FIGURE 5.

In an in vivo microscopy rat study of subpleural alveoli, normal healthy lungs (control) were compared with airway pressure release ventilation (APRV) in a pulmonary acute respiratory distress syndrome model. a) Time-controlled adaptive ventilation (TCAV) versus control (inspiration); b) TCAV versus control (expiration). The end-expiratory flow (EEF) rate/peak expiratory flow rate (PEFR) ratio was varied to demonstrate the importance of setting APRV with an appropriate release phase (T_Low) (to maintain EEF/PEFR at 75% as described in the TCAV protocol). Regardless of the T_Low, there is an alveolar size distribution similar to that of the control group at inspiration, in spite of the lung injury, suggesting the extended time at P_High is sufficient to maintain alveolar recruitment. However, lengthening the T_Low such that the EEF/PEFR ratio is 75% creates a positive skew with alveolar collapse and instability. Reproduced and modified from [59] with permission.