Respirator triggering of electron beam computed tomography (EBCT): research on vital capacities

In this project we evaluate the dynamic changes during expiration at different levels of positive-end-expiratory pressure (PEEP) in ventilated patients. We wanted to discriminate between normal lung function and acute respiratory distress syndrome (ARDS). After approval by the local Ethic Committee we studied two ventilated patients: (one with normal lung function and one with ARDS) We used the 50 ms scan mode of the EBCT. The beam was positioned 1 cm above the diaphragm while the table position remained unchanged. We developed an electronic trigger that utilizes the respirator's synchronizing signal to start the EBCT at the onset of expiration. During controlled mechanical expiration at two levels of PEEP (0 and 15 cm H2O), pulmonary aeration was rated as: well-aerated (-900HU to -500HU), poorly aerated (-500HU to -100HU) and non-aerated (-100HU to +100HU). Pathological and normal lung functions showed different dynamic changes. The different PEEP levels resulted in a significant change of pulmonary aeration in the same patient. Although we studied only two patients, respiratory triggered EBCT may be accurate in discriminating pathological changes due to the abnormal lung function in a mechanically ventilated patient.