Fig. 6

A Photomicrograph of in vivo subpleural alveoli (in vivo alveoli) at inspiration (top panel) and expiration (bottom panel) following lung injury in rats. Alveoli in the four ventilation treatment groups are depicted in yellow, while collapsed alveoli are in red. The images show the impact of ventilation strategies on alveolar recruitment and collapse using a conventional ventilation strategy with a low tidal volume (LV_T) of 6 mL kg⁻¹ (Vt6) combined with either PEEP 5 cmH₂O (Vt6 PEEP5) or 16 cmH₂O (Vt6 PEEP 16). Also shown for comparison are the results of using APRV with an extended P_High (CPAP Phase, Fig. 4B) combined with two expiratory durations set at either 75% of peak expiratory flow (APRV 75%) or 10% of peak expiratory flow (APRV 10%). APRV 75% has a very short expiratory duration, while APRV 10% has a much longer expiratory duration (Fig. 4B, Release Phase). B The impact of each ventilation strategy on alveolar recruitment at inspiration (light gray bar) and derecruitment at expiration (dark gray bar) expressed as the percent (%) of the microscopic field. Conventional ventilation using LV_T did not effectively recruit alveoli (PEEP5 and PEEP16). Increasing to PEEP16 reduced the number of alveoli that collapsed during expiration (difference between the light and dark gray bars), but did not recruit as many alveoli as APRV with an extended CPAP Phase. However, using APRV with an extended expiratory duration (APRV 10%) caused many of the newly recruited alveoli to re-collapsed. Alveolar collapse at expiration was prevented with the use of a brief expiratory duration (APRV 75%) [58]. (Permission to republish requested)