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Cardiogenic oscillations reflect nonlinear lung mechanics

Introduction

Heartbeats transfer mechanical energy to the lung, inducing variations in local compliance (dV/dP) [1], which translate to cardiogenic oscillations (COS) in the pressure-volume (PV) loop. We hypothesized that the COS-related local dV/dP change reflects intratidal nonlinear lung mechanics modulated by positive end-expiratory pressure (PEEP).

Methods

Ten piglets with atelectasis were investigated during constant inspiratory flow mechanical ventilation with PEEP of 0, 5, 8, 12 and 16 mbar, respectively. The airflow rate, airway pressure and ECG were recorded (sample frequency: 100 Hz). The inspiratory limb of the PV loop was partitioned into segments confined by two consecutive ECG R-peaks and containing one COS. Local compliances were analyzed as the local slope (dV/dp) within consecutive volume windows of 50 ml size.

Results

The COS-related local compliances depend on the PEEP level as shown in one representative animal (Figure 1). They are maximal at PEEP levels of 5 and 8 mbar and are minimal at zero PEEP and at high PEEP levels of 12 and 16 mbar, and they decrease with increasing inspired volume.

figure1

Figure 1

Conclusion

COS-related local compliances reflect nonlinear lung mechanics. The information obtained by COS corresponds to what can be learnt from the sigmoid PV loop of a quasistatic manoeuvre with low compliance at low pressure, high compliance at intermediate pressure and again low compliance with overdistension. The intratidal pattern of COS-related compliances possibly reflects the nonlinearity of pulmonary volume distensibility, which, among others, is modulated by PEEP. Analysis of COS-related local compliances may open a window towards lung mechanics determination in spontaneous breathing.

References

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Wahl, A., Lichtwarck-Aschoff, M., Möller, K. et al. Cardiogenic oscillations reflect nonlinear lung mechanics. Crit Care 12, P311 (2008). https://doi.org/10.1186/cc6532

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Keywords

  • Inspiratory Flow
  • Lung Mechanic
  • Peep Level
  • High Peep
  • Intermediate Pressure