The bimodal quasi-static and dynamic elastance of the murine lung

Abstract

The double sigmoidal nature of the mouse pressure-volume (PV) curve is well recognized but largely ignored. This study systematically examined the effect of inflating the mouse lung to 40 cm H2O transrespiratory pressure (Prs) in vivo. Adult BALB/c mice were anesthetized, tracheostomized, and mechanically ventilated. Thoracic gas volume was calculated using plethysmography and electrical stimulation of the intercostal muscles. Lung mechanics were tracked during inflation-deflation maneuvers using a modification of the forced oscillation technique. Inflation beyond 20 cm H2O caused a shift in subsequent PV curves with an increase in slope of the inflation limb and an increase in lung volume at 20 cm H2O. There was an overall decrease in tissue elastance and a fundamental change in its volume dependence. This apparent "softening" of the lung could be recovered by partial degassing of the lung or applying a negative transrespiratory pressure such that lung volume decreased below functional residual capacity. Allowing the lung to spontaneously recover revealed that the lung required approximately 1 h of mechanical ventilation to return to the original state. We propose a number of possible mechanisms for these observations and suggest that they are most likely explained by the unfolding of alveolar septa and the subsequent redistribution of the fluid lining the alveoli at high transrespiratory pressure.

Cecal ligation and puncture accelerates development of ventilator-induced lung injury

“…Given that rodent lungs demonstrate significantly different responses to increasing pressure than humans (26,38,40), we selected a V T of 30 ml/kg, which is within the range used to generate VILI in rats in the literature; in a recent publication, a range of 18.8 to 51.5 [mean 36.2 Ϯ 2.2 (SE)] ml/kg was reported (2). It is possible that ventilation with lower V T for longer periods of time would confirm the conclusions presented here; however, the V T of 30 ml/kg was chosen because of evidence of lung damage on CT, one of the metrics used to quantify injury in this study.…”

Geogenic PM10 exposure exacerbates responses to influenza infection

“…Thoracic Gas Volume (TGV) was measured as described previously (Jánosi et al, 2006;Zosky et al, 2008). Briefly, ventilation was stopped and the intercostal muscles were electrically stimulated at 20 V for 1-2 ms, to induce inspiratory efforts.…”

Linking lung function and inflammatory responses in ventilator-induced lung injury

“…Lung mechanics were measured using a modification of the lowfrequency forced oscillation technique as described previously (39). Briefly, a 6-s oscillatory signal containing nine pseudorandom frequencies ranging from 4 to 38 Hz was applied to the lung via the tracheal cannula at EELV during pauses in ventilation.…”