Pulmonary blood flow generates cardiogenic oscillations.

Cardiogenic oscillations are small waves produced by heartbeats, which are superimposed on the pressure and flow signals at the airway opening. The aim of this study was to investigate the role of the two main factors believed to generate these oscillations: (1) contact between heart and lungs and (2) pulmonary blood flow. We studied 15 heart surgery patients on cardiopulmonary bypass so both factors could be manipulated independently. At minimal heart-lung contact pressure and flow oscillations were larger than during maximal contact (1.20+/-0.17 cmH(2)O and 2.36+/-0.08 L min(-1) vs 0.92+/-0.15 cmH(2)O and 1.78+/-0.26 L min(-1), mean+/-SD, p<0.05). Cardiogenic oscillations for pressure and flow were smaller at 50% compared to 100% pulmonary blood flow (0.80+/-0.12 cmH(2)O and 1.56+/-0.34 L min(-1) vs 1.19+/-0.14 cmH(2)O and 2.38+/-0.19 L min(-1)). We conclude that the amount of pulmonary blood flow and not the contact between heart and lungs is the main factor determining the amplitude of cardiogenic oscillations.