The control of thermo-hygrometric conditions of gas delivered in neonatal mechanical ventilation appearsto be a particularly difficult task, mainly due to the vast number of parameters to be monitored and thecontrol strategies of heated humidifiers to be adopted.In the present paper, we describe the heat and fluid exchange occurring in a heated humidifier inmathematical terms; we analyze the sensitivity of the relative humidity of outlet gas as a function ofthermo-hygrometric and fluid-dynamic parameters of delivered gas; we propose a control strategy thatwill enable the stability of outlet gas thermo-hygrometric conditions. The mathematical model is representedby a hyper-surface containing the functional relations between the input variables, which mustbe measured, and the output variables, which have to remain constant.Model sensitivity analysis shows that heated humidifier efficacy and stability of outlet gas thermohygrometricconditions are principally influenced by four parameters: liquid surface temperature, gasflow rate, inlet gas temperature and inlet gas relative humidity.The theoretical model has been experimentally validated in typical working conditions of neonatalapplications. The control strategy has been implemented by a minimal measurement system composedof three thermometers, a humidity sensor, and a flow rate sensor, and based on the theoretical model.Outlet relative humidity, contained in the range 90±4% and 94±4%, corresponding with temperaturevariations in the range 28±2 ◦C and 38±2 ◦C respectively, has been obtained in the whole flow rate rangetypical of neonatal ventilation from 1 to 10 L/min.Weconclude that in order to obtain the stability of the thermo-hygrometric conditions of the deliveredgas mixture: (a) a control strategy with a more complex measurement system must be implemented (i.e.providing more input variables); (b) and the gas may also need to be pre-warmed before entering thehumidifying chamber.
Mathematical model and minimal measurement system for optimal control of heated humidifiers in neonatal ventilation
SCHENA E;SILVESTRI S
2010-01-01
Abstract
The control of thermo-hygrometric conditions of gas delivered in neonatal mechanical ventilation appearsto be a particularly difficult task, mainly due to the vast number of parameters to be monitored and thecontrol strategies of heated humidifiers to be adopted.In the present paper, we describe the heat and fluid exchange occurring in a heated humidifier inmathematical terms; we analyze the sensitivity of the relative humidity of outlet gas as a function ofthermo-hygrometric and fluid-dynamic parameters of delivered gas; we propose a control strategy thatwill enable the stability of outlet gas thermo-hygrometric conditions. The mathematical model is representedby a hyper-surface containing the functional relations between the input variables, which mustbe measured, and the output variables, which have to remain constant.Model sensitivity analysis shows that heated humidifier efficacy and stability of outlet gas thermohygrometricconditions are principally influenced by four parameters: liquid surface temperature, gasflow rate, inlet gas temperature and inlet gas relative humidity.The theoretical model has been experimentally validated in typical working conditions of neonatalapplications. The control strategy has been implemented by a minimal measurement system composedof three thermometers, a humidity sensor, and a flow rate sensor, and based on the theoretical model.Outlet relative humidity, contained in the range 90±4% and 94±4%, corresponding with temperaturevariations in the range 28±2 ◦C and 38±2 ◦C respectively, has been obtained in the whole flow rate rangetypical of neonatal ventilation from 1 to 10 L/min.Weconclude that in order to obtain the stability of the thermo-hygrometric conditions of the deliveredgas mixture: (a) a control strategy with a more complex measurement system must be implemented (i.e.providing more input variables); (b) and the gas may also need to be pre-warmed before entering thehumidifying chamber.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
