Effect of inspiratory-to-expiratory time ratio and amplitude of oscillations on the development and magnitude of dynamic hyperinflation and hypoinflation of lungs during HFOV

Anotace: During high-frequency oscillatory ventilation (HFOV), a situation may occur where the mean alveolar pressure (mPalv) differs significantly from the mean airway pressure (mPaw). Studies documenting the differences between these pressures during HFOV have documented states of both higher and lower mPalv compared to mPaw. The effect of HFOV parameters on the pressure difference is not yet understood. The aim of this study is to investigate how this phenomenon is affected by the ratio of inspiratory to expiratory time and the amplitude of HFOV oscillations (ΔP). The effect of the listed ventilation parameters was investigated in vitro in seven laboratory models and in vivo on nine pigs. The study found that an inspiratory to expiratory time ratio of 1:1 always results in a positive pressure difference between mPalv and mPaw, referred to as dynamic hyperinflation. At an inspiratory to expiratory ratio of 1:2 this pressure difference is negative in the majority of in vitro models of the respiratory system and in all animals. In addition, the study found that the magnitude of the pressure difference is affected by the ΔP. There is a critical value of ΔP at which the trend of the pressure gradient between the alveolar space and the airways is reversed in relation to the oscillation amplitude.