Experimental Analysis of the Airway Circuit Effects on Breathing Pattern Generated by Neonatal Pulmonary Ventilators Paolo Cappa, Salvatore Andrea Sciuto, and Sergio Silvestri From the Department of Mechanics and Aeronautics, University of Rome ‘‘La Sapienza,’’ Italy (Mr Cappa); the Department of Mechanical and Industrial Engineering, University of Rome ‘‘Roma Tre,’’ Italy (Mr Sciuto); the Clinical Engineering Service, Children’s Hospital ‘‘Bambino Gesu `’’ of Rome, Italy (Mr Cappa and Mr Sciuto); and Faculty of Biomedical Engineering, University ‘‘Campus Bio-Medico’’ of Rome, Italy (Mr Silvestri). An experiment was performed in vitro to determine the effect of an airway-to-patient circuit on the breathing pattern actually delivered to the patient by a neonatal pulmonary ventilator. To this end, an automatic measuring system was implemented to record: (a) the ventilation parameter analog output signals provided by the ventilator and (b) the pressure value directly measured at the patient delivery site. The experimental analysis was conducted by examining various circuit configurations (tubes that differ in dimensions and rigidity, with and without humidifier, etc) and pressure waveform changes. Noticeable differences between the respiratory pattern set by physicians and that actually delivered to the patient were observed and the measured data provide indication for correct air circuit design. Finally, the results contributed to increase the attention of the medical therapist, who is the only one able to estimate the actual patient ventilatory needs and their ranges of variation, to a more accurate ventilator setting in order to assure the correct breathing pattern for neonate health. In Italy, any year, two-thirds of the about 3000 newborns suffering from serious respiratory insufficiencies need ventilatory support (assisted and mechanical ventilation) performed by means of pulmonary ventilators specific for neonatal use. 1 These devices are widely used in anesthesia and intensive care units 2 to substitute the primary respiratory functions in order to maintain the patient alive, working continuously even for longer than 40-week time periods. With reference to small patients, such as preterm neo- nates, 3 whose mass is often less than 1000 g, fine regulation of mechanical ventilator working parameters becomes critical and, depending on reduced tidal volumes, pulmonary tissues delicateness and vulnerability, even reduced accuracy values, generally tolerated by adults, can be very dangerous for the neonate’s health. 4–6 In ad- dition to fluid-dynamic parameters, respiratory pattern should also be taken into account for patient safety. There are 5 main respiratory patterns 7 for premature infants: (a) apnea; (b) augmented inspiratory reflex; (c) active expira- tory reflex; (d) spontaneous asynchronous breathing; and, finally, (e) synchronous breathing, which is generally considered the most suitable one, partly because signifi- cantly greater variability of blood flow velocity appears when the baby is breathing out of synchrony with the ventilator. 8 However, there is no assurance that the air flow and pressure actually delivered to the patient as a function of time correspond to the respiratory pattern set by the physicians depending on the specific pulmonary disease. In Corresponding author: Salvatore Andrea Sciuto, Mechanical and Thermal Measurements, Department of Mechanical and Industrial Engineering, University of Rome ‘‘Roma Tre,’’ Via della Vasca Navate 79, 00146 Rome, Italy. Paolo Cappa is full professor of mechanical measurements, Faculty of Engineering, University of Rome ‘‘La Sapienza.’’ He is currently chairman of the Department of Mechanics and Aeronau- tics at the University of Rome ‘‘La Sapienza.’’ He has authored or coauthored over 80 publications in the field of experimental mechanics and clinical engineering, most of them published on international scientific refereed journals or on international conference proceedings. Salvatore Andrea Sciuto is professor of mechanical and ther- mal measurements at the Department of Mechanical and Industrial Engineering of the University of Rome ‘‘Roma Tre.’’ He is also active in clinical engineering as a consultant of several Italian hospitals. He has authored or coauthored over 50 publications in the field of instrumentation and measurements and clinical engineering, most of them published on international scientific refereed journals or on international conference proceedings. Sergio Silvestri is assistant professor of biomedical instrumen- tation at the Faculty of Biomedical Engineering of the University ‘‘Campus Bio-Medico’’ of Rome. He has authored or coauthored about 20 publications in the field of biomedical engineering, most of them published on international scientific refereed journals or on international conference proceedings. PEER-REVIEW PAPER 134 Journal of Clinical Engineering  July/September 2004