Influence of the breathing mode on the time course and amplitude of the cyclic inter-atrial pressure reversal in postoperative coronary bypass surgery patients.

The haemodynamic basis for paradoxical embolization in patients with stroke and decompression sickness has not yet been fully elucidated. Therefore right and left atrial pressures were measured simultaneously with peroperatively placed catheters after coronary artery bypass grafting in 17 patients with sinus rhythm and normal left ventricular function. Recordings were made both during spontaneous breathing and positive pressure ventilation. A cyclic pressure reversal in which right atrial pressure exceeded left atrial pressure was reproducibly recorded. It started on average 215 +/- 5 ms (mean +/- SEM) after the onset of the electrocardiographic P-wave, lasted on average 179 +/- 14 ms and had a maximal amplitude of on average 4.1 +/- 0.3 mmHg. During the expiration phase of spontaneous breathing and inspiration phase of positive pressure ventilation, the onset of the pressure reversal occurred later, its duration was shorter and its amplitude smaller. These observations demonstrate the presence of a cyclic inter-atrial pressure reversal and illustrate the importance of the breathing mode for the time course and amplitude of this reversal.