[The source and influential factors in signals of trans-esophageal oxygen saturation]

This paper is aimed to investigate the signal source and influential factors in signals of trans-esophageal pulse oxygen saturation (SeO2). The red light of the SeO2 probe was faced directly to the descending aorta (DA) of the mongrel dogs. The readings and waveform of SeO2 signals were recorded under following conditions: before and after DA was shield; before and after the blood supply of esophagus was cut off; under the different touch pressures between the SeO2 probe and the esophageal wall. The readings and waveform of SeO2 signals were also recorded respectively at both different esophageal depth and directions when mechanical ventilation was on and off. The tongue oxygen saturation (StO2) was recorded simultaneously as control. The waveform of SeO2 signals disappeared after DA was shield (P < 0.001). No significant difference was found in the SeO2 signals before and after the blood supply of esophagus was cut off (P > 0.05). Compared with the StO2 readings when the SeO2 probe was placed at different esophageal depth, the waldeyer ring, cervical area and thoracic inlet,the readings of SeOz significantly decreased (P < 0.05) while mechanical ventilation was on and off. However, there was no significant difference in the readings between SeO2 signals from DA, aortic arch (AA) and left subclavian artery and the StO2 signals recorded simultaneously. Mechanical ventilation had a remarkable effect on the SeO2 signals at different esophageal depth (P < 0.05), but the StO2 signals lay in its insensitivity to its influence. The readings of StO2 signals were significantly different from that of StO2 signals when the touch pressure between the SeO2 probe and the esophageal wall below 40 mmHg (P < 0.01). The directions of the optimum SeO2 signals acquired at different esophageal depth were not the same. The SeO2 signals were primarily derived from deeper arteries around the esophagus. All of Mechanical ventilation, location of the SeO2 probe in the esophagus and the touch pressure between the probe and esophageal wall can influence SeO2 signals.