conducting airways [ 49 ], the tissue parameters damping and elastance include not only pulmonary components but are also influenced by other structures of the total respiratory system, mainly the chest wall [ 49 ]. Previous literature attributed a chest wall contribution of approximately 30–50% to these parameters [ 50 ] and since the chest wall contribution is not expected to change after lung injury and mechanical ventilation [ 51 ], the observed changes are interpreted as being mainly of pulmonary origin. Therefore, the corresponding changes registered in tissue damping and elastance are predictably underestimating the real pulmonary changes.…”