Atelectasis and overdistension are detected by heartbeat-induced disturbances in the pressure-volume loop

Introduction

Heartbeats transfer mechanical energy to the lungs causing flow and pressure disturbances that appear as cardiogenic oscillations (COS) at the airway opening. Here we adopt a new approach for analyzing respiratory system mechanics. We consider the beating heart as a natural intrathoracic mechanical oscillator transferring mechanical energy to the lungs that travels across the lung parenchyma. COS therefore convey information on the mechanical conditions of the lung parenchyma that they cross.

Methods

In 25 piglets with either healthy or atelectatic lungs, the pressure-volume relationship and the ECG signal were recorded during mechanical ventilation at different levels of end-expiratory pressure (PEEP: 0, 5, 10 and 15 cmH₂O). The heartbeat-related disturbance of the PV loop was quantified as the maximal compliance following an R-wave in the ECG signal, as determined by the gliding-SLICE method. Atelectasis was assessed by CT.

Results

The intratidal pattern of heartbeat-induced C_COS changed with PEEP and atelectasis in a characteristic way. With PEEP and tidal volume levels assumed to be lung protective C_COS was high with little intratidal changes, compared with atelectasis and overdistension that were signaled by low C_COS that either increased (atelectasis) or decreased (overdistension) intratidally. The systolic pressure variations did not parallel the C_COS pattern, hinting at a negligible impact of hemodynamics on the inspiratory C_COS pattern.

Conclusions

Heartbeats induce fluctuations in the PV loop and, as a consequence, peaks in compliance, which show characteristic patterns depending on the presence of atelectasis or overdistension. The gliding-SLICE method has the potential to detect those intratidal nonlinearities without requiring additional technical equipment making use of the ECG signal and the pressure and flow signals already required for controlling the ventilator.