Alveolar pressure estimation in total liquid ventilation during pauses impeded by tube resonance

Total liquid ventilation is an innovative experimental method of mechanical assisted ventilation in which lungs are totally filled and then ventilated with a tidal volume of perfluorochemical liquid (PFC) by using a dedicated liquid ventilator. The positive end-inspiratory and end-expiratory pressures (PEIP and PEEP) are static pressure measurements that are critic to the safe and efficient control of the ventilation. However, their measurement is impeded by large oscillations of pressure caused by the propagation of pressure waves along the flexible tubes carrying the PFC to the patient. The aim of this paper is to describe a method to accurately estimate the PEEP and the PEIP from noisy data hindered by flexible tubing resonance during short respiratory pauses. The method developped makes use of the least squares technique to estimate the steady state pressure. Preliminary in vivo validation of the algorithm shows that the method gives accurate estimations with respiratory pauses as short as 0.3 second.