Abstract
In experimental acute respiratory distress syndrome (ARDS), random variation of tidal volumes (VT) during volume controlled ventilation improves gas exchange and respiratory system mechanics (so-called stochastic resonance hypothesis). It is unknown whether those positive effects may be further enhanced by periodic VT fluctuation at distinct frequencies, also known as deterministic frequency resonance. We hypothesized that the positive effects of variable ventilation on lung function may be further amplified by periodic VT fluctuation at specific frequencies. In anesthetized and mechanically ventilated pigs, severe ARDS was induced by saline lung lavage and injurious VT (double-hit model). Animals were then randomly assigned to 6 h of protective ventilation with one of four VT patterns: (1) random variation of VT (WN); (2) P04, main VT frequency of 0.13 Hz; (3) P10, main VT frequency of 0.05 Hz; (4) VCV, conventional non-variable volume controlled ventilation. In groups with variable VT, the coefficient of variation was identical (30%). We assessed lung mechanics and gas exchange, and determined lung histology and inflammation. Compared to VCV, WN, P04, and P10 resulted in lower respiratory system elastance (63 ± 13 cm H2O/L vs. 50 ± 14 cm H2O/L, 48.4 ± 21 cm H2O/L, and 45.1 ± 5.9 cm H2O/L respectively, P < 0.05 all), but only P10 improved PaO2/FIO2 after 6 h of ventilation (318 ± 96 vs. 445 ± 110 mm Hg, P < 0.05). Cycle-by-cycle analysis of lung mechanics suggested intertidal recruitment/de-recruitment in P10. Lung histologic damage and inflammation did not differ among groups. In this experimental model of severe ARDS, periodic VT fluctuation at a frequency of 0.05 Hz improved oxygenation during variable ventilation, suggesting that deterministic resonance adds further benefit to variable ventilation.
Highlights
In lung injury induced by hydrochloric acid, a VT probability density distribution tailored to maximize recruitment allowed better gas exchange and respiratory mechanics with reduced lung inflammation compared to random variable ventilation (Thammanomai et al, 2008, 2013)
Hemodynamics and gas exchange variables did not differ among groups, except to PaO2/FIO2, which was higher in periodicity of 10 cycles (P10) compared to volume controlled ventilation (VCV) (Figure 3 and Table 2)
Peak airway pressure Paw,peak, plateau airway pressure Paw,plat and mean airway pressure Paw,mean were significantly reduced in white noise pattern (WN), P04 and P10 compared to VCV
Summary
Mechanical ventilation with variable tidal volumes (VT) has been shown to improve gas exchange as well as lung mechanics (Lefevre et al, 1996; Suki et al, 1998; Mutch et al, 2000, 2005; Funk et al, 2004; Bellardine et al, 2006; Graham et al, 2011a,b) and attenuate ventilator induced lung injury (VILI) (Boker et al, 2002; Spieth et al, 2009b; Thammanomai et al, 2013; de Magalhães et al, 2016; Samary et al, 2016) in different models of the acute respiratory distress syndrome (ARDS) In these studies, artificial as well as biologically variable VT patterns have been investigated. In lung injury induced by hydrochloric acid, a VT probability density distribution tailored to maximize recruitment allowed better gas exchange and respiratory mechanics with reduced lung inflammation compared to random variable ventilation (Thammanomai et al, 2008, 2013)
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