Determination of expiratory lung mechanics using cardiogenic oscillations during decelerated expiration

Introduction

Mechanical energy from the beating heart is transferred to the lung, inducing variations in the airway pressure signal called cardiogenic oscillations (COS), which we hypothesize reflect intratidal nonlinear lung mechanics. However, during high flow rate, as characteristic for passive expiration, the analysis of lung mechanics is impractical since COS are almost suppressed and the quantity is low.

Methods

Five piglets with atelectasis were investigated during constant inspiratory flow mechanical ventilation with positive end-expiratory pressure of 0, 5, 8, 12 and 16 mbar. The airflow rate, airway pressure, pleural pressure and ECG were recorded (sample frequency 100 Hz). The expiratory airflow rate was limited using two switchable tubes of different lumen. Signals were separated and compared by each breath.

Results

Compared with passive expiration COS in decelerated expiration became clearly distinguishable (Figure 1). COS amplitudes were increasing with decreasing airflow rate.

Figure 1

Conclusion

By decelerating the expiration, COS become distinguishable and therefore analyzable. With this method, lung mechanics can be determined separately in expiration.