The authors describe the possible risk of inpulsion effect arising during conventional ventilation if TI:TE ratio is less than 0.5 (Ti% < 33%). They analyze changes of expiratory time constant, pressure support, TI:TE ratio, ventilation frequency, FiO2, SpO2, static compliance and respiratory resistance which were monitored during ventilation in pressure support mode (pressure support PS). The authors have found that during prolonged decrease of Ti < 33% (28 ± 3) there could be observed a decrease of static compliance and increase of respiratory tract resistance, evolving gradually during several tens of hours. To maintain the gas exchange (MV) in PS mode there is a need to increase pressure support Pps. Based upon above mentioned findings, there was postulated a theory of persistent inpulsion effect of mechanical ventilation of the lungs that worsens the drainage function of the lungs especially in distal respiratory airways. To eliminate this inpulsion effect, high-frequency jet ventilation (HFJV) was used intermittently for its expulsion effect. After application of expulsion effect using HFJV, improvement of lung mechanics could be documented. At the end the authors stress the possible risk of worsening lung mechanics during ventilation in PS mode (ASB) under the condition that Ti% < 33% is applied for prolonged time.

        Key words: pressure support – inpulsion – expulsion – static compliance – respiratory tract resistance