Cardiogenic oscillations to detect intratidal derecruitment and overdistension in a porcine model of healthy and atelectatic lungs.

Background: Low positive end-expiratory pressure (PEEP) can result in alveolar derecruitment, and high PEEP or high tidal volume (V) in lung overdistension. We investigated cardiogenic oscillations (COS) in the airway pressure signal to investigate whether these oscillations can assess unfavourable intratidal events. COS induce short instantaneous compliance increases within the pressure-volume curve, and consequently in the compliance-volume curve. We hypothesised that increases in COS-induced compliance reflect non-linear intratidal respiratory system mechanics.

Methods: In mechanically ventilated anaesthetised pigs with healthy (n=13) or atelectatic (n=12) lungs, pressure-volume relationships and the ECG were acquired at a PEEP of 0, 5, 10, and 15 cm HO. During inspiration, the peak compliance of successive COS (C) was compared with intratidal respiratory system compliance (C) within incremental volume steps up to the full V of 12 ml kg. We analysed whether C variation corresponded with systolic arterial pressure variation.

Results: C-volume curves showed characteristic intratidal patterns depending on the PEEP level and on atelectasis. Increasing C- or C-volume patterns were associated with intratidal derecruitment with low PEEP, and decreasing patterns above 6 ml kg and high PEEP showed overdistension. C was not associated with systolic arterial pressure variations.

Conclusions: Heartbeat-induced oscillations within the course of the inspiratory pressure-volume curve reflect non-linear intratidal respiratory system mechanics. The analysis of these cardiogenic oscillations can be used to detect intratidal derecruitment and overdistension and, hence, to guide PEEP and V settings that are optimal for respiratory system mechanics.